curl_easy_pause(3)              libcurl 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.

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

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

       The  handle  argument is of course identifying the handle that operates
       on the connection you want to pause or unpause.

       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  will be no data received on this
              connection until this function is called again without this  bit
              set.  Thus,  the write callback (CURLOPT_WRITEFUNCTION(3)) won't
              be called.

       CURLPAUSE_SEND
              Pause sending data. There will be no data sent on  this  connec-
              tion  until  this function is called again without this bit set.
              Thus,  the  read  callback  (CURLOPT_READFUNCTION(3))  won't  be
              called.

       CURLPAUSE_ALL
              Convenience define that pauses both directions.

       CURLPAUSE_CONT
              Convenience define that unpauses both directions.

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 libcurl-errors(3) man page for the full list with descriptions.

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.

AVAILABILITY
       This  function  was added in libcurl 7.18.0. Before this version, there
       was no explicit support for pausing transfers.

USAGE WITH THE MULTI-SOCKET INTERFACE
       Before libcurl 7.32.0, when a specific handle was  unpaused  with  this
       function,  there  was no particular forced rechecking or similar of the
       socket's state, which made the continuation of the transfer get delayed
       until  next multi-socket call invoke or even longer. Alternatively, the
       user could forcibly call for example curl_multi_socket_all(3) - with  a
       rather hefty performance penalty.

       Starting  in libcurl 7.32.0, unpausing a transfer will schedule a time-
       out trigger for that handle 1 millisecond into the future,  so  that  a
       curl_multi_socket_action(  ... CURL_SOCKET_TIMEOUT) can be used immedi-
       ately afterwards to get the transfer going again as desired.

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 reading 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 allo-
       cated to save the data during the pause. This said, you should probably
       consider  not  using  paused reading if you allow libcurl to uncompress
       data automatically.

SEE ALSO
       curl_easy_cleanup(3), curl_easy_reset(3)

libcurl 7.54.0                   May 01, 2016               curl_easy_pause(3)