2013/7/5 Keyur Govande <keyurgovande_at_gmail.com>:
> On Fri, Jul 5, 2013 at 5:26 AM, Evgeny Turnaev <turnaev.e_at_gmail.com> wrote:
>> Hi Keyur,
>> First of i am not really expert in curl. But reading through
>> documentation i can't find evidence that curl_multi_perform should
>> return CURLM_CALL_MULTI_PERFORM untill connection succeeds. Connection
>> can take very long time. Why don't you change your application code so
>> that it selects (poll or whatever) on curl sockets and when there is
>> action - call curl_multi_perform again. I suppose this is a typical
>> usage. Someone please correct me if i am wrong.
>>
>
> Hi Evgeny,
>
> Thanks for the response.
>
> The issue is the inconsistency of the response code.
>
> In the localhost case, when curl_multi_perform returns CURLM_OK, the
> TCP connection is done, the HTTP connection is done, and the request
> has been sent over. If I call a select() on the FDs returned by
> curl_multi_fdset(), I'm actually waiting for a response for the
> server. I don't want this because I want to execute other code while
> the async request is being procesed.
>
> Whereas in the slow-remote-host case, even the TCP connection is not
> done when CURLM_OK is returned by curl_multi_perform(). So when I call
> a select(), I am still waiting for the TCP connect to go through.
>
> There is no way for my code to know which of the two scenarios is it
> currently experiencing.

Hmm. i suppose you should not want to know this. There is nothing
practical you can do knowing this. I thought this is a point of curl
library to hide this kind of stuff from you.

>
> Once curl_multi_perform() has a TCP connection it returns
> CURML_CALL_MULTI_PERFORM until the request is sent over. It seems like
> a miss to not return the same when the TCP connection has not yet gone
> through.

Could you please quote documentation or point me to documentation
saying that curl_multi_perform() should not return CURLM_OK untill
connection is actually established?

>
> Hope that makes sense.
>
> Thanks,
> Keyur.
>
>
>> 2013/7/5 Keyur Govande <keyurgovande_at_gmail.com>:
>>> Hello,
>>>
>>> We're using cURL to do some asynchronous programming in PHP.
>>>
>>> The code fires off a multi-curl request to get some data from a remote
>>> server. Once the request is sent i.e. curl_multi_exec() (PHP's wrapper
>>> around curl_multi_perform() ) returns CURLM_OK, the code continues its
>>> processing and once it is all done and ready, it checks the multi-curl
>>> request for a response.
>>>
>>> We're seeing some unusual behavior that might be a bug. We're
>>> currently on 7.19.7-26.el6_1.2, but I checked the code and the same
>>> behavior is in the latest version as well.
>>>
>>> If the curl request tries to connect to a host that is slow to respond
>>> to the initial connect, then curl_multi_perform() returns CURLM_OK,
>>> even though the connection is not completed and the request not sent.
>>>
>>> Here's a couple of sample straces showing both conditions. The PHP code is:
>>>
>>> // Set up the multi-curl
>>> do {
>>> $cme = curl_multi_exec($this->mc_handle, $this->mc_running);
>>> } while ($cme === CURLM_CALL_MULTI_PERFORM);
>>> // For purposes of the test, sleep. This is where other code would execute
>>> sleep(2);
>>>
>>> Connection to localhost where connect() is super fast:
>>> 1372871818.596930 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 61 <0.000024>
>>> 1372871818.596990 fcntl(61, F_GETFL) = 0x2 (flags O_RDWR) <0.000023>
>>> 1372871818.597044 fcntl(61, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000015>
>>> 1372871818.597086 connect(61, {sa_family=AF_INET, sin_port=htons(80),
>>> sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now
>>> in progress) <0.000186>
>>> 1372871818.597315 poll([{fd=61, events=POLLOUT|POLLWRNORM}], 1, 0) = 1
>>> ([{fd=61, revents=POLLOUT|POLLWRNORM}]) <0.000017>
>>> 1372871818.597370 getsockopt(61, SOL_SOCKET, SO_ERROR, [0], [4]) = 0 <0.000016>
>>> 1372871818.597902 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 62 <0.000020>
>>> 1372871818.597960 fcntl(62, F_GETFL) = 0x2 (flags O_RDWR) <0.000016>
>>> 1372871818.598005 fcntl(62, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000018>
>>> 1372871818.598060 connect(62, {sa_family=AF_INET, sin_port=htons(80),
>>> sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now
>>> in progress) <0.000057>
>>> 1372871818.598162 poll([{fd=62, events=POLLOUT|POLLWRNORM}], 1, 0) = 1
>>> ([{fd=62, revents=POLLOUT|POLLWRNORM}]) <0.000016>
>>> 1372871818.598212 getsockopt(62, SOL_SOCKET, SO_ERROR, [0], [4]) = 0 <0.000015>
>>> 1372871818.598665 sendto(61, "GET /rpc_test.php?sleep=1
>>> HTTP/1.1\r\nAccept: */*\r\nHost: www.example.com\r\n\r\n", 75,
>>> MSG_NOSIGNAL, NULL, 0) = 75 <0.000159>
>>> 1372871818.599054 sendto(62, "GET /rpc_test.php?sleep=1
>>> HTTP/1.1\r\nAccept: */*\r\nHost: www.example.com\r\n\r\n", 75,
>>> MSG_NOSIGNAL, NULL, 0) = 75 <0.000072>
>>> 1372871818.601071 nanosleep({2, 0}, 0x7fff7ce2f4c0) = 0 <2.000130>
>>>
>>> Connecting to a slow remote host:
>>> 1372871825.806179 connect(61, {sa_family=AF_INET, sin_port=htons(80),
>>> sin_addr=inet_addr("10.255.58.37")}, 16) = -1 EINPROGRESS (Operation
>>> now in progress) <0.000195>
>>> 1372871825.806417 poll([{fd=61, events=POLLOUT|POLLWRNORM}], 1, 0) = 0
>>> (Timeout) <0.000017>
>>> 1372871825.806919 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 62 <0.000024>
>>> 1372871825.806976 fcntl(62, F_GETFL) = 0x2 (flags O_RDWR) <0.000016>
>>> 1372871825.807020 fcntl(62, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000016>
>>> 1372871825.807064 connect(62, {sa_family=AF_INET, sin_port=htons(80),
>>> sin_addr=inet_addr("10.255.58.37")}, 16) = -1 EINPROGRESS (Operation
>>> now in progress) <0.000173>
>>> 1372871825.807278 poll([{fd=62, events=POLLOUT|POLLWRNORM}], 1, 0) = 0
>>> (Timeout) <0.000021>
>>> 1372871825.807688 poll([{fd=61, events=POLLOUT|POLLWRNORM}], 1, 0) = 0
>>> (Timeout) <0.000016>
>>> 1372871825.807824 poll([{fd=62, events=POLLOUT|POLLWRNORM}], 1, 0) = 0
>>> (Timeout) <0.000016>
>>> 1372871825.809776 nanosleep({2, 0}, 0x7fff04b17530) = 0 <2.000174>
>>>
>>> For the slow remote host, the sleep is getting triggered even though
>>> the GET request was not yet sent.
>>>
>>> Reading through the code in lib/multi.c, in the
>>> CURLM_STATE_WAITCONNECT block, if connected is false, then the result
>>> should be CURLM_CALL_MULTI_PERFORM in order to keep calling poll until
>>> the connections are established and the requests flushed out.
>>>
>>> Here's the diff on the 7.19.7 branch that I think will fix the issue.
>>> The patch for 7.31.0 would be exactly the same:
>>> diff --git a/lib/multi.c b/lib/multi.c
>>> index 48df928..dc5ec48 100644
>>> --- a/lib/multi.c
>>> +++ b/lib/multi.c
>>> @@ -1077,6 +1077,7 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
>>> break;
>>> }
>>>
>>> + result = CURLM_CALL_MULTI_PERFORM;
>>> if(connected) {
>>> if(!protocol_connect) {
>>> /* We have a TCP connection, but 'protocol_connect' may be false
>>> @@ -1095,8 +1096,6 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
>>> /* after the connect has completed, go WAITDO or DO */
>>> multistate(easy, multi->pipelining_enabled?
>>> CURLM_STATE_WAITDO:CURLM_STATE_DO);
>>> -
>>> - result = CURLM_CALL_MULTI_PERFORM;
>>> }
>>> }
>>> break;
>>>
>>> Is there anything I'm missing, or another way to accomplish this?
>>>
>>> Thanks,
>>> Keyur.
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Received on 2013-07-05