gpollableutils: utility functions for pollable stream implementations

Move g_pollable_source_new() here from gpollableinputstream.c, add
g_pollable_source_new_full(), and add some new methods to do either
blocking or nonblocking reads depending on a boolean argument.

https://bugzilla.gnome.org/show_bug.cgi?id=673997

gio/gpollableutils.h

@@ -0,0 +1,65 @@
+/* GIO - GLib Input, Output and Streaming Library
+ *
+ * Copyright (C) 2012 Red Hat, Inc.
+ *
+ * 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 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, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#if !defined (__GIO_GIO_H_INSIDE__) && !defined (GIO_COMPILATION)
+#error "Only <gio/gio.h> can be included directly."
+#endif
+
+#ifndef __G_POLLABLE_UTILS_H__
+#define __G_POLLABLE_UTILS_H__
+
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+GSource *g_pollable_source_new       (GObject        *pollable_stream);
+
+GLIB_AVAILABLE_IN_2_34
+GSource *g_pollable_source_new_full  (gpointer        pollable_stream,
+				      GSource        *child_source,
+				      GCancellable   *cancellable);
+
+GLIB_AVAILABLE_IN_2_34
+gssize   g_pollable_stream_read      (GInputStream   *stream,
+				      void           *buffer,
+				      gsize           count,
+				      gboolean        blocking,
+				      GCancellable   *cancellable,
+				      GError        **error);
+
+GLIB_AVAILABLE_IN_2_34
+gssize   g_pollable_stream_write     (GOutputStream  *stream,
+				      const void     *buffer,
+				      gsize           count,
+				      gboolean        blocking,
+				      GCancellable   *cancellable,
+				      GError        **error);
+GLIB_AVAILABLE_IN_2_34
+gboolean g_pollable_stream_write_all (GOutputStream  *stream,
+				      const void     *buffer,
+				      gsize           count,
+				      gboolean        blocking,
+				      gsize          *bytes_written,
+				      GCancellable   *cancellable,
+				      GError        **error);
+
+G_END_DECLS
+
+#endif /* _G_POLLABLE_UTILS_H_ */