Handling libcurl abortion on timeout

Question

I am coding a daemon in C with a http client using libcurl. I want it to be resilient to errors because the daemon will live in a risky environnement.

I added timeout control to not wait endlessly.

curl_easy_setopt(ezhandle, CURLOPT_TIMEOUT, 300); //timeout after 5 minutes (use sigalarm)
curl_easy_setopt(ezhandle, CURLOPT_CONNECTTIMEOUT, 2); //timeout after 2 seconds (use sigalarm)
curl_easy_setopt(ezhandle, CURLOPT_NOSIGNAL, 1); // Do not use signal

But when the request timeout (or other type of error) the lib is sending an abortion signal. And my daemon is killed... I got the error:

libcurl: (28) Connection timed out after 2000 milliseconds
Aborted

I tried handling the signal (with signal(6,mycallback)) but according to How to Handle SIGABRT signal? it is not possible.

According to the documentations : https://curl.se/libcurl/c/CURLOPT_TIMEOUT.html and https://curl.se/libcurl/c/CURLOPT_CONNECTTIMEOUT.html it might cause a sigalarm. I tried catching sigalarm with signal(13,myhandler) but it isn't triggered.

What would be the solution ?

PS: I believe threads might be a solution but I never used them and I would like to avoid the trouble.

This code is causing an error:

printf("%04X %04X %04X\n",LIBCURL_VERSION_MAJOR, LIBCURL_VERSION_MINOR, 
LIBCURL_VERSION_PATCH );
res = curl_easy_perform(ezhandle);
if(catchError(res,ezhandle,errbuf)==-1){
  printf("error \n");
  fclose(downloaded_file);
  //return -1;  // THIS IS THE ONLY CHANGE
};

if(CURLE_OK == res){}
if(ezhandle) {
  printf("ezhandle cleanup\n");
  curl_easy_cleanup(ezhandle);
}
printf("Does it execute this instruction ?"); // It stops before
return 0;
}

It gives the following result:

http://192.168.174.61/token
0007 0028 0000
libcurl: (28) Operation timed out after 10000 milliseconds with 0 bytes 
received
error
ezhandle cleanup
Aborted

This correct the problem:

if(catchError(res,ezhandle,errbuf)==-1){
printf("error \n");
fclose(downloaded_file);
return -1;  // THIS IS THE ONLY CHANGE
};

score 1 · Answer 1 · answered Nov 16 '20 at 14:42

1

The comments in your code imply cURL would do a SIGALRM (value 13) signal, which is not SIGABRT (6) which you talk about later.

Have you tried signal(SIGALRM, callback)?

answered Nov 16 '20 at 14:42

AKX

152,115
15
115
172

Damezumari · Accepted Answer · 2020-11-27T08:37:59.423

-1

I found my mistake,

In my function "catchError" i already cleanup ezhandle. Cleaning ezhandle twice in a row is provoking an abortion.

edited Nov 27 '20 at 08:37

answered Nov 16 '20 at 15:29

Damezumari

17
6

2

Did you just accept your own confused answer here? That's just wrong. curl_easy_cleanup() should always be called if curl_easy_init() returned a handle. It will not "abort" in any circumstance. – Daniel Stenberg Nov 19 '20 at 22:43

Handling libcurl abortion on timeout

2 Answers2