CS 580 Client-Server Spring Semester, 2004 Streamless Sockets
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Streamless Socket Access

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VisualWorks

• Read/Write
• Send/Receive

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• readWait

• Blocks until there is data to read on socket

• readWaitWithTimeoutMs: aninteger

• Blocks until there is data to read or socket or time out occurs

• Return true if a time out occurred

• writeWait
• writeWaitWithTimeoutMs: anInteger

• Same as read versions but used on writing data

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Example – From Date Server

processRequest: aSocketAccessor 
   | timedOut readBuffer charactersRead date |
   
   [timedOut := aSocketAccessor readWaitWithTimeoutMs: 10000.
   timedOut ifTrue: [^nil].
   readBuffer := String new: 50.
   charactersRead := aSocketAccessor readInto: readBuffer
            untilFalse: [:count | count < 5].
   (readBuffer startsWith: 'date') 
      ifTrue: 
         [aSocketAccessor writeWait.
         date := Date today printString.
         aSocketAccessor writeFrom: date]] 
         ensure: [aSocketAccessor close]

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Testing

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processWithStreamsRequest: aSocketAccessor 
   | clientRequest aReadStream aWriteStream |
   
   [aReadStream := aSocketAccessor readStream lineEndTransparent.
   aWriteStream := aSocketAccessor writeStream lineEndTransparent.
   (aSocketAccessor readWaitWithTimeoutMs: 10000) ifTrue: [^nil].
   clientRequest := aReadStream through: Character cr.
   (clientRequest startsWith: 'date') 
      ifTrue: 
         [aWriteStream
            nextPutAll: Date today printString;
            commit]] 
         ensure: [aSocketAccessor close]

 aReadStream basicAtEnd not or: 
   [ (aSocketAccessor readWaitWithTimeoutMs: timeout) not ]

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Java JDK 1.4 NIO & Sockets

• Channels
• Buffers
• Encoders
• Decoders

• java.nio
• java.nio.channels
• java.nio.charset

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• Blocking IO
• Multiplexed non-blocking IO with selectors

• Sockets
• Files
• Pipes

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Byte, int, float, char, double, long, short

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Date Server Example

import java.io.*;
import java.net.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.util.*;
public class NIOTimeServer 
   {
   ServerSocketChannel acceptor;
    private static Charset usAscii = Charset.forName("US-ASCII");
    private static CharsetDecoder asciiDecoder = usAscii.newDecoder();
    private static CharsetEncoder asciiEncoder = usAscii.newEncoder();
   
   public static void main(String[] args) throws IOException {
      int port = Integer.parseInt( args[0]);   
      
      NIOTimeServer server = new NIOTimeServer( port );
      server.run();
   }
   
   public NIOTimeServer(int port ) throws IOException {
      InetSocketAddress serverAddress =
         new InetSocketAddress(InetAddress.getLocalHost(), port);
      acceptor = ServerSocketChannel.open();
      acceptor.socket().bind( serverAddress );
   }

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   public void run() 
      {
      while (true) 
         {
         try
            {
            SocketChannel client = acceptor.accept();
            processRequest( client );
            }
         catch (IOException acceptError)
            {
            // for a later lecture
            }
         }
      }
   
   void processRequest( SocketChannel  client) throws IOException
      {
      try
         {
         String request = readLine( client );
         String response = processRequest( request);
         CharBuffer charsOut = CharBuffer.wrap( response + "\r\n");
         ByteBuffer bytesOut = asciiEncoder.encode(charsOut);
         client.write(bytesOut);
         }
      finally  
         {
         client.close();
         }
      }
      
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   String readLine( SocketChannel  client) throws IOException
      {
      ByteBuffer inputBytes = ByteBuffer.allocate(1024);
      String input = "";
      CharBuffer inputChars;
      while (input.lastIndexOf( "\n") < 0 )
         {
         inputBytes.clear();
         client.read( inputBytes );
         inputBytes.flip();
         inputChars = asciiDecoder.decode(inputBytes);
         input = input + inputChars.toString();
         }
      return input;
      }
      
   String processRequest( String request )
      {
      if (request.startsWith("date")) 
         return new Date().toString();
      else
         return "";
      }
   }

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      try
         {
         String request = readLine( client );
         String response = processRequest( request);
         write( client, response);
         }

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How do we Test this?

• Keep the IO separate from the handling of the request

• Allows us to test the logic of handling without IO

• Create a Mock SocketChannel

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