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80 lines
3.5 KiB
Groff
80 lines
3.5 KiB
Groff
.\" **************************************************************************
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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 - 2017, 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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.\"
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.TH CURLOPT_READFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
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.SH NAME
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CURLOPT_READFUNCTION \- read callback for data uploads
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.SH SYNOPSIS
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#include <curl/curl.h>
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size_t read_callback(char *buffer, size_t size, size_t nitems, void *instream);
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_READFUNCTION, read_callback);
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.SH DESCRIPTION
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Pass a pointer to your callback function, as the prototype shows above.
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This callback function gets called by libcurl as soon as it needs to read data
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in order to send it to the peer - like if you ask it to upload or post data to
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the server. The data area pointed at by the pointer \fIbuffer\fP should be
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filled up with at most \fIsize\fP multiplied with \fInitems\fP number of bytes
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by your function.
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Your function must then return the actual number of bytes that it stored in
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that memory area. Returning 0 will signal end-of-file to the library and cause
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it to stop the current transfer.
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If you stop the current transfer by returning 0 "pre-maturely" (i.e before the
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server expected it, like when you've said you will upload N bytes and you
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upload less than N bytes), you may experience that the server "hangs" waiting
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for the rest of the data that won't come.
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The read callback may return \fICURL_READFUNC_ABORT\fP to stop the current
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operation immediately, resulting in a \fICURLE_ABORTED_BY_CALLBACK\fP error
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code from the transfer.
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The callback can return \fICURL_READFUNC_PAUSE\fP to cause reading from this
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connection to pause. See \fIcurl_easy_pause(3)\fP for further details.
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\fBBugs\fP: when doing TFTP uploads, you must return the exact amount of data
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that the callback wants, or it will be considered the final packet by the
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server end and the transfer will end there.
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If you set this callback pointer to NULL, or don't set it at all, the default
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internal read function will be used. It is doing an fread() on the FILE *
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userdata set with \fICURLOPT_READDATA(3)\fP.
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.SH DEFAULT
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The default internal read callback is fread().
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.SH PROTOCOLS
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This is used for all protocols when doing uploads.
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.SH EXAMPLE
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Here's an example setting a read callback for reading that to upload to an FTP
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site: https://curl.haxx.se/libcurl/c/ftpupload.html
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.SH AVAILABILITY
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CURL_READFUNC_PAUSE return code was added in 7.18.0 and CURL_READFUNC_ABORT
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was added in 7.12.1.
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.SH RETURN VALUE
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This will return CURLE_OK.
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.SH "SEE ALSO"
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.BR CURLOPT_READDATA "(3), " CURLOPT_WRITEFUNCTION "(3), "
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.BR CURLOPT_SEEKFUNCTION "(3), " CURLOPT_UPLOAD "(3), " CURLOPT_POST "(3), "
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