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| .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 data has already |
| been sent to the server and needs to be sent again. This may happen when doing |
| an HTTP PUT or POST with a multi-pass authentication method, or when an |
| existing HTTP connection is reused too late and the server closes the |
| connection. 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 |
| .nf |
| static int seek_cb(void *userp, curl_off_t offset, int origin) |
| { |
| struct data *d = (struct data *)userp; |
| lseek(our_fd, offset, origin); |
| return CURL_SEEKFUNC_OK; |
| } |
| |
| { |
| struct data seek_data; |
| curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_cb); |
| curl_easy_setopt(CURL *handle, CURLOPT_SEEKDATA, &seek_data); |
| } |
| .fi |
| .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), " |
