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.\" **************************************************************************
.\" * _ _ ____ _
.\" * Project ___| | | | _ \| |
.\" * / __| | | | |_) | |
.\" * | (__| |_| | _ <| |___
.\" * \___|\___/|_| \_\_____|
.\" *
.\" * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
.\" *
.\" * This software is licensed as described in the file COPYING, which
.\" * you should have received as part of this distribution. The terms
.\" * are also available at http://curl.haxx.se/docs/copyright.html.
.\" *
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
.\" * copies of the Software, and permit persons to whom the Software is
.\" * furnished to do so, under the terms of the COPYING file.
.\" *
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
.\" * KIND, either express or implied.
.\" *
.\" **************************************************************************
.\"
.TH CURLOPT_SEEKFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
.SH NAME
CURLOPT_SEEKFUNCTION \- user callback for seeking in input stream
.SH SYNOPSIS
.nf
#include <curl/curl.h>
/* These are the return codes for the seek callbacks */
#define CURL_SEEKFUNC_OK 0
#define CURL_SEEKFUNC_FAIL 1 /* fail the entire transfer */
#define CURL_SEEKFUNC_CANTSEEK 2 /* tell libcurl seeking can't be done, so
libcurl might try other means instead */
int seek_callback(void *userp, curl_off_t offset, int origin);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_callback);
.SH DESCRIPTION
Pass a pointer to your callback function, which should match the prototype
shown above.
This function gets called by libcurl to seek to a certain position in the
input stream and can be used to fast forward a file in a resumed upload
(instead of reading all uploaded bytes with the normal read
function/callback). It is also called to rewind a stream when doing a HTTP PUT
or POST with a multi-pass authentication method. The function shall work like
fseek(3) or lseek(3) and it gets SEEK_SET, SEEK_CUR or SEEK_END as argument
for \fIorigin\fP, although libcurl currently only passes SEEK_SET.
\fIuserp\fP is the pointer you set with \fICURLOPT_SEEKDATA(3)\fP.
The callback function must return \fICURL_SEEKFUNC_OK\fP on success,
\fICURL_SEEKFUNC_FAIL\fP to cause the upload operation to fail or
\fICURL_SEEKFUNC_CANTSEEK\fP to indicate that while the seek failed, libcurl
is free to work around the problem if possible. The latter can sometimes be
done by instead reading from the input or similar.
If you forward the input arguments directly to fseek(3) or lseek(3), note that
the data type for \fIoffset\fP is not the same as defined for curl_off_t on
many systems!
.SH DEFAULT
By default, this is NULL and unused.
.SH PROTOCOLS
HTTP, FTP, SFTP
.SH EXAMPLE
TODO
.SH AVAILABILITY
Added in 7.18.0
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_SEEKDATA "(3), " CURLOPT_IOCTLFUNCTION "(3), "
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