curl/docs/libcurl/opts/CURLOPT_XFERINFOFUNCTION.3

.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at https://curl.se/docs/copyright.html.
.\" *
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
.\" * copies of the Software, and permit persons to whom the Software is
.\" * furnished to do so, under the terms of the COPYING file.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" * SPDX-License-Identifier: curl
.\" *
.\" **************************************************************************
.\"
.TH CURLOPT_XFERINFOFUNCTION 3 "17 Jun 2014" libcurl libcurl
.SH NAME
CURLOPT_XFERINFOFUNCTION \- progress meter callback
.SH SYNOPSIS
.nf
#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);
.fi
.SH 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 will be called
frequently, and during slow periods like when nothing is being transferred it
can slow down to about one call per second.

\fIclientp\fP is the pointer set with \fICURLOPT_XFERINFODATA(3)\fP, 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 will transfer and has
transferred, in number of bytes. \fIdltotal\fP is the total number of bytes
libcurl expects to download in this transfer. \fIdlnow\fP is the number of
bytes downloaded so far. \fIultotal\fP is the total number of bytes libcurl
expects to upload in this transfer. \fIulnow\fP is the number of bytes
uploaded so far.

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

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

Returning any other non-zero value from this callback will cause libcurl to
abort the transfer and return \fICURLE_ABORTED_BY_CALLBACK\fP.

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

\fICURLOPT_NOPROGRESS(3)\fP must be set to 0 to make this function actually
get called.
.SH DEFAULT
By default, libcurl has an internal progress meter. That is rarely wanted by
users.
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
 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 = (struct progress *)clientp;

   /* use the values */

   return 0; /* all is good */
 }

 struct progress data;

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

 curl_easy_setopt(curl_handle, CURLOPT_XFERINFOFUNCTION, progress_callback);
.fi
.SH AVAILABILITY
Added in 7.32.0. This callback replaces \fICURLOPT_PROGRESSFUNCTION(3)\fP
.SH RETURN VALUE
Returns CURLE_OK.
.SH "SEE ALSO"
.BR CURLOPT_XFERINFODATA "(3), " CURLOPT_NOPROGRESS "(3), "