Re: MQTT sub times out

From: Henrik Holst via curl-library <curl-library_at_lists.haxx.se>
Date: Mon, 24 Oct 2022 22:48:41 +0200

Hi,

  this happens because you do return nmemb; in write_data() instead of
return nmemb*size; since that is the actual data size in bytes, so
curl_easy_perform is waiting for you to consume all data and thus hangs
since you never do (or rather don't tell curl that you do).

/HH

Den mån 24 okt. 2022 kl 22:40 skrev Hamza Farooq via curl-library <
curl-library_at_lists.haxx.se>:

> Hello,
>
> I am using libcurl for receiving mqtt data (subscribe) with following
> configuration:
>
> curl_easy_setopt( g_curl, CURLOPT_VERBOSE, 0 ); /* set verbosity */
> curl_easy_setopt( g_curl, CURLOPT_URL, buf ); /* Set the URL/path */
> curl_easy_setopt( g_curl, CURLOPT_PORT, g_port ); /* Set the port */
> curl_easy_setopt( g_curl, CURLOPT_DEFAULT_PROTOCOL, "mqtt"); /* if URL
> misses scheme */
> curl_easy_setopt( g_curl, CURLOPT_NOPROGRESS, 1); /* turn off progress
> meter */
> curl_easy_setopt( g_curl, CURLOPT_TIMEOUT, 30); /* connection timeout */
> curl_easy_setopt( g_curl, CURLOPT_WRITEFUNCTION, write_data);
> curl_easy_setopt( g_curl, CURLOPT_WRITEDATA, user_data);
>
> cc = curl_easy_perform(g_curl);
> curl_easy_cleanup(g_curl);
> if (cc != CURLE_OK) {
> fprintf( stderr, "could not get MQTT data (%d)\n",
> cc );
> return sz;
> }
>
> Here is what my write_data() looks like:
>
> size_t write_data(char *in_data, size_t size, size_t nmemb, void
> *user_data){
>
> fprintf( stdout, "entered write_data\n");
> fprintf( stdout, "Received msg: %s\n", in_data+2);
>
> //perform data operations
> return nmemb;
> }
>
> Problem:
> I receive the data in my write_data function, but the
> curl_easy_perform() call in the main function does not return. It only
> returns after the timeout is over, regardless of how many times the
> data is published by the MQTT broker and received by the app. Is this
> expected behavior? How can I make curl_easy_perform return?
>
> PS: If there is any sample code for libcurl that uses MQTT, please
> point me in that direction.
>
> Best regards,
> Hamza
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Received on 2022-10-24