curl_multi_info_read.3

.\" **************************************************************************
.\" *                                  _   _ ____  _
.\" *  Project                     ___| | | |  _ \| |
.\" *                             / __| | | | |_) | |
.\" *                            | (__| |_| |  _ <| |___
.\" *                             \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2022, 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 curl_multi_info_read 3 "18 Dec 2004" "libcurl 7.10.3" "libcurl Manual"
.SH NAME
curl_multi_info_read - read multi stack information
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLMsg *curl_multi_info_read(CURLM *multi_handle, int *msgs_in_queue);
.fi
.SH DESCRIPTION
Ask the multi handle if there are any messages from the individual
transfers. Messages may include information such as an error code from the
transfer or just the fact that a transfer is completed. More details on these
should be written down as well.

Repeated calls to this function will return a new struct each time, until a
NULL is returned as a signal that there is no more to get at this point. The
integer pointed to with \fImsgs_in_queue\fP will contain the number of
remaining messages after this function was called.

When you fetch a message using this function, it is removed from the internal
queue so calling this function again will not return the same message
again. It will instead return new messages at each new invoke until the queue
is emptied.

\fBWARNING:\fP The data the returned pointer points to will not survive
calling \fIcurl_multi_cleanup(3)\fP, \fIcurl_multi_remove_handle(3)\fP or
\fIcurl_easy_cleanup(3)\fP.

The \fICURLMsg\fP struct is simple and only contains basic information. If
more involved information is wanted, the particular "easy handle" is present
in that struct and can be used in subsequent regular
\fIcurl_easy_getinfo(3)\fP calls (or similar):

.nf
 struct CURLMsg {
   CURLMSG msg;       /* what this message means */
   CURL *easy_handle; /* the handle it concerns */
   union {
     void *whatever;    /* message-specific data */
     CURLcode result;   /* return code for transfer */
   } data;
 };
.fi
When \fBmsg\fP is \fICURLMSG_DONE\fP, the message identifies a transfer that
is done, and then \fBresult\fP contains the return code for the easy handle
that just completed.

At this point, there are no other \fBmsg\fP types defined.
.SH EXAMPLE
.nf
struct CURLMsg *m;

/* call curl_multi_perform or curl_multi_socket_action first, then loop
   through and check if there are any transfers that have completed */

do {
  int msgq = 0;
  m = curl_multi_info_read(multi_handle, &msgq);
  if(m && (m->msg == CURLMSG_DONE)) {
    CURL *e = m->easy_handle;
    transfers--;
    curl_multi_remove_handle(multi_handle, e);
    curl_easy_cleanup(e);
  }
} while(m);
.fi
.SH AVAILABILITY
Added in 7.9.6
.SH RETURN VALUE
A pointer to a filled-in struct, or NULL if it failed or ran out of
structs. It also writes the number of messages left in the queue (after this
read) in the integer the second argument points to.
.SH "SEE ALSO"
.BR curl_multi_cleanup "(3), " curl_multi_init "(3), " curl_multi_perform "(3)"