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 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
       _LOW_SPEED_LIMIT&section=3">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)) won't
              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)) 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.

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.

AVAILABILITY
       Added in libcurl 7.18.0.

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 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 very 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.

SEE ALSO
       curl_easy_cleanup(3), curl_easy_reset(3)

libcurl 7.77.0                 December 22, 2020            curl_easy_pause(3)