/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * SPDX-License-Identifier: curl
 *
 ***************************************************************************/
#include "curl_setup.h"

#include "urldata.h"
#include "transfer.h"
#include "url.h"
#include "cfilters.h"
#include "connect.h"
#include "progress.h"
#include "curl_share.h"
#include "psl.h"
#include "multiif.h"
#include "multi_ev.h"
#include "sendf.h"
#include "curl_trc.h"
#include "http.h"
#include "select.h"
#include "curlx/wait.h"
#include "conncache.h"
#include "multihandle.h"
#include "sigpipe.h"
#include "vtls/vtls.h"
#include "vtls/vtls_scache.h"
#include "http_proxy.h"
#include "http2.h"
#include "socketpair.h"
#include "bufref.h"

/* initial multi->xfers table size for a full multi */
#define CURL_XFER_TABLE_SIZE 512

/* CURL_SOCKET_HASH_TABLE_SIZE should be a prime number. Increasing it from 97
   to 911 takes on a 32-bit machine 4 x 804 = 3211 more bytes. Still, every
   curl handle takes 6K memory, therefore this 3K are not significant. */
#ifndef CURL_SOCKET_HASH_TABLE_SIZE
#define CURL_SOCKET_HASH_TABLE_SIZE 911
#endif

#ifndef CURL_CONNECTION_HASH_SIZE
#define CURL_CONNECTION_HASH_SIZE 97
#endif

#ifndef CURL_DNS_HASH_SIZE
#define CURL_DNS_HASH_SIZE 71
#endif

#ifndef CURL_TLS_SESSION_SIZE
#define CURL_TLS_SESSION_SIZE 25
#endif

static void move_pending_to_connect(struct Curl_multi *multi,
                                    struct Curl_easy *data);
static CURLMcode add_next_timeout(const struct curltime *pnow,
                                  struct Curl_multi *multi,
                                  struct Curl_easy *data);
static void multi_timeout(struct Curl_multi *multi,
                          struct curltime *expire_time,
                          long *timeout_ms);
static void multi_schedule_pending(struct Curl_multi *multi);
static void multi_xfer_bufs_free(struct Curl_multi *multi);
#ifdef DEBUGBUILD
static void multi_xfer_tbl_dump(struct Curl_multi *multi);
#endif

static const struct curltime *multi_now(struct Curl_multi *multi)
{
  curlx_pnow(&multi->now);
  return &multi->now;
}

/* function pointer called once when entering a state */
typedef void (*mstate_enter_func)(struct Curl_easy *data,
                                  CURLMstate from_state);

static void mstate_enter_connect(struct Curl_easy *data,
                                 CURLMstate from_state)
{
  (void)from_state;
  Curl_init_CONNECT(data);
}

static void mstate_enter_did(struct Curl_easy *data,
                             CURLMstate from_state)
{
  (void)from_state;
  data->req.chunk = FALSE;
  Curl_pgrsTime(data, TIMER_PRETRANSFER);
  if(!CURL_REQ_WANT_SEND(data))
    Curl_pgrsTime(data, TIMER_POSTRANSFER);
}

static void mstate_enter_done(struct Curl_easy *data,
                              CURLMstate from_state)
{
  (void)from_state;
  CURLM_NTFY(data, CURLMNOTIFY_EASY_DONE);
}

static void mstate_enter_completed(struct Curl_easy *data,
                                   CURLMstate from_state)
{
  /* we sometimes directly jump to COMPLETED, trigger things
   * we then missed. */
  if(from_state < MSTATE_DID) {
    Curl_pgrsTime(data, TIMER_PRETRANSFER);
    Curl_pgrsTime(data, TIMER_POSTRANSFER);
    Curl_pgrsTime(data, TIMER_STARTTRANSFER);
  }
  Curl_pgrsCompleted(data);
  if(from_state < MSTATE_DONE)
    CURLM_NTFY(data, CURLMNOTIFY_EASY_DONE);
  /* changing to COMPLETED means it is in process and needs to go */
  DEBUGASSERT(Curl_uint32_bset_contains(&data->multi->process, data->mid));
  Curl_uint32_bset_remove(&data->multi->process, data->mid);
  Curl_uint32_bset_remove(&data->multi->pending, data->mid); /* to be sure */

  if(Curl_uint32_bset_empty(&data->multi->process)) {
    /* free the transfer buffer when we have no more active transfers */
    multi_xfer_bufs_free(data->multi);
  }
  /* Important: reset the conn pointer so that we do not point to memory
     that could be freed anytime */
  Curl_detach_connection(data);
  Curl_expire_clear(data); /* stop all timers */
}

/* always use this function to change state, to make debugging easier */
static void mstate(struct Curl_easy *data, CURLMstate state
#ifdef DEBUGBUILD
                   , int lineno
#endif
)
{
  CURLMstate oldstate = data->mstate;
  static const mstate_enter_func state_enter[MSTATE_LAST] = {
    NULL,                      /* INIT */
    NULL,                      /* PENDING */
    NULL,                      /* SETUP */
    mstate_enter_connect,      /* CONNECT */
    NULL,                      /* CONNECTING */
    NULL,                      /* PROTOCONNECT */
    NULL,                      /* PROTOCONNECTING */
    NULL,                      /* DO */
    NULL,                      /* DOING */
    NULL,                      /* DOING_MORE */
    mstate_enter_did,          /* DID */
    NULL,                      /* PERFORMING */
    NULL,                      /* RATELIMITING */
    mstate_enter_done,         /* DONE */
    mstate_enter_completed,    /* COMPLETED */
    NULL                       /* MSGSENT */
  };

  if(oldstate == state)
    /* do not bother when the new state is the same as the old state */
    return;

#ifdef DEBUGBUILD
  NOVERBOSE((void)lineno);
  CURL_TRC_M(data, "-> [%s] (line %d)", CURL_MSTATE_NAME(state), lineno);
#else
  CURL_TRC_M(data, "-> [%s]", CURL_MSTATE_NAME(state));
#endif

  /* really switching state */
  data->mstate = state;
  if(state_enter[state])
    state_enter[state](data, oldstate);
}

#ifndef DEBUGBUILD
#define multistate(x, y) mstate(x, y)
#else
#define multistate(x, y) mstate(x, y, __LINE__)
#endif

/* multi->proto_hash destructor. Should never be called as elements
 * MUST be added with their own destructor */
static void ph_freeentry(void *p)
{
  (void)p;
  /* Always FALSE. Cannot use a 0 assert here since compilers
   * are not in agreement if they then want a NORETURN attribute or
   * not. *sigh* */
  DEBUGASSERT(!p);
}

/*
 * multi_addmsg()
 *
 * Called when a transfer is completed. Adds the given msg pointer to
 * the list kept in the multi handle.
 */
static void multi_addmsg(struct Curl_multi *multi, struct Curl_message *msg)
{
  if(!Curl_llist_count(&multi->msglist))
    CURLM_NTFY(multi->admin, CURLMNOTIFY_INFO_READ);
  Curl_llist_append(&multi->msglist, msg, &msg->list);
}

static void multi_timeouts_init(struct Curl_easy *data);

struct Curl_multi *Curl_multi_handle(uint32_t xfer_table_size,
                                     size_t ev_hashsize,  /* event hash */
                                     size_t chashsize, /* connection hash */
                                     size_t dnssize,   /* dns hash */
                                     size_t sesssize)  /* TLS session cache */
{
  struct Curl_multi *multi = curlx_calloc(1, sizeof(struct Curl_multi));

  if(!multi)
    return NULL;

  multi->magic = CURLMULTI_MAGIC_NUMBER;

  Curl_dnscache_init(&multi->dnscache, dnssize);
  Curl_mntfy_init(multi);
  Curl_multi_ev_init(multi, ev_hashsize);
  Curl_uint32_tbl_init(&multi->xfers, NULL);
  Curl_uint32_bset_init(&multi->process);
  Curl_uint32_bset_init(&multi->dirty);
  Curl_uint32_bset_init(&multi->pending);
  Curl_uint32_bset_init(&multi->msgsent);
  Curl_hash_init(&multi->proto_hash, 23,
                 Curl_hash_str, curlx_str_key_compare, ph_freeentry);
  Curl_llist_init(&multi->msglist, NULL);

  multi->multiplexing = TRUE;
  multi->max_concurrent_streams = 100;
  multi->last_timeout_ms = -1;
#ifdef ENABLE_WAKEUP
  multi->wakeup_pair[0] = CURL_SOCKET_BAD;
  multi->wakeup_pair[1] = CURL_SOCKET_BAD;
#endif
#ifdef ENABLE_INTERNAL_WAKEUP
  multi->wakeup_internal[0] = CURL_SOCKET_BAD;
  multi->wakeup_internal[1] = CURL_SOCKET_BAD;
#endif

  if(Curl_mntfy_resize(multi) ||
     Curl_uint32_bset_resize(&multi->process, xfer_table_size) ||
     Curl_uint32_bset_resize(&multi->pending, xfer_table_size) ||
     Curl_uint32_bset_resize(&multi->dirty, xfer_table_size) ||
     Curl_uint32_bset_resize(&multi->msgsent, xfer_table_size) ||
     Curl_uint32_tbl_resize(&multi->xfers, xfer_table_size))
    goto error;

  multi->admin = curl_easy_init();
  if(!multi->admin)
    goto error;
  /* Initialize admin handle to operate inside this multi */
  multi->admin->multi = multi;
  multi->admin->state.internal = TRUE;
  multi_timeouts_init(multi->admin);

#ifdef DEBUGBUILD
  if(getenv("CURL_DEBUG"))
    multi->admin->set.verbose = TRUE;
#endif
  Curl_uint32_tbl_add(&multi->xfers, multi->admin, &multi->admin->mid);
  Curl_uint32_bset_add(&multi->process, multi->admin->mid);

  if(Curl_cshutdn_init(&multi->cshutdn, multi))
    goto error;

  Curl_cpool_init(&multi->cpool, multi->admin, NULL, chashsize);

#ifdef USE_SSL
  if(Curl_ssl_scache_create(sesssize, 2, &multi->ssl_scache))
    goto error;
#else
  (void)sesssize;
#endif

#ifdef USE_WINSOCK
  multi->wsa_event = WSACreateEvent();
  if(multi->wsa_event == WSA_INVALID_EVENT)
    goto error;
#endif
#ifdef ENABLE_WAKEUP
  /* When enabled, rely on this to work. We ignore this in previous
   * versions, but that seems an unnecessary complication. */
  if(Curl_wakeup_init(multi->wakeup_pair, TRUE) < 0)
    goto error;
#endif
#ifdef ENABLE_INTERNAL_WAKEUP
  if(Curl_wakeup_init(multi->wakeup_internal, TRUE) < 0)
    goto error;
#endif

  if(Curl_probeipv6(multi))
    goto error;

#ifdef USE_RESOLV_THREADED
  if(xfer_table_size < CURL_XFER_TABLE_SIZE) { /* easy multi */
    if(Curl_async_thrdd_multi_init(multi, 0, 2, 10))
      goto error;
  }
  else { /* real multi handle */
    if(Curl_async_thrdd_multi_init(multi, 0, 20, 2000))
      goto error;
  }
#endif

  return multi;

error:

#ifdef USE_RESOLV_THREADED
  Curl_async_thrdd_multi_destroy(multi, TRUE);
#endif
  Curl_multi_ev_cleanup(multi);
  Curl_hash_destroy(&multi->proto_hash);
  Curl_dnscache_destroy(&multi->dnscache);
  Curl_cpool_destroy(&multi->cpool);
  Curl_cshutdn_destroy(&multi->cshutdn, multi->admin);
#ifdef USE_SSL
  Curl_ssl_scache_destroy(multi->ssl_scache);
#endif
  if(multi->admin) {
    Curl_multi_ev_xfer_done(multi, multi->admin);
    multi->admin->multi = NULL;
    Curl_close(&multi->admin);
  }
  Curl_mntfy_cleanup(multi);

  Curl_uint32_bset_destroy(&multi->process);
  Curl_uint32_bset_destroy(&multi->dirty);
  Curl_uint32_bset_destroy(&multi->pending);
  Curl_uint32_bset_destroy(&multi->msgsent);
  Curl_uint32_tbl_destroy(&multi->xfers);
#ifdef ENABLE_WAKEUP
  Curl_wakeup_destroy(multi->wakeup_pair);
#endif
#ifdef ENABLE_INTERNAL_WAKEUP
  Curl_wakeup_destroy(multi->wakeup_internal);
#endif

  curlx_free(multi);
  return NULL;
}

CURLM *curl_multi_init(void)
{
  return Curl_multi_handle(CURL_XFER_TABLE_SIZE,
                           CURL_SOCKET_HASH_TABLE_SIZE,
                           CURL_CONNECTION_HASH_SIZE,
                           CURL_DNS_HASH_SIZE,
                           CURL_TLS_SESSION_SIZE);
}

#if defined(DEBUGBUILD) && defined(CURLVERBOSE)
static void multi_warn_debug(struct Curl_multi *multi, struct Curl_easy *data)
{
  if(!multi->warned) {
    infof(data, "!!! WARNING !!!");
    infof(data, "This is a debug build of libcurl, "
                "do not use in production.");
    multi->warned = TRUE;
  }
}
#else
#define multi_warn_debug(x, y) Curl_nop_stmt
#endif

bool Curl_is_connecting(struct Curl_easy *data)
{
  return data->mstate < MSTATE_DO;
}

static CURLMcode multi_assess_wakeup(struct Curl_multi *multi)
{
#ifdef ENABLE_INTERNAL_WAKEUP
  if(multi->socket_cb)
    return Curl_multi_ev_assess_xfer(multi, multi->admin);
#else
  (void)multi;
#endif
  return CURLM_OK;
}

static CURLMcode multi_xfers_add(struct Curl_multi *multi,
                                 struct Curl_easy *data)
{
  uint32_t capacity = Curl_uint32_tbl_capacity(&multi->xfers);
  uint32_t new_size = 0;
  /* Prepare to make this into a CURLMOPT_MAX_TRANSFERS, because some
   * applications may want to prevent a run-away of their memory use. */
  /* UINT_MAX is our "invalid" id, do not let the table grow up to that. */
  const uint32_t max_capacity = UINT_MAX - 1;

  if(capacity < max_capacity) {
    /* We want `multi->xfers` to have "sufficient" free rows, so that we do
     * not have to reuse the `mid` from a removed easy right away.
     * Since uint_tbl and uint_bset are memory efficient,
     * regard less than 25% free as insufficient.
     * (for low capacities, e.g. multi_easy, 4 or less). */
    uint32_t used = Curl_uint32_tbl_count(&multi->xfers);
    uint32_t unused = capacity - used;
    uint32_t min_unused = CURLMAX(capacity >> 2, 4);
    if(unused <= min_unused) {
      /* Make sure the uint arithmetic here works on the corner
       * cases where we are close to max_capacity or UINT_MAX */
      if((min_unused >= max_capacity) ||
         ((max_capacity - min_unused) <= capacity) ||
         ((UINT_MAX - min_unused - 63) <= capacity)) {
        new_size = max_capacity; /* can not be larger than this */
      }
      else {
        /* make it a 64 multiple, since our bitsets grow by that and
         * small (easy_multi) grows to at least 64 on first resize. */
        new_size = (((used + min_unused) + 63) / 64) * 64;
      }
    }
  }

  if(new_size > capacity) {
    /* Grow the bitsets first. Should one fail, we do not need
     * to downsize the already resized ones. The sets continue
     * to work properly when larger than the table, but not
     * the other way around. */
    CURL_TRC_M(data, "increasing xfer table size to %u", new_size);
    if(Curl_uint32_bset_resize(&multi->process, new_size) ||
       Curl_uint32_bset_resize(&multi->dirty, new_size) ||
       Curl_uint32_bset_resize(&multi->pending, new_size) ||
       Curl_uint32_bset_resize(&multi->msgsent, new_size) ||
       Curl_uint32_tbl_resize(&multi->xfers, new_size))
      return CURLM_OUT_OF_MEMORY;
  }

  /* Insert the easy into the table now */
  if(!Curl_uint32_tbl_add(&multi->xfers, data, &data->mid)) {
    /* MUST only happen when table is full */
    DEBUGASSERT(Curl_uint32_tbl_capacity(&multi->xfers) <=
                Curl_uint32_tbl_count(&multi->xfers));
    return CURLM_OUT_OF_MEMORY;
  }
  return CURLM_OK;
}

CURLMcode Curl_multi_add_handle(struct Curl_multi *multi,
                                struct Curl_easy *data)
{
  CURLMcode mresult;

  /* Prevent users from adding same easy handle more than once and prevent
     adding to more than one multi stack */
  if(data->multi)
    return CURLM_ADDED_ALREADY;

  if(multi->dead) {
    /* a "dead" handle cannot get added transfers while any existing easy
       handles are still alive - but if there are none alive anymore, it is
       fine to start over and unmark the "deadness" of this handle.
       This means only the admin handle MUST be present. */
    if((Curl_uint32_tbl_count(&multi->xfers) != 1) ||
       !Curl_uint32_tbl_contains(&multi->xfers, 0))
      return CURLM_ABORTED_BY_CALLBACK;
    multi->dead = FALSE;
    Curl_uint32_bset_clear(&multi->process);
    Curl_uint32_bset_clear(&multi->dirty);
    Curl_uint32_bset_clear(&multi->pending);
    Curl_uint32_bset_clear(&multi->msgsent);
  }

  if(data->multi_easy) {
    /* if this easy handle was previously used for curl_easy_perform(), there
       is a private multi handle here that we can kill */
    curl_multi_cleanup(data->multi_easy);
    data->multi_easy = NULL;
  }

  /* Insert the easy into the multi->xfers table, assigning it a `mid`. */
  if(multi_xfers_add(multi, data))
    return CURLM_OUT_OF_MEMORY;

  /* Initialize timeouts for this handle */
  multi_timeouts_init(data);

  /*
   * No failure allowed in this function beyond this point. No modification
   * of easy nor multi handle allowed before this except for potential
   * multi's connection pool growing which will not be undone in this
   * function no matter what.
   */
  if(data->set.errorbuffer)
    data->set.errorbuffer[0] = 0;

  data->state.os_errno = 0;

  /* make the Curl_easy refer back to this multi handle - before
     Curl_expire() is called. */
  data->multi = multi;

  /* set the easy handle */
  multistate(data, MSTATE_INIT);
  /* not yet passed INIT state */
  data->state.really_alive = FALSE;

#ifdef USE_LIBPSL
  /* Do the same for PSL. */
  if(data->share && (data->share->specifier & (1 << CURL_LOCK_DATA_PSL)))
    data->psl = &data->share->psl;
  else
    data->psl = &multi->psl;
#endif

  /* add the easy handle to the process set */
  Curl_uint32_bset_add(&multi->process, data->mid);
  ++multi->xfers_alive;
  ++multi->xfers_total_ever;

  Curl_cpool_xfer_init(data);
  multi_warn_debug(multi, data);

  /* Make sure the new handle will run */
  Curl_multi_mark_dirty(data);

  /* Necessary in event based processing, where dirty handles trigger
   * a timeout callback invocation. */
  mresult = Curl_update_timer(multi);
  if(mresult) {
    data->multi = NULL; /* not anymore */
    Curl_uint32_tbl_remove(&multi->xfers, data->mid);
    data->mid = UINT32_MAX;
    return mresult;
  }

  /* The admin handle only ever has default timeouts set. To improve the
     state somewhat we clone the timeouts from each added handle so that the
     admin handle always has the same timeouts as the most recently added
     easy handle. */
  multi->admin->set.timeout = data->set.timeout;
  multi->admin->set.server_response_timeout =
    data->set.server_response_timeout;
  multi->admin->set.no_signal = data->set.no_signal;

  CURL_TRC_M(data, "added to multi, mid=%u, running=%u, total=%u",
             data->mid, Curl_multi_xfers_running(multi),
             Curl_uint32_tbl_count(&multi->xfers));
  return CURLM_OK;
}

CURLMcode curl_multi_add_handle(CURLM *m, CURL *curl)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_add_handle, &mresult)) {
    struct Curl_easy *data = curl;
    /* Verify that we got a somewhat good easy handle too */
    if(!GOOD_EASY_HANDLE(data))
      mresult = CURLM_BAD_EASY_HANDLE;
    else
      mresult = Curl_multi_add_handle(m, data);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

struct multi_done_ctx {
  BIT(premature);
};

static bool multi_conn_should_close(struct connectdata *conn,
                                    struct Curl_easy *data,
                                    bool premature)
{
  /* if conn->bits.close is TRUE, it means that the connection should be
     closed in spite of everything else. */
  if(conn->bits.close)
    return TRUE;

  /* if data->set.reuse_forbid is TRUE, it means the libcurl client has
     forced us to close this connection. This is ignored for requests taking
     place in a NTLM/NEGOTIATE authentication handshake. */
  if(data->set.reuse_forbid
#ifdef USE_NTLM
     && !(conn->http_ntlm_state == NTLMSTATE_TYPE2 ||
          conn->proxy_ntlm_state == NTLMSTATE_TYPE2)
#endif
#ifdef USE_SPNEGO
     && !(conn->http_negotiate_state == GSS_AUTHRECV ||
          conn->proxy_negotiate_state == GSS_AUTHRECV)
#endif
    )
    return TRUE;

  /* Unless this connection is for a "connect-only" transfer, it
   * needs to be closed if the protocol handler does not support reuse. */
  if(!data->set.connect_only && conn->scheme &&
     !(conn->scheme->flags & PROTOPT_CONN_REUSE))
    return TRUE;

  /* if premature is TRUE, it means this connection was said to be DONE before
     the entire request operation is complete and thus we cannot know in what
     state it is for reusing, so we are forced to close it. In a perfect world
     we can add code that keep track of if we really must close it here or not,
     but currently we have no such detail knowledge. */
  if(premature && !Curl_conn_is_multiplex(conn, FIRSTSOCKET))
    return TRUE;

  return FALSE;
}

static void multi_done_locked(struct connectdata *conn,
                              struct Curl_easy *data,
                              void *userdata)
{
  struct multi_done_ctx *mdctx = userdata;

  Curl_detach_connection(data);

  CURL_TRC_M(data, "multi_done_locked, in use=%u", conn->attached_xfers);
  if(CONN_INUSE(conn)) {
    /* Stop if still used. */
    CURL_TRC_M(data, "Connection still in use %u, no more multi_done now!",
               conn->attached_xfers);
    return;
  }

  data->state.done = TRUE; /* called now! */
  data->state.recent_conn_id = conn->connection_id;

  Curl_dnscache_prune(data);

  if(multi_conn_should_close(conn, data, (bool)mdctx->premature)) {
    CURL_TRC_M(data, "multi_done, terminating conn #%" FMT_OFF_T " to %s, "
               "forbid=%d, close=%d, premature=%d, conn_multiplex=%d",
               conn->connection_id, conn->destination,
               data->set.reuse_forbid, conn->bits.close, mdctx->premature,
               Curl_conn_is_multiplex(conn, FIRSTSOCKET));
    connclose(conn);
    Curl_conn_terminate(data, conn, (bool)mdctx->premature);
  }
  else if(!Curl_conn_get_max_concurrent(data, conn, FIRSTSOCKET)) {
    CURL_TRC_M(data, "multi_done, conn #%" FMT_OFF_T " to %s was shutdown"
               " by server, not reusing", conn->connection_id,
               conn->destination);
    connclose(conn);
    Curl_conn_terminate(data, conn, (bool)mdctx->premature);
  }
  else {
    /* the connection is no longer in use by any transfer */
    if(Curl_cpool_conn_now_idle(data, conn)) {
      /* connection kept in the cpool */
      data->state.lastconnect_id = conn->connection_id;
      infof(data, "Connection #%" FMT_OFF_T " to host %s left intact",
            conn->connection_id, conn->destination);
    }
    else {
      /* connection was removed from the cpool and destroyed. */
      data->state.lastconnect_id = -1;
    }
  }
}

static CURLcode multi_done(struct Curl_easy *data,
                           CURLcode status,  /* an error if this is called
                                                after an error was detected */
                           bool premature)
{
  CURLcode result;
  struct connectdata *conn = data->conn;

  CURL_TRC_M(data, "multi_done: status: %d prem: %d done: %d",
             (int)status, (int)premature, data->state.done);

  if(data->state.done)
    /* Stop if multi_done() has already been called */
    return CURLE_OK;

  /* Shut down any ongoing async resolver operation. */
  Curl_resolv_shutdown_all(data);

  /* Cleanup possible redirect junk */
  curlx_safefree(data->req.newurl);
  curlx_safefree(data->req.location);

  switch(status) {
  case CURLE_ABORTED_BY_CALLBACK:
  case CURLE_READ_ERROR:
  case CURLE_WRITE_ERROR:
    /* When we are aborted due to a callback return code it has to be counted
       as premature as there is trouble ahead if we do not. We have many
       callbacks and protocols work differently, we could potentially do this
       more fine-grained in the future. */
    premature = TRUE;
    FALLTHROUGH();
  default:
    break;
  }

  /* this calls the protocol-specific function pointer previously set */
  if(conn && conn->scheme->run->done && (data->mstate >= MSTATE_PROTOCONNECT))
    result = conn->scheme->run->done(data, status, premature);
  else
    result = status;

  if(data->mstate > MSTATE_CONNECTING &&
     (result != CURLE_ABORTED_BY_CALLBACK)) {
    /* avoid this if
     * - the transfer has not connected
     * - we already aborted by callback to avoid this calling another callback
     */
    int rc = Curl_pgrsDone(data);
    if(!result && rc)
      result = CURLE_ABORTED_BY_CALLBACK;
  }

  /* Make sure that transfer client writes are really done now. */
  result = Curl_1st_fatal(result, Curl_xfer_write_done(data, premature));

  /* Inform connection filters that this transfer is done */
  if(conn)
    Curl_conn_ev_data_done(data, premature);

  multi_schedule_pending(data->multi); /* connection / multiplex */

  if(!result)
    result = Curl_req_done(&data->req, data, premature);

  if(conn) {
    /* Under the potential connection pool's share lock, decide what to
     * do with the transfer's connection. */
    struct multi_done_ctx mdctx;

    memset(&mdctx, 0, sizeof(mdctx));
    mdctx.premature = premature;
    Curl_cpool_do_locked(data, data->conn, multi_done_locked, &mdctx);
  }

  /* flush the netrc cache */
  Curl_netrc_cleanup(&data->state.netrc);
  return result;
}

CURLMcode Curl_multi_remove_handle(struct Curl_multi *multi,
                                   struct Curl_easy *data)
{
  CURLMcode mresult;
  bool premature;
  struct Curl_llist_node *e;
  uint32_t mid;

  /* Prevent users from trying to remove same easy handle more than once */
  if(!data->multi)
    return CURLM_OK; /* it is already removed so let's say it is fine! */

  /* Prevent users from trying to remove an easy handle from the wrong multi */
  if(data->multi != multi)
    return CURLM_BAD_EASY_HANDLE;

  if(data->mid == UINT32_MAX) {
    DEBUGASSERT(0);
    return CURLM_INTERNAL_ERROR;
  }
  if(Curl_uint32_tbl_get(&multi->xfers, data->mid) != data) {
    DEBUGASSERT(0);
    return CURLM_INTERNAL_ERROR;
  }

  premature = (data->mstate < MSTATE_COMPLETED);

  if(data->conn) {
    /* If the 'state' is not INIT or COMPLETED, we might need to do something
       nice to put the easy_handle in a good known state when this returns. */
    if(premature && (data->mstate > MSTATE_DO))
      streamclose(data->conn);

    /* multi_done() clears the association between the easy handle and the
       connection.
       Note that this ignores the return code because there is
       nothing really useful to do with it anyway! */
    (void)multi_done(data, data->result, premature);
  }

  /* The timer must be shut down before data->multi is set to NULL, else
     data's splaynode would remain in the splay tree after curl_easy_cleanup is
     called. Do it after multi_done() in case that sets another time! */
  Curl_expire_clear(data);

  /* If in `msgsent`, it was deducted from `multi->xfers_alive` already. */
  if(!Curl_uint32_bset_contains(&multi->msgsent, data->mid))
    --multi->xfers_alive;

  if(data->state.really_alive) {
    data->state.really_alive = FALSE;
    --multi->xfers_really_alive;
    if(!multi->xfers_really_alive)
      (void)multi_assess_wakeup(multi);
  }

  Curl_wildcard_dtor(&data->wildcard);

  data->mstate = MSTATE_COMPLETED;

  /* Remove the association between the connection and the handle */
  Curl_detach_connection(data);

  /* Tell event handling that this transfer is definitely going away */
  Curl_multi_ev_xfer_done(multi, data);

  if(data->set.connect_only) {
    if(data->multi_easy) {
      if(data->state.lastconnect_id != -1) {
        /* Mark any connect-only connection for closure */
        struct connectdata *conn;
        (void)Curl_getconnectinfo(data, &conn);
        if(conn && conn->bits.connect_only)
          connclose(conn);
      }
    }
    else {
      /* This removes a handle that was part the multi interface that used
         CONNECT_ONLY, that connection is now left alive but since this handle
         has bits.close set nothing can use that connection anymore and it is
         forbidden from reuse. This easy handle cannot find the connection
         anymore once removed from the multi handle

         Better close the connection here, at once. */
      struct connectdata *conn;
      (void)Curl_getconnectinfo(data, &conn);
      if(conn)
        Curl_conn_terminate(data, conn, TRUE);
    }
  }

#ifdef USE_LIBPSL
  /* Remove the PSL association. */
  if(data->psl == &multi->psl)
    data->psl = NULL;
#endif

  /* make sure there is no pending message in the queue sent from this easy
     handle */
  for(e = Curl_llist_head(&multi->msglist); e; e = Curl_node_next(e)) {
    struct Curl_message *msg = Curl_node_elem(e);

    if(msg->extmsg.easy_handle == data) {
      Curl_node_remove(e);
      /* there can only be one from this specific handle */
      break;
    }
  }

  /* clear the association to this multi handle */
  mid = data->mid;
  DEBUGASSERT(Curl_uint32_tbl_contains(&multi->xfers, mid));
  Curl_uint32_tbl_remove(&multi->xfers, mid);
  Curl_uint32_bset_remove(&multi->process, mid);
  Curl_uint32_bset_remove(&multi->dirty, mid);
  Curl_uint32_bset_remove(&multi->pending, mid);
  Curl_uint32_bset_remove(&multi->msgsent, mid);
  data->multi = NULL;
  data->mid = UINT32_MAX;
  data->master_mid = UINT32_MAX;

  /* A pending transfer *might* be able to run now. */
  multi_schedule_pending(multi);
  mresult = Curl_update_timer(multi);
  if(mresult)
    return mresult;

  mresult = multi_assess_wakeup(multi);
  if(mresult) {
    failf(data, "error enabling wakeup listening: %d", mresult);
    return mresult;
  }

  CURL_TRC_M(data, "removed from multi, mid=%u, running=%u, total=%u",
             mid, Curl_multi_xfers_running(multi),
             Curl_uint32_tbl_count(&multi->xfers));
  return CURLM_OK;
}

CURLMcode curl_multi_remove_handle(CURLM *m, CURL *curl)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_remove_handle, &mresult)) {
    struct Curl_easy *data = curl;
    if(!GOOD_EASY_HANDLE(data))
      mresult = CURLM_BAD_EASY_HANDLE;
    else
      mresult = Curl_multi_remove_handle(m, data);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

/* Return TRUE if the application asked for multiplexing */
bool Curl_multiplex_wanted(const struct Curl_multi *multi)
{
  return multi && multi->multiplexing;
}

/*
 * Curl_detach_connection() removes the given transfer from the connection.
 *
 * This is the only function that should clear data->conn. This will
 * occasionally be called with the data->conn pointer already cleared.
 */
void Curl_detach_connection(struct Curl_easy *data)
{
  struct connectdata *conn = data->conn;
  if(conn) {
    /* this should never happen, prevent underflow */
    DEBUGASSERT(conn->attached_xfers);
    if(conn->attached_xfers) {
      conn->attached_xfers--;
      if(!conn->attached_xfers)
        conn->attached_multi = NULL;
    }
  }
  data->conn = NULL;
}

/*
 * Curl_attach_connection() attaches this transfer to this connection.
 *
 * This is the only function that should assign data->conn
 */
void Curl_attach_connection(struct Curl_easy *data,
                            struct connectdata *conn)
{
  DEBUGASSERT(data);
  DEBUGASSERT(!data->conn);
  DEBUGASSERT(conn);
  DEBUGASSERT(conn->attached_xfers < UINT32_MAX);
  data->conn = conn;
  conn->attached_xfers++;
  /* all attached transfers must be from the same multi */
  if(!conn->attached_multi)
    conn->attached_multi = data->multi;
  DEBUGASSERT(conn->attached_multi == data->multi);

  if(conn->scheme && conn->scheme->run->attach)
    conn->scheme->run->attach(data, conn);
}

/* adjust pollset for rate limits/pauses */
static CURLcode multi_adjust_pollset(struct Curl_easy *data,
                                     struct easy_pollset *ps)
{
  CURLcode result = CURLE_OK;

  if(ps->n) {
    bool send_blocked, recv_blocked;

    recv_blocked = (Curl_rlimit_avail(&data->progress.dl.rlimit, NULL) <= 0);
    send_blocked = (Curl_rlimit_avail(&data->progress.ul.rlimit, NULL) <= 0);
    if(send_blocked || recv_blocked) {
      int i;
      for(i = 0; i <= SECONDARYSOCKET; ++i) {
        curl_socket_t sock = data->conn->sock[i];
        if(sock == CURL_SOCKET_BAD)
          continue;
        if(recv_blocked && Curl_pollset_want_recv(data, ps, sock)) {
          result = Curl_pollset_remove_in(data, ps, sock);
          if(result)
            break;
        }
        if(send_blocked && Curl_pollset_want_send(data, ps, sock)) {
          result = Curl_pollset_remove_out(data, ps, sock);
          if(result)
            break;
        }
      }
    }

    /* Not blocked and wanting to receive. If there is data pending
     * in the connection filters, make transfer run again. */
    if(!recv_blocked &&
       ((Curl_pollset_want_recv(data, ps, data->conn->sock[FIRSTSOCKET]) &&
         Curl_conn_data_pending(data, FIRSTSOCKET)) ||
        (Curl_pollset_want_recv(data, ps, data->conn->sock[SECONDARYSOCKET]) &&
         Curl_conn_data_pending(data, SECONDARYSOCKET)))) {
      CURL_TRC_M(data, "pollset[] has POLLIN, but there is still "
                 "buffered input -> mark as dirty");
      Curl_multi_mark_dirty(data);
    }
  }
  return result;
}

static CURLcode mstate_connecting_pollset(struct Curl_easy *data,
                                          struct easy_pollset *ps)
{
  struct connectdata *conn = data->conn;
  curl_socket_t sockfd;
  CURLcode result = CURLE_OK;

  if(Curl_xfer_recv_is_paused(data))
    return CURLE_OK;
  /* If a socket is set, receiving is default. If the socket
   * has not been determined yet (eyeballing), always ask the
   * connection filters for what to monitor. */
  sockfd = Curl_conn_get_first_socket(data);
  if(sockfd != CURL_SOCKET_BAD) {
    result = Curl_pollset_change(data, ps, sockfd, CURL_POLL_IN, 0);
    if(!result)
      result = multi_adjust_pollset(data, ps);
  }
  if(!result)
    result = Curl_conn_adjust_pollset(data, conn, ps);
  return result;
}

static CURLcode mstate_protocol_pollset(struct Curl_easy *data,
                                        struct easy_pollset *ps)
{
  struct connectdata *conn = data->conn;
  CURLcode result = CURLE_OK;

  if(conn->scheme->run->proto_pollset)
    result = conn->scheme->run->proto_pollset(data, ps);
  else {
    curl_socket_t sockfd = conn->sock[FIRSTSOCKET];
    if(sockfd != CURL_SOCKET_BAD) {
      /* Default is to wait to something from the server */
      result = Curl_pollset_change(data, ps, sockfd, CURL_POLL_IN, 0);
    }
  }
  if(!result)
    result = multi_adjust_pollset(data, ps);
  if(!result)
    result = Curl_conn_adjust_pollset(data, conn, ps);
  return result;
}

static CURLcode mstate_do_pollset(struct Curl_easy *data,
                                  struct easy_pollset *ps)
{
  struct connectdata *conn = data->conn;
  CURLcode result = CURLE_OK;

  if(conn->scheme->run->doing_pollset)
    result = conn->scheme->run->doing_pollset(data, ps);
  else if(CONN_SOCK_IDX_VALID(conn->send_idx)) {
    /* Default is that we want to send something to the server */
    result = Curl_pollset_add_out(data, ps, conn->sock[conn->send_idx]);
  }
  if(!result)
    result = multi_adjust_pollset(data, ps);
  if(!result)
    result = Curl_conn_adjust_pollset(data, conn, ps);
  return result;
}

static CURLcode mstate_domore_pollset(struct Curl_easy *data,
                                      struct easy_pollset *ps)
{
  struct connectdata *conn = data->conn;
  CURLcode result = CURLE_OK;

  if(conn->scheme->run->domore_pollset)
    result = conn->scheme->run->domore_pollset(data, ps);
  else if(CONN_SOCK_IDX_VALID(conn->send_idx)) {
    /* Default is that we want to send something to the server */
    result = Curl_pollset_add_out(data, ps, conn->sock[conn->send_idx]);
  }
  if(!result)
    result = multi_adjust_pollset(data, ps);
  if(!result)
    result = Curl_conn_adjust_pollset(data, conn, ps);
  return result;
}

static CURLcode mstate_perform_pollset(struct Curl_easy *data,
                                       struct easy_pollset *ps)
{
  struct connectdata *conn = data->conn;
  CURLcode result = CURLE_OK;

  if(conn->scheme->run->perform_pollset)
    result = conn->scheme->run->perform_pollset(data, ps);
  else {
    /* Default is to obey the request flags for send/recv */
    if(Curl_req_want_recv(data) && CONN_SOCK_IDX_VALID(conn->recv_idx)) {
      result = Curl_pollset_add_in(data, ps, conn->sock[conn->recv_idx]);
    }
    if(!result && Curl_req_want_send(data) &&
       CONN_SOCK_IDX_VALID(conn->send_idx)) {
      result = Curl_pollset_add_out(data, ps, conn->sock[conn->send_idx]);
    }
  }
  if(!result)
    result = multi_adjust_pollset(data, ps);
  if(!result)
    result = Curl_conn_adjust_pollset(data, conn, ps);
  return result;
}

#ifdef CURLVERBOSE
static size_t multi_timeouts_count(struct expire_timers *timeouts)
{
  size_t n = 0;
  expire_id eid = timeouts->first;
  for(; eid < EXPIRE_LAST; eid = timeouts->next[eid])
    ++n;
  return n;
}
#endif

/* Initializes `poll_set` with the current socket poll actions needed
 * for transfer `data`. */
CURLMcode Curl_multi_pollset(struct Curl_easy *data,
                             struct easy_pollset *ps)
{
  CURLcode result = CURLE_OK;

  Curl_pollset_reset(ps);
#ifdef ENABLE_INTERNAL_WAKEUP
  /* The admin handle always listens on the wakeup socket when there
   * are transfers alive. */
  if(data->multi && (data == data->multi->admin) &&
     data->multi->xfers_really_alive) {
    CURL_TRC_M(data, "adding wakeup, %u xfers really alive",
               data->multi->xfers_really_alive);
    result = Curl_pollset_add_in(data, ps, data->multi->wakeup_internal[0]);
  }
#endif
  /* If the transfer has no connection, this is fine. Happens when
     called via curl_multi_remove_handle() => Curl_multi_ev_assess() =>
     Curl_multi_pollset(). */
  if(!result && data->conn) {
    switch(data->mstate) {
    case MSTATE_INIT:
    case MSTATE_PENDING:
    case MSTATE_SETUP:
    case MSTATE_CONNECT:
      /* nothing to poll for yet */
      break;

    case MSTATE_CONNECTING:
      result = mstate_connecting_pollset(data, ps);
      break;

    case MSTATE_PROTOCONNECT:
    case MSTATE_PROTOCONNECTING:
      result = mstate_protocol_pollset(data, ps);
      break;

    case MSTATE_DO:
    case MSTATE_DOING:
      result = mstate_do_pollset(data, ps);
      break;

    case MSTATE_DOING_MORE:
      result = mstate_domore_pollset(data, ps);
      break;

    case MSTATE_DID: /* same as PERFORMING in regard to polling */
    case MSTATE_PERFORMING:
      result = mstate_perform_pollset(data, ps);
      break;

    case MSTATE_RATELIMITING:
      /* we need to let time pass, ignore socket(s) */
      break;

    case MSTATE_DONE:
    case MSTATE_COMPLETED:
    case MSTATE_MSGSENT:
      /* nothing more to poll for */
      break;

    default:
      failf(data, "multi_getsock: unexpected multi state %d",
            (int)data->mstate);
      DEBUGASSERT(0);
      break;
    }
  }

  if(result) {
    if(result == CURLE_OUT_OF_MEMORY)
      return CURLM_OUT_OF_MEMORY;
    failf(data, "error determining pollset: %d", (int)result);
    return CURLM_INTERNAL_ERROR;
  }

#ifdef CURLVERBOSE
  if(CURL_TRC_M_is_verbose(data)) {
    size_t timeout_count = multi_timeouts_count(&data->state.timeouts);
    switch(ps->n) {
    case 0:
      CURL_TRC_M(data, "pollset[], timeouts=%zu, paused %d/%d (r/w)",
                 timeout_count,
                 Curl_xfer_send_is_paused(data),
                 Curl_xfer_recv_is_paused(data));
      break;
    case 1:
      CURL_TRC_M(data, "pollset[fd=%" FMT_SOCKET_T " %s%s], timeouts=%zu",
                 ps->sockets[0],
                 (ps->actions[0] & CURL_POLL_IN) ? "IN" : "",
                 (ps->actions[0] & CURL_POLL_OUT) ? "OUT" : "",
                 timeout_count);
      break;
    case 2:
      CURL_TRC_M(data, "pollset[fd=%" FMT_SOCKET_T " %s%s, "
                 "fd=%" FMT_SOCKET_T " %s%s], timeouts=%zu",
                 ps->sockets[0],
                 (ps->actions[0] & CURL_POLL_IN) ? "IN" : "",
                 (ps->actions[0] & CURL_POLL_OUT) ? "OUT" : "",
                 ps->sockets[1],
                 (ps->actions[1] & CURL_POLL_IN) ? "IN" : "",
                 (ps->actions[1] & CURL_POLL_OUT) ? "OUT" : "",
                 timeout_count);
      break;
    default:
      CURL_TRC_M(data, "pollset[fds=%u], timeouts=%zu", ps->n, timeout_count);
      break;
    }
    CURL_TRC_EASY_TIMERS(data);
  }
#endif

  return CURLM_OK;
}

CURLMcode curl_multi_fdset(CURLM *m,
                           fd_set *read_fd_set, fd_set *write_fd_set,
                           fd_set *exc_fd_set, int *max_fd)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_fdset, &mresult)) {
    /* Scan through all the easy handles to get the file descriptors set.
       Some easy handles may not have connected to the remote host yet,
       and then we must make sure that is done. */
    struct Curl_multi *multi = m;
    struct easy_pollset ps;
    int this_max_fd = -1;
    unsigned int i;
    uint32_t mid;
    (void)exc_fd_set;

    Curl_pollset_init(&ps);
    if(Curl_uint32_bset_first(&multi->process, &mid)) {
      do {
        struct Curl_easy *data = Curl_multi_get_easy(multi, mid);

        if(!data) {
          DEBUGASSERT(0);
          continue;
        }

        Curl_multi_pollset(data, &ps);
        for(i = 0; i < ps.n; i++) {
          if(!FDSET_SOCK(ps.sockets[i]))
            /* pretend it does not exist */
            continue;
          if(ps.actions[i] & CURL_POLL_IN)
            FD_SET(ps.sockets[i], read_fd_set);
          if(ps.actions[i] & CURL_POLL_OUT)
            FD_SET(ps.sockets[i], write_fd_set);
          if((int)ps.sockets[i] > this_max_fd)
            this_max_fd = (int)ps.sockets[i];
        }
      } while(Curl_uint32_bset_next(&multi->process, mid, &mid));
    }

    Curl_cshutdn_setfds(&multi->cshutdn, multi->admin,
                        read_fd_set, write_fd_set, &this_max_fd);

    *max_fd = this_max_fd;
    Curl_pollset_cleanup(&ps);

    mresult = CURLM_OK;
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_waitfds(CURLM *m,
                             struct curl_waitfd *ufds,
                             unsigned int size,
                             unsigned int *fd_count)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_waitfds, &mresult)) {
    struct Curl_waitfds cwfds;
    struct Curl_multi *multi = m;
    struct easy_pollset ps;
    unsigned int need = 0;
    uint32_t mid;

    if(!ufds && (size || !fd_count)) {
      mresult = CURLM_BAD_FUNCTION_ARGUMENT;
      goto out;
    }

    Curl_pollset_init(&ps);
    Curl_waitfds_init(&cwfds, ufds, size);
    mresult = CURLM_OK;
    if(Curl_uint32_bset_first(&multi->process, &mid)) {
      do {
        struct Curl_easy *data = Curl_multi_get_easy(multi, mid);
        if(!data) {
          DEBUGASSERT(0);
          Curl_uint32_bset_remove(&multi->process, mid);
          Curl_uint32_bset_remove(&multi->dirty, mid);
          continue;
        }
        Curl_multi_pollset(data, &ps);
        need += Curl_waitfds_add_ps(&cwfds, &ps);
      } while(Curl_uint32_bset_next(&multi->process, mid, &mid));
    }

    need += Curl_cshutdn_add_waitfds(&multi->cshutdn, multi->admin, &cwfds);

    if(need != cwfds.n && ufds)
      mresult = CURLM_OUT_OF_MEMORY;

    if(fd_count)
      *fd_count = need;
    Curl_pollset_cleanup(&ps);
  }
out:
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

#ifdef USE_WINSOCK
/* Reset FD_WRITE for TCP sockets. Nothing is actually sent. UDP sockets cannot
 * be reset this way because an empty datagram would be sent. #9203
 *
 * "On Windows the internal state of FD_WRITE as returned from
 * WSAEnumNetworkEvents is only reset after successful send()."
 */
static void reset_socket_fdwrite(curl_socket_t s)
{
  int t;
  int l = (int)sizeof(t);
  if(!getsockopt(s, SOL_SOCKET, SO_TYPE, (char *)&t, &l) && t == SOCK_STREAM)
    swrite(s, NULL, 0);
}

static CURLMcode multi_winsock_select(struct Curl_multi *multi,
                                      struct curl_pollfds *cpfds,
                                      unsigned int curl_nfds,
                                      struct curl_waitfd extra_fds[],
                                      unsigned int extra_nfds,
                                      int timeout_ms,
                                      bool extrawait,
                                      int *pnevents)
{
  CURLMcode mresult = CURLM_OK;
  WSANETWORKEVENTS wsa_events;
  int nevents = 0;
  size_t i;

  DEBUGASSERT(multi->wsa_event != WSA_INVALID_EVENT);

  /* Set the WSA events based on the collected pollds */
  for(i = 0; i < cpfds->n; i++) {
    long mask = 0;
    if(cpfds->pfds[i].events & POLLIN)
      mask |= FD_READ | FD_ACCEPT | FD_CLOSE;
    if(cpfds->pfds[i].events & POLLPRI)
      mask |= FD_OOB;
    if(cpfds->pfds[i].events & POLLOUT) {
      mask |= FD_WRITE | FD_CONNECT | FD_CLOSE;
      reset_socket_fdwrite(cpfds->pfds[i].fd);
    }
    if(mask) {
      if(WSAEventSelect(cpfds->pfds[i].fd, multi->wsa_event, mask) != 0) {
        mresult = CURLM_OUT_OF_MEMORY;
        goto out;
      }
    }
  }

  if(cpfds->n || extrawait) {
    int pollrc = 0;

    if(cpfds->n) {         /* pre-check with Winsock */
      pollrc = Curl_poll(cpfds->pfds, cpfds->n, 0);
      if(pollrc < 0) {
        mresult = CURLM_UNRECOVERABLE_POLL;
        goto out;
      }
      nevents = pollrc;
    }

    if(!nevents) {
      /* now wait... if not ready during the pre-check (pollrc == 0) */
      WSAWaitForMultipleEvents(1, &multi->wsa_event, FALSE, (DWORD)timeout_ms,
                               FALSE);
    }

    /* With Winsock, we have to run the following section unconditionally
       to call WSAEventSelect(fd, event, 0) on all the sockets */
    /* copy revents results from the poll to the curl_multi_wait poll
       struct, the bit values of the actual underlying poll() implementation
       may not be the same as the ones in the public libcurl API! */
    for(i = 0; i < extra_nfds; i++) {
      unsigned short mask = 0;
      curl_socket_t s = extra_fds[i].fd;

      wsa_events.lNetworkEvents = 0;
      if(WSAEnumNetworkEvents(s, NULL, &wsa_events) == 0) {
        if(wsa_events.lNetworkEvents & (FD_READ | FD_ACCEPT | FD_CLOSE))
          mask |= CURL_WAIT_POLLIN;
        if(wsa_events.lNetworkEvents & (FD_WRITE | FD_CONNECT | FD_CLOSE))
          mask |= CURL_WAIT_POLLOUT;
        if(wsa_events.lNetworkEvents & FD_OOB)
          mask |= CURL_WAIT_POLLPRI;
        if(!pollrc && wsa_events.lNetworkEvents)
          nevents++;
      }
      WSAEventSelect(s, multi->wsa_event, 0);
      if(!pollrc) {
        extra_fds[i].revents = (short)mask;
        continue;
      }
      else {
        unsigned r = (unsigned)cpfds->pfds[curl_nfds + i].revents;
        if(r & POLLIN)
          mask |= CURL_WAIT_POLLIN;
        if(r & POLLOUT)
          mask |= CURL_WAIT_POLLOUT;
        if(r & POLLPRI)
          mask |= CURL_WAIT_POLLPRI;
        extra_fds[i].revents = (short)mask;
      }
    }

    /* Count up all our own sockets that had activity,
       and remove them from the event. */
    for(i = 0; i < curl_nfds; ++i) {
      wsa_events.lNetworkEvents = 0;
      if(WSAEnumNetworkEvents(cpfds->pfds[i].fd, NULL, &wsa_events) == 0) {
        if(!pollrc && wsa_events.lNetworkEvents)
          nevents++;
      }
      WSAEventSelect(cpfds->pfds[i].fd, multi->wsa_event, 0);
    }
    WSAResetEvent(multi->wsa_event);
  }

out:
  *pnevents = nevents;
  return mresult;
}

#else /* USE_WINSOCK */

static CURLMcode multi_posix_poll(struct Curl_multi *multi,
                                  struct curl_pollfds *cpfds,
                                  unsigned int curl_nfds,
                                  struct curl_waitfd extra_fds[],
                                  unsigned int extra_nfds,
                                  int timeout_ms,
                                  bool extrawait,
                                  int *pnevents)
{
  CURLMcode mresult = CURLM_OK;
  int nevents = 0;
  size_t i;

  (void)multi;
  if(cpfds->n) {
    int pollrc = Curl_poll(cpfds->pfds, cpfds->n, timeout_ms); /* wait... */
    if(pollrc < 0) {
      mresult = CURLM_UNRECOVERABLE_POLL;
      goto out;
    }
    nevents = pollrc;

    /* copy revents results from the poll to the curl_multi_wait poll
       struct, the bit values of the actual underlying poll() implementation
       may not be the same as the ones in the public libcurl API! */
    for(i = 0; i < extra_nfds; i++) {
      unsigned r = (unsigned)cpfds->pfds[curl_nfds + i].revents;
      unsigned short mask = 0;
      if(r & POLLIN)
        mask |= CURL_WAIT_POLLIN;
      if(r & POLLOUT)
        mask |= CURL_WAIT_POLLOUT;
      if(r & POLLPRI)
        mask |= CURL_WAIT_POLLPRI;
      extra_fds[i].revents = (short)mask;
    }
  }
  else if(extrawait) {
    /* No fds to poll, but asked to obey timeout_ms anyway. We cannot
     * use Curl_poll() as it, on some platforms, returns immediately
     * without fds. */
    curlx_wait_ms(timeout_ms);
  }

out:
  *pnevents = nevents;
  return mresult;
}

#endif /* !USE_WINSOCK */

#define NUM_POLLS_ON_STACK 10

static CURLMcode multi_wait(struct Curl_multi *multi,
                            struct curl_waitfd extra_fds[],
                            unsigned int extra_nfds,
                            int timeout_ms,
                            int *ret,
                            bool extrawait)  /* when no socket, wait */
{
  size_t i;
  struct curltime expire_time;
  long timeout_internal;
  int nevents = 0;
  struct easy_pollset ps;
  struct pollfd a_few_on_stack[NUM_POLLS_ON_STACK];
  struct curl_pollfds cpfds;
  unsigned int curl_nfds = 0; /* how many pfds are for curl transfers */
  struct Curl_easy *data = NULL;
  CURLMcode mresult = CURLM_OK;
  uint32_t mid;
#ifdef ENABLE_WAKEUP
  int wakeup_idx = -1;
#endif

  if(timeout_ms < 0)
    return CURLM_BAD_FUNCTION_ARGUMENT;

  Curl_pollset_init(&ps);
  Curl_pollfds_init(&cpfds, a_few_on_stack, NUM_POLLS_ON_STACK);

  /* Add the curl handles to our pollfds first */
  if(Curl_uint32_bset_first(&multi->process, &mid)) {
    do {
      data = Curl_multi_get_easy(multi, mid);
      if(!data) {
        DEBUGASSERT(0);
        Curl_uint32_bset_remove(&multi->process, mid);
        Curl_uint32_bset_remove(&multi->dirty, mid);
        continue;
      }
      Curl_multi_pollset(data, &ps);
      if(Curl_pollfds_add_ps(&cpfds, &ps)) {
        mresult = CURLM_OUT_OF_MEMORY;
        goto out;
      }
    } while(Curl_uint32_bset_next(&multi->process, mid, &mid));
  }

  if(Curl_cshutdn_add_pollfds(&multi->cshutdn, multi->admin, &cpfds)) {
    mresult = CURLM_OUT_OF_MEMORY;
    goto out;
  }

#ifdef ENABLE_WAKEUP
  /* If `extrawait` is TRUE *or* we have `extra_fds`to poll *or* we
   * have transfer sockets to poll, we obey `timeout_ms`.
   * Then we need to also monitor the multi's wakeup
   * socket to catch calls to `curl_multi_wakeup()` during the wait. */
  if(extrawait || cpfds.n || extra_nfds) {
    wakeup_idx = cpfds.n;
    if(Curl_pollfds_add_sock(&cpfds, multi->wakeup_pair[0], POLLIN)) {
      mresult = CURLM_OUT_OF_MEMORY;
      goto out;
    }
  }
#endif

  curl_nfds = cpfds.n; /* what curl internally uses in cpfds */
  /* Add external file descriptions from poll-like struct curl_waitfd */
  for(i = 0; i < extra_nfds; i++) {
    unsigned short events = 0;
    if(extra_fds[i].events & CURL_WAIT_POLLIN)
      events |= POLLIN;
    if(extra_fds[i].events & CURL_WAIT_POLLPRI)
      events |= POLLPRI;
    if(extra_fds[i].events & CURL_WAIT_POLLOUT)
      events |= POLLOUT;
    if(Curl_pollfds_add_sock(&cpfds, extra_fds[i].fd, events)) {
      mresult = CURLM_OUT_OF_MEMORY;
      goto out;
    }
  }

  /* We check the internal timeout *AFTER* we collected all sockets to
   * poll. Collecting the sockets may install new timers by protocols
   * and connection filters.
   * Use the shorter one of the internal and the caller requested timeout.
   * If we are called with `!extrawait` and multi_timeout() reports no
   * timeouts exist, do not wait. */
  multi_timeout(multi, &expire_time, &timeout_internal);
  if((timeout_internal >= 0) && (timeout_internal < (long)timeout_ms))
    timeout_ms = (int)timeout_internal;

  if(data)
    CURL_TRC_M(data, "multi_wait(fds=%u, timeout=%d) tinternal=%ld",
               cpfds.n, timeout_ms, timeout_internal);

#ifdef USE_WINSOCK
  mresult = multi_winsock_select(multi, &cpfds, curl_nfds,
                                 extra_fds, extra_nfds,
                                 timeout_ms, extrawait, &nevents);
#else
  mresult = multi_posix_poll(multi, &cpfds, curl_nfds,
                             extra_fds, extra_nfds,
                             timeout_ms, extrawait, &nevents);
#endif

#ifdef ENABLE_WAKEUP
    if(nevents && (wakeup_idx >= 0)) {
      if(cpfds.pfds[wakeup_idx].revents & POLLIN) {
        (void)Curl_wakeup_consume(multi->wakeup_pair, TRUE);
        /* do not count the wakeup socket into the returned value */
        nevents--;
      }
    }
#endif

out:
  Curl_pollset_cleanup(&ps);
  Curl_pollfds_cleanup(&cpfds);
  if(ret)
    *ret = nevents;
  return mresult;
}

CURLMcode curl_multi_wait(CURLM *m,
                          struct curl_waitfd extra_fds[],
                          unsigned int extra_nfds,
                          int timeout_ms,
                          int *ret)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_wait, &mresult)) {
    mresult = multi_wait(m, extra_fds, extra_nfds, timeout_ms, ret, FALSE);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_poll(CURLM *m,
                          struct curl_waitfd extra_fds[],
                          unsigned int extra_nfds,
                          int timeout_ms,
                          int *ret)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_poll, &mresult)) {
    mresult = multi_wait(m, extra_fds, extra_nfds, timeout_ms, ret, TRUE);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_wakeup(CURLM *m)
{
  /* this function is usually called from another thread,
     it has to be careful only to access parts of the
     Curl_multi struct that are constant */
  struct Curl_multi *multi = m;
  CURLMcode mresult = CURLM_WAKEUP_FAILURE;

  /* GOOD_MULTI_HANDLE can be safely called */
  if(!GOOD_MULTI_HANDLE(multi))
    return CURLM_BAD_HANDLE;

#ifdef ENABLE_WAKEUP
  /* the wakeup_pair variable is only written during init and cleanup,
     making it safe to access from another thread after the init part
     and before cleanup */
  if(!Curl_wakeup_signal(multi->wakeup_pair))
    mresult = CURLM_OK;
#endif
#ifdef USE_WINSOCK
  if(WSASetEvent(multi->wsa_event))
    mresult = CURLM_OK;
#endif
  return mresult;
}

#ifdef ENABLE_INTERNAL_WAKEUP
void Curl_multi_wakeup_internal(struct Curl_multi *multi)
{
  /* This is expected to be invocable from another thread which
   * does NOT outlive the multi handle. Check for sanity. */
  if(GOOD_MULTI_HANDLE(multi))
    Curl_wakeup_signal(multi->wakeup_internal);
  else
    DEBUGASSERT(0);
}
#endif

/*
 * multi_ischanged() is called
 *
 * Returns TRUE/FALSE whether the state is changed to trigger a CONNECT_PEND
 * => CONNECT action.
 *
 * Set 'clear' to TRUE to have it also clear the state variable.
 */
static bool multi_ischanged(struct Curl_multi *multi, bool clear)
{
  bool retval = FALSE;
  DEBUGASSERT(multi);
  if(multi) {
    retval = (bool)multi->recheckstate;
    if(clear)
      multi->recheckstate = FALSE;
  }
  return retval;
}

/*
 * Curl_multi_connchanged() is called to tell that there is a connection in
 * this multi handle that has changed state (multiplexing become possible, the
 * number of allowed streams changed or similar), and a subsequent use of this
 * multi handle should move CONNECT_PEND handles back to CONNECT to have them
 * retry.
 */
void Curl_multi_connchanged(struct Curl_multi *multi)
{
  multi->recheckstate = TRUE;
}

CURLMcode Curl_multi_add_perform(struct Curl_multi *multi,
                                 struct Curl_easy *data,
                                 struct connectdata *conn)
{
  CURLMcode mresult;

  mresult = Curl_multi_add_handle(multi, data);
  if(!mresult) {
    CURLcode result;

    /* pass in NULL for 'conn' here since we do not want to init the
       connection, only this transfer */
    result = Curl_init_transfer(data, NULL);
    if(result) {
      Curl_multi_remove_handle(multi, data);
      return CURLM_INTERNAL_ERROR;
    }

    /* take this handle to the perform state right away */
    multistate(data, MSTATE_PERFORMING);
    Curl_attach_connection(data, conn);
    CURL_REQ_SET_RECV(data);
  }
  return mresult;
}

static CURLcode multi_do(struct Curl_easy *data, bool *done)
{
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;

  DEBUGASSERT(conn);
  DEBUGASSERT(conn->scheme);

  if(conn->scheme->run->do_it)
    result = conn->scheme->run->do_it(data, done);

  return result;
}

/*
 * multi_do_more() is called during the DO_MORE multi state. It is a second
 * stage DO state which (wrongly) was introduced to support FTP's second
 * connection.
 *
 * 'complete' can return DOMORE_INCOMPLETE, DOMORE_DONE or DOMORE_GOBACK
 * (to DOING state when there is more work to do)
 */

static CURLcode multi_do_more(struct Curl_easy *data, domore *complete)
{
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;

  *complete = DOMORE_INCOMPLETE;

  if(conn->scheme->run->do_more)
    result = conn->scheme->run->do_more(data, complete);

  return result;
}

/*
 * Check whether a timeout occurred, and handle it if it did
 */
static bool multi_handle_timeout(struct Curl_easy *data,
                                 bool *stream_error,
                                 CURLcode *result)
{
  timediff_t timeout_ms;

  timeout_ms = Curl_timeleft_ms(data);
  if(timeout_ms < 0) {
    /* Handle timed out */
    struct curltime since;
    if(Curl_is_connecting(data))
      since = data->progress.t_startsingle;
    else
      since = data->progress.t_startop;
    if(data->mstate == MSTATE_CONNECTING)
      failf(data, "%s timed out after %" FMT_TIMEDIFF_T " milliseconds",
            data->conn->bits.dns_resolved ? "Connection" : "Resolving",
            curlx_ptimediff_ms(Curl_pgrs_now(data), &since));
    else {
      struct SingleRequest *k = &data->req;
      if(k->size != -1) {
        failf(data, "Operation timed out after %" FMT_TIMEDIFF_T
              " milliseconds with %" FMT_OFF_T " out of %"
              FMT_OFF_T " bytes received",
              curlx_ptimediff_ms(Curl_pgrs_now(data), &since),
              k->bytecount, k->size);
      }
      else {
        failf(data, "Operation timed out after %" FMT_TIMEDIFF_T
              " milliseconds with %" FMT_OFF_T " bytes received",
              curlx_ptimediff_ms(Curl_pgrs_now(data), &since),
              k->bytecount);
      }
    }
    *result = CURLE_OPERATION_TIMEDOUT;
    if(data->conn) {
      /* Force connection closed if the connection has indeed been used */
      if(data->mstate > MSTATE_DO) {
        streamclose(data->conn);
        *stream_error = TRUE;
      }
      (void)multi_done(data, *result, TRUE);
    }
    return TRUE;
  }

  return FALSE;
}

/*
 * We are doing protocol-specific connecting and this is being called over and
 * over from the multi interface until the connection phase is done on
 * protocol layer.
 */

static CURLcode protocol_connecting(struct Curl_easy *data, bool *done)
{
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;

  if(conn && conn->scheme->run->connecting) {
    *done = FALSE;
    result = conn->scheme->run->connecting(data, done);
  }
  else
    *done = TRUE;

  return result;
}

/*
 * We are DOING this is being called over and over from the multi interface
 * until the DOING phase is done on protocol layer.
 */

static CURLcode protocol_doing(struct Curl_easy *data, bool *done)
{
  CURLcode result = CURLE_OK;
  struct connectdata *conn = data->conn;

  if(conn && conn->scheme->run->doing) {
    *done = FALSE;
    result = conn->scheme->run->doing(data, done);
  }
  else
    *done = TRUE;

  return result;
}

/*
 * We have discovered that the TCP connection has been successful, we can now
 * proceed with some action.
 *
 */
static CURLcode protocol_connect(struct Curl_easy *data, bool *protocol_done)
{
  struct connectdata *conn = data->conn;
  CURLcode result = CURLE_OK;

  DEBUGASSERT(conn);
  DEBUGASSERT(protocol_done);
  DEBUGASSERT(Curl_conn_is_connected(conn, FIRSTSOCKET));

  *protocol_done = FALSE;
  if(!conn->bits.protoconnstart) {
    if(conn->scheme->run->connect_it) {
      /* Call the protocol-specific connect function */
      result = conn->scheme->run->connect_it(data, protocol_done);
      if(result)
        return result;
    }
    conn->bits.protoconnstart = TRUE;
  }

  /* Unless this protocol does not have any protocol-connect callback, as
     then we know we are done. */
  if(!conn->scheme->run->connecting)
    *protocol_done = TRUE;
  return CURLE_OK;
}

/*
 * posttransfer() is called immediately after a transfer ends
 */
static void multi_posttransfer(struct Curl_easy *data)
{
#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(MSG_NOSIGNAL)
  /* restore the signal handler for SIGPIPE before we get back */
  if(!data->set.no_signal)
    signal(SIGPIPE, data->state.prev_signal);
#else
  (void)data;
#endif
}

/*
 * multi_follow() handles the URL redirect magic. Pass in the 'newurl' string
 * as given by the remote server and set up the new URL to request.
 *
 * This function DOES NOT FREE the given URL.
 */
static CURLcode multi_follow(struct Curl_easy *data,
                             const struct Curl_scheme *handler,
                             const char *newurl, /* the Location: string */
                             followtype type) /* see transfer.h */
{
  if(handler && handler->run->follow)
    return handler->run->follow(data, newurl, type);

  if(type == FOLLOW_RETRY)
    /* Retries are generic and do not require protocol-specific redirect
       handling. */
    return CURLE_OK;

  return CURLE_TOO_MANY_REDIRECTS;
}

static CURLcode mspeed_check(struct Curl_easy *data)
{
  if(Curl_rlimit_active(&data->progress.dl.rlimit) ||
     Curl_rlimit_active(&data->progress.ul.rlimit)) {
    /* check if our send/recv limits require idle waits */
    const struct curltime *pnow = Curl_pgrs_now(data);
    timediff_t recv_ms, send_ms;

    send_ms = Curl_rlimit_wait_ms(&data->progress.ul.rlimit, pnow);
    recv_ms = Curl_rlimit_wait_ms(&data->progress.dl.rlimit, pnow);

    if(send_ms || recv_ms) {
      if(data->mstate != MSTATE_RATELIMITING) {
        multistate(data, MSTATE_RATELIMITING);
      }
      Curl_expire(data, CURLMAX(send_ms, recv_ms), EXPIRE_TOOFAST);
      Curl_multi_clear_dirty(data);
      CURL_TRC_M(data, "[RLIMIT] waiting %" FMT_TIMEDIFF_T "ms",
                 CURLMAX(send_ms, recv_ms));
      return CURLE_AGAIN;
    }
    else {
      /* when will the rate limits increase next? The transfer needs
       * to run again at that time or it may stall. */
      send_ms = Curl_rlimit_next_step_ms(&data->progress.ul.rlimit, pnow);
      recv_ms = Curl_rlimit_next_step_ms(&data->progress.dl.rlimit, pnow);
      if(send_ms || recv_ms) {
        timediff_t next_ms = CURLMIN(send_ms, recv_ms);
        if(!next_ms)
          next_ms = CURLMAX(send_ms, recv_ms);
        Curl_expire(data, next_ms, EXPIRE_TOOFAST);
        CURL_TRC_M(data, "[RLIMIT] next token update in %" FMT_TIMEDIFF_T "ms",
                   next_ms);
      }
    }
  }

  if(data->mstate != MSTATE_PERFORMING) {
    CURL_TRC_M(data, "[RLIMIT] wait over, continue");
    multistate(data, MSTATE_PERFORMING);
  }
  return CURLE_OK;
}

static CURLMcode multistate_performing(struct Curl_easy *data,
                                       bool *stream_errorp,
                                       CURLcode *resultp)
{
  char *newurl = NULL;
  bool retry = FALSE;
  CURLMcode mresult = CURLM_OK;
  CURLcode result = *resultp = CURLE_OK;
  *stream_errorp = FALSE;

  if(mspeed_check(data) == CURLE_AGAIN)
    return CURLM_OK;

  /* read/write data if it is ready to do so */
  result = Curl_sendrecv(data);

  if(data->req.done || (result == CURLE_RECV_ERROR)) {
    /* If CURLE_RECV_ERROR happens early enough, we assume it was a race
     * condition and the server closed the reused connection exactly when we
     * wanted to use it, so figure out if that is indeed the case.
     */
    CURLcode ret = Curl_retry_request(data, &newurl);
    if(!ret)
      retry = !!newurl;
    else if(!result)
      result = ret;

    if(retry) {
      /* if we are to retry, set the result to OK and consider the
         request as done */
      result = CURLE_OK;
      data->req.done = TRUE;
    }
  }
#ifndef CURL_DISABLE_HTTP
  else if((result == CURLE_HTTP2_STREAM) &&
          Curl_h2_http_1_1_error(data)) {
    CURLcode ret = Curl_retry_request(data, &newurl);

    if(!ret) {
      infof(data, "Downgrades to HTTP/1.1");
      streamclose(data->conn);
      data->state.http_neg.wanted = CURL_HTTP_V1x;
      data->state.http_neg.allowed = CURL_HTTP_V1x;
      /* clear the error message bit too as we ignore the one we got */
      data->state.errorbuf = FALSE;
      if(!newurl)
        /* typically for HTTP_1_1_REQUIRED error on first flight */
        newurl = Curl_bufref_dup(&data->state.url);
      if(!newurl) {
        result = CURLE_OUT_OF_MEMORY;
      }
      else {
        /* if we are to retry, set the result to OK and consider the request
          as done */
        retry = TRUE;
        result = CURLE_OK;
        data->req.done = TRUE;
      }
    }
    else
      result = ret;
  }
#endif

  if(result) {
    /*
     * The transfer phase returned error, we mark the connection to get closed
     * to prevent being reused. This is because we cannot possibly know if the
     * connection is in a good shape or not now. Unless it is a protocol which
     * uses two "channels" like FTP, as then the error happened in the data
     * connection.
     */

    if(!(data->conn->scheme->flags & PROTOPT_DUAL) &&
       result != CURLE_HTTP2_STREAM)
      streamclose(data->conn);

    multi_posttransfer(data);
    multi_done(data, result, TRUE);
  }
  else if(data->req.done && !Curl_cwriter_is_paused(data)) {
    const struct Curl_scheme *handler = data->conn->scheme;

    /* call this even if the readwrite function returned error */
    multi_posttransfer(data);

    /* When we follow redirects or is set to retry the connection, we must to
       go back to the CONNECT state */
    if(data->req.newurl || retry) {
      followtype follow = FOLLOW_NONE;
      if(!retry) {
        /* if the URL is a follow-location and not a retried request then
           figure out the URL here */
        curlx_free(newurl);
        newurl = data->req.newurl;
        data->req.newurl = NULL;
        follow = FOLLOW_REDIR;
      }
      else
        follow = FOLLOW_RETRY;
      (void)multi_done(data, CURLE_OK, FALSE);
      /* multi_done() might return CURLE_GOT_NOTHING */
      result = multi_follow(data, handler, newurl, follow);
      if(!result) {
        multistate(data, MSTATE_SETUP);
        mresult = CURLM_CALL_MULTI_PERFORM;
      }
    }
    else {
      /* after the transfer is done, go DONE */

      /* but first check to see if we got a location info even though we are
         not following redirects */
      if(data->req.location) {
        curlx_free(newurl);
        newurl = data->req.location;
        data->req.location = NULL;
        result = multi_follow(data, handler, newurl, FOLLOW_FAKE);
        if(result) {
          *stream_errorp = TRUE;
          result = multi_done(data, result, TRUE);
        }
      }

      if(!result) {
        multistate(data, MSTATE_DONE);
        mresult = CURLM_CALL_MULTI_PERFORM;
      }
    }
  }
  else { /* not errored, not done */
    mspeed_check(data);
  }
  curlx_free(newurl);
  *resultp = result;
  return mresult;
}

static CURLMcode multistate_do(struct Curl_easy *data,
                               bool *stream_errorp,
                               CURLcode *resultp)
{
  CURLMcode mresult = CURLM_OK;
  CURLcode result = CURLE_OK;
  if(data->set.fprereq) {
    struct Curl_mapi_guard guard;
    int prereq_rc;

    /* call the prerequest callback function */
    CURL_CBAPI_START(&guard, data, easy_fprereq);
    prereq_rc = data->set.fprereq(data->set.prereq_userp,
                                  data->info.primary.remote_ip,
                                  data->info.primary.local_ip,
                                  data->info.primary.remote_port,
                                  data->info.primary.local_port);
    CURL_CBAPI_END(&guard);
    if(prereq_rc != CURL_PREREQFUNC_OK) {
      failf(data, "operation aborted by pre-request callback");
      /* failure in pre-request callback - do not do any other processing */
      result = CURLE_ABORTED_BY_CALLBACK;
      multi_posttransfer(data);
      multi_done(data, result, FALSE);
      *stream_errorp = TRUE;
      goto end;
    }
  }

  if(data->set.connect_only && !data->set.connect_only_ws) {
    multistate(data, MSTATE_DONE);
    mresult = CURLM_CALL_MULTI_PERFORM;
  }
  else {
    bool dophase_done = FALSE;
    /* Perform the protocol's DO action */
    result = multi_do(data, &dophase_done);

    if(!result) {
      if(!dophase_done) {
#ifndef CURL_DISABLE_FTP
        /* some steps needed for wildcard matching */
        if(data->state.wildcardmatch) {
          struct WildcardData *wc = data->wildcard;
          if(wc->state == CURLWC_DONE || wc->state == CURLWC_SKIP) {
            /* skip some states if it is important */
            multi_done(data, CURLE_OK, FALSE);

            /* if there is no connection left, skip the DONE state */
            multistate(data, data->conn ? MSTATE_DONE : MSTATE_COMPLETED);
            mresult = CURLM_CALL_MULTI_PERFORM;
            goto end;
          }
        }
#endif
        /* DO was not completed in one function call, we must continue
           DOING... */
        multistate(data, MSTATE_DOING);
        mresult = CURLM_CALL_MULTI_PERFORM;
      }

      /* after DO, go DO_DONE... or DO_MORE */
      else if(data->conn->bits.do_more) {
        /* we are supposed to do more, but we need to sit down, relax and wait
           a little while first */
        multistate(data, MSTATE_DOING_MORE);
        mresult = CURLM_CALL_MULTI_PERFORM;
      }
      else {
        /* we are done with the DO, now DID */
        multistate(data, MSTATE_DID);
        mresult = CURLM_CALL_MULTI_PERFORM;
      }
    }
    else if((result == CURLE_SEND_ERROR) &&
            data->conn->bits.reuse) {
      /*
       * In this situation, a connection that we were trying to use may have
       * unexpectedly died. If possible, send the connection back to the
       * CONNECT phase so we can try again.
       */
      const struct Curl_scheme *handler = data->conn->scheme;
      char *newurl = NULL;
      followtype follow = FOLLOW_NONE;
      CURLcode drc;

      drc = Curl_retry_request(data, &newurl);
      if(drc) {
        /* a failure here pretty much implies an out of memory */
        result = drc;
        *stream_errorp = TRUE;
      }

      multi_posttransfer(data);
      drc = multi_done(data, result, FALSE);

      /* When set to retry the connection, we must go back to the CONNECT
       * state */
      if(newurl) {
        if(!drc || (drc == CURLE_SEND_ERROR)) {
          follow = FOLLOW_RETRY;
          drc = multi_follow(data, handler, newurl, follow);
          if(!drc) {
            multistate(data, MSTATE_SETUP);
            mresult = CURLM_CALL_MULTI_PERFORM;
            result = CURLE_OK;
          }
          else {
            /* Follow failed */
            result = drc;
          }
        }
        else {
          /* done did not return OK or SEND_ERROR */
          result = drc;
        }
      }
      else {
        /* Have error handler disconnect conn if we cannot retry */
        *stream_errorp = TRUE;
      }
      curlx_free(newurl);
    }
    else {
      /* failure detected */
      multi_posttransfer(data);
      if(data->conn)
        multi_done(data, result, FALSE);
      *stream_errorp = TRUE;
    }
  }
end:
  *resultp = result;
  return mresult;
}

static CURLMcode multistate_ratelimiting(struct Curl_easy *data,
                                         CURLcode *resultp)
{
  CURLcode result = CURLE_OK;
  CURLMcode mresult = CURLM_OK;
  DEBUGASSERT(data->conn);
  /* if both rates are within spec, resume transfer */
  result = Curl_pgrsCheck(data);

  if(result) {
    if(!(data->conn->scheme->flags & PROTOPT_DUAL) &&
       result != CURLE_HTTP2_STREAM)
      streamclose(data->conn);

    multi_posttransfer(data);
    multi_done(data, result, TRUE);
  }
  else {
    if(!mspeed_check(data))
      mresult = CURLM_CALL_MULTI_PERFORM;
  }
  *resultp = result;
  return mresult;
}

static CURLMcode multistate_connect(struct Curl_multi *multi,
                                    struct Curl_easy *data,
                                    CURLcode *resultp)
{
  /* Connect. We want to get a connection identifier filled in. This state can
     be entered from SETUP and from PENDING. */
  bool connected;
  CURLMcode mresult = CURLM_OK;
  CURLcode result = Curl_connect(data, &connected);
  if(result == CURLE_NO_CONNECTION_AVAILABLE) {
    /* There was no connection available. We will go to the pending state and
       wait for an available connection. */
    multistate(data, MSTATE_PENDING);
    /* move from process to pending set */
    Curl_uint32_bset_remove(&multi->process, data->mid);
    Curl_uint32_bset_remove(&multi->dirty, data->mid);
    Curl_uint32_bset_add(&multi->pending, data->mid);
    *resultp = CURLE_OK;
    return mresult;
  }
  else
    multi_schedule_pending(data->multi);

  if(!result) {
    /* after the connect has been sent off, go WAITCONNECT unless the
       protocol connect is already done and we can go directly to WAITDO or
       DO! */
    mresult = CURLM_CALL_MULTI_PERFORM;

    if(connected) {
      if(!data->conn->bits.reuse &&
         Curl_conn_is_multiplex(data->conn, FIRSTSOCKET)) {
        /* new connection, can multiplex, wake pending handles */
        multi_schedule_pending(data->multi);
      }
      multistate(data, MSTATE_PROTOCONNECT);
    }
    else {
      multistate(data, MSTATE_CONNECTING);
    }
  }
  *resultp = result;
  return mresult;
}

/* returns the possibly updated result */
static CURLcode is_finished(struct Curl_multi *multi,
                            struct Curl_easy *data,
                            bool stream_error,
                            CURLcode result)
{
  if(data->mstate < MSTATE_COMPLETED) {
    if(result) {
      /*
       * If an error was returned, and we are not in completed state now,
       * then we go to completed and consider this transfer aborted.
       */

      /* No attempt to disconnect connections must be made before this -
         connection detach and termination happens only here */

      /* Check if we can move pending requests to send pipe */
      multi_schedule_pending(multi); /* connection */

      if(data->conn) {
        if(stream_error) {
          /* Do not attempt to send data over a connection that timed out */
          bool dead_connection = result == CURLE_OPERATION_TIMEDOUT;
          struct connectdata *conn = data->conn;

          /* This is where we make sure that the conn pointer is reset.
             We do not have to do this in every case block above where a
             failure is detected */
          Curl_detach_connection(data);
          Curl_conn_terminate(data, conn, dead_connection);
        }
      }
      else if(data->mstate == MSTATE_CONNECT) {
        /* Curl_connect() failed */
        multi_posttransfer(data);
        Curl_pgrsUpdate_nometer(data);
      }

      multistate(data, MSTATE_COMPLETED);
      return result;
    }
    /* if there is still a connection to use, call the progress function */
    else if(data->conn && Curl_conn_is_connected(data->conn, FIRSTSOCKET)) {
      result = Curl_pgrsUpdate(data);
      if(result) {
        /* aborted due to progress callback return code must close the
           connection */
        streamclose(data->conn);

        /* if not yet in DONE state, go there, otherwise COMPLETED */
        multistate(data, (data->mstate < MSTATE_DONE) ?
                   MSTATE_DONE : MSTATE_COMPLETED);
        return result;
      }
    }
  }
  return result;
}

static void handle_completed(struct Curl_multi *multi,
                             struct Curl_easy *data,
                             CURLcode result)
{
  if(data->master_mid != UINT32_MAX) {
    /* A sub transfer, not for msgsent to application. Is anyone still
     * interested in processing its results? */
    if(data->sub_xfer_done) {
      struct Curl_easy *master = Curl_multi_get_easy(multi, data->master_mid);

      CURL_TRC_M(data, "sub xfer done for master %u", data->master_mid);
      if(master)
        data->sub_xfer_done(data, master, result);
      else
        CURL_TRC_M(data, "master easy %u already gone.", data->master_mid);
    }
  }
  else {
    /* now fill in the Curl_message with this info */
    struct Curl_message *msg = &data->msg;

    msg->extmsg.msg = CURLMSG_DONE;
    msg->extmsg.easy_handle = data;
    msg->extmsg.data.result = result;

    multi_addmsg(multi, msg);
    DEBUGASSERT(!data->conn);
  }
  multistate(data, MSTATE_MSGSENT);

  /* remove from the other sets, add to msgsent */
  Curl_uint32_bset_remove(&multi->process, data->mid);
  Curl_uint32_bset_remove(&multi->dirty, data->mid);
  Curl_uint32_bset_remove(&multi->pending, data->mid);
  Curl_uint32_bset_add(&multi->msgsent, data->mid);
  if(data->state.really_alive) {
    data->state.really_alive = FALSE;
    --multi->xfers_really_alive;
    if(!multi->xfers_really_alive)
      (void)multi_assess_wakeup(multi);
  }
  --multi->xfers_alive;
  if(!multi->xfers_alive)
    multi_assess_wakeup(multi);
}

static CURLMcode multistate_init(struct Curl_easy *data, CURLcode *result)
{
  if(!data->state.really_alive) {
    data->state.really_alive = TRUE;
    ++data->multi->xfers_really_alive;
    if(data->multi->xfers_really_alive == 1) {
      CURLMcode mresult = multi_assess_wakeup(data->multi);
      if(mresult) {
        failf(data, "error enabling wakeup listening: %d", mresult);
        return mresult;
      }
    }
  }

  *result = Curl_pretransfer(data);
  if(*result)
    return CURLM_OK;

  /* after init, go SETUP */
  multistate(data, MSTATE_SETUP);
  Curl_pgrsTime(data, TIMER_STARTOP);
  return CURLM_CALL_MULTI_PERFORM;
}

static CURLMcode multistate_setup(struct Curl_easy *data)
{
  Curl_pgrsTime(data, TIMER_STARTSINGLE);
  if(data->set.timeout)
    Curl_expire(data, data->set.timeout, EXPIRE_TIMEOUT);
  if(data->set.connecttimeout)
    /* Since a connection might go to pending and back to CONNECT several
       times before it actually takes off, we need to set the timeout once
       in SETUP before we enter CONNECT the first time. */
    Curl_expire(data, data->set.connecttimeout, EXPIRE_CONNECTTIMEOUT);

  multistate(data, MSTATE_CONNECT);
  return CURLM_CALL_MULTI_PERFORM;
}

static CURLMcode multistate_connecting(struct Curl_easy *data,
                                       bool *stream_error,
                                       CURLcode *result)
{
  bool connected;

  if(!data->conn) {
    DEBUGASSERT(0);
    *result = CURLE_FAILED_INIT;
    return CURLM_OK;
  }
  if(!Curl_xfer_recv_is_paused(data)) {
    *result = Curl_conn_connect(data, FIRSTSOCKET, FALSE, &connected);
    if(connected && !*result) {
      if(!data->conn->bits.reuse &&
         Curl_conn_is_multiplex(data->conn, FIRSTSOCKET)) {
        /* new connection, can multiplex, wake pending handles */
        multi_schedule_pending(data->multi);
      }
      multistate(data, MSTATE_PROTOCONNECT);
      return CURLM_CALL_MULTI_PERFORM;
    }
    else if(*result) {
      /* failure detected */
      CURL_TRC_M(data, "connect failed -> %d", (int)*result);
      multi_posttransfer(data);
      multi_done(data, *result, TRUE);
      *stream_error = TRUE;
      return CURLM_OK;
    }
  }
  return CURLM_OK;
}

static CURLMcode multistate_protoconnect(struct Curl_easy *data,
                                         bool *stream_error,
                                         CURLcode *result)
{
  bool protocol_connected = FALSE;

  if(!*result && data->conn->bits.reuse) {
    /* ftp seems to hang when protoconnect on reused connection since we
     * handle PROTOCONNECT in general inside the filters, it seems wrong to
     * restart this on a reused connection.
     */
    multistate(data, MSTATE_DO);
    return CURLM_CALL_MULTI_PERFORM;
  }
  if(!*result)
    *result = protocol_connect(data, &protocol_connected);
  if(!*result && !protocol_connected) {
    /* switch to waiting state */
    multistate(data, MSTATE_PROTOCONNECTING);
    return CURLM_CALL_MULTI_PERFORM;
  }
  else if(!*result) {
    /* protocol connect has completed, go WAITDO or DO */
    multistate(data, MSTATE_DO);
    return CURLM_CALL_MULTI_PERFORM;
  }

  /* failure detected */
  multi_posttransfer(data);
  multi_done(data, *result, TRUE);
  *stream_error = TRUE;
  return CURLM_OK;
}

static CURLMcode multistate_protoconnecting(struct Curl_easy *data,
                                            bool *stream_error,
                                            CURLcode *result)
{
  bool protocol_connected = FALSE;

  /* protocol-specific connect phase */
  *result = protocol_connecting(data, &protocol_connected);
  if(!*result && protocol_connected) {
    /* after the connect has completed, go WAITDO or DO */
    multistate(data, MSTATE_DO);
    return CURLM_CALL_MULTI_PERFORM;
  }
  else if(*result) {
    /* failure detected */
    multi_posttransfer(data);
    multi_done(data, *result, TRUE);
    *stream_error = TRUE;
  }
  return CURLM_OK;
}

static CURLMcode multistate_doing(struct Curl_easy *data,
                                  bool *stream_error,
                                  CURLcode *result)
{
  bool dophase_done = FALSE;

  /* we continue DOING until the DO phase is complete */
  DEBUGASSERT(data->conn);
  *result = protocol_doing(data, &dophase_done);
  if(!*result) {
    if(dophase_done) {
      /* after DO, go DO_DONE or DO_MORE */
      multistate(data, data->conn->bits.do_more ?
                 MSTATE_DOING_MORE : MSTATE_DID);
      return CURLM_CALL_MULTI_PERFORM;
    } /* dophase_done */
  }
  else {
    /* failure detected */
    multi_posttransfer(data);
    multi_done(data, *result, FALSE);
    *stream_error = TRUE;
  }
  return CURLM_OK;
}

static CURLMcode multistate_doing_more(struct Curl_easy *data,
                                       bool *stream_error,
                                       CURLcode *result)
{
  domore control;

  /*
   * When we are connected, DOING MORE and then go DID
   */
  DEBUGASSERT(data->conn);
  *result = multi_do_more(data, &control);

  if(!*result) {
    if(control != DOMORE_INCOMPLETE) {
      /* if DONE, advance to DO_DONE
         if GOBACK, go back to DOING */
      multistate(data, control == DOMORE_DONE ? MSTATE_DID : MSTATE_DOING);
      return CURLM_CALL_MULTI_PERFORM;
    }
    /* else
       stay in DO_MORE */
  }
  else {
    /* failure detected */
    multi_posttransfer(data);
    multi_done(data, *result, FALSE);
    *stream_error = TRUE;
  }
  return CURLM_OK;
}

static CURLMcode multistate_did(struct Curl_multi *multi,
                                struct Curl_easy *data)
{
  DEBUGASSERT(data->conn);
  if(data->conn->bits.multiplex)
    /* Check if we can move pending requests to send pipe */
    multi_schedule_pending(multi); /* multiplexed */

  /* Only perform the transfer if there is a good socket to work with.
     Having both BAD is a signal to skip immediately to DONE */
  if(CONN_SOCK_IDX_VALID(data->conn->recv_idx) ||
     CONN_SOCK_IDX_VALID(data->conn->send_idx))
    multistate(data, MSTATE_PERFORMING);
  else {
#ifndef CURL_DISABLE_FTP
    if(data->state.wildcardmatch &&
       ((data->conn->scheme->flags & PROTOPT_WILDCARD) == 0)) {
      data->wildcard->state = CURLWC_DONE;
    }
#endif
    multistate(data, MSTATE_DONE);
  }
  return CURLM_CALL_MULTI_PERFORM;
}

static CURLMcode multistate_done(struct Curl_easy *data, CURLcode *presult)
{
  if(data->conn) {
    CURLcode result;

    /* post-transfer command */
    result = multi_done(data, *presult, FALSE);

    /* allow a previously set error code take precedence */
    if(!(*presult))
      *presult = result;
  }

#ifndef CURL_DISABLE_FTP
  if(data->state.wildcardmatch) {
    if(data->wildcard->state != CURLWC_DONE) {
      /* if a wildcard is set and we are not ending -> lets start again
         with MSTATE_INIT */
      multistate(data, MSTATE_INIT);
      return CURLM_CALL_MULTI_PERFORM;
    }
  }
#endif
  /* after we have DONE what we are supposed to do, go COMPLETED, and
     it does not matter what the multi_done() returned! */
  multistate(data, MSTATE_COMPLETED);
  return CURLM_CALL_MULTI_PERFORM;
}

static CURLMcode multi_runsingle(struct Curl_multi *multi,
                                 struct Curl_easy *data,
                                 struct Curl_sigpipe_ctx *sigpipe_ctx)
{
  CURLMcode mresult;
  CURLcode result = CURLE_OK;

  if(multi->dead) {
    /* a multi-level callback returned error before, meaning every individual
     transfer now has failed */
    result = CURLE_ABORTED_BY_CALLBACK;
    multi_posttransfer(data);
    multi_done(data, result, FALSE);
    multistate(data, MSTATE_COMPLETED);
  }

  multi_warn_debug(multi, data);

  /* transfer runs now, clear the dirty bit. This may be set
   * again during processing, triggering a re-run later. */
  Curl_uint32_bset_remove(&multi->dirty, data->mid);

  if(data == multi->admin) {
#ifdef ENABLE_INTERNAL_WAKEUP
    /* Consume any pending wakeup signals before processing.
     * This is necessary for event based processing. See #21547 */
    (void)Curl_wakeup_consume(multi->wakeup_internal, TRUE);
#endif
#ifdef USE_RESOLV_THREADED
    Curl_async_thrdd_multi_process(multi);
#endif
    Curl_cshutdn_perform(&multi->cshutdn, multi->admin, sigpipe_ctx);
    return CURLM_OK;
  }

  sigpipe_apply(data, sigpipe_ctx);
  do {
    /* A "stream" here is a logical stream if the protocol can handle that
       (HTTP/2), or the full connection for older protocols */
    bool stream_error = FALSE;
    mresult = CURLM_OK;

    if(multi_ischanged(multi, TRUE)) {
      CURL_TRC_M(data, "multi changed, check CONNECT_PEND queue");
      multi_schedule_pending(multi); /* multiplexed */
    }

    if(data->mstate > MSTATE_CONNECT &&
       data->mstate < MSTATE_COMPLETED) {
      /* Make sure we set the connection's current owner */
      DEBUGASSERT(data->conn);
      if(!data->conn)
        return CURLM_INTERNAL_ERROR;
    }

    /* Wait for the connect state as only then is the start time stored, but
       we must not check already completed handles */
    if((data->mstate >= MSTATE_CONNECT) && (data->mstate < MSTATE_COMPLETED) &&
       multi_handle_timeout(data, &stream_error, &result))
      /* Skip the statemachine and go directly to error handling section. */
      goto statemachine_end;

    switch(data->mstate) {
    case MSTATE_INIT:
      /* Transitional state. init this transfer. A handle never comes back to
         this state. */
      mresult = multistate_init(data, &result);
      break;

    case MSTATE_SETUP:
      /* Transitional state. Setup things for a new transfer. The handle
         can come back to this state on a redirect. */
      mresult = multistate_setup(data);
      break;

    case MSTATE_CONNECT:
      mresult = multistate_connect(multi, data, &result);
      break;

    case MSTATE_CONNECTING:
      /* awaiting a completion of an asynch TCP connect */
      mresult = multistate_connecting(data, &stream_error, &result);
      break;

    case MSTATE_PROTOCONNECT:
      mresult = multistate_protoconnect(data, &stream_error, &result);
      break;

    case MSTATE_PROTOCONNECTING:
      /* protocol-specific connect phase */
      mresult = multistate_protoconnecting(data, &stream_error, &result);
      break;

    case MSTATE_DO:
      mresult = multistate_do(data, &stream_error, &result);
      break;

    case MSTATE_DOING:
      /* we continue DOING until the DO phase is complete */
      mresult = multistate_doing(data, &stream_error, &result);
      break;

    case MSTATE_DOING_MORE:
      /*
       * When we are connected, DOING MORE and then go DID
       */
      mresult = multistate_doing_more(data, &stream_error, &result);
      break;

    case MSTATE_DID:
      mresult = multistate_did(multi, data);
      break;

    case MSTATE_RATELIMITING: /* limit-rate exceeded in either direction */
      mresult = multistate_ratelimiting(data, &result);
      break;

    case MSTATE_PERFORMING:
      mresult = multistate_performing(data, &stream_error, &result);
      break;

    case MSTATE_DONE:
      mresult = multistate_done(data, &result);
      break;

    case MSTATE_COMPLETED:
      break;

    case MSTATE_PENDING:
    case MSTATE_MSGSENT:
      /* handles in these states should NOT be in this list */
      break;

    default:
      return CURLM_INTERNAL_ERROR;
    }

    if(data->mstate >= MSTATE_CONNECT &&
       data->mstate < MSTATE_DO &&
       mresult != CURLM_CALL_MULTI_PERFORM &&
       !multi_ischanged(multi, FALSE)) {
      /* We now handle stream timeouts if and only if this will be the last
       * loop iteration. We only check this on the last iteration to ensure
       * that if we know we have additional work to do immediately
       * (i.e. CURLM_CALL_MULTI_PERFORM == TRUE) then we should do that before
       * declaring the connection timed out as we may almost have a completed
       * connection. */
      multi_handle_timeout(data, &stream_error, &result);
    }

statemachine_end:

    result = is_finished(multi, data, stream_error, result);
    if(result)
      mresult = CURLM_CALL_MULTI_PERFORM;

    if(MSTATE_COMPLETED == data->mstate) {
      handle_completed(multi, data, result);
      return CURLM_OK;
    }
  } while((mresult == CURLM_CALL_MULTI_PERFORM) ||
          multi_ischanged(multi, FALSE));

  data->result = result;
  return mresult;
}

static CURLMcode multi_perform(struct Curl_multi *multi,
                               int *running_handles)
{
  CURLMcode returncode = CURLM_OK;
  struct curltime start = *multi_now(multi);
  uint32_t mid;
  struct Curl_sigpipe_ctx sigpipe_ctx;

  sigpipe_init(&sigpipe_ctx);

  if(Curl_uint32_bset_first(&multi->process, &mid)) {
    CURL_TRC_M(multi->admin, "multi_perform(running=%u)",
               Curl_multi_xfers_running(multi));
    do {
      struct Curl_easy *data = Curl_multi_get_easy(multi, mid);
      CURLMcode mresult;
      if(!data) {
        DEBUGASSERT(0);
        Curl_uint32_bset_remove(&multi->process, mid);
        Curl_uint32_bset_remove(&multi->dirty, mid);
        continue;
      }
      mresult = multi_runsingle(multi, data, &sigpipe_ctx);
      if(mresult)
        returncode = mresult;
    } while(Curl_uint32_bset_next(&multi->process, mid, &mid));
  }
  sigpipe_restore(&sigpipe_ctx);

  if(multi_ischanged(multi, TRUE))
    multi_schedule_pending(multi);

  if(!returncode && CURL_MNTFY_HAS_ENTRIES(multi))
    returncode = Curl_mntfy_dispatch_all(multi);

  /*
   * Remove all expired timers from the splay since handles are dealt
   * with unconditionally by this function and curl_multi_timeout() requires
   * that already passed/handled expire times are removed from the splay.
   *
   * It is important that the 'now' value is set at the entry of this function
   * and not for the current time as it may have ticked a little while since
   * then and then we risk this loop to remove timers that actually have not
   * been handled!
   */
  if(multi->timetree) {
    struct Curl_tree *t = NULL;
    do {
      multi->timetree = Curl_splaygetbest(&start, multi->timetree, &t);
      if(t) {
        /* the removed may have another timeout in queue */
        struct Curl_easy *data = Curl_splayget(t);
        data->state.timeouts.registered = FALSE;
        (void)add_next_timeout(&start, multi, data);
        if(data->mstate == MSTATE_PENDING) {
          bool stream_unused;
          CURLcode result_unused;
          if(multi_handle_timeout(data, &stream_unused, &result_unused)) {
            infof(data, "PENDING handle timeout");
            move_pending_to_connect(multi, data);
          }
        }
      }
    } while(t);
  }

  if(running_handles) {
    unsigned int running = Curl_multi_xfers_running(multi);
    *running_handles = (running < INT_MAX) ? (int)running : INT_MAX;
  }

  if(CURLM_OK >= returncode)
    returncode = Curl_update_timer(multi);

  return returncode;
}

CURLMcode curl_multi_perform(CURLM *m, int *running_handles)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_perform, &mresult)) {
    mresult = multi_perform(m, running_handles);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_cleanup(CURLM *m)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_cleanup, &mresult)) {
    struct Curl_multi *multi = m;
    void *entry;
    uint32_t mid;

    /* First remove all remaining easy handles,
     * close internal ones. admin handle is special */
    if(Curl_uint32_tbl_first(&multi->xfers, &mid, &entry)) {
      do {
        struct Curl_easy *data = entry;
        if(!GOOD_EASY_HANDLE(data)) {
          mresult = CURLM_BAD_HANDLE;
          goto out;
        }

#ifdef DEBUGBUILD
        if(mid != data->mid) {
          CURL_TRC_M(data, "multi_cleanup: still present with mid=%u, "
                     "but unexpected data->mid=%u\n", mid, data->mid);
          DEBUGASSERT(0);
        }
#endif

        if(data == multi->admin)
          continue;

        if(!data->state.done && data->conn)
          /* if DONE was never called for this handle */
          (void)multi_done(data, CURLE_OK, TRUE);

        data->multi = NULL; /* clear the association */
        Curl_uint32_tbl_remove(&multi->xfers, mid);
        data->mid = UINT32_MAX;

#ifdef USE_LIBPSL
        if(data->psl == &multi->psl)
          data->psl = NULL;
#endif
        if(data->state.internal)
          Curl_close(&data);
      } while(Curl_uint32_tbl_next(&multi->xfers, mid, &mid, &entry));
    }

#ifdef USE_RESOLV_THREADED
    Curl_async_thrdd_multi_destroy(multi, !multi->quick_exit);
#endif
    Curl_cpool_destroy(&multi->cpool);
    Curl_cshutdn_destroy(&multi->cshutdn, multi->admin);
    if(multi->admin) {
      CURL_TRC_M(multi->admin, "multi_cleanup, closing admin handle, done");
      multi->admin->multi = NULL;
      Curl_uint32_tbl_remove(&multi->xfers, multi->admin->mid);
      Curl_close(&multi->admin);
    }

    multi->magic = 0; /* not good anymore */

    Curl_multi_ev_cleanup(multi);
    Curl_hash_destroy(&multi->proto_hash);
    Curl_dnscache_destroy(&multi->dnscache);
    Curl_psl_destroy(&multi->psl);
#ifdef USE_SSL
    Curl_ssl_scache_destroy(multi->ssl_scache);
#endif

#ifdef USE_WINSOCK
    WSACloseEvent(multi->wsa_event);
#endif
#ifdef ENABLE_WAKEUP
  Curl_wakeup_destroy(multi->wakeup_pair);
#endif
#ifdef ENABLE_INTERNAL_WAKEUP
  Curl_wakeup_destroy(multi->wakeup_internal);
#endif

    multi_xfer_bufs_free(multi);
    Curl_mntfy_cleanup(multi);
#ifdef DEBUGBUILD
    if(Curl_uint32_tbl_count(&multi->xfers)) {
      multi_xfer_tbl_dump(multi);
      DEBUGASSERT(0);
    }
#endif
    Curl_uint32_bset_destroy(&multi->process);
    Curl_uint32_bset_destroy(&multi->dirty);
    Curl_uint32_bset_destroy(&multi->pending);
    Curl_uint32_bset_destroy(&multi->msgsent);
    Curl_uint32_tbl_destroy(&multi->xfers);
    curlx_memzero(multi, sizeof(*multi));
    curlx_free(multi);

    mresult = CURLM_OK;
  }
out:
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

/*
 * curl_multi_info_read()
 *
 * This function is the primary way for a multi/multi_socket application to
 * figure out if a transfer has ended. We MUST make this function as fast as
 * possible as it will be polled frequently and we MUST NOT scan any lists in
 * here to figure out things. We must scale fine to thousands of handles and
 * beyond. The current design is fully O(1).
 */

CURLMsg *curl_multi_info_read(CURLM *m, int *msgs_in_queue)
{
  struct Curl_mapi_guard guard;
  CURLMsg *msg_result = NULL;

  *msgs_in_queue = 0; /* default to none */
  if(CURL_MAPI_ENTER(&guard, m, multi_info_read, NULL)) {
    struct Curl_multi *multi = m;
    if(Curl_llist_count(&multi->msglist)) {
      /* there is one or more messages in the list */
      struct Curl_llist_node *e;
      struct Curl_message *msg;

      /* extract the head of the list to return */
      e = Curl_llist_head(&multi->msglist);

      msg = Curl_node_elem(e);

      /* remove the extracted entry */
      Curl_node_remove(e);

      *msgs_in_queue = curlx_uztosi(Curl_llist_count(&multi->msglist));

      msg_result = &msg->extmsg;
    }
  }
  CURL_MAPI_LEAVE(&guard);
  return msg_result;
}

void Curl_multi_will_close(struct Curl_easy *data, curl_socket_t s)
{
  if(data) {
    struct Curl_multi *multi = data->multi;
    if(multi) {
      CURL_TRC_M(data, "Curl_multi_will_close fd=%" FMT_SOCKET_T, s);
      Curl_multi_ev_socket_done(multi, data, s);
    }
  }
}

static void multi_timeouts_init(struct Curl_easy *data)
{
  data->state.timeouts.first = EXPIRE_LAST;
  data->state.timeouts.registered = FALSE;
}

/*
 * add_next_timeout()
 *
 * Each Curl_easy has a list of timeouts. The add_next_timeout() is called
 * when it has been removed from the splay tree because the timeout has
 * expired. This function is then to advance in the list to pick the next
 * timeout to use (skip the already expired ones) and add this node back to
 * the splay tree again.
 *
 * The splay tree only has each Curl_easy as a single node and the nearest
 * timeout is used to sort it on.
 */
static CURLMcode add_next_timeout(const struct curltime *pnow,
                                  struct Curl_multi *multi,
                                  struct Curl_easy *data)
{
  struct expire_timers *timeouts = &data->state.timeouts;

  DEBUGASSERT(!timeouts->registered);
  while(timeouts->first < EXPIRE_LAST) {
    timediff_t us = curlx_ptimediff_us(&timeouts->time[timeouts->first], pnow);
    if(us <= 0)  /* remove already expired timer */
      timeouts->first = timeouts->next[timeouts->first];
    else /* timeouts are sorted, first is first in the future now */
      break;
  }

  if(timeouts->first < EXPIRE_LAST) {
    /* Insert this node again into the splay. Keep the timer in the list in
       case we need to recompute future timers. */
    Curl_splayset(&timeouts->splaynode, data);
    multi->timetree = Curl_splayinsert(&timeouts->time[timeouts->first],
                                       multi->timetree, &timeouts->splaynode);
    timeouts->registered = TRUE;
  }
  return CURLM_OK;
}

static void multi_mark_expired_as_dirty(struct Curl_multi *multi,
                                        const struct curltime *ts)
{
  struct Curl_easy *data = NULL;
  struct Curl_tree *t = NULL;

  /*
   * The loop following here will go on as long as there are expire-times left
   * to process (compared to `ts`) in the splay and 'data' will be
   * re-assigned for every expired handle we deal with.
   */
  while(1) {
    /* Check if there is one (more) expired timer to deal with! This function
       extracts a matching node if there is one */
    multi->timetree = Curl_splaygetbest(ts, multi->timetree, &t);
    if(!t)
      return;

    data = Curl_splayget(t); /* assign this for next loop */
    if(!data)
      continue;
    data->state.timeouts.registered = FALSE;
#ifdef CURLVERBOSE
    if(CURL_TRC_TIMER_is_verbose(data)) {
      if(data->state.timeouts.first < EXPIRE_LAST) {
        CURL_TRC_TIMER(data, data->state.timeouts.first, "has expired");
      }
    }
#endif
    (void)add_next_timeout(ts, multi, data);
    Curl_multi_mark_dirty(data);
  }
}

static CURLMcode multi_run_dirty(struct Curl_multi *multi,
                                 struct Curl_sigpipe_ctx *sigpipe_ctx,
                                 uint32_t *pnum)
{
  CURLMcode mresult = CURLM_OK;
  uint32_t mid;

  *pnum = 0;
  if(Curl_uint32_bset_first(&multi->dirty, &mid)) {
    do {
      struct Curl_easy *data = Curl_multi_get_easy(multi, mid);
      if(data) {
        CURL_TRC_M(data, "multi_run_dirty");

        if(!Curl_uint32_bset_contains(&multi->process, mid)) {
          /* We are no longer processing this transfer */
          Curl_uint32_bset_remove(&multi->dirty, mid);
          continue;
        }

        (*pnum)++;
        /* runsingle() clears the dirty mid */
        mresult = multi_runsingle(multi, data, sigpipe_ctx);

        if(CURLM_OK >= mresult) {
          /* reassess event handling of data */
          mresult = Curl_multi_ev_assess_xfer(multi, data);
          if(mresult)
            goto out;
        }
      }
      else {
        CURL_TRC_M(multi->admin, "multi_run_dirty, %u no longer found", mid);
        Curl_uint32_bset_remove(&multi->dirty, mid);
      }
    } while(Curl_uint32_bset_next(&multi->dirty, mid, &mid));
  }

out:
  return mresult;
}

static CURLMcode multi_socket(struct Curl_multi *multi,
                              bool checkall,
                              curl_socket_t s,
                              int ev_bitmask,
                              int *running_handles)
{
  CURLMcode mresult = CURLM_OK;
  struct Curl_sigpipe_ctx pipe_ctx;
  uint32_t run_xfers;

  (void)ev_bitmask;
  sigpipe_init(&pipe_ctx);

  if(checkall) {
    /* *perform() deals with running_handles on its own */
    mresult = multi_perform(multi, running_handles);

    if(mresult != CURLM_BAD_HANDLE) {
      /* Reassess event status of all active transfers */
      mresult = Curl_multi_ev_assess_xfer_bset(multi, &multi->process);
    }
    goto out;
  }

  if(s != CURL_SOCKET_TIMEOUT) {
    /* Mark all transfers of that socket as dirty */
    Curl_multi_ev_dirty_xfers(multi, s);
  }
  else {
    /* Asked to run due to time-out. Clear the 'last_expire_ts' variable to
       force Curl_update_timer() to trigger a callback to the app again even
       if the same timeout is still the one to run after this call. That
       handles the case when the application asks libcurl to run the timeout
       prematurely. */
    memset(&multi->last_expire_ts, 0, sizeof(multi->last_expire_ts));

    /* Applications may set `socket_cb` *after* having added transfers
     * first. *Then* kick off processing with a
     * curl_multi_socket_action(TIMEOUT) afterwards. Make sure our
     * admin handle registers its pollset with the callbacks present. */
    mresult = multi_assess_wakeup(multi);
    if(mresult)
      goto out;
  }

  multi_mark_expired_as_dirty(multi, multi_now(multi));
  mresult = multi_run_dirty(multi, &pipe_ctx, &run_xfers);
  if(mresult)
    goto out;

  if(run_xfers) {
    /* Running transfers takes time. With a new timestamp, we might catch
     * other expires which are due now. Instead of telling the application
     * to set a 0 timeout and call us again, we run them here.
     * Do that only once or it might be unfair to transfers on other
     * sockets. */
    multi_mark_expired_as_dirty(multi, &multi->now);
    mresult = multi_run_dirty(multi, &pipe_ctx, &run_xfers);
  }

out:
  sigpipe_restore(&pipe_ctx);

  if(multi_ischanged(multi, TRUE))
    multi_schedule_pending(multi);

  if(!mresult && CURL_MNTFY_HAS_ENTRIES(multi))
    mresult = Curl_mntfy_dispatch_all(multi);

  if(running_handles) {
    unsigned int running = Curl_multi_xfers_running(multi);
    *running_handles = (running < INT_MAX) ? (int)running : INT_MAX;
  }

  if(CURLM_OK >= mresult)
    mresult = Curl_update_timer(multi);
  return mresult;
}

#undef curl_multi_setopt
CURLMcode curl_multi_setopt(CURLM *m, CURLMoption option, ...)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult = CURLM_OK;

  if(CURL_MAPI_ENTER(&guard, m, multi_setopt, &mresult)) {
    struct Curl_multi *multi = m;
    va_list param;
    unsigned long uarg;

    va_start(param, option);

    switch(option) {
    case CURLMOPT_SOCKETFUNCTION:
      multi->socket_cb = va_arg(param, curl_socket_callback);
      break;
    case CURLMOPT_SOCKETDATA:
      multi->socket_userp = va_arg(param, void *);
      break;
    case CURLMOPT_PUSHFUNCTION:
      multi->push_cb = va_arg(param, curl_push_callback);
      break;
    case CURLMOPT_PUSHDATA:
      multi->push_userp = va_arg(param, void *);
      break;
    case CURLMOPT_PIPELINING:
      multi->multiplexing = va_arg(param, long) & CURLPIPE_MULTIPLEX ? 1 : 0;
      break;
    case CURLMOPT_TIMERFUNCTION:
      multi->timer_cb = va_arg(param, curl_multi_timer_callback);
      break;
    case CURLMOPT_TIMERDATA:
      multi->timer_userp = va_arg(param, void *);
      break;
    case CURLMOPT_MAXCONNECTS:
      uarg = va_arg(param, unsigned long);
      if(uarg <= UINT_MAX)
        multi->maxconnects = (unsigned int)uarg;
      break;
    case CURLMOPT_MAX_HOST_CONNECTIONS:
      if(!curlx_sltouz(va_arg(param, long), &multi->max_host_connections))
        mresult = CURLM_BAD_FUNCTION_ARGUMENT;
      break;
    case CURLMOPT_MAX_TOTAL_CONNECTIONS:
      if(!curlx_sltouz(va_arg(param, long), &multi->max_total_connections))
        mresult = CURLM_BAD_FUNCTION_ARGUMENT;
      break;
      /* options formerly used for pipelining */
    case CURLMOPT_MAX_PIPELINE_LENGTH:
      break;
    case CURLMOPT_CONTENT_LENGTH_PENALTY_SIZE:
      break;
    case CURLMOPT_CHUNK_LENGTH_PENALTY_SIZE:
      break;
    case CURLMOPT_PIPELINING_SITE_BL:
      break;
    case CURLMOPT_PIPELINING_SERVER_BL:
      break;
    case CURLMOPT_MAX_CONCURRENT_STREAMS: {
      long streams = va_arg(param, long);
      if((streams < 1) || (streams > INT_MAX))
        streams = 100;
      multi->max_concurrent_streams = (unsigned int)streams;
      break;
    }
    case CURLMOPT_NETWORK_CHANGED: {
      long val = va_arg(param, long);
      if(val & CURLMNWC_CLEAR_ALL)
        /* In the beginning, all values available to set were 1 by mistake. We
           converted this to mean "all", thus setting all the bits
           automatically */
        val = CURLMNWC_CLEAR_DNS | CURLMNWC_CLEAR_CONNS;
      if(val & CURLMNWC_CLEAR_DNS) {
        Curl_dnscache_clear(multi->admin);
      }
      if(val & CURLMNWC_CLEAR_CONNS) {
        Curl_cpool_nw_changed(multi->admin);
      }
      break;
    }
    case CURLMOPT_NOTIFYFUNCTION:
      multi->ntfy.ntfy_cb = va_arg(param, curl_notify_callback);
      break;
    case CURLMOPT_NOTIFYDATA:
      multi->ntfy.ntfy_cb_data = va_arg(param, void *);
      break;
    case CURLMOPT_RESOLVE_THREADS_MAX:
#ifdef USE_RESOLV_THREADED
      uarg = va_arg(param, long);
      if((uarg <= 0) || (uarg > UINT32_MAX))
        mresult = CURLM_BAD_FUNCTION_ARGUMENT;
      else {
        CURLcode result = Curl_async_thrdd_multi_set_props(
          multi, 0, (uint32_t)uarg, 2000);
        switch(result) {
        case CURLE_OK:
          mresult = CURLM_OK;
          break;
        case CURLE_BAD_FUNCTION_ARGUMENT:
          mresult = CURLM_BAD_FUNCTION_ARGUMENT;
          break;
        case CURLE_OUT_OF_MEMORY:
          mresult = CURLM_OUT_OF_MEMORY;
          break;
        default:
          mresult = CURLM_INTERNAL_ERROR;
          break;
        }
      }
#endif
      break;
    case CURLMOPT_QUICK_EXIT:
      multi->quick_exit = va_arg(param, long) ? 1 : 0;
      break;
    default:
      mresult = CURLM_UNKNOWN_OPTION;
      break;
    }
    va_end(param);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

/* we define curl_multi_socket() in the public multi.h header */
#undef curl_multi_socket

CURLMcode curl_multi_socket(CURLM *m, curl_socket_t s, int *running_handles)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_socket, &mresult)) {
    mresult = multi_socket(m, FALSE, s, 0, running_handles);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_socket_action(CURLM *m, curl_socket_t s,
                                   int ev_bitmask, int *running_handles)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_socket_action, &mresult)) {
    mresult = multi_socket(m, FALSE, s, ev_bitmask, running_handles);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_socket_all(CURLM *m, int *running_handles)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_socket_all, &mresult)) {
    mresult = multi_socket(m, TRUE, CURL_SOCKET_BAD, 0, running_handles);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

static bool multi_has_dirties(struct Curl_multi *multi)
{
  uint32_t mid;
  if(Curl_uint32_bset_first(&multi->dirty, &mid)) {
    do {
      struct Curl_easy *data = Curl_multi_get_easy(multi, mid);
      if(data) {
        if(Curl_uint32_bset_contains(&multi->process, mid))
          return TRUE;
        /* We are no longer processing this transfer */
        Curl_uint32_bset_remove(&multi->dirty, mid);
      }
      else {
        CURL_TRC_M(multi->admin, "dirty transfer %u no longer found", mid);
        Curl_uint32_bset_remove(&multi->dirty, mid);
      }
    } while(Curl_uint32_bset_next(&multi->dirty, mid, &mid));
  }
  return FALSE;
}

static void multi_timeout(struct Curl_multi *multi,
                          struct curltime *expire_time,
                          long *timeout_ms)
{
  static const struct curltime tv_zero = { 0, 0 };
  VERBOSE(struct Curl_easy *data = NULL);

  if(multi->dead) {
    *expire_time = tv_zero;
    *timeout_ms = 0;
    return;
  }

  if(multi_has_dirties(multi)) {
    *expire_time = *multi_now(multi);
    *timeout_ms = 0;
    return;
  }
  else if(multi->timetree) {
    const struct curltime *pnow = multi_now(multi);
    /* splay the lowest to the bottom */
    multi->timetree = Curl_splay(&tv_zero, multi->timetree);
    /* this will not return NULL from a non-empty tree, but some compilers
     * are not convinced of that. Analyzers are hard. */
    *expire_time = multi->timetree ? multi->timetree->key : tv_zero;

    /* 'multi->timetree' will be non-NULL here but the compilers sometimes
       yell at us if we assume so */
    if(multi->timetree &&
       curlx_ptimediff_us(&multi->timetree->key, pnow) > 0) {
      /* some time left before expiration */
      timediff_t diff_ms =
        curlx_timediff_ceil_ms(multi->timetree->key, *pnow);
      VERBOSE(data = Curl_splayget(multi->timetree));
      /* this should be safe even on 32-bit archs, as we do not use that
         overly long timeouts */
      *timeout_ms = (long)diff_ms;
    }
    else {
      if(multi->timetree)
        VERBOSE(data = Curl_splayget(multi->timetree));
      /* 0 means immediately */
      *timeout_ms = 0;
    }
  }
  else {
    *expire_time = tv_zero;
    *timeout_ms = -1;
  }

#ifdef CURLVERBOSE
  if(CURL_TRC_TIMER_is_verbose(data) &&
     (data->state.timeouts.first < EXPIRE_LAST)) {
    CURL_TRC_TIMER(data, data->state.timeouts.first,
                   "gives multi timeout in %ldms", *timeout_ms);
  }
#endif
}

CURLMcode curl_multi_timeout(CURLM *m,
                             long *timeout_ms)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_timeout, &mresult)) {
    struct curltime expire_time;

    multi_timeout(m, &expire_time, timeout_ms);
    mresult = CURLM_OK;
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

/*
 * Tell the application it should update its timers, if it subscribes to the
 * update timer callback.
 */
CURLMcode Curl_update_timer(struct Curl_multi *multi)
{
  struct curltime expire_ts = { 0, 0 };
  long timeout_ms;
  int rc;
  bool set_value = FALSE;

  if(!multi->timer_cb || multi->dead)
    return CURLM_OK;
  multi_timeout(multi, &expire_ts, &timeout_ms);

  if(timeout_ms < 0 && multi->last_timeout_ms < 0) {
    /* nothing to do */
  }
  else if(timeout_ms < 0) {
    /* there is no timeout now but there was one previously */
    CURL_TRC_M(multi->admin, "[TIMER] clear");
    timeout_ms = -1; /* normalize */
    set_value = TRUE;
  }
  else if(multi->last_timeout_ms < 0) {
    CURL_TRC_M(multi->admin, "[TIMER] set %ldms, none before", timeout_ms);
    set_value = TRUE;
  }
  else if(curlx_ptimediff_us(&multi->last_expire_ts, &expire_ts)) {
    /* We had a timeout before and have one now, the absolute timestamp
     * differs. The relative timeout_ms may be the same, but the starting
     * point differs. Let the application restart its timer. */
    CURL_TRC_M(multi->admin, "[TIMER] set %ldms, replace previous",
               timeout_ms);
    set_value = TRUE;
  }
  else {
    /* We have same expire time as previously. Our relative 'timeout_ms'
     * may be different now, but the application has the timer running
     * and we do not to tell it to start this again. */
  }

  if(set_value) {
    struct Curl_mapi_guard guard;

    multi->last_expire_ts = expire_ts;
    multi->last_timeout_ms = timeout_ms;
    CURL_CBAPI_MULTI_START(&guard, multi, multi_timer_cb);
    rc = multi->timer_cb(multi, timeout_ms, multi->timer_userp);
    CURL_CBAPI_MULTI_END(&guard);
    if(rc == -1) {
      multi->dead = TRUE;
      return CURLM_ABORTED_BY_CALLBACK;
    }
  }
  return CURLM_OK;
}

#ifdef DEBUGBUILD
static bool multi_timeouts_check(struct Curl_easy *data)
{
  struct expire_timers *timeouts = &data->state.timeouts;
  expire_id eid;
  int i = 0;
  for(eid = timeouts->first; eid < EXPIRE_LAST; eid = timeouts->next[eid]) {
    if(++i >= EXPIRE_LAST) {
      failf(data, "expire timeouts looped: %d iterations and no end", i);
      return FALSE;
    }
    if(eid == timeouts->next[eid]) {
      failf(data, "expire timeouts wrong: %d points to itself", (int)eid);
      return FALSE;
    }
    if((timeouts->next[eid] < EXPIRE_LAST) &&
       (curlx_ptimediff_ms(&timeouts->time[eid],
                           &timeouts->time[timeouts->next[eid]]) > 0)) {
      failf(data, "expire timeouts not sorted: %d happens after %d but "
            "is listed before", (int)eid, (int)timeouts->next[eid]);
      return FALSE;
    }
  }
  return TRUE;
}
#endif

/*
 * multi_deltimeout()
 *
 * Remove a given timestamp from the list of timeouts.
 */
static void multi_deltimeout(struct Curl_easy *data, expire_id eid)
{
  struct expire_timers *timeouts = &data->state.timeouts;
  expire_id orig_first = timeouts->first;
  expire_id *anchor = &timeouts->first;

  while(*anchor < EXPIRE_LAST) {
    if(*anchor == eid) {
      *anchor = timeouts->next[eid];
      break;
    }
    anchor = &timeouts->next[*anchor];
  }
  DEBUGASSERT(multi_timeouts_check(data));
  if(timeouts->registered) {
    struct Curl_multi *multi = data->multi;
    int rc;

    if(!multi) {
      DEBUGASSERT(0);
      return;
    }
    if((timeouts->first >= EXPIRE_LAST) || /* no more timeouts */
       (timeouts->first != orig_first)) {  /* active timeout changed */
      rc = Curl_splayremove(multi->timetree, &timeouts->splaynode,
                            &multi->timetree);
      if(rc)
        infof(data, "Internal error removing splay node = %d", rc);
      timeouts->registered = FALSE;
    }
    if((timeouts->first < EXPIRE_LAST) && !timeouts->registered) {
      multi->timetree = Curl_splayinsert(&timeouts->time[timeouts->first],
                                         multi->timetree,
                                         &timeouts->splaynode);
      timeouts->registered = TRUE;
    }
  }
}

/*
 * multi_addtimeout()
 *
 * Add a timestamp to the list of timeouts. Keep the list sorted so that head
 * of list is always the timeout nearest in time.
 *
 */
static CURLMcode multi_addtimeout(struct Curl_easy *data,
                                  struct curltime *stamp,
                                  expire_id eid)
{
  struct expire_timers *timeouts = &data->state.timeouts;
  expire_id *anchor = &timeouts->first;

  if(eid >= EXPIRE_LAST) {
    DEBUGASSERT(0);
    return CURLM_BAD_FUNCTION_ARGUMENT;
  }
  /* remove from list, store time and re-insert */
  multi_deltimeout(data, eid);
  memcpy(&timeouts->time[eid], stamp, sizeof(*stamp));
  while(*anchor < EXPIRE_LAST) {
    timediff_t ms = curlx_ptimediff_ms(&timeouts->time[*anchor], stamp);
    if(ms > 0) /* *anchor's time is after eid's time */
      break;
    anchor = &timeouts->next[*anchor];
  }
  timeouts->next[eid] = *anchor;
  timeouts->next[eid] = *anchor;
  *anchor = eid;
  DEBUGASSERT(multi_timeouts_check(data));
  CURL_TRC_TIMER(data, eid, "set for %" FMT_TIMEDIFF_T "us",
                 curlx_ptimediff_us(stamp, Curl_pgrs_now(data)));
  return CURLM_OK;
}

void Curl_expire_ex(struct Curl_easy *data,
                    timediff_t milli, expire_id eid)
{
  struct Curl_multi *multi = data->multi;
  struct expire_timers *timeouts = &data->state.timeouts;
  expire_id prev_id = timeouts->first;
  struct curltime set;

  /* this is only interesting while there is still an associated multi struct
     remaining! */
  if(!multi)
    return;
  DEBUGASSERT(eid < EXPIRE_LAST);

  set = *Curl_pgrs_now(data);
  set.tv_sec += (time_t)(milli / 1000); /* may be a 64 to 32-bit conversion */
  set.tv_usec += (int)(milli % 1000) * 1000;

  if(set.tv_usec >= 1000000) {
    set.tv_sec++;
    set.tv_usec -= 1000000;
  }

  /* Add the timeout, will replace any previous value for this timer. */
  multi_addtimeout(data, &set, eid);
  DEBUGASSERT(timeouts->first < EXPIRE_LAST);

  if(timeouts->registered) {
    int rc;
    /* timeouts->splaynode is in splay tree already. If the first timer
     * was NOT the one we just set AND is still the first one,
     * nothing changed from the splay tree's point of view. The
     * set timer triggers after the one already in the tree. Leave. */
    if((prev_id != eid) && (prev_id == timeouts->first))
      return;

    /* Since this is an updated time, we must remove the previous entry from
       the splay tree first and then re-add the new value */
    rc = Curl_splayremove(multi->timetree, &timeouts->splaynode,
                          &multi->timetree);
    if(rc)
      infof(data, "Internal error removing splay node = %d", rc);
  }

  /* Indicate that we are in the splay tree and insert the new timer expiry
     value since it is our local minimum. */
  Curl_splayset(&timeouts->splaynode, data);
  multi->timetree = Curl_splayinsert(&timeouts->time[timeouts->first],
                                     multi->timetree, &timeouts->splaynode);
  timeouts->registered = TRUE;
}

/*
 * Curl_expire()
 *
 * given a number of milliseconds from now to use to set the 'act before
 * this'-time for the transfer, to be extracted by curl_multi_timeout()
 *
 * The timeout will be added to a queue of timeouts if it defines a moment in
 * time that is later than the current head of queue.
 *
 * Expire replaces a former timeout using the same id if already set.
 */
void Curl_expire(struct Curl_easy *data, timediff_t milli, expire_id id)
{
  Curl_expire_ex(data, milli, id);
}

/*
 * Curl_expire_done()
 *
 * Removes the expire timer. Marks it as done.
 *
 */
void Curl_expire_done(struct Curl_easy *data, expire_id id)
{
  /* remove the timer, if there */
  multi_deltimeout(data, id);
  CURL_TRC_TIMER(data, id, "cleared");
}

/*
 * Curl_expire_clear()
 *
 * Clear ALL timeout values for this handle.
 */
void Curl_expire_clear(struct Curl_easy *data)
{
  struct Curl_multi *multi = data->multi;
  struct expire_timers *timeouts = &data->state.timeouts;

  /* this is only interesting while there is still an associated multi struct
     remaining! */
  if(!multi)
    return;

  if(timeouts->registered) {
    /* Since this is an cleared time, we must remove the previous entry from
       the splay tree */
    int rc;

    rc = Curl_splayremove(multi->timetree, &timeouts->splaynode,
                          &multi->timetree);
    if(rc)
      infof(data, "Internal error clearing splay node = %d", rc);

    /* clear the timeouts */
    multi_timeouts_init(data);

    if(data->id >= 0)
      CURL_TRC_M(data, "[TIMEOUT] all cleared");
  }
}

CURLMcode curl_multi_assign(CURLM *m, curl_socket_t sockfd,
                            void *sockp)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult;

  if(CURL_MAPI_ENTER(&guard, m, multi_assign, &mresult)) {
    mresult = Curl_multi_ev_assign(m, sockfd, sockp);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

static void move_pending_to_connect(struct Curl_multi *multi,
                                    struct Curl_easy *data)
{
  DEBUGASSERT(data->mstate == MSTATE_PENDING);

  /* Remove this node from the pending set, add into process set */
  Curl_uint32_bset_remove(&multi->pending, data->mid);
  Curl_uint32_bset_add(&multi->process, data->mid);

  multistate(data, MSTATE_CONNECT);
  Curl_multi_mark_dirty(data); /* make it run */
}

/* multi_schedule_pending() moves a handle from PENDING back into the process
   list and change state to CONNECT.

   We do not move all transfers because that can be a significant amount.
   Since this is tried every now and then doing too many too often becomes a
   performance problem.

   When there is a change for connection limits like max host connections etc,
   this likely only allows one new transfer. When there is a pipewait change,
   it can potentially allow hundreds of new transfers.

   We could consider an improvement where we store the queue reason and allow
   more pipewait rechecks than others. */
static void multi_schedule_pending(struct Curl_multi *multi)
{
  uint32_t mid = multi->last_pending_mid;

  if(mid) {
    while(Curl_uint32_bset_next(&multi->pending, mid, &mid)) {
      struct Curl_easy *data = Curl_multi_get_easy(multi, mid);
      if(data) {
        move_pending_to_connect(multi, data);
        multi->last_pending_mid = mid;
        return;
      }
      /* transfer no longer known, should not happen */
      Curl_uint32_bset_remove(&multi->pending, mid);
      DEBUGASSERT(0);
    }
    /* found no pending transfers with `mid` larger than `last_pending_mid`.
     * Start at the beginning of the pending set again. */
    multi->last_pending_mid = 0;
  }

  if(Curl_uint32_bset_first(&multi->pending, &mid)) {
    do {
      struct Curl_easy *data = Curl_multi_get_easy(multi, mid);
      if(data) {
        move_pending_to_connect(multi, data);
        multi->last_pending_mid = mid;
        return;
      }
      /* transfer no longer known, should not happen */
      Curl_uint32_bset_remove(&multi->pending, mid);
      DEBUGASSERT(0);
    } while(Curl_uint32_bset_next(&multi->pending, mid, &mid));
  }
}

unsigned int Curl_multi_max_concurrent_streams(struct Curl_multi *multi)
{
  DEBUGASSERT(multi);
  return multi->max_concurrent_streams;
}

CURL **curl_multi_get_handles(CURLM *m)
{
  struct Curl_mapi_guard guard;
  CURL **a = NULL;

  if(CURL_MAPI_ENTER(&guard, m, multi_get_handles, NULL)) {
    struct Curl_multi *multi = m;
    void *entry;
    size_t count = Curl_uint32_tbl_count(&multi->xfers);

    a = curlx_malloc(sizeof(struct Curl_easy *) * (count + 1));
    if(a) {
      unsigned int i = 0;
      uint32_t mid;

      if(Curl_uint32_tbl_first(&multi->xfers, &mid, &entry)) {
        do {
          struct Curl_easy *data = entry;
          DEBUGASSERT(i < count);
          if(!data->state.internal)
            a[i++] = data;
        } while(Curl_uint32_tbl_next(&multi->xfers, mid, &mid, &entry));
      }
      a[i] = NULL; /* last entry is a NULL */
    }
  }
  CURL_MAPI_LEAVE(&guard);
  return a;
}

CURLMcode curl_multi_get_offt(CURLM *m,
                              CURLMinfo_offt info,
                              curl_off_t *pvalue)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult = CURLM_OK;

  if(CURL_MAPI_ENTER(&guard, m, multi_get_offt, &mresult)) {
    struct Curl_multi *multi = m;
    uint32_t n;

    if(!pvalue) {
      mresult = CURLM_BAD_FUNCTION_ARGUMENT;
      goto out;
    }

    switch(info) {
    case CURLMINFO_XFERS_CURRENT:
      n = Curl_uint32_tbl_count(&multi->xfers);
      if(n && multi->admin)
        --n;
      *pvalue = (curl_off_t)n;
      break;
    case CURLMINFO_XFERS_RUNNING:
      n = Curl_uint32_bset_count(&multi->process);
      if(n && Curl_uint32_bset_contains(&multi->process, multi->admin->mid))
        --n;
      *pvalue = (curl_off_t)n;
      break;
    case CURLMINFO_XFERS_PENDING:
      *pvalue = (curl_off_t)Curl_uint32_bset_count(&multi->pending);
      break;
    case CURLMINFO_XFERS_DONE:
      *pvalue = (curl_off_t)Curl_uint32_bset_count(&multi->msgsent);
      break;
    case CURLMINFO_XFERS_ADDED:
      *pvalue = multi->xfers_total_ever;
      break;
    default:
      *pvalue = -1;
      mresult = CURLM_UNKNOWN_OPTION;
      break;
    }
  }
out:
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLcode Curl_multi_xfer_buf_borrow(struct Curl_easy *data,
                                    char **pbuf, size_t *pbuflen)
{
  DEBUGASSERT(data);
  DEBUGASSERT(data->multi);
  *pbuf = NULL;
  *pbuflen = 0;
  if(!data->multi) {
    failf(data, "transfer has no multi handle");
    return CURLE_FAILED_INIT;
  }
  if(!data->set.buffer_size) {
    failf(data, "transfer buffer size is 0");
    return CURLE_FAILED_INIT;
  }
  if(data->multi->xfer_buf_borrowed) {
    failf(data, "attempt to borrow xfer_buf when already borrowed");
    return CURLE_AGAIN;
  }

  if(data->multi->xfer_buf &&
     data->set.buffer_size > data->multi->xfer_buf_len) {
    /* not large enough, get a new one */
    curlx_safefree(data->multi->xfer_buf);
    data->multi->xfer_buf_len = 0;
  }

  if(!data->multi->xfer_buf) {
    data->multi->xfer_buf = curlx_malloc(curlx_uitouz(data->set.buffer_size));
    if(!data->multi->xfer_buf) {
      failf(data, "could not allocate xfer_buf of %u bytes",
            data->set.buffer_size);
      return CURLE_OUT_OF_MEMORY;
    }
    data->multi->xfer_buf_len = data->set.buffer_size;
  }

  data->multi->xfer_buf_borrowed = TRUE;
  *pbuf = data->multi->xfer_buf;
  *pbuflen = data->multi->xfer_buf_len;
  return CURLE_OK;
}

void Curl_multi_xfer_buf_release(struct Curl_easy *data, char *buf)
{
  (void)buf;
  DEBUGASSERT(data);
  DEBUGASSERT(data->multi);
  DEBUGASSERT(!buf || data->multi->xfer_buf == buf);
  data->multi->xfer_buf_borrowed = FALSE;
}

CURLcode Curl_multi_xfer_ulbuf_borrow(struct Curl_easy *data,
                                      char **pbuf, size_t *pbuflen)
{
  DEBUGASSERT(data);
  DEBUGASSERT(data->multi);
  *pbuf = NULL;
  *pbuflen = 0;
  if(!data->multi) {
    failf(data, "transfer has no multi handle");
    return CURLE_FAILED_INIT;
  }
  if(!data->set.upload_buffer_size) {
    failf(data, "transfer upload buffer size is 0");
    return CURLE_FAILED_INIT;
  }
  if(data->multi->xfer_ulbuf_borrowed) {
    failf(data, "attempt to borrow xfer_ulbuf when already borrowed");
    return CURLE_AGAIN;
  }

  if(data->multi->xfer_ulbuf &&
     data->set.upload_buffer_size > data->multi->xfer_ulbuf_len) {
    /* not large enough, get a new one */
    curlx_safefree(data->multi->xfer_ulbuf);
    data->multi->xfer_ulbuf_len = 0;
  }

  if(!data->multi->xfer_ulbuf) {
    data->multi->xfer_ulbuf =
      curlx_malloc(curlx_uitouz(data->set.upload_buffer_size));
    if(!data->multi->xfer_ulbuf) {
      failf(data, "could not allocate xfer_ulbuf of %u bytes",
            data->set.upload_buffer_size);
      return CURLE_OUT_OF_MEMORY;
    }
    data->multi->xfer_ulbuf_len = data->set.upload_buffer_size;
  }

  data->multi->xfer_ulbuf_borrowed = TRUE;
  *pbuf = data->multi->xfer_ulbuf;
  *pbuflen = data->multi->xfer_ulbuf_len;
  return CURLE_OK;
}

void Curl_multi_xfer_ulbuf_release(struct Curl_easy *data, char *buf)
{
  (void)buf;
  DEBUGASSERT(data);
  DEBUGASSERT(data->multi);
  DEBUGASSERT(!buf || data->multi->xfer_ulbuf == buf);
  data->multi->xfer_ulbuf_borrowed = FALSE;
}

CURLcode Curl_multi_xfer_sockbuf_borrow(struct Curl_easy *data,
                                        size_t blen, char **pbuf)
{
  DEBUGASSERT(data);
  *pbuf = NULL;
  if(!data->multi) {
    /* When a SHARE gets destroyed and has a connection pool, we get
     * call with share->admin which does not have a multi handle. */
    *pbuf = curlx_malloc(blen);
    return *pbuf ? CURLE_OK : CURLE_OUT_OF_MEMORY;
  }
  if(data->multi->xfer_sockbuf_borrowed) {
    failf(data, "attempt to borrow xfer_sockbuf when already borrowed");
    return CURLE_AGAIN;
  }

  if(data->multi->xfer_sockbuf && blen > data->multi->xfer_sockbuf_len) {
    /* not large enough, get a new one */
    curlx_safefree(data->multi->xfer_sockbuf);
    data->multi->xfer_sockbuf_len = 0;
  }

  if(!data->multi->xfer_sockbuf) {
    data->multi->xfer_sockbuf = curlx_malloc(blen);
    if(!data->multi->xfer_sockbuf) {
      failf(data, "could not allocate xfer_sockbuf of %zu bytes", blen);
      return CURLE_OUT_OF_MEMORY;
    }
    data->multi->xfer_sockbuf_len = blen;
  }

  data->multi->xfer_sockbuf_borrowed = TRUE;
  *pbuf = data->multi->xfer_sockbuf;
  return CURLE_OK;
}

void Curl_multi_xfer_sockbuf_release(struct Curl_easy *data, char *buf)
{
  DEBUGASSERT(data);
  if(!data->multi) {
    /* When a SHARE gets destroyed and has a connection pool, we get
     * call with share->admin which does not have a multi handle. */
    curlx_free(buf);
  }
  else {
    DEBUGASSERT(!buf || data->multi->xfer_sockbuf == buf);
    data->multi->xfer_sockbuf_borrowed = FALSE;
  }
}

static void multi_xfer_bufs_free(struct Curl_multi *multi)
{
  DEBUGASSERT(multi);
  curlx_safefree(multi->xfer_buf);
  multi->xfer_buf_len = 0;
  multi->xfer_buf_borrowed = FALSE;
  curlx_safefree(multi->xfer_ulbuf);
  multi->xfer_ulbuf_len = 0;
  multi->xfer_ulbuf_borrowed = FALSE;
  curlx_safefree(multi->xfer_sockbuf);
  multi->xfer_sockbuf_len = 0;
  multi->xfer_sockbuf_borrowed = FALSE;
}

struct Curl_easy *Curl_multi_get_easy(struct Curl_multi *multi,
                                      uint32_t mid)
{
  struct Curl_easy *data = Curl_uint32_tbl_get(&multi->xfers, mid);
  if(GOOD_EASY_HANDLE(data))
    return data;
  CURL_TRC_M(multi->admin, "invalid easy handle in xfer table for mid=%u",
             mid);
  Curl_uint32_tbl_remove(&multi->xfers, mid);
  return NULL;
}

bool Curl_multi_knows_easy(struct Curl_multi *multi, struct Curl_easy *data)
{
  return Curl_uint32_tbl_get(&multi->xfers, data->mid) == data;
}

unsigned int Curl_multi_xfers_running(struct Curl_multi *multi)
{
  DEBUGASSERT(multi);
  if(!multi)
    return 0;
  return multi->xfers_alive;
}

void Curl_multi_mark_dirty(struct Curl_easy *data)
{
  if(data->multi && data->mid != UINT32_MAX)
    Curl_uint32_bset_add(&data->multi->dirty, data->mid);
}

void Curl_multi_clear_dirty(struct Curl_easy *data)
{
  if(data->multi && data->mid != UINT32_MAX)
    Curl_uint32_bset_remove(&data->multi->dirty, data->mid);
}

CURLMcode curl_multi_notify_enable(CURLM *m, unsigned int notification)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult = CURLM_OK;

  if(CURL_MAPI_ENTER(&guard, m, multi_notify_enable, &mresult)) {
    mresult = Curl_mntfy_enable(m, notification);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

CURLMcode curl_multi_notify_disable(CURLM *m, unsigned int notification)
{
  struct Curl_mapi_guard guard;
  CURLMcode mresult = CURLM_OK;

  if(CURL_MAPI_ENTER(&guard, m, multi_notify_disable, &mresult)) {
    mresult = Curl_mntfy_disable(m, notification);
  }
  CURL_MAPI_LEAVE(&guard);
  return mresult;
}

#ifdef DEBUGBUILD
static void multi_xfer_dump(struct Curl_multi *multi, uint32_t mid,
                            void *entry)
{
  struct Curl_easy *data = entry;

  (void)multi;
  if(!data) {
    curl_mfprintf(stderr, "mid=%u, entry=NULL, bug in xfer table?\n", mid);
  }
  else {
    curl_mfprintf(stderr, "mid=%u, magic=%s, p=%p, id=%" FMT_OFF_T
                  ", url=%s\n",
                  mid,
                  (data->magic == CURLEASY_MAGIC_NUMBER) ? "GOOD" : "BAD!",
                  (void *)data, data->id, Curl_bufref_ptr(&data->state.url));
  }
}

static void multi_xfer_tbl_dump(struct Curl_multi *multi)
{
  uint32_t mid;
  void *entry;
  curl_mfprintf(stderr, "=== multi xfer table (count=%u, capacity=%u\n",
                Curl_uint32_tbl_count(&multi->xfers),
                Curl_uint32_tbl_capacity(&multi->xfers));
  if(Curl_uint32_tbl_first(&multi->xfers, &mid, &entry)) {
    multi_xfer_dump(multi, mid, entry);
    while(Curl_uint32_tbl_next(&multi->xfers, mid, &mid, &entry))
      multi_xfer_dump(multi, mid, entry);
  }
  curl_mfprintf(stderr, "===\n");
  fflush(stderr);
}
#endif /* DEBUGBUILD */
