Package com.perforce.p4java.impl.mapbased.rpc.packet

Class RpcPacketPreamble

java.lang.Object
com.perforce.p4java.impl.mapbased.rpc.packet.RpcPacketPreamble
public class RpcPacketPreamble extends Object
The five byte preamble appended to every text packet payload.

The format (as divined from the C++ API) is designed to provide a very simple sanity check checksum and encode the length in bytes of the accompanying RPC payload: 

      byte[1] = ( payload_length / 0x1 ) % 0x100;
      byte[2] = ( payload_length / 0x100 ) % 0x100;
      byte[3] = ( payload_length / 0x10000 ) % 0x100;
      byte[4] = ( payload_length / 0x1000000 ) % 0x100;
      byte[0] = byte[1] ^ byte[2] ^ byte[3] ^ byte[4];
This can generally only be calculated after the other packet elements have been serialized, which is irritating but not too annoying.

  • Field Details

    • RPC_PREAMBLE_CHKSUM_SIZE

      public static final int RPC_PREAMBLE_CHKSUM_SIZE
      Size in bytes of the preamble checksum. This is a very fundamental value; changing it will probably cause total destruction within P4Java...
      See Also:

    • RPC_PREAMBLE_SIZE

      public static final int RPC_PREAMBLE_SIZE
      The size in bytes of the standard text packet RPC packet preamble.
      See Also:

  • Method Details

    • constructPreamble

      public static RpcPacketPreamble constructPreamble(ByteBuffer payload)
      Calculate and construct a suitable preamble for the passed-in payload buffer. Does not affect the incoming buffer at all (i.e. marks and limits, etc. are unaffected). Assumes the payload starts at buffer byte position zero and uses the buffer's limit as the length.
      Parameters:
      payload - non-null byte buffer representing the payload
      Returns:
      new RpcPacketPreamble for the payload

    • constructPreamble

      public static RpcPacketPreamble constructPreamble(int payloadLength)
      Calculate and construct a suitable preamble for the passed-in payload buffer length.
      Parameters:
      payloadLength - payloadLength
      Returns:
      RpcPacketPreamble

    • retrievePreamble

      public static RpcPacketPreamble retrievePreamble(ByteBuffer payload)
      Retrieve a preamble from the passed-in payload byte buffer. Will move the byte buffer pointer accordingly.
      Parameters:
      payload - non-null payload
      Returns:
      new RpcPacketPreamble as retrieved from the payload buffer.

    • retrievePreamble

      public static RpcPacketPreamble retrievePreamble(byte[] bytes)
      Retrieve the preamble from raw bytes. Most sanity checking is done in the RpcPacketPreamble constructor.
      Parameters:
      bytes - bytes
      Returns:
      RpcPacketPreamble

    • getPayloadSize

      public int getPayloadSize()
      Return the payload size (in bytes) specified by this preamble.
      Returns:
      the associated payload size in bytes.

    • isValidChecksum

      public boolean isValidChecksum()
      Returns:
      true iff the simple checksum checks out.

    • marshal

      public ByteBuffer marshal()
      Return a ByteBuffer representing the marshaled version of this preamble. Buffer will need to be flipped before sending...
      Returns:
      non-null ByteBuffer ready for sending

    • marshalAsBytes

      public byte[] marshalAsBytes()