curlopt_writefunction(3) [mojave man page]

CURLOPT_WRITEFUNCTION(3)				     curl_easy_setopt options					  CURLOPT_WRITEFUNCTION(3)

NAME

       CURLOPT_WRITEFUNCTION - set callback for writing received data

SYNOPSIS

       #include <curl/curl.h>

       size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);

DESCRIPTION

       Pass a pointer to your callback function, which should match the prototype shown above.

       This  callback function gets called by libcurl as soon as there is data received that needs to be saved.  ptr points to the delivered data,
       and the size of that data is size multiplied with nmemb.

       The callback function will be passed as much data as possible in all invokes, but you must not make any assumptions. It may be one byte, it
       may  be	thousands.  The  maximum  amount  of  body  data  that	will be passed to the write callback is defined in the curl.h header file:
       CURL_MAX_WRITE_SIZE (the usual default is 16K). If CURLOPT_HEADER(3) is enabled, which makes header data get passed to the write  callback,
       you can get up to CURL_MAX_HTTP_HEADER bytes of header data passed into it. This usually means 100K.

       This function may be called with zero bytes data if the transferred file is empty.

       The data passed to this function will not be zero terminated!

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

       Your  callback  should  return  the  number of bytes actually taken care of. If that amount differs from the amount passed to your callback
       function, it'll signal an error condition to the library. This will cause the transfer to get aborted and the libcurl  function	used  will
       return CURLE_WRITE_ERROR.

       If  your  callback  function returns CURL_WRITEFUNC_PAUSE it will cause this transfer to become paused.	See curl_easy_pause(3) for further
       details.

       Set this option to NULL to get the internal default function used instead of your callback. The internal default function  will	write  the
       data to the FILE * given with CURLOPT_WRITEDATA(3).

DEFAULT

       libcurl will use 'fwrite' as a callback by default.

PROTOCOLS

       For all protocols

AVAILABILITY

       Support for the CURL_WRITEFUNC_PAUSE return code was added in version 7.18.0.

RETURN VALUE

       This will return CURLE_OK.

EXAMPLE

       A  common technique is to use this callback to store the incoming data into a dynamically growing allocated buffer. Like in the getinmemory
       example: https://curl.haxx.se/libcurl/c/getinmemory.html

SEE ALSO

       CURLOPT_WRITEDATA(3), CURLOPT_READFUNCTION(3),

libcurl 7.54.0							 February 03, 2016					  CURLOPT_WRITEFUNCTION(3)

curl_easy_pause(3)						  libcurl Manual						curl_easy_pause(3)

NAME

       curl_easy_pause - pause and unpause a connection

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_pause(CURL *handle, int bitmask );

DESCRIPTION

       Using  this  function,  you  can  explicitly  mark a running connection to get paused, and you can unpause a connection that was previously
       paused.

       A connection can be paused by using this function or by letting the read or the	write  callbacks  return  the  proper  magic  return  code
       (CURL_READFUNC_PAUSE  and  CURL_WRITEFUNC_PAUSE).  A write callback that returns pause signals to the library that it couldn't take care of
       any data at all, and that data will then be delivered again to the callback when the writing is later unpaused.

       NOTE: while it may feel tempting, take care and notice that you cannot call this function from another thread.

       When this function is called to unpause reading, the chance is high that you will get your  write  callback  called  before  this  function
       returns.

       The handle argument is of course identifying the handle that operates on the connection you want to pause or unpause.

       The bitmask argument is a set of bits that sets the new state of the connection. The following bits can be used:

       CURLPAUSE_RECV
	      Pause  receiving	data.  There will be no data received on this connection until this function is called again without this bit set.
	      Thus, the write callback (CURLOPT_WRITEFUNCTION) won't be called.

       CURLPAUSE_SEND
	      Pause sending data. There will be no data sent on this connection until this function is called again without this  bit  set.  Thus,
	      the read callback (CURLOPT_READFUNCTION) won't be called.

       CURLPAUSE_ALL
	      Convenience define that pauses both directions.

       CURLPAUSE_CONT
	      Convenience define that unpauses both directions

RETURN VALUE

       CURLE_OK  (zero)  means that the option was set properly, and a non-zero return code means something wrong occurred after the new state was
       set.  See the libcurl-errors(3) man page for the full list with descriptions.

AVAILABILITY

       This function was added in libcurl 7.18.0. Before this version, there was no explicit support for pausing transfers.

MEMORY USE

       When pausing a read by returning the magic return code from a write callback, the read data is already in  libcurl's  internal  buffers	so
       it'll have to keep it in an allocated buffer until the reading is again unpaused using this function.

       If  the	downloaded  data is compressed and is asked to get uncompressed automatically on download, libcurl will continue to uncompress the
       entire downloaded chunk and it will cache the data uncompressed. This has the side- effect that if you  download  something  that  is  com-
       pressed	a  lot, it can result in a very large data amount needing to be allocated to save the data during the pause. This said, you should
       probably consider not using paused reading if you allow libcurl to uncompress data automatically.

SEE ALSO

       curl_easy_cleanup(3), curl_easy_reset(3)

libcurl 7.18.0							    17 Dec 2007 						curl_easy_pause(3)