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
       could  not 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
       (CURLOPT_PROGRESSFUNCTION(3)), 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 handle argument identifies the transfer you want to pause or unpause.

       A paused transfer is excluded from low speed cancels  via  the  CURLOPT_LOW_SPEED_LIMIT(3)
       option  and  unpausing  a  transfer  will reset 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 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)) will not be called.

       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
              (CURLOPT_READFUNCTION(3)) will not be 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, will  cause
       problems in the worst case or an error in the best case.

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.

EXAMPLE

       /* pause a transfer in both directions */
       curl_easy_pause(curl, CURL_READFUNC_PAUSE | CURL_WRITEFUNC_PAUSE);

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 will 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 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.

AVAILABILITY

       Added in 7.18.0.

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.

SEE ALSO

       curl_easy_cleanup(3), curl_easy_reset(3)