Tribblix: manual page: CURLOPT

CURLOPT_XFERINFOFUNCTION(3) Introduction to Library Functions

NAME

CURLOPT_XFERINFOFUNCTION - progress meter callback

SYNOPSIS

#include <curl/curl.h>

int progress_callback(void *clientp,
curl_off_t dltotal,
curl_off_t dlnow,
curl_off_t ultotal,
curl_off_t ulnow);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_XFERINFOFUNCTION,
progress_callback);

DESCRIPTION

Pass a pointer to your callback function, which should match the
prototype shown above.

This function gets called by libcurl instead of its internal
equivalent with a frequent interval. While data is being transferred
it gets called frequently, and during slow periods like when nothing
is being transferred it can slow down to about one call per second.

clientp is the pointer set with CURLOPT_XFERINFODATA(3), it is not
used by libcurl but is only passed along from the application to the
callback.

The callback gets told how much data libcurl is about to transfer and
has already transferred, in number of bytes. dltotal is the total
number of bytes libcurl expects to download in this transfer. dlnow
is the number of bytes downloaded so far. ultotal is the total number
of bytes libcurl expects to upload in this transfer. ulnow is the
number of bytes uploaded so far.

Unknown/unused argument values passed to the callback are set to zero
(like if you only download data, the upload size remains 0). Many
times the callback is called one or more times first, before it knows
the data sizes so a program must be made to handle that.

Return zero from the callback if everything is fine.

Return 1 from this callback to make libcurl abort the transfer and
return CURLE_ABORTED_BY_CALLBACK.

If your callback function returns CURL_PROGRESSFUNC_CONTINUE it makes
libcurl to continue executing the default progress function.

If you transfer data with the multi interface, this function is not
called during periods of idleness unless you call the appropriate
libcurl function that performs transfers.

CURLOPT_NOPROGRESS(3) must be set to 0 to make this function actually
get called.

DEFAULT

NULL - use the internal progress meter. That is rarely wanted by
users.

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

struct progress {
char *private;
size_t size;
};

static size_t progress_callback(void *clientp,
curl_off_t dltotal,
curl_off_t dlnow,
curl_off_t ultotal,
curl_off_t ulnow)
{
struct progress *memory = clientp;
printf("my ptr: %p\n", memory->private);

/* use the values */

return 0; /* all is good */
}

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
struct progress data;

/* pass struct to callback */
curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &data);

/* enable progress callback getting called */
curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);

curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, progress_callback);
}
}

AVAILABILITY

Added in curl 7.32.0

RETURN VALUE

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).