gio/gpollableoutputstream.c

   1 /* GIO - GLib Input, Output and Streaming Library
   2  *
   3  * Copyright (C) 2010 Red Hat, Inc.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General
  16  * Public License along with this library; if not, write to the
  17  * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  18  * Boston, MA 02111-1307, USA.
  19  */
  20
  21 #include "config.h"
  22
  23 #include <errno.h>
  24
  25 #include "gpollableoutputstream.h"
  26 #include "gasynchelper.h"
  27 #include "gfiledescriptorbased.h"
  28 #include "glibintl.h"
  29
  30 /**
  31  * SECTION:gpollableoutputstream
  32  * @short_description: Interface for pollable output streams
  33  * @include: gio/gio.h
  34  * @see_also: #GOutputStream, #GFileDescriptorBased, #GPollableInputStream
  35  *
  36  * #GPollableOutputStream is implemented by #GOutputStream<!-- -->s that
  37  * can be polled for readiness to write. This can be used when
  38  * interfacing with a non-GIO API that expects
  39  * UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.
  40  *
  41  * Since: 2.28
  42  */
  43
  44 G_DEFINE_INTERFACE (GPollableOutputStream, g_pollable_output_stream, G_TYPE_OUTPUT_STREAM)
  45
  46 static gboolean g_pollable_output_stream_default_can_poll          (GPollableOutputStream *stream);
  47 static gssize   g_pollable_output_stream_default_write_nonblocking (GPollableOutputStream  *stream,
  48                                                                     const void             *buffer,
  49                                                                     gsize                   size,
  50                                                                     GError                **error);
  51
  52 static void
  53 g_pollable_output_stream_default_init (GPollableOutputStreamInterface *iface)
  54 {
  55   iface->can_poll          = g_pollable_output_stream_default_can_poll;
  56   iface->write_nonblocking = g_pollable_output_stream_default_write_nonblocking;
  57 }
  58
  59 static gboolean
  60 g_pollable_output_stream_default_can_poll (GPollableOutputStream *stream)
  61 {
  62   return TRUE;
  63 }
  64
  65 /**
  66  * g_pollable_output_stream_can_poll:
  67  * @stream: a #GPollableOutputStream.
  68  *
  69  * Checks if @stream is actually pollable. Some classes may implement
  70  * #GPollableOutputStream but have only certain instances of that
  71  * class be pollable. If this method returns %FALSE, then the behavior
  72  * of other #GPollableOutputStream methods is undefined.
  73  *
  74  * For any given stream, the value returned by this method is constant;
  75  * a stream cannot switch from pollable to non-pollable or vice versa.
  76  *
  77  * Returns: %TRUE if @stream is pollable, %FALSE if not.
  78  *
  79  * Since: 2.28
  80  */
  81 gboolean
  82 g_pollable_output_stream_can_poll (GPollableOutputStream *stream)
  83 {
  84   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), FALSE);
  85
  86   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->can_poll (stream);
  87 }
  88
  89 /**
  90  * g_pollable_output_stream_is_writable:
  91  * @stream: a #GPollableOutputStream.
  92  *
  93  * Checks if @stream can be written.
  94  *
  95  * Note that some stream types may not be able to implement this 100%
  96  * reliably, and it is possible that a call to g_output_stream_write()
  97  * after this returns %TRUE would still block. To guarantee
  98  * non-blocking behavior, you should always use
  99  * g_pollable_output_stream_write_nonblocking(), which will return a
 100  * %G_IO_ERROR_WOULD_BLOCK error rather than blocking.
 101  *
 102  * Returns: %TRUE if @stream is writable, %FALSE if not. If an error
 103  *   has occurred on @stream, this will result in
 104  *   g_pollable_output_stream_is_writable() returning %TRUE, and the
 105  *   next attempt to write will return the error.
 106  *
 107  * Since: 2.28
 108  */
 109 gboolean
 110 g_pollable_output_stream_is_writable (GPollableOutputStream *stream)
 111 {
 112   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), FALSE);
 113
 114   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->is_writable (stream);
 115 }
 116
 117 /**
 118  * g_pollable_output_stream_create_source:
 119  * @stream: a #GPollableOutputStream.
 120  * @cancellable: (allow-none): a #GCancellable, or %NULL
 121  *
 122  * Creates a #GSource that triggers when @stream can be written, or
 123  * @cancellable is triggered or an error occurs. The callback on the
 124  * source is of the #GPollableSourceFunc type.
 125  *
 126  * As with g_pollable_output_stream_is_writable(), it is possible that
 127  * the stream may not actually be writable even after the source
 128  * triggers, so you should use g_pollable_output_stream_write_nonblocking()
 129  * rather than g_output_stream_write() from the callback.
 130  *
 131  * Returns: (transfer full): a new #GSource
 132  *
 133  * Since: 2.28
 134  */
 135 GSource *
 136 g_pollable_output_stream_create_source (GPollableOutputStream *stream,
 137                                         GCancellable          *cancellable)
 138 {
 139   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), NULL);
 140
 141   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->
 142           create_source (stream, cancellable);
 143 }
 144
 145 static gssize
 146 g_pollable_output_stream_default_write_nonblocking (GPollableOutputStream  *stream,
 147                                                     const void             *buffer,
 148                                                     gsize                   size,
 149                                                     GError                **error)
 150 {
 151   if (!g_pollable_output_stream_is_writable (stream))
 152     {
 153       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK,
 154                            g_strerror (EAGAIN));
 155       return -1;
 156     }
 157
 158   return g_output_stream_write (G_OUTPUT_STREAM (stream), buffer, size,
 159                                 NULL, error);
 160 }
 161
 162 /**
 163  * g_pollable_output_stream_write_nonblocking:
 164  * @stream: a #GPollableOutputStream
 165  * @buffer: (array length=size) (element-type guint8): a buffer to write
 166  *     data from
 167  * @size: the number of bytes you want to write
 168  * @cancellable: (allow-none): a #GCancellable, or %NULL
 169  * @error: #GError for error reporting, or %NULL to ignore.
 170  *
 171  * Attempts to write up to @size bytes from @buffer to @stream, as
 172  * with g_output_stream_write(). If @stream is not currently writable,
 173  * this will immediately return %G_IO_ERROR_WOULD_BLOCK, and you can
 174  * use g_pollable_output_stream_create_source() to create a #GSource
 175  * that will be triggered when @stream is writable.
 176  *
 177  * Note that since this method never blocks, you cannot actually
 178  * use @cancellable to cancel it. However, it will return an error
 179  * if @cancellable has already been cancelled when you call, which
 180  * may happen if you call this method after a source triggers due
 181  * to having been cancelled.
 182  *
 183  * Virtual: write_nonblocking
 184  * Return value: the number of bytes written, or -1 on error (including
 185  *   %G_IO_ERROR_WOULD_BLOCK).
 186  */
 187 gssize
 188 g_pollable_output_stream_write_nonblocking (GPollableOutputStream  *stream,
 189                                             const void             *buffer,
 190                                             gsize                   size,
 191                                             GCancellable           *cancellable,
 192                                             GError                **error)
 193 {
 194   g_return_val_if_fail (G_IS_POLLABLE_OUTPUT_STREAM (stream), -1);
 195
 196   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 197     return -1;
 198
 199   return G_POLLABLE_OUTPUT_STREAM_GET_INTERFACE (stream)->
 200     write_nonblocking (stream, buffer, size, error);
 201 }