| .\" ************************************************************************** |
| .\" * _ _ ____ _ |
| .\" * 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 curl_easy_pause 3 "17 Dec 2007" "libcurl" "libcurl" |
| .SH NAME |
| curl_easy_pause - pause and unpause a connection |
| .SH SYNOPSIS |
| .nf |
| #include <curl/curl.h> |
| |
| CURLcode curl_easy_pause(CURL *handle, int bitmask ); |
| .fi |
| .SH DESCRIPTION |
| Using this function, you can explicitly mark a running connection to get |
| paused, and you can unpause a connection that was previously paused. Unlike |
| most other libcurl functions, \fIcurl_easy_pause(3)\fP can be used from within |
| callbacks. |
| |
| A connection can be paused by using this function or by letting the read or |
| the write callbacks return the proper magic return code |
| (\fICURL_READFUNC_PAUSE\fP and \fICURL_WRITEFUNC_PAUSE\fP). A write callback |
| that returns pause signals to the library that it could not take care of any |
| data at all, and that data is then delivered again to the callback when the |
| transfer is unpaused. |
| |
| While it may feel tempting, take care and notice that you cannot call this |
| function from another thread. To unpause, you may for example call it from the |
| progress callback (\fICURLOPT_PROGRESSFUNCTION(3)\fP). |
| |
| When this function is called to unpause receiving, the write callback might |
| get called before this function returns to deliver cached content. When |
| libcurl delivers such cached data to the write callback, it is delivered as |
| fast as possible, which may overstep the boundary set in |
| \fICURLOPT_MAX_RECV_SPEED_LARGE(3)\fP etc. |
| |
| The \fBhandle\fP argument identifies the transfer you want to pause or |
| unpause. |
| |
| A paused transfer is excluded from low speed cancels via the |
| \fICURLOPT_LOW_SPEED_LIMIT(3)\fP option and unpausing a transfer resets the |
| time period required for the low speed limit to be met. |
| |
| The \fBbitmask\fP argument is a set of bits that sets the new state of the |
| connection. The following bits can be used: |
| .IP CURLPAUSE_RECV |
| Pause receiving data. There is no data received on this connection until this |
| function is called again without this bit set. Thus, the write callback |
| (\fICURLOPT_WRITEFUNCTION(3)\fP) is not called. |
| .IP CURLPAUSE_SEND |
| Pause sending data. There is no data sent on this connection until this |
| function is called again without this bit set. Thus, the read callback |
| (\fICURLOPT_READFUNCTION(3)\fP) is not called. |
| .IP CURLPAUSE_ALL |
| Convenience define that pauses both directions. |
| .IP CURLPAUSE_CONT |
| Convenience define that unpauses both directions. |
| .SH LIMITATIONS |
| The pausing of transfers does not work with protocols that work without |
| network connectivity, like FILE://. Trying to pause such a transfer, in any |
| direction, might cause problems or error. |
| .SH MULTIPLEXED |
| When a connection is used multiplexed, like for HTTP/2, and one of the |
| transfers over the connection is paused and the others continue flowing, |
| libcurl might end up buffering contents for the paused transfer. It has to do |
| this because it needs to drain the socket for the other transfers and the |
| already announced window size for the paused transfer allows the server to |
| continue sending data up to that window size amount. By default, libcurl |
| announces a 32 megabyte window size, which thus can make libcurl end up |
| buffering 32 megabyte of data for a paused stream. |
| |
| When such a paused stream is unpaused again, any buffered data is delivered |
| first. |
| .SH EXAMPLE |
| .nf |
| int main(void) |
| { |
| CURL *curl = curl_easy_init(); |
| if(curl) { |
| /* pause a transfer in both directions */ |
| curl_easy_pause(curl, CURL_READFUNC_PAUSE | CURL_WRITEFUNC_PAUSE); |
| |
| } |
| } |
| .fi |
| .SH "MEMORY USE" |
| When pausing a download transfer by returning the magic return code from a |
| write callback, the read data is already in libcurl's internal buffers so it |
| has to keep it in an allocated buffer until the receiving is again unpaused |
| using this function. |
| |
| If the downloaded data is compressed and is asked to get uncompressed |
| automatically on download, libcurl continues to uncompress the entire |
| downloaded chunk and it caches the data uncompressed. This has the side- |
| effect that if you download something that is compressed a lot, it can result |
| in a large data amount needing to be allocated to save the data during the |
| pause. consider not using paused receiving if you allow libcurl to uncompress |
| data automatically. |
| |
| If the download is done with HTTP/2 or HTTP/3, there is up to a stream window |
| size worth of data that curl cannot stop but instead needs to cache while the |
| transfer is paused. This means that if a window size of 64 MB is used, libcurl |
| might end up having to cache 64 MB of data. |
| .SH AVAILABILITY |
| Added in 7.18.0. |
| .SH RETURN VALUE |
| CURLE_OK (zero) means that the option was set properly, and a non-zero return |
| code means something wrong occurred after the new state was set. See the |
| \fIlibcurl-errors(3)\fP man page for the full list with descriptions. |
| .SH "SEE ALSO" |
| .BR curl_easy_cleanup (3), |
| .BR curl_easy_reset (3) |