- Clean up RTP parser

- Add support for RTP padding

By the way, the MPEG-Video parser seems to ignore the MP2V specific
extra header (i.e. it passes it onto the demux instead of removing it).
Not sure if this is intended (any MPEG expert?)

modules/access/udp.c

@@ -531,54 +531,86 @@ static inline vlc_bool_t rtp_ChainInsert( access_t *p_access, block_t *p_block )
  *****************************************************************************/
 static block_t *BlockParseRTP( access_t *p_access, block_t *p_block )
 {
-    int      i_rtp_version;
-    int      i_CSRC_count;
     int      i_payload_type;
-    int      i_skip = 0;
-    int      i_extension_flag = 0;
-    int      i_extension_length = 0;
-    uint16_t i_sequence_number = 0;
+    size_t   i_skip = RTP_HEADER_LEN;
 
     if( p_block == NULL )
         return NULL;
 
     if( p_block->i_buffer < RTP_HEADER_LEN )
+    {
+        msg_Dbg( p_access, "short RTP packet received" );
         goto trash;
+    }
 
     /* Parse the header and make some verifications.
      * See RFC 3550. */
-    i_rtp_version     = ( p_block->p_buffer[0] & 0xC0 ) >> 6;
-    i_CSRC_count      = p_block->p_buffer[0] & 0x0F;
-    i_extension_flag  = p_block->p_buffer[0] & 0x10;
+    // Version number:
+    if( ( p_block->p_buffer[0] >> 6 ) != 2)
+    {
+        msg_Dbg( p_access, "RTP version is %u instead of 2",
+                 p_block->p_buffer[0] >> 6 );
+        goto trash;
+    }
+    // Padding bit:
+    uint8_t pad = (p_block->p_buffer[0] & 0x20)
+                    ? p_block->p_buffer[p_block->i_buffer - 1] : 0;
+    // Extension header:
+    if ((p_block->p_buffer[0] & 0x10)) /* Extension header */
+    {
+        i_skip += 4;
+        if ((size_t)p_block->i_buffer < i_skip)
+            goto trash;
+
+        i_skip += 4 * GetWBE( p_block->p_buffer + 14 );
+    }
+    // CSRC count:
+    i_skip += (p_block->p_buffer[0] & 0x0F) * 4;
+
     i_payload_type    = p_block->p_buffer[1] & 0x7F;
-    i_sequence_number = (p_block->p_buffer[2] << 8 ) + p_block->p_buffer[3];
 
-    if( i_rtp_version != 2 )
-        msg_Dbg( p_access, "RTP version is %u, should be 2", i_rtp_version );
+    /* Remember sequence number in i_dts */
+    p_block->i_pts = mdate();
+    p_block->i_dts = (mtime_t) GetWBE( p_block->p_buffer + 2 );
 
-    if( i_payload_type == 14 || i_payload_type == 32)
-        i_skip = 4;
-    else if( i_payload_type !=  33 )
-        msg_Dbg( p_access, "unsupported RTP payload type (%u)", i_payload_type );
-    if( i_extension_flag )
+    /* FIXME: use ptmap */
+    switch( i_payload_type )
     {
-        if( p_block->i_buffer < 16 )
+        case 14: // MPA: MPEG Audio (RFC2250, §3.4)
+            i_skip += 4; // 32 bits RTP/MPA header
+            break;
+
+        case 32: // MPV: MPEG Video (RFC2250, §3.5)
+            i_skip += 4; // 32 bits RTP/MPV header
+            if( (size_t)p_block->i_buffer < i_skip )
                 goto trash;
-        i_extension_length = 4 +
-            4 * ( (p_block->p_buffer[14] << 8) + p_block->p_buffer[15] );
+            if( p_block->p_buffer[i_skip - 3] & 0x4 )
+            {
+                /* MPEG2 Video extension header */
+                /* TODO: shouldn't we skip this too ? */
             }
+            break;
+
+        case 33: // MP2: MPEG TS (RFC2250, §2)
+            /* plain TS over RTP */
+            break;
 
-    /* Skip header + CSRC extension field n*(32 bits) + extension */
-    i_skip += RTP_HEADER_LEN + 4*i_CSRC_count + i_extension_length;
+        default:
+            msg_Dbg( p_access, "unsupported RTP payload type: %u", i_payload_type );
+            goto trash;
+    }
 
-    if( i_skip >= p_block->i_buffer )
+    if( (size_t)p_block->i_buffer < (i_skip + pad) )
         goto trash;
 
-    /* Return the packet without the RTP header, remember seqno in i_dts */
+    /* Remove the RTP header */
     p_block->i_buffer -= i_skip;
     p_block->p_buffer += i_skip;
-    p_block->i_pts = mdate();
-    p_block->i_dts = (mtime_t) i_sequence_number;
+
+    /* This is the place for deciphering and authentication */
+
+    /* Remove padding (at the end) */
+    p_block->i_buffer -= pad;
 
 #if 0
     /* Emulate packet loss */
@@ -593,7 +625,6 @@ static block_t *BlockParseRTP( access_t *p_access, block_t *p_block )
     return p_block;
 
 trash:
-    msg_Warn( p_access, "received a too short packet for RTP" );
     block_Release( p_block );
     return NULL;
 }