ModbusASCIITransport.java

/***
 * Copyright 2002-2010 jamod development team
 *
 * 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 net.wimpi.modbus.io;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.commons.io.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import net.wimpi.modbus.Modbus;
import net.wimpi.modbus.ModbusCoupler;
import net.wimpi.modbus.ModbusIOException;
import net.wimpi.modbus.msg.ModbusMessage;
import net.wimpi.modbus.msg.ModbusRequest;
import net.wimpi.modbus.msg.ModbusResponse;
import net.wimpi.modbus.util.ModbusUtil;

/**
 * Class that implements the Modbus/ASCII transport
 * flavor.
 *
 * @author Dieter Wimberger
 * @author John Charlton
 * @version @version@ (@date@)
 */
public class ModbusASCIITransport extends ModbusSerialTransport {

    private static final Logger logger = LoggerFactory.getLogger(ModbusASCIITransport.class);

    private DataInputStream m_InputStream; // used to read from
    private ASCIIOutputStream m_OutputStream; // used to write to

    private byte[] m_InBuffer;
    private BytesInputStream m_ByteIn; // to read message from
    private BytesOutputStream m_ByteInOut; // to buffer message to
    private BytesOutputStream m_ByteOut; // write frames

    /**
     * Constructs a new <tt>MobusASCIITransport</tt> instance.
     */
    public ModbusASCIITransport() {
    }// constructor

    @Override
    public void close() throws IOException {
        IOUtils.closeQuietly(m_InputStream);
        IOUtils.closeQuietly(m_OutputStream);
        super.close();
    }// close

    @Override
    public void writeMessage(ModbusMessage msg) throws ModbusIOException {

        try {
            synchronized (m_ByteOut) {
                // write message to byte out
                msg.setHeadless();
                msg.writeTo(m_ByteOut);
                byte[] buf = m_ByteOut.getBuffer();
                int len = m_ByteOut.size();

                // write message
                m_OutputStream.write(FRAME_START); // FRAMESTART
                m_OutputStream.write(buf, 0, len); // PDU
                logger.debug("Writing: {}", ModbusUtil.toHex(buf, 0, len));
                m_OutputStream.write(ModbusUtil.calculateLRC(buf, 0, len)); // LRC
                m_OutputStream.write(FRAME_END); // FRAMEEND
                m_OutputStream.flush();
                m_ByteOut.reset();
                // clears out the echoed message
                // for RS485
                if (m_Echo) {
                    // read back the echoed message
                    readEcho(len + 3);
                }
            }
        } catch (Exception ex) {
            throw new ModbusIOException("I/O failed to write" + ex);
        }
    }// writeMessage

    @Override
    public ModbusRequest readRequest() throws ModbusIOException {

        boolean done = false;
        ModbusRequest request = null;

        int in = -1;

        try {
            do {
                // 1. Skip to FRAME_START
                while ((in = m_InputStream.read()) != FRAME_START) {
                    ;
                }
                // 2. Read to FRAME_END
                synchronized (m_InBuffer) {
                    m_ByteInOut.reset();
                    while ((in = m_InputStream.read()) != FRAME_END) {
                        if (in == -1) {
                            throw new IOException("readRequest: I/O exception - Serial port timeout.");
                        }
                        m_ByteInOut.writeByte(in);
                    }
                    // check LRC
                    if ((m_InBuffer[m_ByteInOut.size() - 1] & 0xff) != ModbusUtil.calculateLRC(m_InBuffer, 0,
                            m_ByteInOut.size() - 1)) {
                        continue;
                    }
                    ;
                    m_ByteIn.reset(m_InBuffer, m_ByteInOut.size());
                    in = m_ByteIn.readUnsignedByte();
                    // check message with this slave unit identifier
                    if (in != ModbusCoupler.getReference().getUnitID()) {
                        continue;
                    }
                    in = m_ByteIn.readUnsignedByte();
                    // create request
                    request = ModbusRequest.createModbusRequest(in);
                    request.setHeadless();
                    // read message
                    m_ByteIn.reset(m_InBuffer, m_ByteInOut.size());
                    request.readFrom(m_ByteIn);
                }
                done = true;
            } while (!done);
            return request;
        } catch (Exception ex) {
            final String errMsg = "I/O exception - failed to read";
            logger.debug("{}: {}", errMsg, ex.getMessage());
            throw new ModbusIOException("readRequest: " + errMsg);
        }

    }// readRequest

    @Override
    public ModbusResponse readResponse() throws ModbusIOException {

        boolean done = false;
        ModbusResponse response = null;
        int in = -1;
        setReceiveThreshold(1);
        try {
            do {
                // 1. Skip to FRAME_START
                while ((in = m_InputStream.read()) != FRAME_START) {
                    if (in == -1) {
                        throw new IOException("readResponse: I/O exception - Serial port timeout.");
                    }
                }
                logger.trace("Managed to read at least one byte");
                // 2. Read to FRAME_END
                synchronized (m_InBuffer) {
                    m_ByteInOut.reset();
                    while ((in = m_InputStream.read()) != FRAME_END) {
                        if (in == -1) {
                            throw new IOException("I/O exception - Serial port timeout.");
                        }
                        m_ByteInOut.writeByte(in);
                    }
                    int len = m_ByteInOut.size();
                    logger.debug("Received: {}", ModbusUtil.toHex(m_InBuffer, 0, len));
                    // check LRC
                    if ((m_InBuffer[len - 1] & 0xff) != ModbusUtil.calculateLRC(m_InBuffer, 0, len - 1)) {
                        logger.debug("LRC is wrong: received={} calculated={}", (m_InBuffer[len - 1] & 0xff),
                                ModbusUtil.calculateLRC(m_InBuffer, 0, len - 1));
                        continue;
                    }

                    m_ByteIn.reset(m_InBuffer, m_ByteInOut.size());
                    in = m_ByteIn.readUnsignedByte();
                    // JDC: To check slave unit identifier in a response we need to know
                    // the slave id in the request. This is not tracked since slaves
                    // only respond when a master request is made and there is only one
                    // master. We are the only master, so we can assume that this
                    // response message is from the slave responding to the last request.
                    // if (in != ModbusCoupler.getReference().getUnitID()) {
                    // continue;
                    // }
                    in = m_ByteIn.readUnsignedByte();
                    // create request
                    response = ModbusResponse.createModbusResponse(in);
                    response.setHeadless();
                    // read message
                    m_ByteIn.reset(m_InBuffer, m_ByteInOut.size());
                    response.readFrom(m_ByteIn);
                }
                done = true;
            } while (!done);
            return response;
        } catch (Exception ex) {
            final String errMsg = String.format("I/O exception - failed to read: %s", ex.getMessage());
            logger.debug("{}", errMsg);
            throw new ModbusIOException("readResponse " + errMsg);
        } finally {
            m_CommPort.disableReceiveThreshold();
        }
    }// readResponse

    /**
     * Prepares the input and output streams of this
     * <tt>ModbusASCIITransport</tt> instance.
     * The raw input stream will be wrapped into a
     * filtered <tt>DataInputStream</tt>.
     *
     * @param in the input stream to be used for reading.
     * @param out the output stream to be used for writing.
     * @throws IOException if an I\O related error occurs.
     */
    @Override
    public void prepareStreams(InputStream in, OutputStream out) throws IOException {
        m_InputStream = new DataInputStream(new ASCIIInputStream(in));
        m_OutputStream = new ASCIIOutputStream(out);
        m_ByteOut = new BytesOutputStream(Modbus.MAX_MESSAGE_LENGTH);
        m_InBuffer = new byte[Modbus.MAX_MESSAGE_LENGTH];
        m_ByteIn = new BytesInputStream(m_InBuffer);
        m_ByteInOut = new BytesOutputStream(m_InBuffer);
    }// prepareStreams

    /**
     * Defines a virtual number for the FRAME START token (COLON).
     */
    public static final int FRAME_START = 1000;

    /**
     * Defines a virtual number for the FRAME_END token (CR LF).
     */
    public static final int FRAME_END = 2000;

}// class ModbusASCIITransport