1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_XFERINFOFUNCTION
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_NOPROGRESS (3)
9  - CURLOPT_XFERINFODATA (3)
10Protocol:
11  - All
12---
13
14# NAME
15
16CURLOPT_XFERINFOFUNCTION - progress meter callback
17
18# SYNOPSIS
19
20~~~c
21#include <curl/curl.h>
22
23int progress_callback(void *clientp,
24                      curl_off_t dltotal,
25                      curl_off_t dlnow,
26                      curl_off_t ultotal,
27                      curl_off_t ulnow);
28
29CURLcode curl_easy_setopt(CURL *handle, CURLOPT_XFERINFOFUNCTION,
30                          progress_callback);
31~~~
32
33# DESCRIPTION
34
35Pass a pointer to your callback function, which should match the prototype
36shown above.
37
38This function gets called by libcurl instead of its internal equivalent with a
39frequent interval. While data is being transferred it gets called frequently,
40and during slow periods like when nothing is being transferred it can slow
41down to about one call per second.
42
43*clientp* is the pointer set with CURLOPT_XFERINFODATA(3), it is not
44used by libcurl but is only passed along from the application to the callback.
45
46The callback gets told how much data libcurl is about to transfer and has
47already transferred, in number of bytes. *dltotal* is the total number of
48bytes libcurl expects to download in this transfer. *dlnow* is the number
49of bytes downloaded so far. *ultotal* is the total number of bytes libcurl
50expects to upload in this transfer. *ulnow* is the number of bytes
51uploaded so far.
52
53Unknown/unused argument values passed to the callback are set to zero (like if
54you only download data, the upload size remains 0). Many times the callback is
55called one or more times first, before it knows the data sizes so a program
56must be made to handle that.
57
58If your callback function returns CURL_PROGRESSFUNC_CONTINUE it makes libcurl
59to continue executing the default progress function.
60
61Returning any other non-zero value from this callback makes libcurl abort the
62transfer and return *CURLE_ABORTED_BY_CALLBACK*.
63
64If you transfer data with the multi interface, this function is not called
65during periods of idleness unless you call the appropriate libcurl function
66that performs transfers.
67
68CURLOPT_NOPROGRESS(3) must be set to 0 to make this function actually
69get called.
70
71# DEFAULT
72
73By default, libcurl has an internal progress meter. That is rarely wanted by
74users.
75
76# EXAMPLE
77
78~~~c
79struct progress {
80  char *private;
81  size_t size;
82};
83
84static size_t progress_callback(void *clientp,
85                                curl_off_t dltotal,
86                                curl_off_t dlnow,
87                                curl_off_t ultotal,
88                                curl_off_t ulnow)
89{
90  struct progress *memory = clientp;
91  printf("my ptr: %p\n", memory->private);
92
93  /* use the values */
94
95  return 0; /* all is good */
96}
97
98int main(void)
99{
100  CURL *curl = curl_easy_init();
101  if(curl) {
102    struct progress data;
103
104    /* pass struct to callback  */
105    curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &data);
106
107    /* enable progress callback getting called */
108    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);
109
110    curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, progress_callback);
111  }
112}
113~~~
114
115# AVAILABILITY
116
117Added in 7.32.0. This callback replaces CURLOPT_PROGRESSFUNCTION(3)
118
119# RETURN VALUE
120
121Returns CURLE_OK.
122