gio/gpollableoutputstream.c - third_party/glib - Git at Google

 /* GIO - GLib Input, Output and Streaming Library
  *
  * Copyright (C) 2010 Red Hat, Inc.
  *
  * SPDX-License-Identifier: LGPL-2.1-or-later
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General
  * Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
  */

 #include "config.h"

 #include <errno.h>

 #include "gpollableoutputstream.h"
 #include "gasynchelper.h"
 #include "gfiledescriptorbased.h"
 #include "glibintl.h"

 /**
  * GPollableOutputStream:
  *
  * `GPollableOutputStream` is implemented by [class@Gio.OutputStream]s that
  * can be polled for readiness to write. This can be used when
  * interfacing with a non-GIO API that expects
  * UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.
  *
  * Some classes may implement `GPollableOutputStream` but have only certain
  * instances of that class be pollable. If [method@Gio.PollableOutputStream.can_poll]
  * returns false, then the behavior of other `GPollableOutputStream` methods is
  * undefined.
  *
  * Since: 2.28
  */

 G_DEFINE_INTERFACE (GPollableOutputStream, g_pollable_output_stream, G_TYPE_OUTPUT_STREAM)

 static gboolean g_pollable_output_stream_default_can_poll           (GPollableOutputStream *stream);
 static gssize   g_pollable_output_stream_default_write_nonblocking  (GPollableOutputStream  *stream,
 								     const void             *buffer,
 								     gsize                   count,
 								     GError                **error);
 static GPollableReturn g_pollable_output_stream_default_writev_nonblocking (GPollableOutputStream  *stream,
 									    const GOutputVector    *vectors,
 									    gsize                   n_vectors,
 									    gsize                  *bytes_written,
 									    GError                **error);

 static void
 g_pollable_output_stream_default_init (GPollableOutputStreamInterface *iface)
 {
   iface->can_poll           = g_pollable_output_stream_default_can_poll;
   iface->write_nonblocking  = g_pollable_output_stream_default_write_nonblocking;
   iface->writev_nonblocking = g_pollable_output_stream_default_writev_nonblocking;
 }

 static gboolean
 g_pollable_output_stream_default_can_poll (GPollableOutputStream *stream)
 {
   return TRUE;
 }

 /**
  * g_pollable_output_stream_can_poll:
  * @stream: a #GPollableOutputStream.
  *
  * Checks if @stream is actually pollable. Some classes may implement
  * #GPollableOutputStream but have only certain instances of that
  * class be pollable. If this method returns %FALSE, then the behavior
  * of other #GPollableOutputStream methods is undefined.
  *
  * For any given stream, the value returned by this method is constant;
  * a stream cannot switch from pollable to non-pollable or vice versa.
  *
  * Returns: %TRUE if @stream is pollable, %FALSE if not.
  *
  * Since: 2.28
  */
 gboolean
 g_pollable_output_stream_can_poll (GPollableOutputStream *stream)
 {
   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), FALSE);

   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->can_poll (stream);
 }

 /**
  * g_pollable_output_stream_is_writable:
  * @stream: a #GPollableOutputStream.
  *
  * Checks if @stream can be written.
  *
  * Note that some stream types may not be able to implement this 100%
  * reliably, and it is possible that a call to g_output_stream_write()
  * after this returns %TRUE would still block. To guarantee
  * non-blocking behavior, you should always use
  * g_pollable_output_stream_write_nonblocking(), which will return a
  * %G_IO_ERROR_WOULD_BLOCK error rather than blocking.
  *
  * The behaviour of this method is undefined if
  * g_pollable_output_stream_can_poll() returns %FALSE for @stream.
  *
  * Returns: %TRUE if @stream is writable, %FALSE if not. If an error
  *   has occurred on @stream, this will result in
  *   g_pollable_output_stream_is_writable() returning %TRUE, and the
  *   next attempt to write will return the error.
  *
  * Since: 2.28
  */
 gboolean
 g_pollable_output_stream_is_writable (GPollableOutputStream *stream)
 {
   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), FALSE);

   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->is_writable (stream);
 }

 /**
  * g_pollable_output_stream_create_source:
  * @stream: a #GPollableOutputStream.
  * @cancellable: (nullable): a #GCancellable, or %NULL
  *
  * Creates a #GSource that triggers when @stream can be written, or
  * @cancellable is triggered or an error occurs. The callback on the
  * source is of the #GPollableSourceFunc type.
  *
  * As with g_pollable_output_stream_is_writable(), it is possible that
  * the stream may not actually be writable even after the source
  * triggers, so you should use g_pollable_output_stream_write_nonblocking()
  * rather than g_output_stream_write() from the callback.
  *
  * The behaviour of this method is undefined if
  * g_pollable_output_stream_can_poll() returns %FALSE for @stream.
  *
  * Returns: (transfer full): a new #GSource
  *
  * Since: 2.28
  */
 GSource *
 g_pollable_output_stream_create_source (GPollableOutputStream *stream,
 					GCancellable          *cancellable)
 {
   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), NULL);

   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->
 	  create_source (stream, cancellable);
 }

 static gssize
 g_pollable_output_stream_default_write_nonblocking (GPollableOutputStream  *stream,
 						    const void             *buffer,
 						    gsize                   count,
 						    GError                **error)
 {
   if (!g_pollable_output_stream_is_writable (stream))
     {
       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK,
                            g_strerror (EAGAIN));
       return -1;
     }

   return G_OUTPUT_STREAM_GET_CLASS (stream)->
     write_fn (G_OUTPUT_STREAM (stream), buffer, count, NULL, error);
 }

 static GPollableReturn
 g_pollable_output_stream_default_writev_nonblocking (GPollableOutputStream  *stream,
 						     const GOutputVector    *vectors,
 						     gsize                   n_vectors,
 						     gsize                  *bytes_written,
 						     GError                **error)
 {
   gsize _bytes_written = 0;
   GPollableOutputStreamInterface *iface = G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream);
   gsize i;
   GError *err = NULL;

   for (i = 0; i < n_vectors; i++)
     {
       gssize res;

       /* Would we overflow here? In that case simply return and let the caller
        * handle this like a short write */
       if (_bytes_written > G_MAXSIZE - vectors[i].size)
         break;

       res = iface->write_nonblocking (stream, vectors[i].buffer, vectors[i].size, &err);
       if (res == -1)
         {
           if (bytes_written)
             *bytes_written = _bytes_written;

           /* If something was written already we handle this like a short
            * write and assume that the next call would either give the same
            * error again or successfully finish writing without errors or data
            * loss
            */
           if (_bytes_written > 0)
             {
               g_clear_error (&err);
               return G_POLLABLE_RETURN_OK;
             }
           else if (g_error_matches (err, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK))
             {
               g_clear_error (&err);
               return G_POLLABLE_RETURN_WOULD_BLOCK;
             }
           else
             {
               g_propagate_error (error, err);
               return G_POLLABLE_RETURN_FAILED;
             }
         }

       _bytes_written += res;
       /* if we had a short write break the loop here */
       if ((gsize) res < vectors[i].size)
         break;
     }

   if (bytes_written)
     *bytes_written = _bytes_written;

   return G_POLLABLE_RETURN_OK;
 }

 /**
  * g_pollable_output_stream_write_nonblocking: (virtual write_nonblocking)
  * @stream: a #GPollableOutputStream
  * @buffer: (array length=count) (element-type guint8): a buffer to write
  *     data from
  * @count: the number of bytes you want to write
  * @cancellable: (nullable): a #GCancellable, or %NULL
  * @error: #GError for error reporting, or %NULL to ignore.
  *
  * Attempts to write up to @count bytes from @buffer to @stream, as
  * with g_output_stream_write(). If @stream is not currently writable,
  * this will immediately return %G_IO_ERROR_WOULD_BLOCK, and you can
  * use g_pollable_output_stream_create_source() to create a #GSource
  * that will be triggered when @stream is writable.
  *
  * Note that since this method never blocks, you cannot actually
  * use @cancellable to cancel it. However, it will return an error
  * if @cancellable has already been cancelled when you call, which
  * may happen if you call this method after a source triggers due
  * to having been cancelled.
  *
  * Also note that if %G_IO_ERROR_WOULD_BLOCK is returned some underlying
  * transports like D/TLS require that you re-send the same @buffer and
  * @count in the next write call.
  *
  * The behaviour of this method is undefined if
  * g_pollable_output_stream_can_poll() returns %FALSE for @stream.
  *
  * Returns: the number of bytes written, or -1 on error (including
  *   %G_IO_ERROR_WOULD_BLOCK).
  */
 gssize
 g_pollable_output_stream_write_nonblocking (GPollableOutputStream  *stream,
 					    const void             *buffer,
 					    gsize                   count,
 					    GCancellable           *cancellable,
 					    GError                **error)
 {
   gssize res;

   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), -1);
   g_return_val_if_fail (buffer != NULL, 0);

   if (g_cancellable_set_error_if_cancelled (cancellable, error))
     return -1;

   if (count == 0)
     return 0;

   if (((gssize) count) < 0)
     {
       g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_ARGUMENT,
 		   _("Too large count value passed to %s"), G_STRFUNC);
       return -1;
     }

   if (cancellable)
     g_cancellable_push_current (cancellable);

   res = G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->
     write_nonblocking (stream, buffer, count, error);

   if (cancellable)
     g_cancellable_pop_current (cancellable);

   return res;
 }

 /**
  * g_pollable_output_stream_writev_nonblocking: (virtual writev_nonblocking)
  * @stream: a #GPollableOutputStream
  * @vectors: (array length=n_vectors): the buffer containing the #GOutputVectors to write.
  * @n_vectors: the number of vectors to write
  * @bytes_written: (out) (optional): location to store the number of bytes that were
  *     written to the stream
  * @cancellable: (nullable): a #GCancellable, or %NULL
  * @error: #GError for error reporting, or %NULL to ignore.
  *
  * Attempts to write the bytes contained in the @n_vectors @vectors to @stream,
  * as with g_output_stream_writev(). If @stream is not currently writable,
  * this will immediately return %@G_POLLABLE_RETURN_WOULD_BLOCK, and you can
  * use g_pollable_output_stream_create_source() to create a #GSource
  * that will be triggered when @stream is writable. @error will *not* be
  * set in that case.
  *
  * Note that since this method never blocks, you cannot actually
  * use @cancellable to cancel it. However, it will return an error
  * if @cancellable has already been cancelled when you call, which
  * may happen if you call this method after a source triggers due
  * to having been cancelled.
  *
  * Also note that if %G_POLLABLE_RETURN_WOULD_BLOCK is returned some underlying
  * transports like D/TLS require that you re-send the same @vectors and
  * @n_vectors in the next write call.
  *
  * The behaviour of this method is undefined if
  * g_pollable_output_stream_can_poll() returns %FALSE for @stream.
  *
  * Returns: %@G_POLLABLE_RETURN_OK on success, %G_POLLABLE_RETURN_WOULD_BLOCK
  * if the stream is not currently writable (and @error is *not* set), or
  * %G_POLLABLE_RETURN_FAILED if there was an error in which case @error will
  * be set.
  *
  * Since: 2.60
  */
 GPollableReturn
 g_pollable_output_stream_writev_nonblocking (GPollableOutputStream  *stream,
 					     const GOutputVector    *vectors,
 					     gsize                   n_vectors,
 					     gsize                  *bytes_written,
 					     GCancellable           *cancellable,
 					     GError                **error)
 {
   GPollableOutputStreamInterface *iface;
   GPollableReturn res;
   gsize _bytes_written = 0;

   if (bytes_written)
     *bytes_written = 0;

   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), G_POLLABLE_RETURN_FAILED);
   g_return_val_if_fail (vectors != NULL || n_vectors == 0, G_POLLABLE_RETURN_FAILED);
   g_return_val_if_fail (cancellable == NULL || G_IS_CANCELLABLE (cancellable), G_POLLABLE_RETURN_FAILED);
   g_return_val_if_fail (error == NULL || *error == NULL, G_POLLABLE_RETURN_FAILED);

   if (g_cancellable_set_error_if_cancelled (cancellable, error))
     return G_POLLABLE_RETURN_FAILED;

   if (n_vectors == 0)
     return G_POLLABLE_RETURN_OK;

   iface = G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream);
   g_return_val_if_fail (iface->writev_nonblocking != NULL, G_POLLABLE_RETURN_FAILED);

   if (cancellable)
     g_cancellable_push_current (cancellable);

   res = iface->
     writev_nonblocking (stream, vectors, n_vectors, &_bytes_written, error);

   if (cancellable)
     g_cancellable_pop_current (cancellable);

   if (res == G_POLLABLE_RETURN_FAILED)
     g_warn_if_fail (error == NULL || (*error != NULL && !g_error_matches (*error, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK)));
   else if (res == G_POLLABLE_RETURN_WOULD_BLOCK)
     g_warn_if_fail (error == NULL || *error == NULL);

   /* in case of not-OK nothing must've been written */
   g_warn_if_fail (res == G_POLLABLE_RETURN_OK || _bytes_written == 0);

   if (bytes_written)
     *bytes_written = _bytes_written;

   return res;
 }
	/* GIO - GLib Input, Output and Streaming Library
	*
	* Copyright (C) 2010 Red Hat, Inc.
	*
	* SPDX-License-Identifier: LGPL-2.1-or-later
	*
	* This library is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public
	* License as published by the Free Software Foundation; either
	* version 2.1 of the License, or (at your option) any later version.
	*
	* This library is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Lesser General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General
	* Public License along with this library; if not, see <http://www.gnu.org/licenses/>.
	*/

	#include "config.h"

	#include <errno.h>

	#include "gpollableoutputstream.h"
	#include "gasynchelper.h"
	#include "gfiledescriptorbased.h"
	#include "glibintl.h"

	/**
	* GPollableOutputStream:
	*
	* `GPollableOutputStream` is implemented by [class@Gio.OutputStream]s that
	* can be polled for readiness to write. This can be used when
	* interfacing with a non-GIO API that expects
	* UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.
	*
	* Some classes may implement `GPollableOutputStream` but have only certain
	* instances of that class be pollable. If [method@Gio.PollableOutputStream.can_poll]
	* returns false, then the behavior of other `GPollableOutputStream` methods is
	* undefined.
	*
	* Since: 2.28
	*/

	G_DEFINE_INTERFACE (GPollableOutputStream, g_pollable_output_stream, G_TYPE_OUTPUT_STREAM)

	static gboolean g_pollable_output_stream_default_can_poll (GPollableOutputStream *stream);
	static gssize g_pollable_output_stream_default_write_nonblocking (GPollableOutputStream *stream,
	const void *buffer,
	gsize count,
	GError **error);
	static GPollableReturn g_pollable_output_stream_default_writev_nonblocking (GPollableOutputStream *stream,
	const GOutputVector *vectors,
	gsize n_vectors,
	gsize *bytes_written,
	GError **error);

	static void
	g_pollable_output_stream_default_init (GPollableOutputStreamInterface *iface)
	{
	iface->can_poll = g_pollable_output_stream_default_can_poll;
	iface->write_nonblocking = g_pollable_output_stream_default_write_nonblocking;
	iface->writev_nonblocking = g_pollable_output_stream_default_writev_nonblocking;
	}

	static gboolean
	g_pollable_output_stream_default_can_poll (GPollableOutputStream *stream)
	{
	return TRUE;
	}

	/**
	* g_pollable_output_stream_can_poll:
	* @stream: a #GPollableOutputStream.
	*
	* Checks if @stream is actually pollable. Some classes may implement
	* #GPollableOutputStream but have only certain instances of that
	* class be pollable. If this method returns %FALSE, then the behavior
	* of other #GPollableOutputStream methods is undefined.
	*
	* For any given stream, the value returned by this method is constant;
	* a stream cannot switch from pollable to non-pollable or vice versa.
	*
	* Returns: %TRUE if @stream is pollable, %FALSE if not.
	*
	* Since: 2.28
	*/
	gboolean
	g_pollable_output_stream_can_poll (GPollableOutputStream *stream)
	{
	g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), FALSE);

	return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->can_poll (stream);
	}

	/**
	* g_pollable_output_stream_is_writable:
	* @stream: a #GPollableOutputStream.
	*
	* Checks if @stream can be written.
	*
	* Note that some stream types may not be able to implement this 100%
	* reliably, and it is possible that a call to g_output_stream_write()
	* after this returns %TRUE would still block. To guarantee
	* non-blocking behavior, you should always use
	* g_pollable_output_stream_write_nonblocking(), which will return a
	* %G_IO_ERROR_WOULD_BLOCK error rather than blocking.
	*
	* The behaviour of this method is undefined if
	* g_pollable_output_stream_can_poll() returns %FALSE for @stream.
	*
	* Returns: %TRUE if @stream is writable, %FALSE if not. If an error
	* has occurred on @stream, this will result in
	* g_pollable_output_stream_is_writable() returning %TRUE, and the
	* next attempt to write will return the error.
	*
	* Since: 2.28
	*/
	gboolean
	g_pollable_output_stream_is_writable (GPollableOutputStream *stream)
	{
	g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), FALSE);

	return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->is_writable (stream);
	}

	/**
	* g_pollable_output_stream_create_source:
	* @stream: a #GPollableOutputStream.
	* @cancellable: (nullable): a #GCancellable, or %NULL
	*
	* Creates a #GSource that triggers when @stream can be written, or
	* @cancellable is triggered or an error occurs. The callback on the
	* source is of the #GPollableSourceFunc type.
	*
	* As with g_pollable_output_stream_is_writable(), it is possible that
	* the stream may not actually be writable even after the source
	* triggers, so you should use g_pollable_output_stream_write_nonblocking()
	* rather than g_output_stream_write() from the callback.
	*
	* The behaviour of this method is undefined if
	* g_pollable_output_stream_can_poll() returns %FALSE for @stream.
	*
	* Returns: (transfer full): a new #GSource
	*
	* Since: 2.28
	*/
	GSource *
	g_pollable_output_stream_create_source (GPollableOutputStream *stream,
	GCancellable *cancellable)
	{
	g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), NULL);

	return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->
	create_source (stream, cancellable);
	}

	static gssize
	g_pollable_output_stream_default_write_nonblocking (GPollableOutputStream *stream,
	const void *buffer,
	gsize count,
	GError **error)
	{
	if (!g_pollable_output_stream_is_writable (stream))
	{
	g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK,
	g_strerror (EAGAIN));
	return -1;
	}

	return G_OUTPUT_STREAM_GET_CLASS (stream)->
	write_fn (G_OUTPUT_STREAM (stream), buffer, count, NULL, error);
	}

	static GPollableReturn
	g_pollable_output_stream_default_writev_nonblocking (GPollableOutputStream *stream,
	const GOutputVector *vectors,
	gsize n_vectors,
	gsize *bytes_written,
	GError **error)
	{
	gsize _bytes_written = 0;
	GPollableOutputStreamInterface *iface = G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream);
	gsize i;
	GError *err = NULL;

	for (i = 0; i < n_vectors; i++)
	{
	gssize res;

	/* Would we overflow here? In that case simply return and let the caller
	* handle this like a short write */
	if (_bytes_written > G_MAXSIZE - vectors[i].size)
	break;

	res = iface->write_nonblocking (stream, vectors[i].buffer, vectors[i].size, &err);
	if (res == -1)
	{
	if (bytes_written)
	*bytes_written = _bytes_written;

	/* If something was written already we handle this like a short
	* write and assume that the next call would either give the same
	* error again or successfully finish writing without errors or data
	* loss
	*/
	if (_bytes_written > 0)
	{
	g_clear_error (&err);
	return G_POLLABLE_RETURN_OK;
	}
	else if (g_error_matches (err, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK))
	{
	g_clear_error (&err);
	return G_POLLABLE_RETURN_WOULD_BLOCK;
	}
	else
	{
	g_propagate_error (error, err);
	return G_POLLABLE_RETURN_FAILED;
	}
	}

	_bytes_written += res;
	/* if we had a short write break the loop here */
	if ((gsize) res < vectors[i].size)
	break;
	}

	if (bytes_written)
	*bytes_written = _bytes_written;

	return G_POLLABLE_RETURN_OK;
	}

	/**
	* g_pollable_output_stream_write_nonblocking: (virtual write_nonblocking)
	* @stream: a #GPollableOutputStream
	* @buffer: (array length=count) (element-type guint8): a buffer to write
	* data from
	* @count: the number of bytes you want to write
	* @cancellable: (nullable): a #GCancellable, or %NULL
	* @error: #GError for error reporting, or %NULL to ignore.
	*
	* Attempts to write up to @count bytes from @buffer to @stream, as
	* with g_output_stream_write(). If @stream is not currently writable,
	* this will immediately return %G_IO_ERROR_WOULD_BLOCK, and you can
	* use g_pollable_output_stream_create_source() to create a #GSource
	* that will be triggered when @stream is writable.
	*
	* Note that since this method never blocks, you cannot actually
	* use @cancellable to cancel it. However, it will return an error
	* if @cancellable has already been cancelled when you call, which
	* may happen if you call this method after a source triggers due
	* to having been cancelled.
	*
	* Also note that if %G_IO_ERROR_WOULD_BLOCK is returned some underlying
	* transports like D/TLS require that you re-send the same @buffer and
	* @count in the next write call.
	*
	* The behaviour of this method is undefined if
	* g_pollable_output_stream_can_poll() returns %FALSE for @stream.
	*
	* Returns: the number of bytes written, or -1 on error (including
	* %G_IO_ERROR_WOULD_BLOCK).
	*/
	gssize
	g_pollable_output_stream_write_nonblocking (GPollableOutputStream *stream,
	const void *buffer,
	gsize count,
	GCancellable *cancellable,
	GError **error)
	{
	gssize res;

	g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), -1);
	g_return_val_if_fail (buffer != NULL, 0);

	if (g_cancellable_set_error_if_cancelled (cancellable, error))
	return -1;

	if (count == 0)
	return 0;

	if (((gssize) count) < 0)
	{
	g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_ARGUMENT,
	_("Too large count value passed to %s"), G_STRFUNC);
	return -1;
	}

	if (cancellable)
	g_cancellable_push_current (cancellable);

	res = G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->
	write_nonblocking (stream, buffer, count, error);

	if (cancellable)
	g_cancellable_pop_current (cancellable);

	return res;
	}

	/**
	* g_pollable_output_stream_writev_nonblocking: (virtual writev_nonblocking)
	* @stream: a #GPollableOutputStream
	* @vectors: (array length=n_vectors): the buffer containing the #GOutputVectors to write.
	* @n_vectors: the number of vectors to write
	* @bytes_written: (out) (optional): location to store the number of bytes that were
	* written to the stream
	* @cancellable: (nullable): a #GCancellable, or %NULL
	* @error: #GError for error reporting, or %NULL to ignore.
	*
	* Attempts to write the bytes contained in the @n_vectors @vectors to @stream,
	* as with g_output_stream_writev(). If @stream is not currently writable,
	* this will immediately return %@G_POLLABLE_RETURN_WOULD_BLOCK, and you can
	* use g_pollable_output_stream_create_source() to create a #GSource
	* that will be triggered when @stream is writable. @error will not be
	* set in that case.
	*
	* Note that since this method never blocks, you cannot actually
	* use @cancellable to cancel it. However, it will return an error
	* if @cancellable has already been cancelled when you call, which
	* may happen if you call this method after a source triggers due
	* to having been cancelled.
	*
	* Also note that if %G_POLLABLE_RETURN_WOULD_BLOCK is returned some underlying
	* transports like D/TLS require that you re-send the same @vectors and
	* @n_vectors in the next write call.
	*
	* The behaviour of this method is undefined if
	* g_pollable_output_stream_can_poll() returns %FALSE for @stream.
	*
	* Returns: %@G_POLLABLE_RETURN_OK on success, %G_POLLABLE_RETURN_WOULD_BLOCK
	* if the stream is not currently writable (and @error is not set), or
	* %G_POLLABLE_RETURN_FAILED if there was an error in which case @error will
	* be set.
	*
	* Since: 2.60
	*/
	GPollableReturn
	g_pollable_output_stream_writev_nonblocking (GPollableOutputStream *stream,
	const GOutputVector *vectors,
	gsize n_vectors,
	gsize *bytes_written,
	GCancellable *cancellable,
	GError **error)
	{
	GPollableOutputStreamInterface *iface;
	GPollableReturn res;
	gsize _bytes_written = 0;

	if (bytes_written)
	*bytes_written = 0;

	g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), G_POLLABLE_RETURN_FAILED);
	g_return_val_if_fail (vectors != NULL \|\| n_vectors == 0, G_POLLABLE_RETURN_FAILED);
	g_return_val_if_fail (cancellable == NULL \|\| G_IS_CANCELLABLE (cancellable), G_POLLABLE_RETURN_FAILED);
	g_return_val_if_fail (error == NULL \|\| *error == NULL, G_POLLABLE_RETURN_FAILED);

	if (g_cancellable_set_error_if_cancelled (cancellable, error))
	return G_POLLABLE_RETURN_FAILED;

	if (n_vectors == 0)
	return G_POLLABLE_RETURN_OK;

	iface = G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream);
	g_return_val_if_fail (iface->writev_nonblocking != NULL, G_POLLABLE_RETURN_FAILED);

	if (cancellable)
	g_cancellable_push_current (cancellable);

	res = iface->
	writev_nonblocking (stream, vectors, n_vectors, &_bytes_written, error);

	if (cancellable)
	g_cancellable_pop_current (cancellable);

	if (res == G_POLLABLE_RETURN_FAILED)
	g_warn_if_fail (error == NULL \|\| (error != NULL && !g_error_matches (error, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK)));
	else if (res == G_POLLABLE_RETURN_WOULD_BLOCK)
	g_warn_if_fail (error == NULL \|\| *error == NULL);

	/* in case of not-OK nothing must've been written */
	g_warn_if_fail (res == G_POLLABLE_RETURN_OK \|\| _bytes_written == 0);

	if (bytes_written)
	*bytes_written = _bytes_written;

	return res;
	}