CURLOPT_XFERINFOFUNCTION(3) Library Functions ManualCURLOPT_XFERINFOFUNCTION(3)
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 proto-
type 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 trans-
ferred 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 call-
back.
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 num-
ber 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 re-
turn 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 int xferinfo_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, xferinfo_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).
SEE ALSO
CURLOPT_NOPROGRESS(3), CURLOPT_XFERINFODATA(3)
libcurl 2026-07-12 CURLOPT_XFERINFOFUNCTION(3)
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