On 8/4/2014 4:16 PM, Madhurima Das wrote:
> I want to retrieve the information data of a particular website (url)
> and also find its follow-up url (url_new) but getting too many errors
> after running Valgrind along with memory leakage.
>
> The function and part of the main program is as follows:
>
> void handle_url_followup(char* url, char** mapping_data, char** url_n)
> {
> CURL *curl;
> char *url_new="NULL";

Don't put quote marks here; you would be assigning a constant string to
a non-const pointer. Even though you are not writing into the buffer,
it is a risky practice. Just use NULL without quotes.

>
> struct url_data data;
> data.size = 0;
> data.data = malloc(4096); /* reasonable size initial buffer */
> if(NULL == data.data)
> {
> fprintf(stderr, "Failed to allocate memory.\n");
> return NULL;
> }
>
> data.data[0] = '\0';
>
> CURLcode res;
>
> curl = curl_easy_init();
> if (curl)
> {
> curl_easy_setopt(curl, CURLOPT_URL, url);
> curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
> curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
> curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
> curl_easy_perform(curl);
> curl_easy_getinfo(curl,CURLINFO_EFFECTIVE_URL,&url_new);

You need to copy the effective URL to a safe place; this call returns a
pointer to an internal cURL data structure. I would not expect cURL to
guarantee that this pointer would survive another call to
curl_easy_perform().

> res = curl_easy_perform(curl);
> if(res != CURLE_OK)
> {
> fprintf(stderr, "curl_easy_perform() failed: %s\n",
> curl_easy_strerror(res));
> }
> }
> curl_easy_cleanup(curl);

And now the effective URL has been freed.

> *mapping_data=data.data;
> *url_n=url_new;

The returned string url_new needs to be freed by the caller.

Fix this, then see if you still have valgrind errors.

> }
>
> int main(int argc,char *argv[])
> {
> char url[100]="NULL";
> char *mapping_data="NULL";
> char *url_new="NULL";
>
> //FIRST URLprintf("URL: %s\n", url);
> handle_url_followup(url,&mapping_data,&url_new);
> //SECOND URL
> printf("%s\n",url_new);
>
>
> I get both the urls but in addition get 973 errors with Valgrind and
> memory leakage of 403 bytes in 9 blocks. A few errors are:
>
> ==6599== Invalid read of size 1
> ==6599== at 0x1000124F6: strlen (mc_replace_strmem.c:282)
> ==6599== by 0x10010AEF4: puts (in /usr/lib/libSystem.B.dylib)
> ==6599== by 0x1000019F9: main (prog.c:247)
> ==6599== Address 0x1011db5d0 is 0 bytes inside a block of size 51 free'd
> ==6599== at 0x100010E9F: free (vg_replace_malloc.c:366)
> ==6599== by 0x100037C6B: Curl_close (in /usr/lib/libcurl.4.dylib)
> ==6599== by 0x100001055: handle_url_followup (prog.c:113)
> ==6599== by 0x1000019ED: main (prog.c:245)
>
> ==6599== Invalid read of size 8
> ==6599== at 0x100013C30: memcpy (mc_replace_strmem.c:635)
> ==6599== by 0x100096E74: __sfvwrite (in /usr/lib/libSystem.B.dylib)
> ==6599== by 0x10010AF66: puts (in /usr/lib/libSystem.B.dylib)
> ==6599== by 0x1000019F9: main (prog.c:247)
> ==6599== Address 0x1011db5d0 is 0 bytes inside a block of size 51 free'd
> ==6599== at 0x100010E9F: free (vg_replace_malloc.c:366)
> ==6599== by 0x100037C6B: Curl_close (in /usr/lib/libcurl.4.dylib)
> ==6599== by 0x100001055: handle_url_followup (prog.c:113)
> ==6599== by 0x1000019ED: main (prog.c:245)
> ==6599==
>
> ==6599==
> ==6599== HEAP SUMMARY:
> ==6599== in use at exit: 320,629 bytes in 3,035 blocks
> ==6599== total heap usage: 5,023 allocs, 1,988 frees, 925,560 bytes
> allocated
> ==6599==
> ==6599== 403 bytes in 9 blocks are definitely lost in loss record 827
> of 897
> ==6599== at 0x10001155D: realloc (vg_replace_malloc.c:525)
> ==6599== by 0x100000D05: write_data (Gwidd_uniprot_map2.c:23)
> ==6599== by 0x10002DD9A: Curl_client_write (in
> /usr/lib/libcurl.4.dylib)
> ==6599== by 0x1000431F9: Curl_readwrite (in /usr/lib/libcurl.4.dylib)
> ==6599== by 0x1000439C1: Curl_perform (in /usr/lib/libcurl.4.dylib)
> ==6599== by 0x10000101D: handle_url_followup (Gwidd_uniprot_map2.c:106)
> ==6599== by 0x1000019ED: main (Gwidd_uniprot_map2.c:245)
> ==6599==
> ==6599== LEAK SUMMARY:
> ==6599== definitely lost: 403 bytes in 9 blocks
>
>
> Any suggestion would be highly appreciated.
>
> Thanks!
>
> N.B. The other functions are:
>
> struct url_data
> {
> size_t size;
> char* data;
> };
>
> size_t write_data(void *ptr, size_t size, size_t nmemb, struct
> url_data *data)
> {
> size_t index = data->size;
> size_t n = (size * nmemb);
> char* tmp;
>
> data->size += (size * nmemb);
>
> #ifdef DEBUG
> fprintf(stderr, "data at %p size=%ld nmemb=%ld\n", ptr, size, nmemb);
> #endif
> tmp = realloc(data->data, data->size + 1); /* +1 for '\0' */
>
> if(tmp)
> {
> data->data = tmp;
> }
> else
> {
> if(data->data)
> {
> free(data->data);
> }
> fprintf(stderr, "Failed to allocate memory.\n");
> return 0;
> }
> memcpy((data->data + index), ptr, n);
> data->data[data->size] = '\0';
>
> return size * nmemb;
> }
>
>
>
> -------------------------------------------------------------------
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-- 
     David Chapman      dcchapman_at_acm.org
     Chapman Consulting -- San Jose, CA
     Software Development Done Right.
     www.chapman-consulting-sj.com

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Received on 2014-08-05