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
12Added-in: 7.32.0
13---
14
15# NAME
16
17CURLOPT_XFERINFOFUNCTION - progress meter callback
18
19# SYNOPSIS
20
21~~~c
22#include <curl/curl.h>
23
24int progress_callback(void *clientp,
25                      curl_off_t dltotal,
26                      curl_off_t dlnow,
27                      curl_off_t ultotal,
28                      curl_off_t ulnow);
29
30CURLcode curl_easy_setopt(CURL *handle, CURLOPT_XFERINFOFUNCTION,
31                          progress_callback);
32~~~
33
34# DESCRIPTION
35
36Pass a pointer to your callback function, which should match the prototype
37shown above.
38
39This function gets called by libcurl instead of its internal equivalent with a
40frequent interval. While data is being transferred it gets called frequently,
41and during slow periods like when nothing is being transferred it can slow
42down to about one call per second.
43
44*clientp* is the pointer set with CURLOPT_XFERINFODATA(3), it is not
45used by libcurl but is only passed along from the application to the callback.
46
47The callback gets told how much data libcurl is about to transfer and has
48already transferred, in number of bytes. *dltotal* is the total number of
49bytes libcurl expects to download in this transfer. *dlnow* is the number
50of bytes downloaded so far. *ultotal* is the total number of bytes libcurl
51expects to upload in this transfer. *ulnow* is the number of bytes
52uploaded so far.
53
54Unknown/unused argument values passed to the callback are set to zero (like if
55you only download data, the upload size remains 0). Many times the callback is
56called one or more times first, before it knows the data sizes so a program
57must be made to handle that.
58
59Return zero from the callback if everything is fine.
60
61Return 1 from this callback to make libcurl abort the transfer and return
62*CURLE_ABORTED_BY_CALLBACK*.
63
64If your callback function returns CURL_PROGRESSFUNC_CONTINUE it makes libcurl
65to continue executing the default progress function.
66
67If you transfer data with the multi interface, this function is not called
68during periods of idleness unless you call the appropriate libcurl function
69that performs transfers.
70
71CURLOPT_NOPROGRESS(3) must be set to 0 to make this function actually
72get called.
73
74# DEFAULT
75
76NULL - use the internal progress meter. That is rarely wanted by users.
77
78# %PROTOCOLS%
79
80# EXAMPLE
81
82~~~c
83struct progress {
84  char *private;
85  size_t size;
86};
87
88static size_t progress_callback(void *clientp,
89                                curl_off_t dltotal,
90                                curl_off_t dlnow,
91                                curl_off_t ultotal,
92                                curl_off_t ulnow)
93{
94  struct progress *memory = clientp;
95  printf("my ptr: %p\n", memory->private);
96
97  /* use the values */
98
99  return 0; /* all is good */
100}
101
102int main(void)
103{
104  CURL *curl = curl_easy_init();
105  if(curl) {
106    struct progress data;
107
108    /* pass struct to callback  */
109    curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &data);
110
111    /* enable progress callback getting called */
112    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);
113
114    curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, progress_callback);
115  }
116}
117~~~
118
119# %AVAILABILITY%
120
121# RETURN VALUE
122
123Returns CURLE_OK.
124