/***************************************************************************
 *                                  _   _ ____  _
 *  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
 *
 ***************************************************************************/
/* <DESC>
 * Upload to SFTP, resuming a previously aborted transfer.
 * </DESC>
 */
#ifdef _MSC_VER
#ifndef _CRT_SECURE_NO_WARNINGS
#define _CRT_SECURE_NO_WARNINGS  /* for fopen() */
#endif
#endif

#include <stdlib.h>
#include <stdio.h>

#include <curl/curl.h>

/* read data to upload */
static size_t read_cb(char *ptr, size_t size, size_t nmemb, void *stream)
{
  FILE *f = (FILE *)stream;
  size_t n;

  if(ferror(f))
    return CURL_READFUNC_ABORT;

  n = fread(ptr, size, nmemb, f) * size;

  return n;
}

/*
 * sftpGetRemoteFileSize returns the remote file size in byte; -1 on error
 */
static curl_off_t sftpGetRemoteFileSize(const char *i_remoteFile)
{
  curl_off_t remoteFileSizeByte = -1;
  CURL *curl = curl_easy_init();

  if(curl) {
    CURLcode result;

    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

    curl_easy_setopt(curl, CURLOPT_URL, i_remoteFile);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 1L);
    curl_easy_setopt(curl, CURLOPT_NOBODY, 1L);
    curl_easy_setopt(curl, CURLOPT_HEADER, 1L);
    curl_easy_setopt(curl, CURLOPT_FILETIME, 1L);

    result = curl_easy_perform(curl);
    if(result == CURLE_OK) {
      result = curl_easy_getinfo(curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD_T,
                                 &remoteFileSizeByte);
      if(result != CURLE_OK)
        return -1;
      printf("filesize: %" CURL_FORMAT_CURL_OFF_T "\n", remoteFileSizeByte);
    }
    curl_easy_cleanup(curl);
  }

  return remoteFileSizeByte;
}

static int sftpResumeUpload(CURL *curl, const char *remotepath,
                            const char *localpath)
{
  FILE *f = NULL;
  CURLcode result = CURLE_GOT_NOTHING;

  curl_off_t remoteFileSizeByte = sftpGetRemoteFileSize(remotepath);
  if(remoteFileSizeByte == -1) {
    printf("Error reading the remote file size: unable to resume upload\n");
    return -1;
  }

  f = fopen(localpath, "rb");
  if(!f) {
    perror(NULL);
    return 0;
  }

  curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
  curl_easy_setopt(curl, CURLOPT_URL, remotepath);
  curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_cb);
  curl_easy_setopt(curl, CURLOPT_READDATA, f);

#ifdef _WIN32
  _fseeki64(f, remoteFileSizeByte, SEEK_SET);
#else
  fseek(f, (long)remoteFileSizeByte, SEEK_SET);
#endif
  curl_easy_setopt(curl, CURLOPT_APPEND, 1L);
  result = curl_easy_perform(curl);

  fclose(f);

  if(result == CURLE_OK)
    return 1;
  else {
    fprintf(stderr, "%s\n", curl_easy_strerror(result));
    return 0;
  }
}

int main(void)
{
  CURL *curl = NULL;

  CURLcode result = curl_global_init(CURL_GLOBAL_ALL);
  if(result != CURLE_OK)
    return (int)result;

  curl = curl_easy_init();
  if(curl) {
    static const char remote[] = "sftp://user:pass@example.com/path/filename";
    static const char filename[] = "filename";

    if(!sftpResumeUpload(curl, remote, filename)) {
      printf("resumed upload using curl %s failed\n", curl_version());
    }

    curl_easy_cleanup(curl);
  }
  curl_global_cleanup();

  return 0;
}
