Sockets For Servers

1
Sockets For Servers

• Instructors
• Fu-Chiung Cheng
• (???)
• Associate Professor
• Computer Science Engineering
• Tatung University

2
Contents

• The ServerSocket class
• Examples

3
Server Socket

• A socket is a connection between two hosts
• Client connects to a Server and requests services
  from the server
• Servers are like receptionists who sit by the
  phone and wait for incoming call.
• Servers dont know in advance who will call
• Java uses ServerSocket for servers

4
ServerSocket

• Basic life cycle of a server
• A new ServerSocket is created on a particular
  port using a ServerSocket() constructor
• The ServerSocket linstens for incoming
  connection on the port (method accept() blocks
  until a client attempt to make a connect)
• Server accepts a connection and returns a Socket
  objects connecting the client and the server
• Using Sockets getInputStream() and
  getOutputStream for sending to and receiving data
  from the client
• The client, the server or both close the
  connection

5
ServerSocket

• ServerSocket public ServerSocket(int port)
• Creates a server socket on a specified port.
• A port of 0 creates a socket on any free port.
• The maximum queue length for incoming connection
  indications (a request to connect) is set to 50.
• If a connection indication arrives when the queue
  is full, the connection is refused.

6
ServerSocket

• public ServerSocket(int port, int backlog)
• Creates a server socket and binds it to the
  specified local port number, with the specified
  backlog.
• A port number of 0 creates a socket on any free
  port.
• The maximum queue length for incoming connection
  indications (a request to connect) is set to the
  backlog parameter.
• If a connection indication arrives when the queue
  is full, the connection is refused.

7
ServerSocket

• public ServerSocket(int port, int backlog,
  InetAddress bindAddr)
• Create a server with the specified port, listen
  backlog, and local IP address to bind to.
• The bindAddr argument can be used on a
  multi-homed host for a ServerSocket that will
  only accept connect requests to one of its
  addresses.
• If bindAddr is null, it will default accepting
  connections on any/all local addresses.
• The port must be between 0 and 65535, inclusive.

8
ServerSocket Example

• Example 11-1 LocalPortScan on page 353
• List all the services for this machine
• Output from Win 2000
• There is a server on port 135.
• There is a server on port 139.
• There is a server on port 445.
• There is a server on port 1028.
• There is a server on port 1041.
• There is a server on port 1204.
• There is a server on port 2145.
• There is a server on port 2348.
• There is a server on port 3207.
• There is a server on port 8888.

9
ServerSocket

• public Socket accept()
• Listens for a connection to be made to this
  socket and accepts it.
• The method blocks until a connection is made.
• A new Socket s is created and, if there is a
  security manager, the security manager's
  checkAccept method is called with
  s.getInetAddress().getHostAddress() and
  s.getPort() as its arguments to ensure the
  operation is allowed.
• This could result in a SecurityException.
• Returnsthe new Socket

10
ServerSocket

• Example 11-2 (Daytime Server) on page 357
• No new thread is created for incoming call
• Current date is returned

11
ServerSocket Information

• public int getLocalPort()
• Returns the port on which this socket is
  listening.
• public InetAddress getInetAddress()
• Returns the local address of this server socket.
• null if the socket is not yet connected.
• Example 11-4 RandomPort on page 362

12
Closing the ServerSocket

• public void close()
• Closes this socket.
• Example
• for (int port 1 port lt 65535 port)
• try
• ServerSocket server new
  ServerSocket(port)
• server.close()
• catch (IOException e)
• System.out.println(Server on port "
  port ".")
• // end try
• // end for

13
ServerSocket Options

• Accept will wait for an incoming connection for
  SO_TIMEOUT milliseconds.
• public void setSoTimeout(int timeout)
• With this option set to a non-zero timeout, a
  call to accept() for this ServerSocket will block
  for only this amount of time.
• If the timeout expires, a java.io.InterruptedIOExc
  eption is raised
• The option must be enabled prior to entering the
  blocking operation to have effect.
• A timeout of zero is interpreted as an infinite
  timeout.

14
ServerSocket Options

• public int getSoTimeout()
• Retrive setting for SO_TIMEOUT.
• 0 returns implies that the option is disabled
  (i.e., timeout of infinity).
• Examples in page 363

15
Client Test

• Example 11-5 on page 365
• InputThread reads data from IE
• OuputThread sends data to IE

16
Single File Server

• Page 370
• InputThread and OutputThread are executed in
  parallel.
• Can send a file to say IE or Netscape

17
Redirector

• Redirector redirects users from one web site to
  another
• See Example 11-7.
• Try telnet 140.129.20.250 80
• type GET / HTTP 1.0 (get index.html)
• response HTTP 1.0 302 found ..
• java Redirector http//140.129.20.250/
• Redirect all http requests to 140.129.20.250

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Redirector

• Ask Browser to redirect the request to newSite
• out.write("HTTP/1.0 302 FOUND\r\n")
• -- tell client to expect to be redirected
• out.write("Date " now "\r\n")
• -- optional (give current time of
  server)
• out.write("Server Redirector 1.0\r\n")
• -- Optional (version of the server)
• out.write("Location " newSite theFile
  "\r\n")
• -- redirect to newSite

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Redirector

• Note that some browser does not support
  redirection (OK for IE 5.0 and up and Netscape
  4.7 and up)
• Print the website is moved to newSite message.
• See page 378 (ltHTMLgtltHEADgtltTITLEgtDocument
  movedlt/TITLEgtlt/HEADgt .)
• You may telnet to request redirector service
• Can be used to
• firewall and
• load balance control
• Thread pool provides better performance

20
JHTTP

• JHTTP Full-blown HTTP server
• JHTTP can serve an entire document tree
• Images
• Applets
• HTML and text files
• JHTTP uses thread pool to serve request
• Threads are created when the server is started
• If there is no request, thread are put to sleep
  (wait)
• A request from a client will wake up all threads
  in the thread pool for service (notifyAll)

21
JHTTP

• When the thread is serving the request, it is
  just like a simple file transfer.
• JHTTP thread check (parse) the request and send
  the response
• JHTTP thread close the connection and go to
  sleep if there is no more request to be service

22
JHTTP

• JHTTP is functional but still rather simple
• A few features that can be added
• A server administration interface
• Support CGI programs and/or Java Servlet API
• Support for other request methods such as POST,
  HEAD, and PUT
• Server-side includes and/or Java server page

23
JHTTP

• Performance Issues
• Use Just-in-time compiler such as Hotspot
• 2x 10x
• Smart caching
• Use Hashtable
• Use low-priority thread to update the cache