104 lines
5.2 KiB
Groff
104 lines
5.2 KiB
Groff
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.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * / __| | | | |_) | |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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.\" * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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.\" * are also available at https://curl.haxx.se/docs/copyright.html.
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" **************************************************************************
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.TH curl_easy_pause 3 "17 Dec 2007" "libcurl 7.18.0" "libcurl Manual"
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.SH NAME
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curl_easy_pause - pause and unpause a connection
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.SH SYNOPSIS
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.B #include <curl/curl.h>
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.BI "CURLcode curl_easy_pause(CURL *"handle ", int "bitmask " );"
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.SH DESCRIPTION
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Using this function, you can explicitly mark a running connection to get
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paused, and you can unpause a connection that was previously paused.
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A connection can be paused by using this function or by letting the read or
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the write callbacks return the proper magic return code
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(\fICURL_READFUNC_PAUSE\fP and \fICURL_WRITEFUNC_PAUSE\fP). A write callback
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that returns pause signals to the library that it couldn't take care of any
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data at all, and that data will then be delivered again to the callback when
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the writing is later unpaused.
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While it may feel tempting, take care and notice that you cannot call this
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function from another thread. To unpause, you may for example call it from the
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progress callback (\fICURLOPT_PROGRESSFUNCTION(3)\fP), which gets called at
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least once per second, even if the connection is paused.
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When this function is called to unpause reading, the chance is high that you
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will get your write callback called before this function returns.
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The \fBhandle\fP argument is of course identifying the handle that operates on
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the connection you want to pause or unpause.
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The \fBbitmask\fP argument is a set of bits that sets the new state of the
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connection. The following bits can be used:
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.IP CURLPAUSE_RECV
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Pause receiving data. There will be no data received on this connection until
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this function is called again without this bit set. Thus, the write callback
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(\fICURLOPT_WRITEFUNCTION(3)\fP) won't be called.
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.IP CURLPAUSE_SEND
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Pause sending data. There will be no data sent on this connection until this
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function is called again without this bit set. Thus, the read callback
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(\fICURLOPT_READFUNCTION(3)\fP) won't be called.
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.IP CURLPAUSE_ALL
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Convenience define that pauses both directions.
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.IP CURLPAUSE_CONT
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Convenience define that unpauses both directions.
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.SH RETURN VALUE
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CURLE_OK (zero) means that the option was set properly, and a non-zero return
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code means something wrong occurred after the new state was set. See the
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\fIlibcurl-errors(3)\fP man page for the full list with descriptions.
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.SH LIMITATIONS
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The pausing of transfers does not work with protocols that work without
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network connectivity, like FILE://. Trying to pause such a transfer, in any
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direction, will cause problems in the worst case or an error in the best case.
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.SH AVAILABILITY
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This function was added in libcurl 7.18.0. Before this version, there was no
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explicit support for pausing transfers.
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.SH "USAGE WITH THE MULTI-SOCKET INTERFACE"
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Before libcurl 7.32.0, when a specific handle was unpaused with this function,
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there was no particular forced rechecking or similar of the socket's state,
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which made the continuation of the transfer get delayed until next
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multi-socket call invoke or even longer. Alternatively, the user could
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forcibly call for example \fIcurl_multi_socket_all(3)\fP - with a rather hefty
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performance penalty.
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Starting in libcurl 7.32.0, unpausing a transfer will schedule a timeout
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trigger for that handle 1 millisecond into the future, so that a
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curl_multi_socket_action( ... CURL_SOCKET_TIMEOUT) can be used immediately
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afterwards to get the transfer going again as desired.
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.SH "MEMORY USE"
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When pausing a read by returning the magic return code from a write callback,
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the read data is already in libcurl's internal buffers so it'll have to keep
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it in an allocated buffer until the reading is again unpaused using this
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function.
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If the downloaded data is compressed and is asked to get uncompressed
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automatically on download, libcurl will continue to uncompress the entire
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downloaded chunk and it will cache the data uncompressed. This has the side-
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effect that if you download something that is compressed a lot, it can result
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in a very large data amount needing to be allocated to save the data during
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the pause. This said, you should probably consider not using paused reading if
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you allow libcurl to uncompress data automatically.
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.SH "SEE ALSO"
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.BR curl_easy_cleanup "(3), " curl_easy_reset "(3)"
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