source: trunk/third/gnome-vfs/libgnomevfs/gnome-vfs-mime-sniff-buffer.c @ 17128

/* -*- Mode: C; indent-tabs-mode: t; c-basic-offset: 8; tab-width: 8 -*- */

/*
 * gnome-vfs-mime-sniff-buffer.c
 * Utility for implementing gnome_vfs_mime_type_from_magic, and other
 * mime-type sniffing calls.
 *
 * Copyright (C) 2000 Eazel, Inc.
 * All rights reserved.
 *
 * This file is part of the Gnome Library.
 *
 * The Gnome Library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * The Gnome 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with the Gnome Library; see the file COPYING.LIB.  If not,
 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include <config.h>
#include "gnome-vfs-mime-sniff-buffer.h"

#include "gnome-vfs-handle.h"
#include "gnome-vfs-mime-sniff-buffer-private.h"
#include "gnome-vfs-ops.h"
#include <string.h>

static GnomeVFSResult
handle_seek_glue (gpointer context, GnomeVFSSeekPosition whence, 
        GnomeVFSFileOffset offset)
{
        GnomeVFSHandle *handle = (GnomeVFSHandle *)context;
        return gnome_vfs_seek (handle, whence, offset);
}

static GnomeVFSResult
handle_read_glue (gpointer context, gpointer buffer, 
        GnomeVFSFileSize bytes, GnomeVFSFileSize *bytes_read)
{
        GnomeVFSHandle *handle = (GnomeVFSHandle *)context;
        return gnome_vfs_read (handle, buffer, bytes, bytes_read);
}

GnomeVFSMimeSniffBuffer *
gnome_vfs_mime_sniff_buffer_new_from_handle (GnomeVFSHandle *file)
{
        GnomeVFSMimeSniffBuffer *result;

        result = g_new0 (GnomeVFSMimeSniffBuffer, 1);
        result->owning = TRUE;
        result->context = file;
        result->seek = handle_seek_glue;
        result->read = handle_read_glue;

        return result;
}

GnomeVFSMimeSniffBuffer *
gnome_vfs_mime_sniff_buffer_new_generic (GnomeVFSSniffBufferSeekCall seek_callback, 
                                         GnomeVFSSniffBufferReadCall read_callback,
                                         gpointer context)
{
        GnomeVFSMimeSniffBuffer * result;
        
        result = g_new0 (GnomeVFSMimeSniffBuffer, 1);

        result->owning = TRUE;
        result->seek = seek_callback;
        result->read = read_callback;
        result->context = context;

        return result;
}

GnomeVFSMimeSniffBuffer * 
gnome_vfs_mime_sniff_buffer_new_from_memory (const guchar *buffer, 
                                             gssize buffer_length)
{
        GnomeVFSMimeSniffBuffer *result;

        result = g_new0 (GnomeVFSMimeSniffBuffer, 1);
        result->owning = TRUE;
        result->buffer = g_malloc (buffer_length);
        result->buffer_length = buffer_length;
        memcpy (result->buffer, buffer, buffer_length);
        result->read_whole_file = TRUE;

        return result;
}

GnomeVFSMimeSniffBuffer *
gnome_vfs_mime_sniff_buffer_new_from_existing_data (const guchar *buffer, 
                                                    gssize buffer_length)
{
        GnomeVFSMimeSniffBuffer *result;

        result = g_new0 (GnomeVFSMimeSniffBuffer, 1);
        result->owning = FALSE;
        result->buffer = (guchar *)buffer;
        result->buffer_length = buffer_length;
        result->read_whole_file = TRUE;

        return result;
}

void
gnome_vfs_mime_sniff_buffer_free (GnomeVFSMimeSniffBuffer *buffer)
{
        if (buffer->owning)
                g_free (buffer->buffer);
        g_free (buffer);
}

enum {
        GNOME_VFS_SNIFF_BUFFER_INITIAL_CHUNK = 256,
        GNOME_VFS_SNIFF_BUFFER_MIN_CHUNK = 128
};

GnomeVFSResult
gnome_vfs_mime_sniff_buffer_get (GnomeVFSMimeSniffBuffer *buffer,
                                 gssize size)
{
        GnomeVFSResult result;
        GnomeVFSFileSize bytes_to_read, bytes_read;

        /* check to see if we already have enough data */
        if (buffer->buffer_length >= size) {
                return GNOME_VFS_OK;
        }

        /* if we've read the whole file, don't try to read any more */
        if (buffer->read_whole_file) {
                return GNOME_VFS_ERROR_EOF;
        }

        /* figure out how much to read */
        bytes_to_read = size - buffer->buffer_length;

        /* don't bother to read less than this */
        if (bytes_to_read < GNOME_VFS_SNIFF_BUFFER_MIN_CHUNK) {
                bytes_to_read = GNOME_VFS_SNIFF_BUFFER_MIN_CHUNK;
        }

        /* make room in buffer for new data */
        buffer->buffer = g_realloc (buffer->buffer,
                                    buffer->buffer_length + bytes_to_read);

        /* read in more data */
        result = (* buffer->read) (buffer->context, 
                                   buffer->buffer + buffer->buffer_length,
                                   bytes_to_read,
                                   &bytes_read);
        if (result == GNOME_VFS_ERROR_EOF) {
                /* only happens with 0-byte files, due to other logic */
                buffer->read_whole_file = TRUE;
        }
        if (result != GNOME_VFS_OK) {
                return result;
        }
        if (bytes_read < bytes_to_read) {
                buffer->read_whole_file = TRUE;
        }
        buffer->buffer_length += bytes_read;

        /* check to see if we have enough data */
        if (buffer->buffer_length >= size) {
                return GNOME_VFS_OK;
        }

        /* not enough data */
        return GNOME_VFS_ERROR_EOF;
}