libavformat/subfile.c

   1 /*
   2  * Copyright (c) 2014 Nicolas George
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public License
   8  * as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * FFmpeg is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with FFmpeg; if not, write to the Free Software Foundation, Inc.,
  18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #include "libavutil/avassert.h"
  22 #include "libavutil/avstring.h"
  23 #include "libavutil/opt.h"
  24 #include "avformat.h"
  25 #include "url.h"
  26
  27 typedef struct SubfileContext {
  28     const AVClass *class;
  29     URLContext *h;
  30     int64_t start;
  31     int64_t end;
  32     int64_t pos;
  33 } SubfileContext;
  34
  35 #define OFFSET(field) offsetof(SubfileContext, field)
  36 #define D AV_OPT_FLAG_DECODING_PARAM
  37
  38 static const AVOption subfile_options[] = {
  39     { "start", "start offset", OFFSET(start), AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX, D },
  40     { "end",   "end offset",   OFFSET(end),   AV_OPT_TYPE_INT64, {.i64 = 0}, 0, INT64_MAX, D },
  41     { NULL }
  42 };
  43
  44 #undef OFFSET
  45 #undef D
  46
  47 static const AVClass subfile_class = {
  48     .class_name = "subfile",
  49     .item_name  = av_default_item_name,
  50     .option     = subfile_options,
  51     .version    = LIBAVUTIL_VERSION_INT,
  52 };
  53
  54 static int slave_seek(URLContext *h)
  55 {
  56     SubfileContext *c = h->priv_data;
  57     int64_t ret;
  58
  59     if ((ret = ffurl_seek(c->h, c->pos, SEEK_SET)) != c->pos) {
  60         if (ret >= 0)
  61             ret = AVERROR_BUG;
  62         av_log(h, AV_LOG_ERROR, "Impossible to seek in file: %s\n",
  63                av_err2str(ret));
  64         return ret;
  65     }
  66     return 0;
  67 }
  68
  69 static int subfile_open(URLContext *h, const char *filename, int flags,
  70                         AVDictionary **options)
  71 {
  72     SubfileContext *c = h->priv_data;
  73     int ret;
  74
  75     if (!c->end)
  76         c->end = INT64_MAX;
  77
  78     if (c->end <= c->start) {
  79         av_log(h, AV_LOG_ERROR, "end before start\n");
  80         return AVERROR(EINVAL);
  81     }
  82     av_strstart(filename, "subfile:", &filename);
  83     ret = ffurl_open_whitelist(&c->h, filename, flags, &h->interrupt_callback,
  84                                options, h->protocol_whitelist, h->protocol_blacklist, h);
  85     if (ret < 0)
  86         return ret;
  87     c->pos = c->start;
  88     if ((ret = slave_seek(h)) < 0) {
  89         ffurl_closep(&c->h);
  90         return ret;
  91     }
  92     return 0;
  93 }
  94
  95 static int subfile_close(URLContext *h)
  96 {
  97     SubfileContext *c = h->priv_data;
  98     return ffurl_closep(&c->h);
  99 }
 100
 101 static int subfile_read(URLContext *h, unsigned char *buf, int size)
 102 {
 103     SubfileContext *c = h->priv_data;
 104     int64_t rest = c->end - c->pos;
 105     int ret;
 106
 107     if (rest <= 0)
 108         return AVERROR_EOF;
 109     size = FFMIN(size, rest);
 110     ret = ffurl_read(c->h, buf, size);
 111     if (ret >= 0)
 112         c->pos += ret;
 113     return ret;
 114 }
 115
 116 static int64_t subfile_seek(URLContext *h, int64_t pos, int whence)
 117 {
 118     SubfileContext *c = h->priv_data;
 119     int64_t new_pos, end;
 120     int ret;
 121
 122     if (whence == AVSEEK_SIZE || whence == SEEK_END) {
 123         end = c->end;
 124         if (end == INT64_MAX && (end = ffurl_seek(c->h, 0, AVSEEK_SIZE)) < 0)
 125             return end;
 126     }
 127
 128     switch (whence) {
 129     case AVSEEK_SIZE:
 130         return end - c->start;
 131     case SEEK_SET:
 132         new_pos = c->start + pos;
 133         break;
 134     case SEEK_CUR:
 135         new_pos = c->pos + pos;
 136         break;
 137     case SEEK_END:
 138         new_pos = end + pos;
 139         break;
 140     default:
 141         av_assert0(0);
 142     }
 143     if (new_pos < c->start)
 144         return AVERROR(EINVAL);
 145     c->pos = new_pos;
 146     if ((ret = slave_seek(h)) < 0)
 147         return ret;
 148     return c->pos - c->start;
 149 }
 150
 151 const URLProtocol ff_subfile_protocol = {
 152     .name                = "subfile",
 153     .url_open2           = subfile_open,
 154     .url_read            = subfile_read,
 155     .url_seek            = subfile_seek,
 156     .url_close           = subfile_close,
 157     .priv_data_size      = sizeof(SubfileContext),
 158     .priv_data_class     = &subfile_class,
 159     .default_whitelist   = "file",
 160 };