ASCIIInputStream.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.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Class implementing a specialized <tt>InputStream</tt> which
 * decodes characters read from the raw stream into bytes.
 *
 * Note that the characters denoting start and end of a frame
 * as given by the specification are exceptions;
 * They are translated to the "virtual" FRAME_START and FRAME_END.
 *
 * @author Dieter Wimberger
 * @version @version@ (@date@)
 *
 * @see net.wimpi.modbus.io.ModbusASCIITransport#FRAME_START
 * @see net.wimpi.modbus.io.ModbusASCIITransport#FRAME_END
 */
public class ASCIIInputStream extends FilterInputStream {

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

    /**
     * Constructs a new <tt>ASCIIInputStream</tt> instance
     * reading from the given <tt>InputStream</tt>.
     *
     * @param in a base input stream to be wrapped.
     */
    public ASCIIInputStream(InputStream in) {
        super(in);
    }// constructor

    /**
     * Reads a byte from the ASCII encoded stream.
     *
     * @return int the byte read from the stream.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read() throws IOException {
        StringBuffer sbuf = new StringBuffer(2);
        int ch = in.read(); // !@todo that thing blocks until something was received
        if (ch == -1) {
            return -1;
        }
        // System.out.println("Read "+ch+ "="+(char)ch);
        sbuf.append((char) ch);
        if (sbuf.charAt(0) == ':') {
            // System.out.println("FRAME START");
            return ModbusASCIITransport.FRAME_START;
        } else {
            if (sbuf.charAt(0) == '\r') {
                if (in.read() == 10) {
                    // System.out.println("FRAME END");
                    return ModbusASCIITransport.FRAME_END;
                } else {
                    // malformed stream
                    throw new IOException("Malformed Stream No Frame Delims");
                }
            } else {
                try {
                    sbuf.append((char) in.read());
                    logger.trace("Read byte: {}", sbuf.toString().toLowerCase());
                    return Integer.parseInt(sbuf.toString().toLowerCase(), 16);
                } catch (NumberFormatException ex) {
                    // malformed stream
                    final String errMsg = "Malformed Stream - Wrong Characters";
                    logger.debug("{}: {}", errMsg, sbuf.toString());
                    throw new IOException(errMsg);
                }
            }
        }
    }// read

}// class ASCIIInputStream