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)

libcurl 7.81.0                                  November 26, 2021                             curl_easy_pause(3)