org.jitsi.impl.neomedia.rtcp.NACKPacket Maven / Gradle / Ivy
/*
* Copyright @ 2015 Atlassian Pty Ltd
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.jitsi.impl.neomedia.rtcp;
import java.util.*;
import net.sf.fmj.media.rtp.*;
import org.jitsi.service.neomedia.*;
import org.jitsi.util.*;
import org.jitsi.utils.*;
/**
* A class which represents an RTCP Generic NACK feedback message, as defined
* in RFC4585 Section 6.2.1.
*
* The RTCP packet structure is:
*
* {@code
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* |V=2|P| FMT=1 | PT=205 | length |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | SSRC of packet sender |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | SSRC of media source |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | FCI |
* | [...] |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*
* The Feedback Control Information (FCI) field consists of one or more
* 32-bit words, each with the following structure:
*
* 0 1 2 3
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | PID | BLP |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* }
*
* @author Boris Grozev
* @author George Politis
*/
public class NACKPacket
extends RTCPFBPacket
{
/**
* Gets a boolean indicating whether or not the RTCP packet specified in the
* {@link ByteArrayBuffer} that is passed as an argument is a NACK packet or
* not.
*
* @param baf the {@link ByteArrayBuffer}
* @return true if the byte array buffer holds a NACK packet, otherwise
* false.
*/
public static boolean isNACKPacket(ByteArrayBuffer baf)
{
int rc = RTCPUtils.getReportCount(baf);
return rc == FMT && isRTPFBPacket(baf);
}
/**
* @return the set of sequence numbers reported lost in a NACK packet
* represented by a {@link ByteArrayBuffer}.
* @param baf the NACK packet.
*/
public static Collection getLostPackets(ByteArrayBuffer baf)
{
return getLostPacketsFci(getFCI(baf));
}
/**
* @return the set of sequence numbers reported lost in the FCI field of a
* NACK packet represented by a {@link ByteArrayBuffer}.
* @param fciBuffer the {@link ByteArrayBuffer} which represents the FCI
* field of a NACK packet.
*/
public static Collection getLostPacketsFci(ByteArrayBuffer fciBuffer)
{
Collection lostPackets = new LinkedList<>();
if (fciBuffer == null)
{
return lostPackets;
}
byte[] fci = fciBuffer.getBuffer();
int off = fciBuffer.getOffset(), len = fciBuffer.getLength();
for (int i = 0; i < (len / 4); i++)
{
int pid = (0xFF & fci[off + i * 4 + 0]) << 8 | (0xFF & fci[off + i * 4 + 1]);
lostPackets.add(pid);
// First byte of the BLP
for (int j = 0; j < 8; j++)
{
if (0 != (fci[off + i * 4 + 2] & (1 << j)))
{
lostPackets.add((pid + 1 + 8 + j) % (1 << 16));
}
}
// Second byte of the BLP
for (int j = 0; j < 8; j++)
{
if (0 != (fci[off + i * 4 + 3] & (1 << j)))
{
lostPackets.add((pid + 1 + j) % (1 << 16));
}
}
}
return lostPackets;
}
/**
* The value of the "fmt" field for a NACK packet.
*/
public static final int FMT = 1;
/**
* The set of sequence numbers described by this packet.
*/
private Collection lostPackets = null;
/**
* Initializes a new NACKPacket instance.
* @param base
*/
public NACKPacket(RTCPCompoundPacket base)
{
super(base);
}
/**
* Initializes a new NACKPacket instance with specific "packet
* sender SSRC" and "media source SSRC" values and which describes a
* specific set of sequence numbers.
* @param senderSSRC the value to use for the "packet sender SSRC" field.
* @param sourceSSRC the value to use for the "media source SSRC" field.
* @param lostPackets the set of RTP sequence numbers which this NACK
* packet is to describe.
*
* Note that this implementation is not optimized and might not always use
* the minimal possible number of bytes to describe a given set of packets.
* Specifically, it does not take into account that sequence numbers wrap
* at 2^16 and fails to pack numbers close to 2^16 with those close to 0.
*/
public NACKPacket(long senderSSRC, long sourceSSRC,
Collection lostPackets)
{
super(FMT, RTPFB, senderSSRC, sourceSSRC);
List sorted = new LinkedList<>(lostPackets);
Collections.sort(sorted);
List nackList = new LinkedList<>();
int currentPid = -1;
byte[] currentNack = null;
for (int seq : sorted)
{
if (currentPid == -1 || currentPid + 16 <= seq)
{
currentPid = seq;
currentNack = new byte[4];
currentNack[0] = (byte) ((seq & 0xff00) >> 8);
currentNack[1] = (byte) (seq & 0x00ff);
currentNack[2] = 0;
currentNack[3] = 0;
nackList.add(currentNack);
continue;
}
// Add seq to the current fci
int diff = seq - currentPid;
if (diff <= 8)
{
currentNack[3] |= (byte) (1 << (diff - 1));
}
else
{
currentNack[2] |= (byte) (1 << (diff - 8 - 1));
}
}
// Set the fci field, which is used when assembling
fci = new byte[nackList.size() * 4];
for (int i = 0; i < nackList.size(); i++)
{
System.arraycopy(nackList.get(i), 0, fci, i * 4, 4);
}
this.lostPackets = sorted;
}
/**
* @return the set of sequence numbers reported lost in this NACK packet.
*/
synchronized public Collection getLostPackets()
{
if (lostPackets == null)
{
// parse this.fci as containing NACK entries and initialize
// this.lostPackets
lostPackets = getLostPacketsFci(new RawPacket(fci, 0, fci.length));
}
return lostPackets;
}
@Override
public String toString()
{
return "RTCP NACK packet; packet sender: " + senderSSRC
+ "; media sources: " + sourceSSRC
+ "; NACK entries: " + (fci == null ? "none" : (fci.length / 4))
+ "; lost packets: "
+ (lostPackets == null ? "none" :
Arrays.toString(lostPackets.toArray()));
}
}
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