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Updated: Thursday, June 13, 2019
 
 

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
*userdata);

CURLcode    curl_easy_setopt(CURL    *handle,     CURLOPT_READFUNCTION,
read_callback);

Description

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
       *userdata);

       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.

       Set the userdata argument with the CURLOPT_READDATA(3) option.

       Your  function must return the actual number of bytes that it stored in
       the data area pointed at by the pointer buffer. 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_READ-
       FUNC_ABORT was added in 7.12.1.

RETURN VALUE
       This will return CURLE_OK.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | web/curl         |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       CURLOPT_READDATA(3), CURLOPT_WRITEFUNCTION(3), CURLOPT_SEEKFUNCTION(3),
       CURLOPT_UPLOAD(3), CURLOPT_POST(3),



NOTES
       This    software    was    built    from    source     available     at
       https://github.com/oracle/solaris-userland.    The  original  community
       source   was    downloaded    from     https://github.com/curl/curl/ar-
       chive/curl-7_64_0.zip

       Further information about this software can be found on the open source
       community website at http://curl.haxx.se/.



libcurl 7.37.0                    16 Jun 2014          CURLOPT_READFUNCTION(3)