/**
   * Tries to find an SSRC paired with {@code ssrc} in an FID group in one of the channels from
   * {@link #channel}'s {@code Content}. Returns -1 on failure.
   *
   * @param pkt the {@code RawPacket} that holds the RTP packet for which to find a paired SSRC.
   * @return An SSRC paired with {@code ssrc} in an FID group, or -1.
   */
  private long getRtxSsrc(RawPacket pkt) {
    StreamRTPManager receiveRTPManager =
        channel.getStream().getRTPTranslator().findStreamRTPManagerByReceiveSSRC(pkt.getSSRC());

    MediaStreamTrackReceiver receiver = null;
    if (receiveRTPManager != null) {
      MediaStream receiveStream = receiveRTPManager.getMediaStream();
      if (receiveStream != null) {
        receiver = receiveStream.getMediaStreamTrackReceiver();
      }
    }

    if (receiver == null) {
      return -1;
    }

    RTPEncoding encoding = receiver.resolveRTPEncoding(pkt);
    if (encoding == null) {
      logger.warn(
          "encoding_not_found"
              + ",stream_hash="
              + channel.getStream().hashCode()
              + " ssrc="
              + pkt.getSSRCAsLong());
      return -1;
    }

    return encoding.getRTXSSRC();
  }
  /** {@inheritDoc} */
  @Override
  public RawPacket transform(RawPacket pkt) {
    byte[] buf = pkt.getBuffer();
    int off = pkt.getOffset();
    int len = pkt.getLength();

    // If the specified pkt represents a DTLS record, then it should pass
    // through this PacketTransformer (e.g. it has been sent through
    // DatagramTransportImpl).
    if (isDtlsRecord(buf, off, len)) return pkt;

    // SRTP
    if (!transformEngine.isSrtpDisabled()) {
      // DTLS-SRTP has not been initialized yet or has failed to
      // initialize.
      SinglePacketTransformer srtpTransformer = waitInitializeAndGetSRTPTransformer();

      if (srtpTransformer != null) pkt = srtpTransformer.transform(pkt);
      else if (DROP_UNENCRYPTED_PKTS) pkt = null;
      // XXX Else, it is our explicit policy to let the received packet
      // pass through and rely on the SrtpListener to notify the user that
      // the session is not secured.
    }
    // Pure/non-SRTP DTLS
    else {
      // The specified pkt will pass through this PacketTransformer only
      // if it gets transformed into a DTLS record.
      pkt = null;

      sendApplicationData(buf, off, len);
    }
    return pkt;
  }
        /** {@inheritDoc} */
        @Override
        public RawPacket transform(RawPacket pkt) {
          if (pkt == null) {
            return pkt;
          }

          RTCPCompoundPacket inPacket;
          try {
            inPacket =
                (RTCPCompoundPacket)
                    parser.parse(pkt.getBuffer(), pkt.getOffset(), pkt.getLength());
          } catch (BadFormatException e) {
            logger.warn("Failed to terminate an RTCP packet. " + "Dropping packet.");
            return null;
          }

          // Update our RTCP stats map (timestamps). This operation is
          // read-only.
          remoteClockEstimator.apply(inPacket);

          cnameRegistry.update(inPacket);

          // Remove SRs and RRs from the RTCP packet.
          pkt = feedbackGateway.gateway(inPacket);

          return pkt;
        }
Beispiel #4
0
      public int write(byte[] buffer, int offset, int length, boolean transform) {
        RawPacket pkt = rawPacketArray[0];
        if (pkt == null) pkt = new RawPacket();
        rawPacketArray[0] = pkt;

        byte[] pktBuf = pkt.getBuffer();
        if (pktBuf == null || pktBuf.length < length) {
          pktBuf = new byte[length];
          pkt.setBuffer(pktBuf);
        }
        System.arraycopy(buffer, offset, pktBuf, 0, length);
        pkt.setOffset(0);
        pkt.setLength(length);

        if (transform) {
          PacketTransformer packetTransformer =
              isControlStream ? rtcpPacketTransformer : rtpPacketTransformer;

          if (packetTransformer != null)
            rawPacketArray = packetTransformer.reverseTransform(rawPacketArray);
        }

        SourceTransferHandler transferHandler;
        PushSourceStream pushSourceStream;

        try {
          if (isControlStream) {
            transferHandler = controlTransferHandler;
            pushSourceStream = getControlInputStream();
          } else {
            transferHandler = dataTransferHandler;
            pushSourceStream = getDataInputStream();
          }
        } catch (IOException ioe) {
          throw new UndeclaredThrowableException(ioe);
        }

        for (int i = 0; i < rawPacketArray.length; i++) {
          RawPacket packet = rawPacketArray[i];

          // keep the first element for reuse
          if (i != 0) rawPacketArray[i] = null;

          if (packet != null) {
            if (isControlStream) pendingControlPacket = packet;
            else pendingDataPacket = packet;

            if (transferHandler != null) {
              transferHandler.transferData(pushSourceStream);
            }
          }
        }

        return length;
      }
Beispiel #5
0
 private void handleRtpPacket(RawPacket pkt) {
   if (pkt != null && pkt.getPayloadType() == vp8PayloadType) {
     int ssrc = pkt.getSSRC();
     if (!activeVideoSsrcs.contains(ssrc & 0xffffffffL)) {
       synchronized (activeVideoSsrcs) {
         if (!activeVideoSsrcs.contains(ssrc & 0xffffffffL)) {
           activeVideoSsrcs.add(ssrc & 0xffffffffL);
           rtcpFeedbackSender.sendFIR(ssrc);
         }
       }
     }
   }
 }
Beispiel #6
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  private void emptyPacketBuffer(long ssrc) {
    RawPacket[] pkts = rtpConnector.packetBuffer.emptyBuffer(ssrc);
    RTPConnectorImpl.OutputDataStreamImpl dataStream;

    try {
      dataStream = rtpConnector.getDataOutputStream();
    } catch (IOException ioe) {
      logger.error("Failed to empty packet buffer for SSRC=" + ssrc + ": " + ioe);
      return;
    }
    for (RawPacket pkt : pkts)
      dataStream.write(
          pkt.getBuffer(), pkt.getOffset(), pkt.getLength(), false /* already transformed */);
  }
  /**
   * Retransmits a packet to {@link #channel}. If the destination supports the RTX format, the
   * packet will be encapsulated in RTX, otherwise, the packet will be retransmitted as-is.
   *
   * @param pkt the packet to retransmit.
   * @param after the {@code TransformEngine} in the chain of {@code TransformEngine}s of the
   *     associated {@code MediaStream} after which the injection of {@code pkt} is to begin
   * @return {@code true} if the packet was successfully retransmitted, {@code false} otherwise.
   */
  public boolean retransmit(RawPacket pkt, TransformEngine after) {
    boolean destinationSupportsRtx = channel.getRtxPayloadType() != -1;
    boolean retransmitPlain;

    if (destinationSupportsRtx) {
      long rtxSsrc = getPairedSsrc(pkt.getSSRC());

      if (rtxSsrc == -1) {
        logger.warn("Cannot find SSRC for RTX, retransmitting plain.");
        retransmitPlain = true;
      } else {
        retransmitPlain = !encapsulateInRtxAndTransmit(pkt, rtxSsrc);
      }
    } else {
      retransmitPlain = true;
    }

    if (retransmitPlain) {
      MediaStream mediaStream = channel.getStream();

      if (mediaStream != null) {
        try {
          mediaStream.injectPacket(pkt, /* data */ true, after);
        } catch (TransmissionFailedException tfe) {
          logger.warn("Failed to retransmit a packet.");
          return false;
        }
      }
    }

    return true;
  }
Beispiel #8
0
            @Override
            public RawPacket reverseTransform(RawPacket pkt) {
              RecorderRtpImpl.this.handleRtcpPacket(pkt);
              if (pkt != null && pkt.getRTCPPayloadType() == 203) {
                // An RTCP BYE packet. Remove the receive stream before
                // it gets to FMJ, because we want to, for example,
                // flush the packet buffer before that.

                long ssrc = pkt.getRTCPSSRC() & 0xffffffffl;
                if (logger.isInfoEnabled()) logger.info("RTCP BYE for SSRC=" + ssrc);

                ReceiveStreamDesc receiveStream = findReceiveStream(ssrc);
                if (receiveStream != null) removeReceiveStream(receiveStream, false);
              }

              return pkt;
            }
    /**
     * Updates this <tt>RTPStatsMap</tt> with information it gets from the <tt>RawPacket</tt>.
     *
     * @param pkt the <tt>RawPacket</tt> that is being transmitted.
     */
    public void apply(RawPacket pkt) {
      int ssrc = pkt.getSSRC();
      if (this.containsKey(ssrc)) {
        RTPStatsEntry oldRtpStatsEntry = this.get(ssrc);

        // Replace whatever was in there before. A feature of the two's
        // complement encoding (which is used by Java integers) is that
        // the bitwise results for add, subtract, and multiply are the
        // same if both inputs are interpreted as signed values or both
        // inputs are interpreted as unsigned values. (Other encodings
        // like one's complement and signed magnitude don't have this
        // properly.)
        this.put(
            ssrc,
            new RTPStatsEntry(
                ssrc,
                oldRtpStatsEntry.getBytesSent()
                    + pkt.getLength()
                    - pkt.getHeaderLength()
                    - pkt.getPaddingSize(),
                oldRtpStatsEntry.getPacketsSent() + 1));
      } else {
        // Add a new <tt>RTPStatsEntry</tt> in this map.
        this.put(
            ssrc,
            new RTPStatsEntry(
                ssrc, pkt.getLength() - pkt.getHeaderLength() - pkt.getPaddingSize(), 1));
      }
    }
Beispiel #10
0
      @Override
      public int read(byte[] buffer, int offset, int length) throws IOException {

        RawPacket pendingPacket;
        if (isControlStream) {
          pendingPacket = pendingControlPacket;
        } else {
          pendingPacket = pendingDataPacket;
        }
        int bytesToRead = 0;
        byte[] pendingPacketBuffer = pendingPacket.getBuffer();
        if (pendingPacketBuffer != null) {
          int pendingPacketLength = pendingPacket.getLength();
          bytesToRead = length > pendingPacketLength ? pendingPacketLength : length;
          System.arraycopy(
              pendingPacketBuffer, pendingPacket.getOffset(), buffer, offset, bytesToRead);
        }
        return bytesToRead;
      }
  /** Implements {@link PacketTransformer#transform(RawPacket[])}. {@inheritDoc} */
  @Override
  public RawPacket transform(RawPacket pkt) {
    byte rtxPt;
    if (pkt != null
        && (rtxPt = channel.getRtxPayloadType()) != -1
        && pkt.getPayloadType() == rtxPt) {
      pkt = handleRtxPacket(pkt);
    }

    return pkt;
  }
  /**
   * Handles an RTX packet and returns it.
   *
   * @param pkt the packet to handle.
   * @return the packet
   */
  private RawPacket handleRtxPacket(RawPacket pkt) {
    boolean destinationSupportsRtx = channel.getRtxPayloadType() != -1;
    RawPacket mediaPacket = createMediaPacket(pkt);

    if (mediaPacket != null) {
      RawPacketCache cache = channel.getStream().getPacketCache();
      if (cache != null) {
        cache.cachePacket(mediaPacket);
      }
    }

    if (destinationSupportsRtx) {
      pkt.setSequenceNumber(
          getNextRtxSequenceNumber(pkt.getSSRC() & 0xffffffffL, pkt.getSequenceNumber()));
    } else {
      // If the media packet was not reconstructed, drop the RTX packet
      // (by returning null).
      return mediaPacket;
    }

    return pkt;
  }
  /**
   * Encapsulates {@code pkt} in the RTX format, using {@code rtxSsrc} as its SSRC, and transmits it
   * to {@link #channel} by injecting it in the {@code MediaStream}.
   *
   * @param pkt the packet to transmit.
   * @param rtxSsrc the SSRC for the RTX stream.
   * @param after the {@code TransformEngine} in the chain of {@code TransformEngine}s of the
   *     associated {@code MediaStream} after which the injection of {@code pkt} is to begin
   * @return {@code true} if the packet was successfully retransmitted, {@code false} otherwise.
   */
  private boolean encapsulateInRtxAndTransmit(RawPacket pkt, long rtxSsrc, TransformEngine after) {
    byte[] buf = pkt.getBuffer();
    int len = pkt.getLength();
    int off = pkt.getOffset();

    byte[] newBuf = new byte[len + 2];
    RawPacket rtxPkt = new RawPacket(newBuf, 0, len + 2);

    int osn = pkt.getSequenceNumber();
    int headerLength = pkt.getHeaderLength();
    int payloadLength = pkt.getPayloadLength();

    // Copy the header.
    System.arraycopy(buf, off, newBuf, 0, headerLength);

    // Set the OSN field.
    newBuf[headerLength] = (byte) ((osn >> 8) & 0xff);
    newBuf[headerLength + 1] = (byte) (osn & 0xff);

    // Copy the payload.
    System.arraycopy(buf, off + headerLength, newBuf, headerLength + 2, payloadLength);

    MediaStream mediaStream = channel.getStream();
    if (mediaStream != null) {
      rtxPkt.setSSRC((int) rtxSsrc);
      rtxPkt.setPayloadType(rtxPayloadType);
      // Only call getNextRtxSequenceNumber() when we're sure we're going
      // to transmit a packet, because it consumes a sequence number.
      rtxPkt.setSequenceNumber(getNextRtxSequenceNumber(rtxSsrc));
      try {
        mediaStream.injectPacket(rtxPkt, /* data */ true, after);
      } catch (TransmissionFailedException tfe) {
        logger.warn("Failed to transmit an RTX packet.");
        return false;
      }
    }

    return true;
  }
  /**
   * Encapsulates {@code pkt} in the RTX format, using {@code rtxSsrc} as its SSRC, and transmits it
   * to {@link #channel} by injecting it in the {@code MediaStream}.
   *
   * @param pkt the packet to transmit.
   * @param rtxSsrc the SSRC for the RTX stream.
   * @return {@code true} if the packet was successfully retransmitted, {@code false} otherwise.
   */
  private boolean encapsulateInRtxAndTransmit(RawPacket pkt, long rtxSsrc) {
    byte[] buf = pkt.getBuffer();
    int len = pkt.getLength();
    int off = pkt.getOffset();
    byte[] newBuf = buf;
    if (buf.length < len + 2) {
      // FIXME The byte array newly allocated and assigned to newBuf must
      // be made known to pkt eventually.
      newBuf = new byte[len + 2];
    }

    int osn = pkt.getSequenceNumber();
    int headerLength = pkt.getHeaderLength();
    int payloadLength = len - headerLength;
    System.arraycopy(buf, off, newBuf, 0, headerLength);
    // FIXME If newBuf is actually buf, then we will override the first two
    // bytes of the payload bellow.
    newBuf[headerLength] = (byte) ((osn >> 8) & 0xff);
    newBuf[headerLength + 1] = (byte) (osn & 0xff);
    System.arraycopy(buf, off + headerLength, newBuf, headerLength + 2, payloadLength);
    // FIXME We tried to extend the payload of pkt by two bytes above but
    // we never told pkt that its length has increased by these two bytes.

    MediaStream mediaStream = channel.getStream();
    if (mediaStream != null) {
      pkt.setSSRC((int) rtxSsrc);
      // Only call getNextRtxSequenceNumber() when we're sure we're going
      // to transmit a packet, because it consumes a sequence number.
      pkt.setSequenceNumber(getNextRtxSequenceNumber(rtxSsrc));
      try {
        mediaStream.injectPacket(pkt, /* data */ true, /* after */ null);
      } catch (TransmissionFailedException tfe) {
        logger.warn("Failed to transmit an RTX packet.");
        return false;
      }
    }

    return true;
  }
  /**
   * Creates a {@code RawPacket} which represents the original packet encapsulated in {@code pkt}
   * using the RTX format.
   *
   * @param pkt the packet from which to extract a media packet.
   * @return the extracted media packet.
   */
  private RawPacket createMediaPacket(RawPacket pkt) {
    RawPacket mediaPacket = null;
    long rtxSsrc = pkt.getSSRC() & 0xffffffffL;

    // We need to know the SSRC paired with rtxSsrc *as seen by the
    // receiver (i.e. this.channel)*. However, we only store SSRCs
    // that endpoints *send* with.
    // We therefore assume that SSRC re-writing has not introduced any
    // new SSRCs and therefor the FID mappings known to the senders
    // also apply to receivers.
    RtpChannel sourceChannel = channel.getContent().findChannelByFidSsrc(rtxSsrc);
    if (sourceChannel != null) {
      long mediaSsrc = sourceChannel.getFidPairedSsrc(rtxSsrc);
      if (mediaSsrc != -1) {
        byte apt = sourceChannel.getRtxAssociatedPayloadType();
        if (apt != -1) {
          mediaPacket = new RawPacket(pkt.getBuffer().clone(), pkt.getOffset(), pkt.getLength());

          // Remove the RTX header by moving the RTP header two bytes
          // right.
          byte[] buf = mediaPacket.getBuffer();
          int off = mediaPacket.getOffset();
          System.arraycopy(buf, off, buf, off + 2, mediaPacket.getHeaderLength());

          mediaPacket.setOffset(off + 2);
          mediaPacket.setLength(pkt.getLength() - 2);

          mediaPacket.setSSRC((int) mediaSsrc);
          mediaPacket.setSequenceNumber(pkt.getOriginalSequenceNumber());
          mediaPacket.setPayloadType(apt);
        }
      }
    }

    return mediaPacket;
  }
  private void runOnDtlsTransport(StreamConnector connector) throws IOException {
    DtlsControlImpl dtlsControl = (DtlsControlImpl) getTransportManager().getDtlsControl(this);
    DtlsTransformEngine engine = dtlsControl.getTransformEngine();
    final DtlsPacketTransformer transformer = (DtlsPacketTransformer) engine.getRTPTransformer();

    byte[] receiveBuffer = new byte[SCTP_BUFFER_SIZE];

    if (LOG_SCTP_PACKETS) {
      System.setProperty(
          ConfigurationService.PNAME_SC_HOME_DIR_LOCATION, System.getProperty("java.io.tmpdir"));
      System.setProperty(
          ConfigurationService.PNAME_SC_HOME_DIR_NAME, SctpConnection.class.getName());
    }

    synchronized (this) {
      // FIXME local SCTP port is hardcoded in bridge offer SDP (Jitsi
      // Meet)
      sctpSocket = Sctp.createSocket(5000);
      assocIsUp = false;
      acceptedIncomingConnection = false;
    }

    // Implement output network link for SCTP stack on DTLS transport
    sctpSocket.setLink(
        new NetworkLink() {
          @Override
          public void onConnOut(SctpSocket s, byte[] packet) throws IOException {
            if (LOG_SCTP_PACKETS) {
              LibJitsi.getPacketLoggingService()
                  .logPacket(
                      PacketLoggingService.ProtocolName.ICE4J,
                      new byte[] {0, 0, 0, (byte) debugId},
                      5000,
                      new byte[] {0, 0, 0, (byte) (debugId + 1)},
                      remoteSctpPort,
                      PacketLoggingService.TransportName.UDP,
                      true,
                      packet);
            }

            // Send through DTLS transport
            transformer.sendApplicationData(packet, 0, packet.length);
          }
        });

    if (logger.isDebugEnabled()) {
      logger.debug("Connecting SCTP to port: " + remoteSctpPort + " to " + getEndpoint().getID());
    }

    sctpSocket.setNotificationListener(this);
    sctpSocket.listen();

    // FIXME manage threads
    threadPool.execute(
        new Runnable() {
          @Override
          public void run() {
            SctpSocket sctpSocket = null;
            try {
              // sctpSocket is set to null on close
              sctpSocket = SctpConnection.this.sctpSocket;
              while (sctpSocket != null) {
                if (sctpSocket.accept()) {
                  acceptedIncomingConnection = true;
                  break;
                }
                Thread.sleep(100);
                sctpSocket = SctpConnection.this.sctpSocket;
              }
              if (isReady()) {
                notifySctpConnectionReady();
              }
            } catch (Exception e) {
              logger.error("Error accepting SCTP connection", e);
            }

            if (sctpSocket == null && logger.isInfoEnabled()) {
              logger.info(
                  "SctpConnection " + getID() + " closed" + " before SctpSocket accept()-ed.");
            }
          }
        });

    // Notify that from now on SCTP connection is considered functional
    sctpSocket.setDataCallback(this);

    // Setup iceSocket
    DatagramSocket datagramSocket = connector.getDataSocket();
    if (datagramSocket != null) {
      this.iceSocket = new IceUdpSocketWrapper(datagramSocket);
    } else {
      this.iceSocket = new IceTcpSocketWrapper(connector.getDataTCPSocket());
    }

    DatagramPacket rcvPacket = new DatagramPacket(receiveBuffer, 0, receiveBuffer.length);

    // Receive loop, breaks when SCTP socket is closed
    try {
      do {
        iceSocket.receive(rcvPacket);

        RawPacket raw =
            new RawPacket(rcvPacket.getData(), rcvPacket.getOffset(), rcvPacket.getLength());

        raw = transformer.reverseTransform(raw);
        // Check for app data
        if (raw == null) continue;

        if (LOG_SCTP_PACKETS) {
          LibJitsi.getPacketLoggingService()
              .logPacket(
                  PacketLoggingService.ProtocolName.ICE4J,
                  new byte[] {0, 0, 0, (byte) (debugId + 1)},
                  remoteSctpPort,
                  new byte[] {0, 0, 0, (byte) debugId},
                  5000,
                  PacketLoggingService.TransportName.UDP,
                  false,
                  raw.getBuffer(),
                  raw.getOffset(),
                  raw.getLength());
        }

        // Pass network packet to SCTP stack
        sctpSocket.onConnIn(raw.getBuffer(), raw.getOffset(), raw.getLength());
      } while (true);
    } finally {
      // Eventually, close the socket although it should happen from
      // expire().
      synchronized (this) {
        assocIsUp = false;
        acceptedIncomingConnection = false;
        if (sctpSocket != null) {
          sctpSocket.close();
          sctpSocket = null;
        }
      }
    }
  }
  /**
   * Removes the RTX encapsulation from a packet.
   *
   * @param pkt the packet to remove the RTX encapsulation from.
   * @return the original media packet represented by {@code pkt}, or null if we couldn't
   *     reconstruct the original packet.
   */
  private RawPacket deRtx(RawPacket pkt) {
    boolean success = false;

    if (pkt.getPayloadLength() - pkt.getPaddingSize() < 2) {
      // We need at least 2 bytes to read the OSN field.
      if (logger.isDebugEnabled()) {
        logger.debug("Dropping an incoming RTX packet with padding only: " + pkt);
      }
      return null;
    }

    long mediaSsrc = getPrimarySsrc(pkt);
    if (mediaSsrc != -1) {
      if (rtxAssociatedPayloadType != -1) {
        int osn = pkt.getOriginalSequenceNumber();
        // Remove the RTX header by moving the RTP header two bytes
        // right.
        byte[] buf = pkt.getBuffer();
        int off = pkt.getOffset();
        System.arraycopy(buf, off, buf, off + 2, pkt.getHeaderLength());

        pkt.setOffset(off + 2);
        pkt.setLength(pkt.getLength() - 2);

        pkt.setSSRC((int) mediaSsrc);
        pkt.setSequenceNumber(osn);
        pkt.setPayloadType(rtxAssociatedPayloadType);
        success = true;
      } else {
        logger.warn(
            "RTX packet received, but no APT is defined. Packet "
                + "SSRC "
                + pkt.getSSRCAsLong()
                + ", associated media"
                + " SSRC "
                + mediaSsrc);
      }
    }

    // If we failed to handle the RTX packet, drop it.
    return success ? pkt : null;
  }
  /** {@inheritDoc} */
  @Override
  public RawPacket reverseTransform(RawPacket pkt) {
    byte[] buf = pkt.getBuffer();
    int off = pkt.getOffset();
    int len = pkt.getLength();

    if (isDtlsRecord(buf, off, len)) {
      if (rtcpmux && Component.RTCP == componentID) {
        // This should never happen.
        logger.warn(
            "Dropping a DTLS record, because it was received on the"
                + " RTCP channel while rtcpmux is in use.");
        return null;
      }

      boolean receive;

      synchronized (this) {
        if (datagramTransport == null) {
          receive = false;
        } else {
          datagramTransport.queueReceive(buf, off, len);
          receive = true;
        }
      }
      if (receive) {
        DTLSTransport dtlsTransport = this.dtlsTransport;

        if (dtlsTransport == null) {
          // The specified pkt looks like a DTLS record and it has
          // been consumed for the purposes of the secure channel
          // represented by this PacketTransformer.
          pkt = null;
        } else {
          try {
            int receiveLimit = dtlsTransport.getReceiveLimit();
            int delta = receiveLimit - len;

            if (delta > 0) {
              pkt.grow(delta);
              buf = pkt.getBuffer();
              off = pkt.getOffset();
              len = pkt.getLength();
            } else if (delta < 0) {
              pkt.shrink(-delta);
              buf = pkt.getBuffer();
              off = pkt.getOffset();
              len = pkt.getLength();
            }

            int received = dtlsTransport.receive(buf, off, len, DTLS_TRANSPORT_RECEIVE_WAITMILLIS);

            if (received <= 0) {
              // No application data was decoded.
              pkt = null;
            } else {
              delta = len - received;
              if (delta > 0) pkt.shrink(delta);
            }
          } catch (IOException ioe) {
            pkt = null;
            // SrtpControl.start(MediaType) starts its associated
            // TransformEngine. We will use that mediaType to signal
            // the normal stop then as well i.e. we will ignore
            // exception after the procedure to stop this
            // PacketTransformer has begun.
            if (mediaType != null && !tlsPeerHasRaisedCloseNotifyWarning) {
              logger.error("Failed to decode a DTLS record!", ioe);
            }
          }
        }
      } else {
        // The specified pkt looks like a DTLS record but it is
        // unexpected in the current state of the secure channel
        // represented by this PacketTransformer. This PacketTransformer
        // has not been started (successfully) or has been closed.
        pkt = null;
      }
    } else if (transformEngine.isSrtpDisabled()) {
      // In pure DTLS mode only DTLS records pass through.
      pkt = null;
    } else {
      // DTLS-SRTP has not been initialized yet or has failed to
      // initialize.
      SinglePacketTransformer srtpTransformer = waitInitializeAndGetSRTPTransformer();

      if (srtpTransformer != null) pkt = srtpTransformer.reverseTransform(pkt);
      else if (DROP_UNENCRYPTED_PKTS) pkt = null;
      // XXX Else, it is our explicit policy to let the received packet
      // pass through and rely on the SrtpListener to notify the user that
      // the session is not secured.
    }
    return pkt;
  }
 /**
  * Determines whether {@code pkt} is an RTX packet.
  *
  * @param pkt the packet to check.
  * @return {@code true} iff {@code pkt} is an RTX packet.
  */
 private boolean isRtx(RawPacket pkt) {
   byte rtxPt = rtxPayloadType;
   return rtxPt != -1 && rtxPt == pkt.getPayloadType();
 }