[vlc-devel] [PATCH 1/2] demux/subtitles: add new implementation for line-peeking

[Filip Roséen]

This added function properly handles streams where an initial BOM is
used to state the encoding used, effectively making sure that we do
not forget about the encoding of the stream while peeking lines.
---
 modules/demux/subtitle_helper.h | 75 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/modules/demux/subtitle_helper.h b/modules/demux/subtitle_helper.h
index b5f18da..fc71c12 100644
--- a/modules/demux/subtitle_helper.h
+++ b/modules/demux/subtitle_helper.h
@@ -18,6 +18,9 @@
  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  *****************************************************************************/
 
+#include <vlc_common.h>
+#include <vlc_stream.h>
+
 inline static char * peek_Readline( stream_t *p_demuxstream, uint64_t *pi_offset )
 {
     uint8_t *p_peek;
@@ -43,3 +46,75 @@ inline static char * peek_Readline( stream_t *p_demuxstream, uint64_t *pi_offset
 
     return psz_line;
 }
+
+/**
+ * Peek next line of stream
+ *
+ * This function returns the next available line in \p p_source
+ * without modifying the read-offset of the stream (meaning that it
+ * effectivelly it behaves like vlc_stream_Peek, but for lines).
+ *
+ * \param source The stream for which line-peeking shall be made
+ * \param peekstate shall be NULL on first invocation, and `*peekstate`
+ *                  will be updated to reflect the internal state of the
+ *                  peeking.
+ *
+ * \warning if `*peekstate` is not NULL, it shall be released by the
+ *          callee when no more data is desired to be peeked (using
+ *          \link vlc_stream_Delete).
+ *
+ * \return pointer to the next line (if any), must be freed by the
+ *         callee.
+ **/
+inline static char * subtitle_PeekLine( stream_t *source, stream_t **peekstate )
+{
+    for( uint64_t offset = 0, size = 0;; )
+    {
+        char* line = NULL;
+
+        if( *peekstate )
+        {
+            if( vlc_stream_GetSize( *peekstate, &size ) )
+                return NULL;
+
+            offset = vlc_stream_Tell( *peekstate );
+            line   = vlc_stream_ReadLine( *peekstate );
+
+            if( line && vlc_stream_Tell( *peekstate ) < size )
+                return line;
+        }
+
+        uint8_t const* data;
+        ssize_t peeked = vlc_stream_Peek( source, &data, size + 2048 );
+
+        if( peeked > 0 && (uint64_t)peeked <= size )
+            return line;
+        else
+            free( line );
+
+        if( peeked < 0 )
+            return NULL;
+
+        if( *peekstate )
+        {
+            vlc_stream_Delete( *peekstate );
+            *peekstate = NULL;
+        }
+
+        *peekstate = vlc_stream_MemoryNew( source, (uint8_t*)data,
+                                           peeked, true );
+        if( unlikely( !*peekstate ) )
+            return NULL;
+
+        if( offset != 0 )
+        {
+            /* read potential BOM */
+            free( vlc_stream_ReadLine( *peekstate ) );
+
+            if( vlc_stream_Seek( *peekstate, offset ) )
+                return NULL;
+        }
+    }
+
+    vlc_assert_unreachable();
+}
-- 
2.10.2