EnipPacket.java

package com.digitalpetri.enip;

import javax.annotation.Nullable;

import com.digitalpetri.enip.commands.Command;
import com.digitalpetri.enip.commands.CommandCode;
import com.digitalpetri.enip.commands.ListIdentity;
import com.digitalpetri.enip.commands.ListInterfaces;
import com.digitalpetri.enip.commands.Nop;
import com.digitalpetri.enip.commands.RegisterSession;
import com.digitalpetri.enip.commands.SendRRData;
import com.digitalpetri.enip.commands.SendUnitData;
import com.digitalpetri.enip.commands.UnRegisterSession;
import io.netty.buffer.ByteBuf;
import io.netty.handler.codec.DecoderException;
import io.netty.handler.codec.EncoderException;

/**
 * All encapsulation messages, sent via TCP or sent to UDP port 0xAF12, shall be composed of a fixed-length header of
 * 24 bytes followed by an optional data portion. The total encapsulation message length (including header) shall be
 * limited to 65535 bytes.
 */
public final class EnipPacket {

    private final CommandCode commandCode;
    private final long sessionHandle;
    private final EnipStatus status;
    private final long senderContext;

    @Nullable
    private final Command command;

    public EnipPacket(CommandCode commandCode,
                      long sessionHandle,
                      EnipStatus status,
                      long senderContext,
                      @Nullable Command command) {

        this.commandCode = commandCode;
        this.sessionHandle = sessionHandle;
        this.status = status;
        this.senderContext = senderContext;
        this.command = command;
    }

    public CommandCode getCommandCode() {
        return commandCode;
    }

    public long getSessionHandle() {
        return sessionHandle;
    }

    public EnipStatus getStatus() {
        return status;
    }

    public long getSenderContext() {
        return senderContext;
    }

    @Nullable
    public Command getCommand() {
        return command;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        EnipPacket that = (EnipPacket) o;

        return senderContext == that.senderContext &&
            sessionHandle == that.sessionHandle &&
            !(command != null ? !command.equals(that.command) : that.command != null) &&
            commandCode == that.commandCode && status == that.status;
    }

    @Override
    public int hashCode() {
        int result = commandCode.hashCode();
        result = 31 * result + (int) (sessionHandle ^ (sessionHandle >>> 32));
        result = 31 * result + status.hashCode();
        result = 31 * result + (int) (senderContext ^ (senderContext >>> 32));
        result = 31 * result + (command != null ? command.hashCode() : 0);
        return result;
    }

    public static ByteBuf encode(EnipPacket packet, ByteBuf buffer) {
        buffer.writeShort(packet.getCommandCode().getCode());

        // Length placeholder...
        int lengthStartIndex = buffer.writerIndex();
        buffer.writeShort(0);

        buffer.writeInt((int) packet.getSessionHandle());
        buffer.writeInt(packet.getStatus().getStatus());
        buffer.writeLong(packet.getSenderContext());
        buffer.writeInt(0);

        int dataStartIndex = buffer.writerIndex();

        if (packet.getCommand() != null) {
            encodeCommand(packet.getCommand(), buffer);
        }

        // Go back and update the length.
        int bytesWritten = buffer.writerIndex() - dataStartIndex;
        buffer.markWriterIndex();
        buffer.writerIndex(lengthStartIndex);
        buffer.writeShort(bytesWritten);
        buffer.resetWriterIndex();

        return buffer;
    }

    public static EnipPacket decode(ByteBuf buffer) {
        CommandCode commandCode = CommandCode.decode(buffer);
        buffer.skipBytes(2); // length
        long sessionHandle = buffer.readUnsignedInt();
        EnipStatus status = EnipStatus.decode(buffer);
        long senderContext = buffer.readLong();
        buffer.skipBytes(4); // options

        Command command = (status == EnipStatus.EIP_SUCCESS) ?
            decodeCommand(commandCode, buffer) : null;

        return new EnipPacket(commandCode, sessionHandle, status, senderContext, command);
    }

    private static ByteBuf encodeCommand(Command command, ByteBuf buffer) {
        switch (command.getCommandCode()) {
            case ListIdentity:
                return ListIdentity.encode((ListIdentity) command, buffer);

            case ListInterfaces:
                return ListInterfaces.encode((ListInterfaces) command, buffer);

            case Nop:
                return Nop.encode((Nop) command, buffer);

            case RegisterSession:
                return RegisterSession.encode((RegisterSession) command, buffer);

            case SendRRData:
                return SendRRData.encode((SendRRData) command, buffer);

            case SendUnitData:
                return SendUnitData.encode((SendUnitData) command, buffer);

            case UnRegisterSession:
                return UnRegisterSession.encode((UnRegisterSession) command, buffer);

            default:
                throw new EncoderException(String.format("unhandled command: %s", command.getCommandCode()));
        }
    }

    private static Command decodeCommand(CommandCode commandCode, ByteBuf buffer) {
        switch (commandCode) {
            case ListIdentity:
                return ListIdentity.decode(buffer);

            case ListInterfaces:
                return ListInterfaces.decode(buffer);

            case Nop:
                return Nop.decode(buffer);

            case RegisterSession:
                return RegisterSession.decode(buffer);

            case SendRRData:
                return SendRRData.decode(buffer);

            case SendUnitData:
                return SendUnitData.decode(buffer);

            case UnRegisterSession:
                return UnRegisterSession.decode(buffer);

            default:
                throw new DecoderException(String.format("unhandled command: %s", commandCode));
        }
    }

}