quickjs-tart

quickjs-based runtime for wallet-core logic
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CURLOPT_SEEKFUNCTION.md (2946B)

      1 ---
      2 c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
      3 SPDX-License-Identifier: curl
      4 Title: CURLOPT_SEEKFUNCTION
      5 Section: 3
      6 Source: libcurl
      7 See-also:
      8   - CURLOPT_DEBUGFUNCTION (3)
      9   - CURLOPT_IOCTLFUNCTION (3)
     10   - CURLOPT_SEEKDATA (3)
     11   - CURLOPT_STDERR (3)
     12 Protocol:
     13   - FTP
     14   - HTTP
     15   - SFTP
     16 Added-in: 7.18.0
     17 ---
     18 
     19 # NAME
     20 
     21 CURLOPT_SEEKFUNCTION - user callback for seeking in input stream
     22 
     23 # SYNOPSIS
     24 
     25 ~~~c
     26 #include <curl/curl.h>
     27 
     28 /* These are the return codes for the seek callbacks */
     29 #define CURL_SEEKFUNC_OK       0
     30 #define CURL_SEEKFUNC_FAIL     1 /* fail the entire transfer */
     31 #define CURL_SEEKFUNC_CANTSEEK 2 /* tell libcurl seeking cannot be done, so
     32                                     libcurl might try other means instead */
     33 
     34 int seek_callback(void *clientp, curl_off_t offset, int origin);
     35 
     36 CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_callback);
     37 ~~~
     38 
     39 # DESCRIPTION
     40 
     41 Pass a pointer to your callback function, which should match the prototype
     42 shown above.
     43 
     44 This function gets called by libcurl to seek to a certain position in the
     45 input stream and can be used to fast forward a file in a resumed upload
     46 (instead of reading all uploaded bytes with the normal read
     47 function/callback). It is also called to rewind a stream when data has already
     48 been sent to the server and needs to be sent again. This may happen when doing
     49 an HTTP PUT or POST with a multi-pass authentication method, or when an
     50 existing HTTP connection is reused too late and the server closes the
     51 connection. The function shall work like fseek(3) or lseek(3) and it gets
     52 SEEK_SET, SEEK_CUR or SEEK_END as argument for *origin*, although libcurl
     53 currently only passes SEEK_SET.
     54 
     55 *clientp* is the pointer you set with CURLOPT_SEEKDATA(3).
     56 
     57 The callback function must return *CURL_SEEKFUNC_OK* on success,
     58 *CURL_SEEKFUNC_FAIL* to cause the upload operation to fail or
     59 *CURL_SEEKFUNC_CANTSEEK* to indicate that while the seek failed, libcurl
     60 is free to work around the problem if possible. The latter can sometimes be
     61 done by instead reading from the input or similar.
     62 
     63 If you forward the input arguments directly to fseek(3) or lseek(3), note that
     64 the data type for *offset* is not the same as defined for curl_off_t on
     65 many systems.
     66 
     67 # DEFAULT
     68 
     69 NULL
     70 
     71 # %PROTOCOLS%
     72 
     73 # EXAMPLE
     74 
     75 ~~~c
     76 #include <unistd.h> /* for lseek */
     77 
     78 struct data {
     79   int our_fd;
     80 };
     81 static int seek_cb(void *clientp, curl_off_t offset, int origin)
     82 {
     83   struct data *d = (struct data *)clientp;
     84   lseek(d->our_fd, offset, origin);
     85   return CURL_SEEKFUNC_OK;
     86 }
     87 
     88 int main(void)
     89 {
     90   struct data seek_data;
     91   CURL *curl = curl_easy_init();
     92   if(curl) {
     93     curl_easy_setopt(curl, CURLOPT_SEEKFUNCTION, seek_cb);
     94     curl_easy_setopt(curl, CURLOPT_SEEKDATA, &seek_data);
     95   }
     96 }
     97 ~~~
     98 
     99 # %AVAILABILITY%
    100 
    101 # RETURN VALUE
    102 
    103 curl_easy_setopt(3) returns a CURLcode indicating success or error.
    104 
    105 CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
    106 libcurl-errors(3).