CURLOPT_READFUNCTION(3) 				     curl_easy_setopt options					   CURLOPT_READFUNCTION(3)

NAME

       CURLOPT_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: https://curl.haxx.se/libcurl/c/ftpupload.html

AVAILABILITY

       CURL_READFUNC_PAUSE return code was added in 7.18.0 and CURL_READFUNC_ABORT was added in 7.12.1.

RETURN VALUE

       This will return CURLE_OK.

SEE ALSO

       CURLOPT_READDATA(3), CURLOPT_WRITEFUNCTION(3), CURLOPT_SEEKFUNCTION(3), CURLOPT_UPLOAD(3), CURLOPT_POST(3),

libcurl 7.54.0							 February 03, 2016					   CURLOPT_READFUNCTION(3)