[HDFS-5445] PacketReceiver populates the packetLen field in PacketHeader incorrectly

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.1.0-beta, 2.2.0
• Fix Version/s: 2.7.0
• Component/s: datanode
• Labels: easyfix

Environment

Ubuntu 12.10, Hadoop 2.1.0-beta

• Target Version/s: 2.7.0
• Tags: PacketHeader PacketReceiver BlockSender BlockReceiver
• Assignee: Jonathan Mace
• Reporter: Jonathan Mace
• Created: 29/Oct/13 22:49
• Updated: 10/Apr/15 20:29
• Resolved: 13/Jan/15 01:11

Description

Summary: PacketReceiver reconstructs PacketHeaders with a packetLen 4 bytes fewer than it should be. It doesn't cause any exceptions because the reconstructed header is never reserialized, and the packetLen field is not used in this part of the code.

In the BlockSender class, when a Packet is constructed it must be passed the field packetLen, which is defined as the data length, checksum data length, PLUS the length of the packetLen field itself (4 byte integer).

BlockSender.java

484:  private int sendPacket(ByteBuffer pkt, int maxChunks, OutputStream out,
485:      boolean transferTo, DataTransferThrottler throttler) throws IOException {
...
491:    int packetLen = dataLen + checksumDataLen + 4;
...
504:    int headerLen = writePacketHeader(pkt, dataLen, packetLen);
...
586:  }
...
792:  private int writePacketHeader(ByteBuffer pkt, int dataLen, int packetLen) {
793:    pkt.clear();
794:    // both syncBlock and syncPacket are false
795:    PacketHeader header = new PacketHeader(packetLen, offset, seqno,
796:        (dataLen == 0), dataLen, false);
...
802:  }

In the PacketReceiver class, the PacketHeader is reconstructed using the method setFieldsFromData. However, the 4 bytes for the packetLen field length are missing.

PacketReceiver.java

112:  private void doRead(ReadableByteChannel ch, InputStream in)
113:      throws IOException {
...
136:    int payloadLen = curPacketBuf.getInt();
...
144:    int dataPlusChecksumLen = payloadLen - Ints.BYTES;
...
181:    curHeader.setFieldsFromData(dataPlusChecksumLen, headerBuf);
...
192:  }

The solution would be instead to do:

PacketReceiver.java

181:    curHeader.setFieldsFromData(payloadLen, headerBuf);

I found this because I was making small modifications to the code that exposed this inconsistency.