Re: Detection of failed connection

From: Ali Nasir via curl-library <curl-library_at_lists.haxx.se>
Date: Wed, 3 Jan 2024 16:04:43 +0530

Sorry for that link. The base code used was from
https://curl.se/libcurl/c/multi-post.html. It is modified as below:
if(curl)
    {
        curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
        multi_handle = curl_multi_init();
        /* Create the form */
        form = curl_mime_init(curl);

        /* Fill in the file upload field */
        field = curl_mime_addpart(form);
        curl_mime_name(field, "files");
        curl_mime_filedata(field, fileName);

        /* initialize custom header list (stating that Expect: 100-continue
is not
           wanted */
        headerlist = curl_slist_append(headerlist, buf);
        /* what URL that receives this POST */
        curl_easy_setopt(curl, CURLOPT_URL, webUrl);
        curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, progress_callback);
        list = curl_slist_append(list, "Shoesize: 10");
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);
        curl_easy_setopt(curl, CURLOPT_MIMEPOST, form);

        curl_multi_add_handle(multi_handle, curl);

        while(still_running)
        {
            CURLMsg *msg;
            int queued;
            CURLMcode mc = curl_multi_perform(multi_handle, &still_running);
            printf("\n\rMulti Perform exit with code %d, still running
%d\n\r", mc, still_running);
            if(still_running)
            {
              /* wait for activity, timeout or "nothing" */
              mc = curl_multi_poll(multi_handle, NULL, 0, 1000, NULL);
            }

            printf("\n\rMulti poll : %d", mc);
            if(mc)
              break;

            do
            {
              msg = curl_multi_info_read(multi_handle, &queued);
              printf("\n\r Queued %d \n\r",queued);
              if(msg)
              {
                printf("\n\rCurl code %d\n\r", msg->data.result);
                if(msg->msg == CURLMSG_DONE)
                {
                  /* a transfer ended */
                  fprintf(stderr, "Transfer completed\n");
                }
              }
            } while(msg);
        }

        res = curl_easy_getinfo(curl, CURLINFO_OS_ERRNO, &error);
        printf("\n\rERRNO %ld\n\r", error);
        curl_multi_remove_handle(multi_handle, curl);
        curl_multi_cleanup(multi_handle);
        /* always cleanup */
        curl_easy_cleanup(curl);
        /* then cleanup the form */
        curl_mime_free(form);
        /* free slist */
        curl_slist_free_all(headerlist);
    }
    printf("\n\r");
    return 0;
}

In the absence of the server running, below is the output on the console:
* Initializing NSS with certpath: none

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0
* Trying 192.168.65.2:80...
* TCP_NODELAY set

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0
* Connected to host.docker.internal (192.168.65.2) port 80 (#0)
> POST /upload HTTP/1.1
Host: host.docker.internal
Accept: */*
Shoesize: 10
Content-Length: 321
Content-Type: multipart/form-data;
boundary=------------------------b2b856525299ec0a

* We are completely uploaded and fine

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0

Multi Perform exit with code 0, still running 1

Multi poll : 0
 Queued 0
* Mark bundle as not supporting multiuse
* HTTP 1.0, assume close after body
< HTTP/1.0 403 connecting to host.docker.internal:80: connecting to
127.0.0.1:80: dial tcp 127.0.0.1:80: connectex: No c
onnection could be made because the target machine actively refused it.
< Connection: close
<
connecting to host.docker.internal:80: connecting to 127.0.0.1:80: dial tcp
127.0.0.1:80: connectex: No connection could be made because t
he target machine actively refused it.
Multi Perform exit with code 0, still running 1
Multi poll : 0
 Queued 0
* Closing connection 0
Multi Perform exit with code 0, still running 0
Multi poll : 0
 Queued 0
Curl code 0
Transfer completed
 Queued 0
ERRNO 0

If we see the output, all the methods are returning 0, although there is a
message (due to verbose enabled) that the machine refused the connection.

On Wed, Jan 3, 2024 at 2:02 PM Ray Satiro via curl-library <
curl-library_at_lists.haxx.se> wrote:

> On 1/3/2024 3:17 AM, Ali Nasir via curl-library wrote:
>
> I am trying to upload a file to an end point using multi interface.
> Example code used is https://curl.se/libcurl/c/postit2.html
> However, i see that when the server is down, there is no error reported
> from any of the curl interfaces.
>
> If i perform the same operation via the curl command from the shell, i get
> the return code as 7. But all the multi interfaces like info_read and
> mulit_perform return CURLE_OK.
> Can anyone guide how to detect failures with libcurl. Specially when the
> server is down.
>
>
> That example uses curl_easy_perform not curl_multi_perform so there must
> be some changes that you made. curl_multi_info_read should return the
> transfer result code (CURLcode) in data.result. [1][2]
>
> Also you could enable verbose mode to see if that's how the transfer is
> actually failing. [3]
>
> [1]: https://curl.se/libcurl/c/curl_multi_info_read.html
> [2]: https://curl.se/libcurl/c/libcurl-errors.html
> [3]: https://curl.se/libcurl/c/CURLOPT_VERBOSE.html
>
>
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Received on 2024-01-03