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wireshark/packet-image-gif.c

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/* packet-image-gif.c
*
* Routines for image/gif media dissection
* Copyright 2003, 2004, Olivier Biot.
*
* $Id: packet-image-gif.c,v 1.4 2004/03/08 22:03:58 obiot Exp $
*
* Refer to the AUTHORS file or the AUTHORS section in the man page
* for contacting the author(s) of this file.
*
* Ethereal - Network traffic analyzer
* By Gerald Combs <gerald@ethereal.com>
* Copyright 1998 Gerald Combs
*
* Compuserve GIF media decoding functionality provided by Olivier Biot.
*
* The two GIF specifications are found at several locations, such as W3C:
* http://www.w3.org/Graphics/GIF/spec-gif87.txt
* http://www.w3.org/Graphics/GIF/spec-gif89a.txt
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*/
/* Edit this file with 4-space tabulation */
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <glib.h>
#ifdef NEED_SNPRINTF_H
# include "snprintf.h"
#endif
#include <epan/packet.h>
/* General-purpose debug logger.
* Requires double parentheses because of variable arguments of printf().
*
* Enable debug logging for GIF by defining AM_CFLAGS
* so that it contains "-DDEBUG_image_gif" or "-DDEBUG_image"
*/
#if (defined(DEBUG_image_gif) || defined(DEBUG_image))
#define DebugLog(x) \
printf("%s:%u: ", __FILE__, __LINE__); \
printf x; \
fflush(stdout)
#else
#define DebugLog(x) ;
#endif
#define PLURALIZE(x) ((x) == 1 ? "" : "s")
#define IMG_GIF "image-gif"
/************************** Variable declarations **************************/
static const value_string vals_true_false[] = {
{ 0, "False" },
{ 1, "True" },
{ 0, NULL },
};
static const value_string vals_extensions[] = {
{ 0xF9, "Graphics Control" },
{ 0xFE, "Comment" },
{ 0xFF, "Application" },
{ 0x01, "Plain Text" },
{ 0x00, NULL, },
};
enum {
GIF_UNKNOWN = 0,
GIF_87a = 0x87,
GIF_89a = 0x89,
GIF_ERROR = 0xFF
};
/* Initialize the protocol and registered fields */
static int proto_gif = -1;
/* header fields */
/* GIF signature */
static gint hf_version = -1;
/* Screen descriptor */
static gint hf_screen_width = -1;
static gint hf_screen_height = -1;
static gint hf_global_color_map_present = -1;
static gint hf_global_color_resolution = -1;
static gint hf_global_color_map_ordered = -1; /* GIF89a */
static gint hf_global_image_bpp = -1;
/* Only makes sense if the global color map is present: */
static gint hf_background_color = -1;
static gint hf_pixel_aspect_ratio = -1; /* GIF89a */
static gint hf_global_color_map = -1;
/* Image descriptor */
static gint hf_image_left = -1;
static gint hf_image_top = -1;
static gint hf_image_width = -1;
static gint hf_image_height = -1;
static gint hf_local_color_map_present = -1;
static gint hf_local_color_resolution = -1;
static gint hf_local_color_map_ordered = -1; /* GIF89a */
static gint hf_local_image_bpp = -1;
static gint hf_local_color_map = -1;
static gint hf_extension = -1;
static gint hf_extension_label = -1;
static gint hf_image = -1;
static gint hf_image_code_size = -1;
/* Trailer (end of GIF data stream) */
static gint hf_trailer = -1;
/* Initialize the subtree pointers */
static gint ett_gif = -1;
static gint ett_global_flags = -1;
static gint ett_local_flags = -1;
static gint ett_extension = -1;
static gint ett_image = -1;
/**************** GIF related declarations and definitions ****************/
/************************** Function prototypes **************************/
static void
dissect_gif(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree);
void
proto_register_gif(void);
/****************** GIF protocol dissection functions ******************/
/* There are two Compuserve GIF standards: GIF87a and GIF89a. GIF image files
* always convey their version in the first 6 bytes, written as an US-ASCII
* string representation of the version: "GIF87a" or "GIF89a".
*/
static void
dissect_gif(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree)
{
proto_item *ti;
proto_tree *gif_tree; /* Main GIF tree */
proto_tree *subtree; /* Main GIF tree */
guint offset = 0, len = 0;
guint8 peek;
gboolean color_map_present;
guint8 color_resolution;
guint8 image_bpp;
guint tvb_len = tvb_reported_length(tvb);
char *str = tvb_get_string(tvb, 0, 6);
guint8 version;
/* Check whether we're processing a GIF object */
if (strcmp(str, "GIF87a") == 0) {
version = GIF_87a;
} else if (strcmp(str, "GIF89a") == 0) {
version = GIF_89a;
} else if (strncmp(str,"GIF", 3) == 0) {
version = GIF_UNKNOWN;
} else {
/* Not a GIF image! */
version = GIF_ERROR;
g_free(str);
return;
}
/* Add summary to INFO column if it is enabled */
if (check_col(pinfo->cinfo, COL_INFO))
col_append_fstr(pinfo->cinfo, COL_INFO, " (%s)", str);
/* In order to speed up dissection, do not add items to the protocol tree
* if it is not visible. However, compute the values that are needed for
* correct protocol dissection if they have more meaning than just adding
* items to the protocol tree.
*/
if (tree) {
ti = proto_tree_add_item(tree, proto_gif, tvb, 0, -1, TRUE);
proto_item_append_text(ti, ", Version: %s", str);
g_free(str);
gif_tree = proto_item_add_subtree(ti, ett_gif);
/* GIF signature */
ti = proto_tree_add_item(gif_tree, hf_version, tvb, 0, 6, TRUE);
if (version == GIF_UNKNOWN) {
proto_item_append_text(ti, " <Error: unknown GIF version>");
}
/* Screen descriptor */
proto_tree_add_item(gif_tree, hf_screen_width, tvb, 6, 2, TRUE);
proto_tree_add_item(gif_tree, hf_screen_height, tvb, 8, 2, TRUE);
peek = tvb_get_guint8(tvb, 10);
/* Bitfield gccc 0ppp
* g... .... : global color map present
* .ccc .... : color resolution in bits (add one)
* .... 0... : GIF87a - reserved (no use)
* GIF89a - ordered (most important color 1st)
* .... .ppp : bits per pixel in image (add one)
*/
color_map_present = peek & 0x80;
color_resolution = 1 + ((peek & 0x60) >> 4);
image_bpp = 1 + (peek & 0x07);
ti = proto_tree_add_text(gif_tree, tvb, 10, 1,
"Global settings:");
if (color_map_present)
proto_item_append_text(ti, " (Global color table present)");
proto_item_append_text(ti,
" (%u bit%s per color) (%u bit%s per pixel)",
color_resolution, PLURALIZE(color_resolution),
image_bpp, PLURALIZE(image_bpp));
subtree = proto_item_add_subtree(ti, ett_global_flags);
proto_tree_add_item(subtree, hf_global_color_map_present,
tvb, 10, 1, TRUE);
proto_tree_add_item(subtree, hf_global_color_resolution,
tvb, 10, 1, TRUE);
if (version == GIF_89a) {
proto_tree_add_item(subtree, hf_global_color_map_ordered,
tvb, 10, 1, TRUE);
}
proto_tree_add_item(subtree, hf_global_image_bpp,
tvb, 10, 1, TRUE);
/* Background color */
proto_tree_add_item(gif_tree, hf_background_color,
tvb, 11, 1, TRUE);
/* byte at offset 12 is 0x00 - reserved in GIF87a but encodes the
* pixel aspect ratio in GIF89a as:
* aspect-ratio = (15 + pixel-aspect-ratio) / 64
* where the aspect-ratio is not computed if pixel-aspect-ratio == 0
*/
if (version == GIF_89a) {
peek = tvb_get_guint8(tvb, 12);
if (peek) {
/* Only display if different from 0 */
proto_tree_add_uint_format(gif_tree, hf_pixel_aspect_ratio,
tvb, 12, 1, peek,
"%u, yields an aspect ratio of (15 + %u) / 64 = %.2f",
peek, peek, (float)(15 + peek) / 64.0);
}
}
/* Global color map
* If present, it takes 2 ^ (image_bpp) byte tuples (R, G, B)
* that contain the Red, Green and Blue intensity of the colors
* in the Global Color Map */
if (color_map_present) {
len = 3 * (1 << image_bpp);
proto_tree_add_item(gif_tree, hf_global_color_map,
tvb, 13, len, TRUE);
} else {
len = 0;
}
offset = 13 + len;
/* From now on, a set of images prefixed with the image separator
* character 0x2C (',') will appear in the byte stream. Each image
* hence consists of:
* - The image separator character 0x2C
* - Image left (16 bits LSB first): pixels from left border
* - Image top (16 bits LSB first): pixels from to border
* - Image width (16 bits LSB first)
* - Image height (16 bits LSB first)
* - A bitfield MI00 0ppp
* M... .... : Use global color map if unset (ignore ppp);
* if set a local color map will be defined.
* .I.. .... : Image formatted in interlaced order if set;
* otherwise it is plain sequential order
* ..0. .... : GIF87a - Reserved
* ..s. .... GIF89a - Set if local color map is ordered
* ...0 0... : Reserved
* .... .ppp : bits per pixel in image (add one)
* - If the local color map bit is set, then a local color table follows
* with length = 3 x 2 ^ (1 + bits per pixel)
* - The raster data
*
* NOTE that the GIF specification only requires that:
* image left + image width <= screen width
* image top + image height <= screen height
*
* The Raster Data is encoded as follows:
* - Code size (1 byte)
* - Blocks consisting of
* o Byte count (1 byte): number of bytes in the block
* o Data bytes: as many as specified in the byte count
* End of data is given with an empty block (byte count == 0).
*
*
* GIF terminator
* This is a synchronization method, based on the final character 0xB3
* (';') at the end of an image
*
*
* GIF extension
* This is a block of data encoded as:
* - The GIF extension block introducer 0x21 ('!')
* - The extension function code (1 byte)
* - Blocks consisting of
* o Byte count (1 byte): number of bytes in the block
* o Data bytes: as many as specified in the byte count
* End of data is given with an empty block (byte count == 0).
*
* NOTE that the GIF extension block can only appear at the following
* locations:
* - Immediately before an Image Descriptor
* - Before the GIF termination character
*/
while (offset < tvb_len) {
peek = tvb_get_guint8(tvb, offset);
if (peek == 0x21) { /* GIF extension block */
guint32 item_len = 2; /* Fixed header consisting of:
* 1 byte : 0x21
* 1 byte : extension_label
*/
ti = proto_tree_add_item(gif_tree, hf_extension,
tvb, offset, 1, TRUE);
subtree = proto_item_add_subtree(ti, ett_extension);
offset++;
proto_tree_add_item(subtree, hf_extension_label,
tvb, offset, 1, TRUE);
peek = tvb_get_guint8(tvb, offset);
proto_item_append_text(ti, ": %s",
val_to_str(peek, vals_extensions,
"<Warning: Unknown extension 0x%02X>"));
offset++;
do {
/* Read length of data block */
len = tvb_get_guint8(tvb, offset);
proto_tree_add_text(subtree, tvb,
offset, 1 + len,
"Data block (length = %u)", len);
offset += (1 + len);
item_len += (1 + len);
} while (len > 0);
proto_item_set_len(ti, item_len);
} else if (peek == 0x2C) { /* Image separator */
proto_tree *subtree2;
proto_item *ti2;
guint32 item_len = 11; /* Fixed header consisting of:
* 1 byte : 0x2C
* 2 bytes: image_left
* 2 bytes: image_top
* 2 bytes: image_width
* 2 bytes: image height
* 1 byte : packed bit field
* 1 byte : image code size
*/
ti = proto_tree_add_item(gif_tree, hf_image,
tvb, offset, 1, TRUE);
subtree = proto_item_add_subtree(ti, ett_image);
offset++;
/* Screen descriptor */
proto_tree_add_item(subtree, hf_image_left,
tvb, offset, 2, TRUE); offset += 2;
proto_tree_add_item(subtree, hf_image_top,
tvb, offset, 2, TRUE); offset += 2;
proto_tree_add_item(subtree, hf_image_width,
tvb, offset, 2, TRUE); offset += 2;
proto_tree_add_item(subtree, hf_image_height,
tvb, offset, 2, TRUE); offset += 2;
/* bit field */
peek = tvb_get_guint8(tvb, offset);
color_map_present = peek & 0x80;
color_resolution = 1 + ((peek & 0x60) >> 4);
image_bpp = 1 + (peek & 0x07);
ti2 = proto_tree_add_text(subtree, tvb, offset, 1,
"Local settings:");
if (color_map_present)
proto_item_append_text(ti2, " (Local color table present)");
proto_item_append_text(ti2,
" (%u bit%s per color) (%u bit%s per pixel)",
color_resolution, PLURALIZE(color_resolution),
image_bpp, PLURALIZE(image_bpp));
subtree2 = proto_item_add_subtree(ti2, ett_local_flags);
proto_tree_add_item(subtree2, hf_local_color_map_present,
tvb, offset, 1, TRUE);
proto_tree_add_item(subtree2, hf_local_color_resolution,
tvb, offset, 1, TRUE);
if (version == GIF_89a) {
proto_tree_add_item(subtree2, hf_local_color_map_ordered,
tvb, offset, 1, TRUE);
}
proto_tree_add_item(subtree2, hf_global_image_bpp,
tvb, offset, 1, TRUE);
offset++;
/* Local color map
* If present, it takes 2 ^ (image_bpp) byte tuples (R, G, B)
* that contain the Red, Green and Blue intensity of the colors
* in the Local Color Map */
if (color_map_present) {
len = 3 * (1 << image_bpp);
proto_tree_add_item(subtree, hf_local_color_map,
tvb, offset, len, TRUE);
} else {
len = 0;
}
offset += len;
item_len += len;
proto_tree_add_item(subtree, hf_image_code_size,
tvb, offset, 1, TRUE);
offset++;
do {
/* Read length of data block */
len = tvb_get_guint8(tvb, offset);
proto_tree_add_text(subtree, tvb,
offset, 1 + len,
"Data block (length = %u)", len);
offset += 1 + len;
item_len += (1 + len);
} while (len > 0);
proto_item_set_len(ti, item_len);
} else {
/* GIF processing stops at this very byte */
proto_tree_add_item(gif_tree, hf_trailer,
tvb, offset, 1, TRUE);
break;
}
} /* while */
}
}
/****************** Register the protocol with Ethereal ******************/
/* This format is required because a script is used to build the C function
* that calls the protocol registration. */
void
proto_register_gif(void)
{
/*
* Setup list of header fields.
*/
static hf_register_info hf[] = {
/*
* GIF signature and version
*/
{ &hf_version,
{ "Version",
IMG_GIF ".version",
FT_STRING, BASE_NONE, NULL, 0x00,
"GIF Version",
HFILL
}
},
/*
* Logical screen descriptor
*/
{ &hf_screen_width,
{ "Screen width",
IMG_GIF ".screen.width",
FT_UINT16, BASE_DEC, NULL, 0x00,
"Screen width",
HFILL
}
},
{ &hf_screen_height,
{ "Screen height",
IMG_GIF ".screen.height",
FT_UINT16, BASE_DEC, NULL, 0x00,
"Screen height",
HFILL
}
},
{ &hf_global_color_map_present,
{ "Global color map is present",
IMG_GIF ".global.color_map.present",
FT_UINT8, BASE_DEC, VALS(vals_true_false), 0x80,
"Indicates if the global color map is present",
HFILL
}
},
{ &hf_global_color_resolution,
{ "Bits per color minus 1",
IMG_GIF ".global.color_bpp",
FT_UINT8, BASE_DEC, NULL, 0x70,
"The number of bits per color is one plus the field value.",
HFILL
}
},
{ &hf_global_color_map_ordered,
{ "Global color map is ordered",
IMG_GIF ".global.color_map.ordered",
FT_UINT8, BASE_DEC, VALS(vals_true_false), 0x08,
"Indicates whether the global color map is ordered.",
HFILL
}
},
{ &hf_global_image_bpp,
{ "Image bits per pixel minus 1",
IMG_GIF ".global.bpp",
FT_UINT8, BASE_DEC, NULL, 0x07,
"The number of bits per pixel is one plus the field value.",
HFILL
}
},
{ &hf_background_color,
{ "Background color index",
IMG_GIF ".image_background_index",
FT_UINT8, BASE_DEC, NULL, 0x00,
"Index of the background color in the color map.",
HFILL
}
},
{ &hf_pixel_aspect_ratio,
{ "Global pixel aspect ratio",
IMG_GIF ".global.pixel_aspect_ratio",
FT_UINT8, BASE_DEC, NULL, 0x00,
"Gives an approximate value of the aspect ratio of the pixels.",
HFILL
}
},
{ &hf_global_color_map,
{ "Global color map",
IMG_GIF ".global.color_map",
FT_BYTES, BASE_NONE, NULL, 0x00,
"Global color map.",
HFILL
}
},
/*
* Local color map (part of image)
*/
{ &hf_local_color_map_present,
{ "Local color map is present",
IMG_GIF ".local.color_map.present",
FT_UINT8, BASE_DEC, VALS(vals_true_false), 0x80,
"Indicates if the local color map is present",
HFILL
}
},
{ &hf_local_color_resolution,
{ "Bits per color minus 1",
IMG_GIF ".local.color_bpp",
FT_UINT8, BASE_DEC, NULL, 0x70,
"The number of bits per color is one plus the field value.",
HFILL
}
},
{ &hf_local_color_map_ordered,
{ "Local color map is ordered",
IMG_GIF ".local.color_map.ordered",
FT_UINT8, BASE_DEC, VALS(vals_true_false), 0x08,
"Indicates whether the local color map is ordered.",
HFILL
}
},
{ &hf_local_image_bpp,
{ "Image bits per pixel minus 1",
IMG_GIF ".local.bpp",
FT_UINT8, BASE_DEC, NULL, 0x07,
"The number of bits per pixel is one plus the field value.",
HFILL
}
},
{ &hf_local_color_map,
{ "Local color map",
IMG_GIF ".local.color_map",
FT_BYTES, BASE_NONE, NULL, 0x00,
"Local color map.",
HFILL
}
},
/*
* Extension
*/
{ &hf_extension,
{ "Extension",
IMG_GIF ".extension",
FT_NONE, BASE_NONE, NULL, 0x00,
"Extension.",
HFILL
}
},
{ &hf_extension_label,
{ "Extension label",
IMG_GIF ".extension.label",
FT_UINT8, BASE_HEX, VALS(vals_extensions), 0x00,
"Extension label.",
HFILL
}
},
/*
* Image
*/
{ &hf_image,
{ "Image",
IMG_GIF ".image",
FT_NONE, BASE_NONE, NULL, 0x80,
"Image.",
HFILL
}
},
{ &hf_image_left,
{ "Image left position",
IMG_GIF ".image.left",
FT_UINT16, BASE_DEC, NULL, 0x00,
"Offset between left of Screen and left of Image.",
HFILL
}
},
{ &hf_image_top,
{ "Image top position",
IMG_GIF ".image.top",
FT_UINT16, BASE_DEC, NULL, 0x00,
"Offset between top of Screen and top of Image.",
HFILL
}
},
{ &hf_image_width,
{ "Image width",
IMG_GIF ".image.width",
FT_UINT16, BASE_DEC, NULL, 0x00,
"Image width.",
HFILL
}
},
{ &hf_image_height,
{ "Image height",
IMG_GIF ".image.height",
FT_UINT16, BASE_DEC, NULL, 0x00,
"Image height.",
HFILL
}
},
{ &hf_image_code_size,
{ "LZW minimum code size",
IMG_GIF ".image.code_size",
FT_UINT8, BASE_DEC, NULL, 0x00,
"Minimum code size for the LZW compression.",
HFILL
}
},
/*
* Trailer
*/
{ &hf_trailer,
{ "Trailer (End of the GIF stream)",
IMG_GIF ".end",
FT_NONE, BASE_NONE, NULL, 0x00,
"This byte tells the decoder that the data stream is finished.",
HFILL
}
},
};
/* Setup protocol subtree array */
static gint *ett[] = {
&ett_gif,
&ett_global_flags,
&ett_local_flags,
&ett_extension,
&ett_image,
};
/* Register the protocol name and description */
proto_gif = proto_register_protocol(
"Compuserve GIF",
"GIF image",
IMG_GIF
);
/* Required function calls to register the header fields
* and subtrees used */
proto_register_field_array(proto_gif, hf, array_length(hf));
proto_register_subtree_array(ett, array_length(ett));
register_dissector("image-gif", dissect_gif, proto_gif);
}
void
proto_reg_handoff_gif(void)
{
dissector_handle_t gif_handle;
gif_handle = create_dissector_handle(dissect_gif, proto_gif);
/* Register the GIF media type */
dissector_add_string("media_type", "image/gif", gif_handle);
}
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