CURLOPT_READFUNCTION(3) curl_easy_setopt options CURLOPT_READFUNCTION(3)NAMECURLOPT_READFUNCTION - read callback for data uploads
SYNOPSIS
#include <curl/curl.h>
size_t read_callback(char *buffer, size_t size, size_t nitems, void
*instream);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_READFUNCTION,
read_callback);
DESCRIPTION
Pass a pointer to your callback function, as the prototype shows above.
This callback function gets called by libcurl as soon as it needs to
read data in order to send it to the peer - like if you ask it to
upload or post data to the server. The data area pointed at by the
pointer buffer should be filled up with at most size multiplied with
nmemb number of bytes by your function.
Your function must then return the actual number of bytes that it
stored in that memory area. Returning 0 will signal end-of-file to the
library and cause it to stop the current transfer.
If you stop the current transfer by returning 0 "pre-maturely" (i.e
before the server expected it, like when you've said you will upload N
bytes and you upload less than N bytes), you may experience that the
server "hangs" waiting for the rest of the data that won't come.
The read callback may return CURL_READFUNC_ABORT to stop the current
operation immediately, resulting in a CURLE_ABORTED_BY_CALLBACK error
code from the transfer.
The callback can return CURL_READFUNC_PAUSE to cause reading from this
connection to pause. See curl_easy_pause(3) for further details.
Bugs: when doing TFTP uploads, you must return the exact amount of data
that the callback wants, or it will be considered the final packet by
the server end and the transfer will end there.
If you set this callback pointer to NULL, or don't set it at all, the
default internal read function will be used. It is doing an fread() on
the FILE * userdata set with CURLOPT_READDATA(3).
DEFAULT
The default internal read callback is fread().
PROTOCOLS
This is used for all protocols when doing uploads.
EXAMPLE
Here's an example setting a read callback for reading that to upload to
an FTP site: http://curl.haxx.se/libcurl/c/ftpupload.html
AVAILABILITY
CURL_READFUNC_PAUSE return code was added in 7.18.0 and CURL_READ‐
FUNC_ABORT was added in 7.12.1.
RETURN VALUE
This will return CURLE_OK.
SEE ALSOCURLOPT_READDATA(3), CURLOPT_WRITEFUNCTION(3), CURLOPT_SEEKFUNCTION(3),
CURLOPT_UPLOAD(3), CURLOPT_POST(3),
libcurl 7.37.0 16 Jun 2014 CURLOPT_READFUNCTION(3)
