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comparison mupdf-source/thirdparty/curl/docs/libcurl/opts/CURLOPT_SEEKFUNCTION.3 @ 2:b50eed0cc0ef upstream

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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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23 .TH CURLOPT_SEEKFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
24 .SH NAME
25 CURLOPT_SEEKFUNCTION \- user callback for seeking in input stream
26 .SH SYNOPSIS
27 .nf
28 #include <curl/curl.h>
29
30 /* These are the return codes for the seek callbacks */
31 #define CURL_SEEKFUNC_OK 0
32 #define CURL_SEEKFUNC_FAIL 1 /* fail the entire transfer */
33 #define CURL_SEEKFUNC_CANTSEEK 2 /* tell libcurl seeking can't be done, so
34 libcurl might try other means instead */
35
36 int seek_callback(void *userp, curl_off_t offset, int origin);
37
38 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_callback);
39 .SH DESCRIPTION
40 Pass a pointer to your callback function, which should match the prototype
41 shown above.
42
43 This function gets called by libcurl to seek to a certain position in the
44 input stream and can be used to fast forward a file in a resumed upload
45 (instead of reading all uploaded bytes with the normal read
46 function/callback). It is also called to rewind a stream when data has already
47 been sent to the server and needs to be sent again. This may happen when doing
48 an HTTP PUT or POST with a multi-pass authentication method, or when an
49 existing HTTP connection is reused too late and the server closes the
50 connection. The function shall work like fseek(3) or lseek(3) and it gets
51 SEEK_SET, SEEK_CUR or SEEK_END as argument for \fIorigin\fP, although libcurl
52 currently only passes SEEK_SET.
53
54 \fIuserp\fP is the pointer you set with \fICURLOPT_SEEKDATA(3)\fP.
55
56 The callback function must return \fICURL_SEEKFUNC_OK\fP on success,
57 \fICURL_SEEKFUNC_FAIL\fP to cause the upload operation to fail or
58 \fICURL_SEEKFUNC_CANTSEEK\fP to indicate that while the seek failed, libcurl
59 is free to work around the problem if possible. The latter can sometimes be
60 done by instead reading from the input or similar.
61
62 If you forward the input arguments directly to fseek(3) or lseek(3), note that
63 the data type for \fIoffset\fP is not the same as defined for curl_off_t on
64 many systems!
65 .SH DEFAULT
66 By default, this is NULL and unused.
67 .SH PROTOCOLS
68 HTTP, FTP, SFTP
69 .SH EXAMPLE
70 .nf
71 static int seek_cb(void *userp, curl_off_t offset, int origin)
72 {
73 struct data *d = (struct data *)userp;
74 lseek(our_fd, offset, origin);
75 return CURL_SEEKFUNC_OK;
76 }
77
78 {
79 struct data seek_data;
80 curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_cb);
81 curl_easy_setopt(CURL *handle, CURLOPT_SEEKDATA, &seek_data);
82 }
83 .fi
84 .SH AVAILABILITY
85 Added in 7.18.0
86 .SH RETURN VALUE
87 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
88 .SH "SEE ALSO"
89 .BR CURLOPT_SEEKDATA "(3), " CURLOPT_IOCTLFUNCTION "(3), "