Spring integration TCP server not receiving messages

Question

I am attempting to create a TCP server that accepts messages on port 5002 from an external program. However, it is not receiving messages from the external program.

@Bean
public TcpReceivingChannelAdapter inbound(AbstractServerConnectionFactory cf) {
   TcpReceivingChannelAdapter adapter = new TcpReceivingChannelAdapter();
   adapter.setConnectionFactory(cf);
   adapter.setOutputChannel(tcpIn());
   return adapter;
 }

@Bean
public MessageChannel tcpIn() {
    return new DirectChannel();
}

@Bean
@Transformer(inputChannel = "tcpIn", outputChannel = "serviceChannel")
public ObjectToStringTransformer transformer() {
    return new ObjectToStringTransformer();
}

@ServiceActivator(inputChannel = "serviceChannel")
public void messageToService(String in) {
    // Message received
}

@Bean
public AbstractServerConnectionFactory serverConnectionFactory() {
    TcpNetServerConnectionFactory tcpNetServerConnectionFactory = new TcpNetServerConnectionFactory(5002);
    tcpNetServerConnectionFactory.setSoTimeout(5000);
    tcpNetServerConnectionFactory.setMapper(new TimeoutMapper());
    return tcpNetServerConnectionFactory;
}

To verify my TCP server is working I used telnet like so, and the program did get the text "hello".

telnet 192.168.1.2 5002
Trying 192.168.1.2...
Connected to 192.168.1.2.
Escape character is '^]'.
hello

Setting up wireshark I can see that the computer is receiving messages from the external program (which I am expecting) on port 5002. Why is my program not able to receive these messages?

Update on final solution:

Since the payload did not have a stop line, I had to implement my own deserializer as described by @Artem Bilan. I used the '~' character to signal an end of line from the client.

@Bean
public AbstractServerConnectionFactory serverConnectionFactory() {
    TcpNetServerConnectionFactory tcpNetServerConnectionFactory = new TcpNetServerConnectionFactory(tcpPort);
    tcpNetServerConnectionFactory.setSoTimeout(0);
  tcpNetServerConnectionFactory.setDeserializer(endOfLineSerializer());
    tcpNetServerConnectionFactory.setSerializer(endOfLineSerializer());
    tcpNetServerConnectionFactory.setMapper(new TimeoutMapper());
    return tcpNetServerConnectionFactory;
}

Sample serializer that I implemented:

public class EndOfLineSerializer extends AbstractPooledBufferByteArraySerializer {

private static final char MANUAL_STOP_LINE = '~';
private static final char AUTO_STOP_LINE = '\t';
private static final byte[] CRLF = "\r\n".getBytes();

/**
 * Reads the data in the inputStream to a byte[]. Data must be terminated
 * by a single byte. Throws a {@link SoftEndOfStreamException} if the stream
 * is closed immediately after the terminator (i.e. no data is in the process of
 * being read).
 */
@Override
protected byte[] doDeserialize(InputStream inputStream, byte[] buffer) throws IOException {
    int n = 0;
    int bite;

    try {
        while (true) {

            try {
                bite = inputStream.read();
            } catch (SocketTimeoutException e) {
                bite = -1;
            }

            if (bite < 0) {
                // Payload complete
                break;
            }

            if ((n > 0 && bite == '\n' && buffer[n - 1] == '\r') || bite == this.MANUAL_STOP_LINE || bite == this.AUTO_STOP_LINE) {
                break;
            }

            buffer[n++] = (byte) bite;
            if (n >= this.maxMessageSize) {
                throw new IOException("Terminator not found before max message length: " + this.maxMessageSize);
            }
        }
        return copyToSizedArray(buffer, n);
    } catch (IOException e) {
        publishEvent(e, buffer, n);
        throw e;
    } catch (RuntimeException e) {
        publishEvent(e, buffer, n);
        throw e;
    }
}

/**
 * Writes the byte[] to the stream and appends the CRLF.
 */
@Override
public void serialize(byte[] bytes, OutputStream outputStream) throws IOException {
    outputStream.write(bytes);
    outputStream.write(this.CRLF);
    }
}

Answer 1

See the documentation; scroll down to

TCP is a streaming protocol; this means that some structure has to be provided to data transported over TCP, so the receiver can demarcate the data into discrete messages. Connection factories are configured to use (de)serializers to convert between the message payload and the bits that are sent over TCP. This is accomplished by providing a deserializer and serializer for inbound and outbound messages respectively. A number of standard (de)serializers are provided.

and read about the standard deserializers. With your configuration, the standard deserializer is waiting for the terminaing \r\n (CRLF).

Telnet appends CRLF, so that's why it's working.

Answer 2

The TcpNetServerConnectionFactory uses ByteArrayCrLfSerializer by default, where this is what is count as a message delimiter:

private static final byte[] CRLF = "\r\n".getBytes();

So, you should be sure that your client send message with the proper symbol in the end.

There are a bunch of out-of-the-box serializers for your choice:

https://docs.spring.io/spring-integration/docs/5.0.3.RELEASE/reference/html/ip.html#tcp-connection-factories

Or you can implement your own Deserializer and inject into the serverConnectionFactory bean definition.