CURLOPT_READFUNCTION(3)

CURLOPT_READFUNCTION(3curl_easy_setopt optionCURLOPT_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 nitems 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 con-
     sidered 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).

libcurl 7.58.0   Last change: December 13, 2017                 1

CURLOPT_READFUNCTION(3curl_easy_setopt optionCURLOPT_READFUNCTION(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 7.58.0   Last change: December 13, 2017                 2