demux: subtitle: dont break non-seekable streams

modules/demux/Makefile.am

@@ -56,7 +56,7 @@ demux_LTLIBRARIES += libaiff_plugin.la
 libmjpeg_plugin_la_SOURCES = demux/mjpeg.c demux/mxpeg_helper.h
 demux_LTLIBRARIES += libmjpeg_plugin.la
 
-libsubtitle_plugin_la_SOURCES = demux/subtitle.c
+libsubtitle_plugin_la_SOURCES = demux/subtitle.c demux/subtitle_helper.h
 libsubtitle_plugin_la_LIBADD = $(LIBM)
 demux_LTLIBRARIES += libsubtitle_plugin.la
 
@@ -64,7 +64,8 @@ libty_plugin_la_SOURCES = demux/ty.c codec/cc.h
 demux_LTLIBRARIES += libty_plugin.la
 
 libvobsub_plugin_la_SOURCES = demux/vobsub.c demux/vobsub.h \
-                              demux/mpeg/ps.h demux/mpeg/pes.h
+                              demux/mpeg/ps.h demux/mpeg/pes.h \
+                              demux/subtitle_helper.h
 demux_LTLIBRARIES += libvobsub_plugin.la
 
 libvoc_plugin_la_SOURCES = demux/voc.c

modules/demux/subtitle.c

@@ -38,10 +38,13 @@
 
 #include <ctype.h>
 #include <math.h>
+#include <assert.h>
 
 #include <vlc_demux.h>
 #include <vlc_charset.h>
 
+#include "subtitle_helper.h"
+
 /*****************************************************************************
  * Module descriptor
  *****************************************************************************/
@@ -299,6 +302,11 @@ static int Open ( vlc_object_t *p_this )
     }
     free( psz_type );
 
+#ifndef NDEBUG
+    const uint64_t i_start_pos = stream_Tell( p_demux->s );
+#endif
+    uint64_t i_read_offset = 0;
+
     /* Detect Unicode while skipping the UTF-8 Byte Order Mark */
     bool unicode = false;
     const uint8_t *p_data;
@@ -306,7 +314,7 @@ static int Open ( vlc_object_t *p_this )
      && !memcmp( p_data, "\xEF\xBB\xBF", 3 ) )
     {
         unicode = true;
-        stream_Seek( p_demux->s, 3 ); /* skip BOM */
+        i_read_offset = 3; /* skip BOM */
         msg_Dbg( p_demux, "detected Unicode Byte Order Mark" );
     }
 
@@ -322,7 +330,7 @@ static int Open ( vlc_object_t *p_this )
             int i_dummy;
             char p_dummy;
 
-            if( ( s = stream_ReadLine( p_demux->s ) ) == NULL )
+            if( (s = peek_Readline( p_demux->s, &i_read_offset )) == NULL )
                 break;
 
             if( strcasestr( s, "<SAMI>" ) )
@@ -474,17 +482,15 @@ static int Open ( vlc_object_t *p_this )
         }
 
         free( s );
-
-        /* It will nearly always work even for non seekable stream thanks the
-         * caching system, and if it fails we lose just a few sub */
-        if( stream_Seek( p_demux->s, unicode ? 3 : 0 ) )
-            msg_Warn( p_demux, "failed to rewind" );
     }
 
     /* Quit on unknown subtitles */
     if( p_sys->i_type == SUB_TYPE_UNKNOWN )
     {
-        stream_Seek( p_demux->s, 0 );
+#ifndef NDEBUG
+        /* Ensure it will work with non seekable streams */
+        assert( i_start_pos == stream_Tell( p_demux->s ) );
+#endif
         msg_Warn( p_demux, "failed to recognize subtitle type" );
         free( p_sys );
         return VLC_EGENERIC;
@@ -503,6 +509,9 @@ static int Open ( vlc_object_t *p_this )
 
     msg_Dbg( p_demux, "loading all subtitles..." );
 
+    if( unicode ) /* skip BOM */
+        stream_Seek( p_demux->s, 3 );
+
     /* Load the whole file */
     TextLoad( &p_sys->txt, p_demux->s );
 

modules/demux/subtitle_helper.h

+/*****************************************************************************
+ * subtitle.h: subtitle helper functions
+ *****************************************************************************
+ * Copyright (C) 2015 VLC authors and VideoLAN
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+inline static char * peek_Readline( stream_t *p_demuxstream, uint64_t *pi_offset )
+{
+    uint8_t *p_peek;
+    ssize_t i_peek = stream_Peek( p_demuxstream, (const uint8_t **) &p_peek,
+                                  *pi_offset + 2048 );
+    if( i_peek <= 0 )
+        return NULL;
+
+    const uint64_t i_bufsize = (uint64_t) i_peek - *pi_offset;
+    char *psz_line = NULL;
+
+    /* Create a stream memory from that offset */
+    stream_t *p_memorystream = stream_MemoryNew( p_demuxstream, &p_peek[*pi_offset],
+                                                 i_bufsize, true );
+    if( p_memorystream )
+    {
+        psz_line = stream_ReadLine( p_memorystream );
+
+        *pi_offset += stream_Tell( p_memorystream );
+        stream_Delete( p_memorystream );
+    }
+
+    return psz_line;
+}

modules/demux/vobsub.c

@@ -39,6 +39,7 @@
 #include "mpeg/pes.h"
 #include "mpeg/ps.h"
 #include "vobsub.h"
+#include "subtitle_helper.h"
 
 /*****************************************************************************
  * Module descriptor
@@ -122,17 +123,14 @@ static int Open ( vlc_object_t *p_this )
     demux_sys_t *p_sys;
     char *psz_vobname, *s;
     int i_len;
+    uint64_t i_read_offset = 0;
 
-    if( ( s = stream_ReadLine( p_demux->s ) ) != NULL )
+    if( ( s = peek_Readline( p_demux->s, &i_read_offset ) ) != NULL )
     {
         if( !strcasestr( s, "# VobSub index file" ) )
         {
             msg_Dbg( p_demux, "this doesn't seem to be a vobsub file" );
             free( s );
-            if( stream_Seek( p_demux->s, 0 ) )
-            {
-                msg_Warn( p_demux, "failed to rewind" );
-            }
             return VLC_EGENERIC;
         }
         free( s );