xref: /curl/docs/libcurl/curl_multi_info_read.md (revision e3fe0200) 
1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: curl_multi_info_read
5Section: 3
6Source: libcurl
7See-also:
8  - curl_multi_cleanup (3)
9  - curl_multi_init (3)
10  - curl_multi_perform (3)
11Protocol:
12  - All
13---
14
15# NAME
16
17curl_multi_info_read - read multi stack information
18
19# SYNOPSIS
20
21~~~c
22#include <curl/curl.h>
23
24CURLMsg *curl_multi_info_read(CURLM *multi_handle, int *msgs_in_queue);
25~~~
26
27# DESCRIPTION
28
29Ask the multi handle if there are any messages from the individual
30transfers. Messages may include information such as an error code from the
31transfer or just the fact that a transfer is completed. More details on these
32should be written down as well.
33
34Repeated calls to this function returns a new struct each time, until a NULL
35is returned as a signal that there is no more to get at this point. The
36integer pointed to with *msgs_in_queue* contains the number of remaining
37messages after this function was called.
38
39When you fetch a message using this function, it is removed from the internal
40queue so calling this function again does not return the same message
41again. It instead returns new messages at each new invoke until the queue is
42emptied.
43
44**WARNING:** The data the returned pointer points to does not survive
45calling curl_multi_cleanup(3), curl_multi_remove_handle(3) or
46curl_easy_cleanup(3).
47
48The *CURLMsg* struct is simple and only contains basic information. If
49more involved information is wanted, the particular "easy handle" is present
50in that struct and can be used in subsequent regular
51curl_easy_getinfo(3) calls (or similar):
52
53~~~c
54 struct CURLMsg {
55   CURLMSG msg;       /* what this message means */
56   CURL *easy_handle; /* the handle it concerns */
57   union {
58     void *whatever;    /* message-specific data */
59     CURLcode result;   /* return code for transfer */
60   } data;
61 };
62~~~
63When **msg** is *CURLMSG_DONE*, the message identifies a transfer that
64is done, and then **result** contains the return code for the easy handle
65that just completed.
66
67At this point, there are no other **msg** types defined.
68
69# EXAMPLE
70
71~~~c
72int main(void)
73{
74  CURLM *multi = curl_multi_init();
75  CURL *curl = curl_easy_init();
76  if(curl) {
77    struct CURLMsg *m;
78
79    /* call curl_multi_perform or curl_multi_socket_action first, then loop
80       through and check if there are any transfers that have completed */
81
82    do {
83      int msgq = 0;
84      m = curl_multi_info_read(multi, &msgq);
85      if(m && (m->msg == CURLMSG_DONE)) {
86        CURL *e = m->easy_handle;
87        /* m->data.result holds the error code for the transfer */
88        curl_multi_remove_handle(multi, e);
89        curl_easy_cleanup(e);
90      }
91    } while(m);
92  }
93}
94~~~
95
96# AVAILABILITY
97
98Added in 7.9.6
99
100# RETURN VALUE
101
102A pointer to a filled-in struct, or NULL if it failed or ran out of
103structs. It also writes the number of messages left in the queue (after this
104read) in the integer the second argument points to.
105