/* 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 * 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 #include #include #include #ifdef NEED_SNPRINTF_H # include "snprintf.h" #endif #include /* 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, " "); } /* 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, "")); 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); }