Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
curl_easy_pause(3)	   Library Functions Manual	    curl_easy_pause(3)

NAME
       curl_easy_pause - pause and unpause a connection

SYNOPSIS
       #include	<curl/curl.h>

       CURLcode	curl_easy_pause(CURL *handle, int bitmask );

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, curl_easy_pause(3)	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
       (CURL_READFUNC_PAUSE and	CURL_WRITEFUNC_PAUSE). 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 (CURLOPT_PROGRESSFUNCTION(3)).

       When this function is called to unpause receiving, the  write  callback
       might  get  called  before this function	returns	to deliver cached con-
       tent. When libcurl delivers such	cached data to the write callback,  it
       is  delivered  as fast as possible, which may overstep the boundary set
       in CURLOPT_MAX_RECV_SPEED_LARGE(3) etc.

       The handle argument identifies the transfer you want to	pause  or  un-
       pause.

       A  paused  transfer  is	excluded  from	low speed cancels via the CUR-
       LOPT_LOW_SPEED_LIMIT(3) option and unpausing a transfer resets the time
       period required for the low speed limit to be met.

       The bitmask argument is a set of	bits that sets the new	state  of  the
       connection. The following bits can be used:

       CURLPAUSE_RECV
	      Pause  receiving data. There is no data received on this connec-
	      tion until this function is called again without this  bit  set.
	      Thus,  the  write	 callback  (CURLOPT_WRITEFUNCTION(3))  is  not
	      called.

       CURLPAUSE_SEND
	      Pause sending data. There	is no data sent	on this	connection un-
	      til this function	is called again	without	this  bit  set.	 Thus,
	      the read callback	(CURLOPT_READFUNCTION(3)) is not called.

       CURLPAUSE_ALL
	      Convenience define that pauses both directions.

       CURLPAUSE_CONT
	      Convenience define that unpauses both directions.

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.

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	 flow-
       ing,  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 de-
       livered first.

PROTOCOLS
       This functionality affects all supported	protocols

EXAMPLE
       int main(void)
       {
	 CURL *curl = curl_easy_init();
	 if(curl) {
	   /* pause a transfer in both directions */
	   curl_easy_pause(curl, CURLPAUSE_RECV	| CURLPAUSE_SEND);

	 }
       }

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.

AVAILABILITY
       Added in	curl 7.18.0

RETURN VALUE
       This function returns a CURLcode	indicating success or error.

       CURLE_OK	(0) means everything was OK, non-zero means an error occurred,
       see  libcurl-errors(3).	If   CURLOPT_ERRORBUFFER(3)   was   set	  with
       curl_easy_setopt(3)  there  can be an error message stored in the error
       buffer when non-zero is returned.

SEE ALSO
       curl_easy_cleanup(3), curl_easy_reset(3)

libcurl				  2025-06-03		    curl_easy_pause(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=curl_easy_pause&sektion=3&manpath=FreeBSD+Ports+14.3.quarterly>

home | help