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)).

       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 will be 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 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)