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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  up-
       load  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 be-
       fore 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).

       You  can	 set  the total	size of	the data you are sending by using CUR-
       LOPT_INFILESIZE_LARGE(3)	or  CURLOPT_POSTFIELDSIZE_LARGE(3),  depending
       on the type of transfer.	For some transfer types	it may be required and
       it allows for better error checking.

DEFAULT
       The default internal read callback is fread().

PROTOCOLS
       This is used for	all protocols when doing uploads.

EXAMPLE
       size_t read_callback(void *ptr, size_t size, size_t nmemb, void *userdata)
       {
	 FILE *readhere	= (FILE	*)userdata;
	 curl_off_t nread;

	 /* copy as much data as possible into the 'ptr' buffer, but no	more than
	    'size' * 'nmemb' bytes! */
	 size_t	retcode	= fread(ptr, size, nmemb, readhere);

	 nread = (curl_off_t)retcode;

	 fprintf(stderr, "*** We read %" CURL_FORMAT_CURL_OFF_T
		 " bytes from file\n", nread);
	 return	retcode;
       }

       void setup(char *uploadthis)
       {
	 FILE *file = fopen(uploadthis,	"rb");
	 CURLcode result;

	 /* set	callback to use	*/
	 curl_easy_setopt(curl,	CURLOPT_READFUNCTION, read_callback);

	 /* pass in suitable argument to callback */
	 curl_easy_setopt(curl,	CURLOPT_READDATA, (void	*)file);

	 result	= curl_easy_perform(curl);
       }

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

libcurl	7.72.0			 June 25, 2020	       CURLOPT_READFUNCTION(3)

NAME | SYNOPSIS | DESCRIPTION | DEFAULT | PROTOCOLS | EXAMPLE | AVAILABILITY | RETURN VALUE | SEE ALSO

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