Re: MQTT sub times out

From: Hamza Farooq via curl-library <curl-library_at_lists.haxx.se>
Date: Tue, 25 Oct 2022 09:23:12 +0200

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
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Received on 2022-10-25