/* 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 */ #define NEW_PROTO_TREE_API #include "config.h" #include #include #include void proto_register_gif(void); void proto_reg_handoff_gif(void); #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_87a = 0x87, GIF_89a = 0x89 }; static dissector_handle_t gif_handle; /* Protocol and registered fields */ static header_field_info *hfi_gif = NULL; #define GIF_HFI_INIT HFI_INIT(proto_gif) /* header fields */ /* GIF signature */ static header_field_info hfi_version GIF_HFI_INIT = { "Version", IMG_GIF ".version", FT_STRING, BASE_NONE, NULL, 0x00, "GIF Version", HFILL }; /* Screen descriptor */ static header_field_info hfi_screen_width GIF_HFI_INIT = { "Screen width", IMG_GIF ".screen.width", FT_UINT16, BASE_DEC, NULL, 0x00, NULL, HFILL }; static header_field_info hfi_screen_height GIF_HFI_INIT = { "Screen height", IMG_GIF ".screen.height", FT_UINT16, BASE_DEC, NULL, 0x00, NULL, HFILL }; static header_field_info hfi_global_color_map_present GIF_HFI_INIT = { "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 }; static header_field_info hfi_global_color_resolution GIF_HFI_INIT = { "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 }; static header_field_info hfi_global_color_map_ordered/* GIF89a */ GIF_HFI_INIT = { "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 }; static header_field_info hfi_global_image_bpp GIF_HFI_INIT = { "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 }; /* Only makes sense if the global color map is present: */ static header_field_info hfi_background_color GIF_HFI_INIT = { "Background color index", IMG_GIF ".image_background_index", FT_UINT8, BASE_DEC, NULL, 0x00, "Index of the background color in the color map.", HFILL }; static header_field_info hfi_pixel_aspect_ratio/* GIF89a */ GIF_HFI_INIT = { "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 }; static header_field_info hfi_global_color_map GIF_HFI_INIT = { "Global color map", IMG_GIF ".global.color_map", FT_BYTES, BASE_NONE, NULL, 0x00, "Global color map.", HFILL }; /* Image descriptor */ static header_field_info hfi_image_left GIF_HFI_INIT = { "Image left position", IMG_GIF ".image.left", FT_UINT16, BASE_DEC, NULL, 0x00, "Offset between left of Screen and left of Image.", HFILL }; static header_field_info hfi_image_top GIF_HFI_INIT = { "Image top position", IMG_GIF ".image.top", FT_UINT16, BASE_DEC, NULL, 0x00, "Offset between top of Screen and top of Image.", HFILL }; static header_field_info hfi_image_width GIF_HFI_INIT = { "Image width", IMG_GIF ".image.width", FT_UINT16, BASE_DEC, NULL, 0x00, "Image width.", HFILL }; static header_field_info hfi_image_height GIF_HFI_INIT = { "Image height", IMG_GIF ".image.height", FT_UINT16, BASE_DEC, NULL, 0x00, "Image height.", HFILL }; static header_field_info hfi_local_color_map_present GIF_HFI_INIT = { "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 }; static header_field_info hfi_local_color_resolution GIF_HFI_INIT = { "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 }; static header_field_info hfi_local_color_map_ordered/* GIF89a */ GIF_HFI_INIT = { "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 }; #if 0 static header_field_info hfi_local_image_bpp GIF_HFI_INIT = { "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 }; #endif static header_field_info hfi_local_color_map GIF_HFI_INIT = { "Local color map", IMG_GIF ".local.color_map", FT_BYTES, BASE_NONE, NULL, 0x00, "Local color map.", HFILL }; /* Extension */ static header_field_info hfi_extension GIF_HFI_INIT = { "Extension", IMG_GIF ".extension", FT_NONE, BASE_NONE, NULL, 0x00, "Extension.", HFILL }; static header_field_info hfi_extension_label GIF_HFI_INIT = { "Extension label", IMG_GIF ".extension.label", FT_UINT8, BASE_HEX, VALS(vals_extensions), 0x00, "Extension label.", HFILL }; static header_field_info hfi_image GIF_HFI_INIT = { "Image", IMG_GIF ".image", FT_NONE, BASE_NONE, NULL, 0x00, "Image.", HFILL }; static header_field_info hfi_image_code_size GIF_HFI_INIT = { "LZW minimum code size", IMG_GIF ".image.code_size", FT_UINT8, BASE_DEC, NULL, 0x00, "Minimum code size for the LZW compression.", HFILL }; /* Trailer (end of GIF data stream) */ static header_field_info hfi_trailer GIF_HFI_INIT = { "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 }; static header_field_info hfi_data_block GIF_HFI_INIT = { "Data block", IMG_GIF ".data_block", FT_UINT_BYTES, BASE_NONE|BASE_ALLOW_ZERO, NULL, 0x00, NULL, HFILL }; /* 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; static expert_field ei_gif_unknown_data_block_type = EI_INIT; /****************** GIF protocol dissection functions ******************/ static gint dissect_gif_data_block_seq(tvbuff_t *tvb, gint offset, proto_tree *tree) { gint offset_start = offset; guint8 len; proto_item *db_ti; do { /* Read length of data block */ len = tvb_get_guint8(tvb, offset); db_ti = proto_tree_add_item(tree, &hfi_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 gint 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; guint offset = 0, len = 0; guint8 peek; gboolean color_map_present; guint8 color_resolution; guint8 image_bpp; const guint8 *ver_str; guint8 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, hfi_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, hfi_version.id, tvb, offset, 6, ENC_ASCII|ENC_NA, wmem_packet_scope(), &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, &hfi_screen_width, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(gif_tree, &hfi_screen_height, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; peek = tvb_get_guint8(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, &hfi_global_color_map_present, tvb, offset, 1, ENC_LITTLE_ENDIAN); proto_tree_add_item(subtree, &hfi_global_color_resolution, tvb, offset, 1, ENC_LITTLE_ENDIAN); if (version == GIF_89a) { proto_tree_add_item(subtree, &hfi_global_color_map_ordered, tvb, offset, 1, ENC_LITTLE_ENDIAN); } proto_tree_add_item(subtree, &hfi_global_image_bpp, tvb, offset, 1, ENC_LITTLE_ENDIAN); offset++; /* Background color */ proto_tree_add_item(gif_tree, &hfi_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_guint8(tvb, offset); if (peek) { /* Only display if different from 0 */ proto_tree_add_uint_format(gif_tree, hfi_pixel_aspect_ratio.id, 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) { len = 3 * (1 << image_bpp); proto_tree_add_item(gif_tree, &hfi_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)) { gint ret; gint offset_start = offset; peek = tvb_get_guint8(tvb, offset); if (peek == 0x21) { /* GIF extension block */ ti = proto_tree_add_item(gif_tree, &hfi_extension, tvb, offset, 1, ENC_NA); subtree = proto_item_add_subtree(ti, ett_extension); offset++; proto_tree_add_item(subtree, &hfi_extension_label, tvb, offset, 1, ENC_LITTLE_ENDIAN); peek = tvb_get_guint8(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, &hfi_image, tvb, offset, 1, ENC_NA); subtree = proto_item_add_subtree(ti, ett_image); offset++; /* Screen descriptor */ proto_tree_add_item(subtree, &hfi_image_left, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(subtree, &hfi_image_top, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(subtree, &hfi_image_width, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2; proto_tree_add_item(subtree, &hfi_image_height, tvb, offset, 2, ENC_LITTLE_ENDIAN); 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); 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, &hfi_local_color_map_present, tvb, offset, 1, ENC_LITTLE_ENDIAN); proto_tree_add_item(subtree2, &hfi_local_color_resolution, tvb, offset, 1, ENC_LITTLE_ENDIAN); if (version == GIF_89a) { proto_tree_add_item(subtree2, &hfi_local_color_map_ordered, tvb, offset, 1, ENC_LITTLE_ENDIAN); } proto_tree_add_item(subtree2, &hfi_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) { len = 3 * (1 << image_bpp); proto_tree_add_item(subtree, &hfi_local_color_map, tvb, offset, len, ENC_NA); offset += len; } proto_tree_add_item(subtree, &hfi_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, &hfi_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 gboolean dissect_gif_heur(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void *data _U_) { return dissect_gif(tvb, pinfo, tree, NULL) > 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) { #ifndef HAVE_HFI_SECTION_INIT /* * Setup list of header fields. */ static header_field_info *hfi[] = { /* * GIF signature and version */ &hfi_version, /* * Logical screen descriptor */ &hfi_screen_width, &hfi_screen_height, &hfi_global_color_map_present, &hfi_global_color_resolution, &hfi_global_color_map_ordered, &hfi_global_image_bpp, &hfi_background_color, &hfi_pixel_aspect_ratio, &hfi_global_color_map, /* * Local color map (part of image) */ &hfi_local_color_map_present, &hfi_local_color_resolution, &hfi_local_color_map_ordered, /* &hfi_local_image_bpp, */ &hfi_local_color_map, /* * Extension */ &hfi_extension, &hfi_extension_label, /* * Image */ &hfi_image, &hfi_image_left, &hfi_image_top, &hfi_image_width, &hfi_image_height, &hfi_image_code_size, /* * Trailer */ &hfi_trailer, &hfi_data_block }; #endif /* Setup protocol subtree array */ static gint *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 } } }; int proto_gif; expert_module_t* expert_gif; /* Register the protocol name and description */ proto_gif = proto_register_protocol( "Compuserve GIF", "GIF image", IMG_GIF ); hfi_gif = proto_registrar_get_nth(proto_gif); /* Required function calls to register the header fields * and subtrees used */ proto_register_fields(proto_gif, hfi, array_length(hfi)); 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(IMG_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", hfi_gif->id, HEURISTIC_ENABLE); heur_dissector_add("wtap_file", dissect_gif_heur, "GIF file", "gif_wtap", hfi_gif->id, HEURISTIC_ENABLE); } /* * Editor modelines - http://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: */