docs/libcurl/curl_easy_pause.3 - platform/external/curl - Git at Google

 .\" **************************************************************************
 .\" *                                  _   _ ____  _
 .\" *  Project                     ___| | | |  _ \| |
 .\" *                             / __| | | | |_) | |
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
 .\" * Copyright (C) 1998 - 2020, 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.
 .\" *
 .\" **************************************************************************
 .TH curl_easy_pause 3 "December 22, 2020" "libcurl 7.78.0" "libcurl Manual"

 .SH NAME
 curl_easy_pause - pause and unpause a connection
 .SH SYNOPSIS
 .nf
 .B #include <curl/curl.h>

 .BI "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.

 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 couldn't take care of any
 data at all, and that data will then be 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), which gets called at
 least once per second, even if the connection is paused.

 When this function is called to unpause receiving, the chance is high that you
 will get your write callback called before this function returns.

 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 will reset
 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 will be no data received on this connection until
 this function is called again without this bit set. Thus, the write callback
 (\fICURLOPT_WRITEFUNCTION(3)\fP) won't be called.
 .IP CURLPAUSE_SEND
 Pause sending data. There will be no data sent on this connection until this
 function is called again without this bit set. Thus, the read callback
 (\fICURLOPT_READFUNCTION(3)\fP) won't be called.
 .IP CURLPAUSE_ALL
 Convenience define that pauses both directions.
 .IP CURLPAUSE_CONT
 Convenience define that unpauses both directions.
 .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 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, will cause problems in the worst case or an error in the best case.
 .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 will allow 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 will be
 delivered first.
 .SH AVAILABILITY
 Added in libcurl 7.18.0.
 .SH "MEMORY USE"
 When pausing a read by returning the magic return code from a write callback,
 the read data is already in libcurl's internal buffers so it'll have 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 will continue to uncompress the entire
 downloaded chunk and it will cache the data uncompressed. This has the side-
 effect that if you download something that is compressed a lot, it can result
 in a very large data amount needing to be allocated to save the data during
 the pause. This said, you should probably consider not using paused receiving
 if you allow libcurl to uncompress data automatically.
 .SH "SEE ALSO"
 .BR curl_easy_cleanup "(3), " curl_easy_reset "(3)"
	.\" **************************************************************************
	.\" * _ _ ____ _
	.\" * Project ___\| \| \| \| _ \\| \|
	.\" * / __\| \| \| \| \|_) \| \|
	.\" * \| (__\| \|_\| \| _ <\| \|___
	.\" * \___\|\___/\|_\| \_\_____\|
	.\" *
	.\" * Copyright (C) 1998 - 2020, 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.
	.\" *
	.\" **************************************************************************
	.TH curl_easy_pause 3 "December 22, 2020" "libcurl 7.78.0" "libcurl Manual"

	.SH NAME
	curl_easy_pause - pause and unpause a connection
	.SH SYNOPSIS
	.nf
	.B #include <curl/curl.h>

	.BI "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.

	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 couldn't take care of any
	data at all, and that data will then be 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), which gets called at
	least once per second, even if the connection is paused.

	When this function is called to unpause receiving, the chance is high that you
	will get your write callback called before this function returns.

	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 will reset
	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 will be no data received on this connection until
	this function is called again without this bit set. Thus, the write callback
	(\fICURLOPT_WRITEFUNCTION(3)\fP) won't be called.
	.IP CURLPAUSE_SEND
	Pause sending data. There will be no data sent on this connection until this
	function is called again without this bit set. Thus, the read callback
	(\fICURLOPT_READFUNCTION(3)\fP) won't be called.
	.IP CURLPAUSE_ALL
	Convenience define that pauses both directions.
	.IP CURLPAUSE_CONT
	Convenience define that unpauses both directions.
	.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 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, will cause problems in the worst case or an error in the best case.
	.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 will allow 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 will be
	delivered first.
	.SH AVAILABILITY
	Added in libcurl 7.18.0.
	.SH "MEMORY USE"
	When pausing a read by returning the magic return code from a write callback,
	the read data is already in libcurl's internal buffers so it'll have 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 will continue to uncompress the entire
	downloaded chunk and it will cache the data uncompressed. This has the side-
	effect that if you download something that is compressed a lot, it can result
	in a very large data amount needing to be allocated to save the data during
	the pause. This said, you should probably consider not using paused receiving
	if you allow libcurl to uncompress data automatically.
	.SH "SEE ALSO"
	.BR curl_easy_cleanup "(3), " curl_easy_reset "(3)"