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CURLOPT_SEEKFUNCTION(3) curl_easy_setopt options CURLOPT_SEEKFUNCTION(3)
CURLOPT_SEEKFUNCTION - user callback for seeking in input stream
/* 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 cannot 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);
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
origin, although libcurl currently only passes SEEK_SET.
userp is the pointer you set with CURLOPT_SEEKDATA(3).
The callback function must return CURL_SEEKFUNC_OK on success,
CURL_SEEKFUNC_FAIL to cause the upload operation to fail or
CURL_SEEKFUNC_CANTSEEK 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 offset is not the same as defined for
curl_off_t on many systems!
By default, this is NULL and unused.
HTTP, FTP, SFTP
static int seek_cb(void *userp, curl_off_t offset, int origin)
struct data *d = (struct data *)userp;
lseek(our_fd, offset, origin);
struct data seek_data;
curl_easy_setopt(CURL *handle, CURLOPT_SEEKFUNCTION, seek_cb);
curl_easy_setopt(CURL *handle, CURLOPT_SEEKDATA, &seek_data);
Added in 7.18.0
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION
libcurl 7.83.1 October 31, 2021 CURLOPT_SEEKFUNCTION(3)