Memory leaks in libcurl

Question

After adding the final touches to my program, I ran valgrind to check for memory leaks. And to my surprise, I read that huge chunks of memory were used and never deallocated, although I made sure I freed every resource I was using before ending the program. Looking closely at the report, I find that almost all of the report said the leaks were coming from libcurl function calls. Here's a sample from the report:

==3555== HEAP SUMMARY:
==3555==     in use at exit: 179,937 bytes in 4,212 blocks
==3555==   total heap usage: 18,080 allocs, 13,868 frees, 10,050,116 bytes allocated
==3555== 
==3555== Searching for pointers to 4,212 not-freed blocks
==3555== Checked 486,368 bytes
==3555== 
==3555== 2 bytes in 2 blocks are still reachable in loss record 1 of 667
==3555==    at 0x4C29F90: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3555==    by 0x542C9C9: strdup (in /usr/lib/libc-2.20.so)
==3555==    by 0x4E58C1E: ??? (in /usr/lib/libcurl.so.4.3.0)
==3555==    by 0x4E6A90F: ??? (in /usr/lib/libcurl.so.4.3.0)
==3555==    by 0x4E6B4A0: curl_multi_perform (in /usr/lib/libcurl.so.4.3.0)
==3555==    by 0x404141: url_fopen (network.c:226)
==3555==    by 0x403737: load_tracks (PlayMusic.c:718)
==3555==    by 0x401E1C: main (PlayMusic.c:145)
==3555== 
==3555== 2 bytes in 2 blocks are still reachable in loss record 2 of 667
==3555==    at 0x4C29F90: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3555==    by 0x542C9C9: strdup (in /usr/lib/libc-2.20.so)
==3555==    by 0x4E58C3A: ??? (in /usr/lib/libcurl.so.4.3.0)
==3555==    by 0x4E6A90F: ??? (in /usr/lib/libcurl.so.4.3.0)
==3555==    by 0x4E6B4A0: curl_multi_perform (in /usr/lib/libcurl.so.4.3.0)
==3555==    by 0x404141: url_fopen (network.c:226)
==3555==    by 0x403737: load_tracks (PlayMusic.c:718)
==3555==    by 0x401E1C: main (PlayMusic.c:145)

Here is the url_fopen function that valgrind complains about:

URL_FILE *url_fopen(const char *url, const char *operation)
{
    /*
       this code could check for URLs or types in the 'url' and
       basicly use the real fopen() for standard files 
     */

    URL_FILE *file;

    file = malloc(sizeof(URL_FILE));
    if (!file)
        return NULL;

    memset(file, 0, sizeof(URL_FILE));

    if ((file->handle.file = fopen(url, operation)))
        file->type = CFTYPE_FILE;   /* marked as URL */

    else {
        file->type = CFTYPE_URL;    /* marked as URL */
        file->handle.curl = curl_easy_init();

        curl_easy_setopt(file->handle.curl, CURLOPT_URL, url);
        curl_easy_setopt(file->handle.curl, CURLOPT_WRITEDATA,
                 file);
        curl_easy_setopt(file->handle.curl, CURLOPT_VERBOSE,
                 0L);
        curl_easy_setopt(file->handle.curl,
                 CURLOPT_WRITEFUNCTION,
                 write_callback);

        if (!multi_handle)
            multi_handle = curl_multi_init();

        curl_multi_add_handle(multi_handle,
                      file->handle.curl);

        /*
           lets start the fetch 
         */
        curl_multi_perform(multi_handle,
                   &file->still_running);

        if ((file->buffer_pos == 0) && (!file->still_running)) {
            /*
               if still_running is 0 now, we should return NULL 
             */

            /*
               make sure the easy handle is not in the multi handle anymore 
             */
            curl_multi_remove_handle(multi_handle,
                         file->handle.curl);

            /*
               cleanup 
             */
            curl_easy_cleanup(file->handle.curl);
            curl_multi_cleanup(multi_handle);
            fclose
            free(file);

            file = NULL;
        }
    }
    return file;
}

Are these just false positives ? If they are, how can I force valgrind to ignore them. If they are not, is there a solution to this leaking problem ?

Answer 1

Try using curl_global_init(CURL_GLOBAL_DEFAULT); at the start of the program. This sets the environment that libcURL requires.

It is recommended that, this function must be called at least once within a program. Also it is not thread-safe so it must be called at the very beginning of the program, before any threads start.

Also you should call curl_global_cleanup(); once for each call to curl_global_init(), at the end of the program when you are done using libcURL. This will clean up all things used by libcURL.