Daniel Stenberg a écrit :
> On Tue, 5 Jan 2010, Daniel Stenberg wrote:
>
>> I think this is because you're using the default (synchronous) name
>> resolver within libcurl, and during the name resolving libcurl has no
>> socket handler to "export". As soon as the resolving is done, libcurl
>> creates a socket and then it _can_ return something in curl_multi_fdset.
>
> No, I'm wrong. During the name resolve the curl_multi_perform() will
> actually block... Thinking further about this, I can't really explain
> it. I guess I need to do some tests of my own first to understand what
> you're describing...
>
In fact, this is not related to the DNS. Here is my test program and the
output log. It may help to understand the problem. As you can see, I
often have no file descriptor set and my "select" is blocking until the
timeout occurs (so the connection is slower, the only workaround I have
to get things faster is to do a busy loop until I have a correct fdset,
or to put a shorter timeout on select)

int main(int argc, char **argv)
{
  CURL *sftp_handle;
  CURLM *multi_handle;
  CURLMcode ret;
  int still_running;

  sftp_handle = curl_easy_init();
  curl_easy_setopt(sftp_handle, CURLOPT_URL,
"sftp://172.25.110.46/cygdrive/c/Temp/file.txt");
  curl_easy_setopt(sftp_handle, CURLOPT_USERPWD, "user:password");
  curl_easy_setopt(sftp_handle, CURLOPT_VERBOSE, 1);
 
  multi_handle = curl_multi_init();
  curl_multi_add_handle(multi_handle, sftp_handle);

  printf("%ld : begin...\n", time(NULL));
  while(CURLM_CALL_MULTI_PERFORM ==
        curl_multi_perform(multi_handle, &still_running));
       
  while(still_running) {
    struct timeval timeout;
    int rc;

    fd_set fdread;
    fd_set fdwrite;
    fd_set fdexcep;
    int maxfd;

    FD_ZERO(&fdread);
    FD_ZERO(&fdwrite);
    FD_ZERO(&fdexcep);

    ret = curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep,
&maxfd);
    printf("%ld : %d process running, maxfd = %d, ret = %d\n",
time(NULL), still_running, maxfd, ret);
   
    timeout.tv_sec = (maxfd == -1) ? 2 : 30;
    timeout.tv_usec = 0;
    rc = select(50, &fdread, &fdwrite, &fdexcep, &timeout);

    switch(rc) {
    case -1:
      still_running = 0;
      printf("select() returns error, this is badness\n");
      break;
    case 0:
    default:
      while(CURLM_CALL_MULTI_PERFORM ==
            curl_multi_perform(multi_handle, &still_running));
      break;
    }
  }

  curl_multi_cleanup(multi_handle);
  curl_easy_cleanup(sftp_handle);
  return 0;
}

And the log :

1262681772 : begin...
* About to connect() to 172.25.110.46 port 22 (#0)
* Trying 172.25.110.46... * connected
* Connected to 172.25.110.46 (172.25.110.46) port 22 (#0)
* Expire cleared
1262681774 : 1 process running, maxfd = -1, ret = 0
1262681776 : 1 process running, maxfd = 3, ret = 0
* SSH authentication methods available:
publickey,password,keyboard-interactive
1262681780 : 1 process running, maxfd = -1, ret = 0
* Using ssh public key file /root/.ssh/id_dsa.pub
* Using ssh private key file /root/.ssh/id_dsa
1262681782 : 1 process running, maxfd = -1, ret = 0
* SSH public key authentication failed: Unable to open public key file
1262681784 : 1 process running, maxfd = -1, ret = 0
1262681786 : 1 process running, maxfd = -1, ret = 0
1262681788 : 1 process running, maxfd = 3, ret = 0
* Initialized password authentication
1262681789 : 1 process running, maxfd = -1, ret = 0
* Authentication complete
1262681791 : 1 process running, maxfd = -1, ret = 0
1262681793 : 1 process running, maxfd = 3, ret = 0
1262681793 : 1 process running, maxfd = 3, ret = 0
1262681793 : 1 process running, maxfd = 3, ret = 0
1262681798 : 1 process running, maxfd = -1, ret = 0
1262681800 : 1 process running, maxfd = 3, ret = 0
1262681800 : 1 process running, maxfd = -1, ret = 0
1262681802 : 1 process running, maxfd = -1, ret = 0
1262681804 : 1 process running, maxfd = 3, ret = 0
1262681804 : 1 process running, maxfd = -1, ret = 0
1262681806 : 1 process running, maxfd = 3, ret = 0
1262681806 : 1 process running, maxfd = 3, ret = 0
* Expire cleared
* Connection #0 to host 172.25.110.46 left intact
file.txt content
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Received on 2010-01-05