gio/gpollableinputstream.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 "gpollableinputstream.h"
  26 #include "gasynchelper.h"
  27 #include "glibintl.h"
  28
  29 /**
  30  * SECTION:gpollableinputstream
  31  * @short_description: Interface for pollable input streams
  32  * @include: gio/gio.h
  33  * @see_also: #GInputStream, #GPollableOutputStream, #GFileDescriptorBased
  34  *
  35  * #GPollableInputStream is implemented by #GInputStreams that
  36  * can be polled for readiness to read. This can be used when
  37  * interfacing with a non-GIO API that expects
  38  * UNIX-file-descriptor-style asynchronous I/O rather than GIO-style.
  39  *
  40  * Since: 2.28
  41  */
  42
  43 G_DEFINE_INTERFACE (GPollableInputStream, g_pollable_input_stream, G_TYPE_INPUT_STREAM)
  44
  45 static gboolean g_pollable_input_stream_default_can_poll         (GPollableInputStream *stream);
  46 static gssize   g_pollable_input_stream_default_read_nonblocking (GPollableInputStream  *stream,
  47                                                                   void                  *buffer,
  48                                                                   gsize                  count,
  49                                                                   GError               **error);
  50
  51 static void
  52 g_pollable_input_stream_default_init (GPollableInputStreamInterface *iface)
  53 {
  54   iface->can_poll         = g_pollable_input_stream_default_can_poll;
  55   iface->read_nonblocking = g_pollable_input_stream_default_read_nonblocking;
  56 }
  57
  58 static gboolean
  59 g_pollable_input_stream_default_can_poll (GPollableInputStream *stream)
  60 {
  61   return TRUE;
  62 }
  63
  64 /**
  65  * g_pollable_input_stream_can_poll:
  66  * @stream: a #GPollableInputStream.
  67  *
  68  * Checks if @stream is actually pollable. Some classes may implement
  69  * #GPollableInputStream but have only certain instances of that class
  70  * be pollable. If this method returns %FALSE, then the behavior of
  71  * other #GPollableInputStream methods is undefined.
  72  *
  73  * For any given stream, the value returned by this method is constant;
  74  * a stream cannot switch from pollable to non-pollable or vice versa.
  75  *
  76  * Returns: %TRUE if @stream is pollable, %FALSE if not.
  77  *
  78  * Since: 2.28
  79  */
  80 gboolean
  81 g_pollable_input_stream_can_poll (GPollableInputStream *stream)
  82 {
  83   g_return_val_if_fail (G_IS_POLLABLE_INPUT_STREAM (stream), FALSE);
  84
  85   return G_POLLABLE_INPUT_STREAM_GET_INTERFACE (stream)->can_poll (stream);
  86 }
  87
  88 /**
  89  * g_pollable_input_stream_is_readable:
  90  * @stream: a #GPollableInputStream.
  91  *
  92  * Checks if @stream can be read.
  93  *
  94  * Note that some stream types may not be able to implement this 100%
  95  * reliably, and it is possible that a call to g_input_stream_read()
  96  * after this returns %TRUE would still block. To guarantee
  97  * non-blocking behavior, you should always use
  98  * g_pollable_input_stream_read_nonblocking(), which will return a
  99  * %G_IO_ERROR_WOULD_BLOCK error rather than blocking.
 100  *
 101  * Returns: %TRUE if @stream is readable, %FALSE if not. If an error
 102  *   has occurred on @stream, this will result in
 103  *   g_pollable_input_stream_is_readable() returning %TRUE, and the
 104  *   next attempt to read will return the error.
 105  *
 106  * Since: 2.28
 107  */
 108 gboolean
 109 g_pollable_input_stream_is_readable (GPollableInputStream *stream)
 110 {
 111   g_return_val_if_fail (G_IS_POLLABLE_INPUT_STREAM (stream), FALSE);
 112
 113   return G_POLLABLE_INPUT_STREAM_GET_INTERFACE (stream)->is_readable (stream);
 114 }
 115
 116 /**
 117  * g_pollable_input_stream_create_source:
 118  * @stream: a #GPollableInputStream.
 119  * @cancellable: (allow-none): a #GCancellable, or %NULL
 120  *
 121  * Creates a #GSource that triggers when @stream can be read, or
 122  * @cancellable is triggered or an error occurs. The callback on the
 123  * source is of the #GPollableSourceFunc type.
 124  *
 125  * As with g_pollable_input_stream_is_readable(), it is possible that
 126  * the stream may not actually be readable even after the source
 127  * triggers, so you should use g_pollable_input_stream_read_nonblocking()
 128  * rather than g_input_stream_read() from the callback.
 129  *
 130  * Returns: (transfer full): a new #GSource
 131  *
 132  * Since: 2.28
 133  */
 134 GSource *
 135 g_pollable_input_stream_create_source (GPollableInputStream *stream,
 136                                        GCancellable         *cancellable)
 137 {
 138   g_return_val_if_fail (G_IS_POLLABLE_INPUT_STREAM (stream), NULL);
 139
 140   return G_POLLABLE_INPUT_STREAM_GET_INTERFACE (stream)->
 141           create_source (stream, cancellable);
 142 }
 143
 144 static gssize
 145 g_pollable_input_stream_default_read_nonblocking (GPollableInputStream  *stream,
 146                                                   void                  *buffer,
 147                                                   gsize                  count,
 148                                                   GError               **error)
 149 {
 150   if (!g_pollable_input_stream_is_readable (stream))
 151     {
 152       g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_WOULD_BLOCK,
 153                            g_strerror (EAGAIN));
 154       return -1;
 155     }
 156
 157   return G_INPUT_STREAM_GET_CLASS (stream)->
 158     read_fn (G_INPUT_STREAM (stream), buffer, count, NULL, error);
 159 }
 160
 161 /**
 162  * g_pollable_input_stream_read_nonblocking:
 163  * @stream: a #GPollableInputStream
 164  * @buffer: a buffer to read data into (which should be at least @count
 165  *     bytes long).
 166  * @count: the number of bytes you want to read
 167  * @cancellable: (allow-none): a #GCancellable, or %NULL
 168  * @error: #GError for error reporting, or %NULL to ignore.
 169  *
 170  * Attempts to read up to @count bytes from @stream into @buffer, as
 171  * with g_input_stream_read(). If @stream is not currently readable,
 172  * this will immediately return %G_IO_ERROR_WOULD_BLOCK, and you can
 173  * use g_pollable_input_stream_create_source() to create a #GSource
 174  * that will be triggered when @stream is readable.
 175  *
 176  * Note that since this method never blocks, you cannot actually
 177  * use @cancellable to cancel it. However, it will return an error
 178  * if @cancellable has already been cancelled when you call, which
 179  * may happen if you call this method after a source triggers due
 180  * to having been cancelled.
 181  *
 182  * Virtual: read_nonblocking
 183  * Return value: the number of bytes read, or -1 on error (including
 184  *   %G_IO_ERROR_WOULD_BLOCK).
 185  */
 186 gssize
 187 g_pollable_input_stream_read_nonblocking (GPollableInputStream  *stream,
 188                                           void                  *buffer,
 189                                           gsize                  count,
 190                                           GCancellable          *cancellable,
 191                                           GError               **error)
 192 {
 193   gssize res;
 194
 195   g_return_val_if_fail (G_IS_POLLABLE_INPUT_STREAM (stream), -1);
 196   g_return_val_if_fail (buffer != NULL, 0);
 197
 198   if (g_cancellable_set_error_if_cancelled (cancellable, error))
 199     return -1;
 200
 201   if (count == 0)
 202     return 0;
 203
 204   if (((gssize) count) < 0)
 205     {
 206       g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_ARGUMENT,
 207                    _("Too large count value passed to %s"), G_STRFUNC);
 208       return -1;
 209     }
 210
 211   if (cancellable)
 212     g_cancellable_push_current (cancellable);
 213
 214   res = G_POLLABLE_INPUT_STREAM_GET_INTERFACE (stream)->
 215     read_nonblocking (stream, buffer, count, error);
 216
 217   if (cancellable)
 218     g_cancellable_pop_current (cancellable);
 219
 220   return res;
 221 }