Provided by: libcurl4-doc_7.55.1-1ubuntu2_all bug

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),