Tribblix: manual page: CURLOPT

CURLOPT_PROGRESSFUNCTION(3) Introduction to Library Functions

NAME

CURLOPT_PROGRESSFUNCTION - progress meter callback

SYNOPSIS

#include <curl/curl.h>

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

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

DESCRIPTION

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

This option is deprecated and we encourage users to use the newer
CURLOPT_XFERINFOFUNCTION(3) instead, if you can.

This function gets called by libcurl instead of its internal
equivalent with a frequent interval. While data is being transferred
it is invoked 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_PROGRESSDATA(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 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 be 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.

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

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

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. libcurl has an 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,
double dltotal,
double dlnow,
double ultotal,
double ulnow)
{
struct progress *memory = clientp;
printf("private: %p\n", memory->private);

/* use the values */

return 0; /* all is good */
}

int main(void)
{
struct progress data;

CURL *curl = curl_easy_init();
if(curl) {
/* pass struct to callback */
curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, &data);
curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_callback);

curl_easy_perform(curl);
}
}

DEPRECATED

Deprecated since 7.32.0.

AVAILABILITY

Added in curl 7.1

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).