/* file-gif.c * * Routines for image/gif media dissection * Copyright 2003, 2004, Olivier Biot. * * Refer to the AUTHORS file or the AUTHORS section in the man page * for contacting the author(s) of this file. * * Wireshark - 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 * * SPDX-License-Identifier: GPL-2.0-or-later */ #include "config.h" #include #include #include void proto_register_gif(void); void proto_reg_handoff_gif(void); /************************** 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_87a = 0x87, GIF_89a = 0x89 }; static dissector_handle_t gif_handle; static int proto_gif; static int hf_background_color; static int hf_data_block; static int hf_extension; static int hf_extension_label; static int hf_global_color_map; static int hf_global_color_map_ordered; static int hf_global_color_map_present; static int hf_global_color_resolution; static int hf_global_image_bpp; static int hf_image; static int hf_image_code_size; static int hf_image_height; static int hf_image_left; static int hf_image_top; static int hf_image_width; static int hf_local_color_map; static int hf_local_color_map_ordered; static int hf_local_color_map_present; static int hf_local_color_resolution; static int hf_local_image_bpp; static int hf_pixel_aspect_ratio; static int hf_screen_height; static int hf_screen_width; static int hf_trailer; static int hf_version; /* Initialize the subtree pointers */ static int ett_gif; static int ett_global_flags; static int ett_local_flags; static int ett_extension; static int ett_image; static expert_field ei_gif_unknown_data_block_type; /****************** GIF protocol dissection functions ******************/ static int dissect_gif_data_block_seq(tvbuff_t *tvb, int offset, proto_tree *tree) { int offset_start = offset; uint8_t len; proto_item *db_ti; do { /* Read length of data block */ len = tvb_get_uint8(tvb, offset); db_ti = proto_tree_add_item(tree, hf_data_block, tvb, offset, 1, ENC_NA); proto_item_append_text(db_ti, " (length = %u)", len); offset += (1 + len); } while (len > 0); return offset - offset_start; } /* 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 int dissect_gif(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_) { proto_item *ti; proto_tree *gif_tree; /* Main GIF tree */ proto_tree *subtree; unsigned offset = 0; uint8_t peek; bool color_map_present; uint8_t color_resolution; uint8_t image_bpp; const uint8_t *ver_str; uint8_t version; if (tvb_reported_length(tvb) < 20) return 0; /* Check whether we're processing a GIF object */ /* see http://www.w3.org/Graphics/GIF/spec-gif89a.txt section 17 */ if (tvb_strneql(tvb, 0, "GIF87a", 6) == 0) { version = GIF_87a; } else if (tvb_strneql(tvb, 0, "GIF89a", 6) == 0) { version = GIF_89a; } else { /* Not a GIF image! */ return 0; } ti = proto_tree_add_item(tree, proto_gif, tvb, offset, -1, ENC_NA); gif_tree = proto_item_add_subtree(ti, ett_gif); /* GIF signature */ proto_tree_add_item_ret_string(gif_tree, hf_version, tvb, offset, 6, ENC_ASCII|ENC_NA, pinfo->pool, &ver_str); proto_item_append_text(ti, ", Version: %s", ver_str); col_append_fstr(pinfo->cinfo, COL_INFO, " (%s)", ver_str); offset += 6; /* Screen descriptor */ proto_tree_add_item(gif_tree, hf_screen_width, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(gif_tree, hf_screen_height, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; peek = tvb_get_uint8(tvb, offset); /* 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); subtree = proto_tree_add_subtree(gif_tree, tvb, offset, 1, ett_global_flags, &ti, "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, plurality(color_resolution, "", "s"), image_bpp, plurality(image_bpp, "", "s")); proto_tree_add_item(subtree, hf_global_color_map_present, tvb, offset, 1, ENC_LITTLE_ENDIAN); proto_tree_add_item(subtree, hf_global_color_resolution, tvb, offset, 1, ENC_LITTLE_ENDIAN); if (version == GIF_89a) { proto_tree_add_item(subtree, hf_global_color_map_ordered, tvb, offset, 1, ENC_LITTLE_ENDIAN); } proto_tree_add_item(subtree, hf_global_image_bpp, tvb, offset, 1, ENC_LITTLE_ENDIAN); offset++; /* Background color */ proto_tree_add_item(gif_tree, hf_background_color, tvb, offset, 1, ENC_LITTLE_ENDIAN); offset++; /* 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_uint8(tvb, offset); if (peek) { /* Only display if different from 0 */ proto_tree_add_uint_format(gif_tree, hf_pixel_aspect_ratio, tvb, offset, 1, peek, "%u, yields an aspect ratio of (15 + %u) / 64 = %.2f", peek, peek, (float)(15 + peek) / 64.0); } } offset++; /* 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) { unsigned len; len = 3 * (1 << image_bpp); proto_tree_add_item(gif_tree, hf_global_color_map, tvb, offset, len, ENC_NA); offset += 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 0x3B * (';') 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 (tvb_reported_length_remaining(tvb, offset)) { int ret; int offset_start = offset; peek = tvb_get_uint8(tvb, offset); if (peek == 0x21) { /* GIF extension block */ ti = proto_tree_add_item(gif_tree, hf_extension, tvb, offset, 1, ENC_NA); subtree = proto_item_add_subtree(ti, ett_extension); offset++; proto_tree_add_item(subtree, hf_extension_label, tvb, offset, 1, ENC_LITTLE_ENDIAN); peek = tvb_get_uint8(tvb, offset); proto_item_append_text(ti, ": %s", val_to_str(peek, vals_extensions, "")); offset++; ret = dissect_gif_data_block_seq(tvb, offset, subtree); if (ret <= 0) break; offset += ret; } else if (peek == 0x2C) { /* Image separator */ proto_tree *subtree2; proto_item *ti2; ti = proto_tree_add_item(gif_tree, hf_image, tvb, offset, 1, ENC_NA); subtree = proto_item_add_subtree(ti, ett_image); offset++; /* Screen descriptor */ proto_tree_add_item(subtree, hf_image_left, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(subtree, hf_image_top, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(subtree, hf_image_width, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(subtree, hf_image_height, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; /* bit field */ peek = tvb_get_uint8(tvb, offset); color_map_present = peek & 0x80; color_resolution = 1 + ((peek & 0x60) >> 4); image_bpp = 1 + (peek & 0x07); subtree2 = proto_tree_add_subtree(subtree, tvb, offset, 1, ett_local_flags, &ti2, "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, plurality(color_resolution, "", "s"), image_bpp, plurality(image_bpp, "", "s")); proto_tree_add_item(subtree2, hf_local_color_map_present, tvb, offset, 1, ENC_LITTLE_ENDIAN); proto_tree_add_item(subtree2, hf_local_color_resolution, tvb, offset, 1, ENC_LITTLE_ENDIAN); if (version == GIF_89a) { proto_tree_add_item(subtree2, hf_local_color_map_ordered, tvb, offset, 1, ENC_LITTLE_ENDIAN); } proto_tree_add_item(subtree2, hf_global_image_bpp, tvb, offset, 1, ENC_LITTLE_ENDIAN); 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) { unsigned len; len = 3 * (1 << image_bpp); proto_tree_add_item(subtree, hf_local_color_map, tvb, offset, len, ENC_NA); offset += len; } proto_tree_add_item(subtree, hf_image_code_size, tvb, offset, 1, ENC_LITTLE_ENDIAN); offset++; ret = dissect_gif_data_block_seq(tvb, offset, subtree); if (ret <= 0) break; offset += ret; } else if (peek == 0x3B) { /* Trailer byte */ /* GIF processing stops at this very byte */ proto_tree_add_item(gif_tree, hf_trailer, tvb, offset, 1, ENC_NA); offset++; break; } else { proto_tree_add_expert(gif_tree, pinfo, &ei_gif_unknown_data_block_type, tvb, offset, 1); offset++; } proto_item_set_len(ti, offset-offset_start); } /* while */ return offset; } static bool dissect_gif_heur(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data) { return dissect_gif(tvb, pinfo, tree, data) > 0; } /****************** Register the protocol with Wireshark ******************/ /* This format is required because a script is used to build the C function * that calls the protocol registration. */ void proto_register_gif(void) { static hf_register_info hf[] = { { &hf_version, { "Version", "image-gif.version", FT_STRING, BASE_NONE, NULL, 0x00, "GIF Version", HFILL } }, { &hf_screen_width, { "Screen width", "image-gif.screen.width", FT_UINT16, BASE_DEC, NULL, 0x00, NULL, HFILL } }, { &hf_screen_height, { "Screen height", "image-gif.screen.height", FT_UINT16, BASE_DEC, NULL, 0x00, NULL, HFILL } }, { &hf_global_color_map_present, { "Global color map is present", "image-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", "image-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", "image-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", "image-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", "image-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", "image-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", "image-gif.global.color_map", FT_BYTES, BASE_NONE, NULL, 0x00, "Global color map.", HFILL } }, { &hf_image_left, { "Image left position", "image-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", "image-gif.image.top", FT_UINT16, BASE_DEC, NULL, 0x00, "Offset between top of Screen and top of Image.", HFILL } }, { &hf_image_width, { "Image width", "image-gif.image.width", FT_UINT16, BASE_DEC, NULL, 0x00, "Image width.", HFILL } }, { &hf_image_height, { "Image height", "image-gif.image.height", FT_UINT16, BASE_DEC, NULL, 0x00, "Image height.", HFILL } }, { &hf_local_color_map_present, { "Local color map is present", "image-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", "image-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", "image-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", "image-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", "image-gif.local.color_map", FT_BYTES, BASE_NONE, NULL, 0x00, "Local color map.", HFILL } }, { &hf_extension, { "Extension", "image-gif.extension", FT_NONE, BASE_NONE, NULL, 0x00, "Extension.", HFILL } }, { &hf_extension_label, { "Extension label", "image-gif.extension.label", FT_UINT8, BASE_HEX, VALS(vals_extensions), 0x00, "Extension label.", HFILL } }, { &hf_image, { "Image", "image-gif.image", FT_NONE, BASE_NONE, NULL, 0x00, "Image.", HFILL } }, { &hf_image_code_size, { "LZW minimum code size", "image-gif.image.code_size", FT_UINT8, BASE_DEC, NULL, 0x00, "Minimum code size for the LZW compression.", HFILL } }, { &hf_trailer, { "Trailer (End of the GIF stream)", "image-gif.end", FT_NONE, BASE_NONE, NULL, 0x00, "This byte tells the decoder that the data stream is finished.", HFILL } }, { &hf_data_block, { "Data block", "image-gif.data_block", FT_UINT_BYTES, BASE_NONE|BASE_ALLOW_ZERO, NULL, 0x00, NULL, HFILL } }, }; /* Setup protocol subtree array */ static int *ett[] = { &ett_gif, &ett_global_flags, &ett_local_flags, &ett_extension, &ett_image, }; static ei_register_info ei[] = { { &ei_gif_unknown_data_block_type, { "gif.data_block_type.unknown", PI_PROTOCOL, PI_WARN, "Unknown GIF data block type", EXPFILL } } }; expert_module_t* expert_gif; /* Register the protocol name and description */ proto_gif = proto_register_protocol( "Compuserve GIF", "GIF image", "image-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)); expert_gif = expert_register_protocol(proto_gif); expert_register_field_array(expert_gif, ei, array_length(ei)); gif_handle = register_dissector("image-gif", dissect_gif, proto_gif); } void proto_reg_handoff_gif(void) { /* Register the GIF media type */ dissector_add_string("media_type", "image/gif", gif_handle); heur_dissector_add("http", dissect_gif_heur, "GIF file in HTTP", "gif_http", proto_gif, HEURISTIC_ENABLE); heur_dissector_add("wtap_file", dissect_gif_heur, "GIF file", "gif_wtap", proto_gif, HEURISTIC_ENABLE); } /* * Editor modelines - https://www.wireshark.org/tools/modelines.html * * Local variables: * c-basic-offset: 4 * tab-width: 8 * indent-tabs-mode: nil * End: * * vi: set shiftwidth=4 tabstop=8 expandtab: * :indentSize=4:tabSize=8:noTabs=true: */