1/*
2 * GIF parser
3 * Copyright (c) 2018 Paul B Mahol
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22/**
23 * @file
24 * GIF parser
25 */
26
27#include "libavutil/bswap.h"
28#include "libavutil/common.h"
29
30#include "gif.h"
31#include "parser.h"
32
33typedef enum GIFParseStates {
34    GIF_HEADER = 1,
35    GIF_EXTENSION,
36    GIF_EXTENSION_BLOCK,
37    GIF_IMAGE,
38    GIF_IMAGE_BLOCK,
39} gif_states;
40
41typedef struct GIFParseContext {
42    ParseContext pc;
43    unsigned found_sig;
44    int found_start;
45    int found_end;
46    int index;
47    int state;
48    int gct_flag;
49    int gct_size;
50    int block_size;
51    int etype;
52    int delay;
53} GIFParseContext;
54
55static int gif_find_frame_end(GIFParseContext *g, const uint8_t *buf,
56                              int buf_size, void *logctx)
57{
58    int index, next = END_NOT_FOUND;
59
60    for (index = 0; index < buf_size; index++) {
61        if (!g->state) {
62            if (!memcmp(buf + index, gif87a_sig, 6) ||
63                !memcmp(buf + index, gif89a_sig, 6)) {
64                g->state = GIF_HEADER;
65                g->found_sig++;
66            } else if (buf[index] == GIF_EXTENSION_INTRODUCER) {
67                g->state = GIF_EXTENSION;
68                g->found_start = 1;
69            } else if (buf[index] == GIF_IMAGE_SEPARATOR) {
70                g->state = GIF_IMAGE;
71            } else if (buf[index] == GIF_TRAILER) {
72                g->state = 0;
73                g->found_end = 1;
74                g->found_sig = 0;
75            } else {
76                g->found_sig = 0;
77            }
78        }
79
80        if (g->state == GIF_HEADER) {
81            if (g->index == 10) {
82                g->gct_flag = !!(buf[index] & 0x80);
83                g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
84            }
85            if (g->index >= 12 + g->gct_flag * g->gct_size) {
86                g->state = 0;
87                g->index = 0;
88                g->gct_flag = 0;
89                g->gct_size = 0;
90                continue;
91            }
92            g->index++;
93        } else if (g->state == GIF_EXTENSION) {
94            if (g->found_start && g->found_end && g->found_sig) {
95                next = index;
96                g->found_start = 0;
97                g->found_end = 0;
98                g->index = 0;
99                g->gct_flag = 0;
100                g->gct_size = 0;
101                g->state = 0;
102                break;
103            }
104            if (g->index == 1) {
105                g->etype = buf[index];
106            }
107            if (g->index >= 2) {
108                g->block_size = buf[index];
109                g->index = 0;
110                g->state = GIF_EXTENSION_BLOCK;
111                continue;
112            }
113            g->index++;
114        } else if (g->state == GIF_IMAGE_BLOCK) {
115            if (!g->index)
116                g->block_size = buf[index];
117            if (g->index >= g->block_size) {
118                g->index = 0;
119                if (!g->block_size) {
120                    g->state = 0;
121                    g->found_end = 1;
122                }
123                continue;
124            }
125            g->index++;
126        } else if (g->state == GIF_EXTENSION_BLOCK) {
127            if (g->etype == GIF_GCE_EXT_LABEL) {
128                if (g->index == 0)
129                    g->delay = 0;
130                if (g->index >= 1 && g->index <= 2) {
131                    g->delay |= buf[index] << (8 * (g->index - 1));
132                }
133            }
134            if (g->index >= g->block_size) {
135                g->block_size = buf[index];
136                g->index = 0;
137                if (!g->block_size)
138                    g->state = 0;
139                continue;
140            }
141            g->index++;
142        } else if (g->state == GIF_IMAGE) {
143            if (g->index == 8) {
144                g->gct_flag = !!(buf[index] & 0x80);
145                g->gct_size = 3 * (1 << ((buf[index] & 0x07) + 1));
146            }
147            if (g->index >= 10 + g->gct_flag * g->gct_size) {
148                g->state = GIF_IMAGE_BLOCK;
149                g->index = 0;
150                g->gct_flag = 0;
151                g->gct_size = 0;
152                continue;
153            }
154            g->index++;
155        }
156    }
157
158    return next;
159}
160
161static int gif_parse(AVCodecParserContext *s, AVCodecContext *avctx,
162                     const uint8_t **poutbuf, int *poutbuf_size,
163                     const uint8_t *buf, int buf_size)
164{
165    GIFParseContext *g = s->priv_data;
166    int next;
167
168    next = gif_find_frame_end(g, buf, buf_size, avctx);
169    if (ff_combine_frame(&g->pc, next, &buf, &buf_size) < 0) {
170        *poutbuf      = NULL;
171        *poutbuf_size = 0;
172        return buf_size;
173    }
174
175    s->duration   = g->delay;
176
177    *poutbuf      = buf;
178    *poutbuf_size = buf_size;
179    return next;
180}
181
182const AVCodecParser ff_gif_parser = {
183    .codec_ids      = { AV_CODEC_ID_GIF },
184    .priv_data_size = sizeof(GIFParseContext),
185    .parser_parse   = gif_parse,
186    .parser_close   = ff_parse_close,
187};
188