curl_easy_pause(3)

1curl_easy_pause(3)              libcurl Manual              curl_easy_pause(3)
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NAME

6       curl_easy_pause - pause and unpause a connection
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SYNOPSIS

9       #include <curl/curl.h>
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11       CURLcode curl_easy_pause(CURL *handle, int bitmask );
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DESCRIPTION

15       Using  this  function,  you can explicitly mark a running connection to
16       get paused, and you  can  unpause  a  connection  that  was  previously
17       paused.
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19       A  connection  can  be  paused by using this function or by letting the
20       read or the  write  callbacks  return  the  proper  magic  return  code
21       (CURL_READFUNC_PAUSE  and  CURL_WRITEFUNC_PAUSE). A write callback that
22       returns pause signals to the library that it couldn't take care of  any
23       data at all, and that data will then be delivered again to the callback
24       when the writing is later unpaused.
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26       While it may feel tempting, take care and notice that you  cannot  call
27       this function from another thread. To unpause, you may for example call
28       it from the progress callback (CURLOPT_PROGRESSFUNCTION(3)), which gets
29       called at least once per second, even if the connection is paused.
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31       When  this  function  is  called to unpause reading, the chance is high
32       that you will get your  write  callback  called  before  this  function
33       returns.
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35       The  handle  argument is of course identifying the handle that operates
36       on the connection you want to pause or unpause.
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38       The bitmask argument is a set of bits that sets the new  state  of  the
39       connection. The following bits can be used:
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41       CURLPAUSE_RECV
42              Pause  receiving  data.  There  will be no data received on this
43              connection until this function is called again without this  bit
44              set.  Thus,  the write callback (CURLOPT_WRITEFUNCTION(3)) won't
45              be called.
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47       CURLPAUSE_SEND
48              Pause sending data. There will be no data sent on  this  connec‐
49              tion  until  this function is called again without this bit set.
50              Thus,  the  read  callback  (CURLOPT_READFUNCTION(3))  won't  be
51              called.
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53       CURLPAUSE_ALL
54              Convenience define that pauses both directions.
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56       CURLPAUSE_CONT
57              Convenience define that unpauses both directions.
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RETURN VALUE

60       CURLE_OK  (zero) means that the option was set properly, and a non-zero
61       return code means something wrong occurred after the new state was set.
62       See the libcurl-errors(3) man page for the full list with descriptions.
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LIMITATIONS

65       The pausing of transfers does not work with protocols that work without
66       network connectivity, like FILE://. Trying to pause such a transfer, in
67       any direction, will cause problems in the worst case or an error in the
68       best case.
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AVAILABILITY

71       This function was added in libcurl 7.18.0. Before this  version,  there
72       was no explicit support for pausing transfers.
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USAGE WITH THE MULTI-SOCKET INTERFACE

75       Before  libcurl  7.32.0,  when a specific handle was unpaused with this
76       function, there was no particular forced rechecking or similar  of  the
77       socket's state, which made the continuation of the transfer get delayed
78       until next multi-socket call invoke or even longer. Alternatively,  the
79       user  could forcibly call for example curl_multi_socket_all(3) - with a
80       rather hefty performance penalty.
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82       Starting in libcurl 7.32.0, unpausing a transfer will schedule a  time‐
83       out  trigger  for  that handle 1 millisecond into the future, so that a
84       curl_multi_socket_action( ... CURL_SOCKET_TIMEOUT) can be used  immedi‐
85       ately afterwards to get the transfer going again as desired.
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MEMORY USE

88       When  pausing  a  read  by returning the magic return code from a write
89       callback, the read data is already in  libcurl's  internal  buffers  so
90       it'll have to keep it in an allocated buffer until the reading is again
91       unpaused using this function.
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93       If the downloaded data is compressed and is asked to  get  uncompressed
94       automatically  on  download,  libcurl  will  continue to uncompress the
95       entire downloaded chunk and it will cache the data  uncompressed.  This
96       has  the side- effect that if you download something that is compressed
97       a lot, it can result in a very large data amount needing  to  be  allo‐
98       cated to save the data during the pause. This said, you should probably
99       consider not using paused reading if you allow  libcurl  to  uncompress
100       data automatically.
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