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comparison mupdf-source/thirdparty/curl/docs/libcurl/opts/CURLOPT_READFUNCTION.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_READFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
24 .SH NAME
25 CURLOPT_READFUNCTION \- read callback for data uploads
26 .SH SYNOPSIS
27 #include <curl/curl.h>
28
29 size_t read_callback(char *buffer, size_t size, size_t nitems, void *userdata);
30
31 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_READFUNCTION, read_callback);
32
33 .SH DESCRIPTION
34 Pass a pointer to your callback function, as the prototype shows above.
35
36 This callback function gets called by libcurl as soon as it needs to read data
37 in order to send it to the peer - like if you ask it to upload or post data to
38 the server. The data area pointed at by the pointer \fIbuffer\fP should be
39 filled up with at most \fIsize\fP multiplied with \fInitems\fP number of bytes
40 by your function.
41
42 Set the \fIuserdata\fP argument with the \fICURLOPT_READDATA(3)\fP option.
43
44 Your function must return the actual number of bytes that it stored in the data
45 area pointed at by the pointer \fIbuffer\fP. Returning 0 will signal
46 end-of-file to the library and cause it to stop the current transfer.
47
48 If you stop the current transfer by returning 0 "pre-maturely" (i.e before the
49 server expected it, like when you've said you will upload N bytes and you
50 upload less than N bytes), you may experience that the server "hangs" waiting
51 for the rest of the data that won't come.
52
53 The read callback may return \fICURL_READFUNC_ABORT\fP to stop the current
54 operation immediately, resulting in a \fICURLE_ABORTED_BY_CALLBACK\fP error
55 code from the transfer.
56
57 The callback can return \fICURL_READFUNC_PAUSE\fP to cause reading from this
58 connection to pause. See \fIcurl_easy_pause(3)\fP for further details.
59
60 \fBBugs\fP: when doing TFTP uploads, you must return the exact amount of data
61 that the callback wants, or it will be considered the final packet by the
62 server end and the transfer will end there.
63
64 If you set this callback pointer to NULL, or don't set it at all, the default
65 internal read function will be used. It is doing an fread() on the FILE *
66 userdata set with \fICURLOPT_READDATA(3)\fP.
67 .SH DEFAULT
68 The default internal read callback is fread().
69 .SH PROTOCOLS
70 This is used for all protocols when doing uploads.
71 .SH EXAMPLE
72 .nf
73 size_t read_callback(void *ptr, size_t size, size_t nmemb, void *userdata)
74 {
75 FILE *readhere = (FILE *)userdata;
76 curl_off_t nread;
77
78 /* copy as much data as possible into the 'ptr' buffer, but no more than
79 'size' * 'nmemb' bytes! */
80 size_t retcode = fread(ptr, size, nmemb, readhere);
81
82 nread = (curl_off_t)retcode;
83
84 fprintf(stderr, "*** We read %" CURL_FORMAT_CURL_OFF_T
85 " bytes from file\\n", nread);
86 return retcode;
87 }
88
89 void setup(char *uploadthis)
90 {
91 FILE *file = fopen("rb", uploadthis);
92 CURLcode result;
93
94 /* set callback to use */
95 curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);
96
97 /* pass in suitable argument to callback */
98 curl_easy_setopt(curl, CURLOPT_READDATA, uploadthis);
99
100 result = curl_easy_perform(curl);
101 }
102 .fi
103 .SH AVAILABILITY
104 CURL_READFUNC_PAUSE return code was added in 7.18.0 and CURL_READFUNC_ABORT
105 was added in 7.12.1.
106 .SH RETURN VALUE
107 This will return CURLE_OK.
108 .SH "SEE ALSO"
109 .BR CURLOPT_READDATA "(3), " CURLOPT_WRITEFUNCTION "(3), "
110 .BR CURLOPT_SEEKFUNCTION "(3), " CURLOPT_UPLOAD "(3), " CURLOPT_POST "(3), "
111 .BR CURLOPT_UPLOAD_BUFFERSIZE "(3), "