hide curl_easy_perform

Question

How can I hide curl_easy_perform output (in a shell)?
This is in regards to a C application.

Curl_easy_perform prints the page content returned in response to a request (post request in my case). I want "hide" that page content (no view) and print my personal message — stdio, May 11 '10 at 23:24

score 25 · Answer 1 · answered Jul 09 '12 at 19:36

25

Use CURLOPT_NOBODY in curl_easy_setopt(). Example:

 ...

CURL *curl;
CURLcode statusCode;

curl = curl_easy_init();
if(curl){
    curl_easy_setopt(curl, CURLOPT_URL, "http://www.google.com/");
    //CURLOPT_NOBODY does the trick
    curl_easy_setopt(curl, CURLOPT_NOBODY, 1);
    curl_easy_perform(curl);

 ...

Link to docs: http://curl.haxx.se/libcurl/c/curl_easy_setopt.html#CURLOPTNOBODY

answered Jul 09 '12 at 19:36

Paul Semionov

491
6
17

I wanted to log into a page https://user:pass@www.example.com/login/ and then use curl to POST to https://www.example.com/upload/ but with CURLOPT_NOBODY I lose the session-id. I solved this by writing to nul – Alexx Roche Nov 19 '15 at 15:59
Am I right to suppose this is useful for POST requests, but probably not so for GET? – xtofl Aug 29 '17 at 09:18
for POST requests, this simply does not send the body, meaning it's not what you would expect. – xtofl Aug 29 '17 at 09:31

score 15 · Accepted Answer · edited Aug 31 '17 at 12:29

15

Set the CURLOPT_WRITEFUNCTION and/or CURLOPT_WRITEDATA options:

FILE *f = fopen("target.txt", "wb");
curl_easy_setopt(handle, CURLOPT_WRITEDATA, f);

By default, libcurl writes output to stdout. When you override this (which is what almost any application will do), it will write to another file or to pass chunks of output to a callback. See the documentation for CURLOPT_WRITEFUNCTION for more details.

edited Aug 31 '17 at 12:29

Daniel Stenberg

54,736
17
146
222

answered May 11 '10 at 23:00

Joey Adams

41,996
18
86
115

Thanks, but I know this. There isn't a way without "deviate" the output (a way to delete it)? – stdio May 11 '10 at 23:41
1

@stdio - If you just want the input to go away, open a NULL device and print everything there. – Tim Post May 12 '10 at 00:27
2

@Tm Post: do you mean /dev/null? if you mean this, the code would not be multiplatform. – stdio May 12 '10 at 00:48
2

FILE* devnull = fopen("nul", "w"); curl_easy_setopt(curl, CURLOPT_WRITEDATA, devnull); – Alexx Roche Nov 19 '15 at 15:55
does `fopen("nul", "w")` works for both linux and windows? – Michel Feinstein Nov 06 '19 at 22:14

score 7 · Answer 3 · edited May 23 '17 at 10:28

As Joey said, CURLOPT_WRITEFUNCTION will allow you to completely disregard all output. Just set up a callback that does absolutely nothing if you want the data to just go away, without being written to any file descriptor.

For instance,

/* Never writes anything, just returns the size presented */
size_t my_dummy_write(char *ptr, size_t size, size_t nmemb, void *userdata)
{
   return size * nmemb;
}

Then in your options:

curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, &my_dummy_write);

Or, point the file handle at a NULL device (a lot easier).

hide curl_easy_perform

3 Answers3