Re: MQTT sub times out

From: Henrik Holst via curl-library <curl-library_at_lists.haxx.se>
Date: Tue, 25 Oct 2022 09:25:55 +0200

ah, sorry now that was the low hanging fruit that I noticed, have no
experience with the mqtt protocol in curl.

/HH


Den tis 25 okt. 2022 kl 09:23 skrev Hamza Farooq <hamzahfrq.sub_at_gmail.com>:

> Hello,
>
> Good hint, thanks! In my case, size is 1, nmemb is 34 so changing it
> to "return nmemb * size" does not make a difference. Do you have any
> other idea what the issue might be?
> Thanks for your help!
>
>
> Hamza
>
> On Mon, Oct 24, 2022 at 10:48 PM Henrik Holst
> <henrik.holst_at_millistream.com> wrote:
> >
> > 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
> >> --
> >> Unsubscribe: https://lists.haxx.se/listinfo/curl-library
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>

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Received on 2022-10-25