Sockets For Clients

1
Sockets For Clients

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

2
Contents

• The Socket class
• Telnet and Telnet protocols
• Socket information
• Socket Options
• InetAddress class

3
Socket

• A socket is a connection between two hosts
• Socket client and server socket
• Socket class (client) and ServerSocket (server)
• Client socket operations
• connect to a remote machine (a.k.a. server)
• send data
• receive data
• close a connection

4
Server Socket

• Server Socket operations
• connect to a remote machine (a.k.a. server)
• send data
• receive data
• close a connection
• bind to a port (register the port to host)
• listen for incoming data
• accept connections from remote machines on the
  bound part

5
Telnet and Telnet Protocols

• Telnet command
• telnet localhost 25 or telnet 140.129.20.87 25
• Port 25 provides SMTP (Simple Mail Transfer
  Protocol) service.
• Protocol Set of rules and conventions used by
  communicating participants
• check page 303 for the SMTP protocol
• Type HELO command
• Reponse 250 gamma. Hello alpha.cse.ttu.edu.tw
  140.129.20.247, pleased to meet you

6
Telnet and Telnet Protocols

• Type HELP
• 214-Commands
• 214- HELO MAIL RCPT DATA RSET
• 214- NOOP QUIT HELP VRFY EXPN
• 214-For more info use "HELP lttopicgt".
• 214-smtp
• 214-To report bugs in the implementation contact
  Sun Microsystems
• 214-Technical Support.
• 214-For local information contact postmaster at
  this site.
• 214 End of HELP info

7
Socket Class

• Client-side TCP operations
• URL, URLConnection, Applet and JEditorPane use
  Socket for client communication.
• Constructors (page 307-310)
• Socket public Socket(InetAddress address,int port)
  
• public Socket(String host, int port,
  InetAddress localAddr, int localPort)
• public Socket(InetAddress address, int port,
  InetAddress localAddr, int localPort)

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Socket Class

• Socket theSocket new Socket("140.129.20.87",
  13)
• Connect to host "140.129.20.87 and
• use port 13 service
• InetAddress fddi new InetAddress(fddisunsie.oit
  .unc.edu)
• Socket theSocket new Socket(www.oreilly.com,
  80, fddi, 0)
• Use fddi network interface
• Local port 102465535

9
Socket Information

• public InetAddress getInetAddress()
• Returns the address to which the socket is
  connected.
• Returns the remote IP address to which this
  socket is connected.
• public InetAddress getLocalAddress()
• Gets the local address to which the socket is
  bound.
• Returnsthe local address to which the socket is
  bound.

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Socket Information

• public int getPort()
• Returns the remote port to which this socket is
  connected.
• Returnsthe remote port number to which this
  socket is connected
• public int getLocalPort()
• Returns the local port to which this socket is
  bound.
• Returnsthe local port number to which this
  socket is connected.

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Socket Information

• Example 10-3 (SocketInfo) on page 313
• Check www.ttu.edu.tw and 140.129.20.83
• Outputs
• Connected to 140.129.20.83/140.129.20.83 on port
  80 from port 1118 of JAVA.ttu.edu.tw/140.129.20.89
  
• Connected to www.ttu.edu.tw/140.129.21.6 on port
  80 from port 1122 of JAVA.ttu.edu.tw/140.129.20.89
  

12
Socket Information

• public InputStream getInputStream()
• Get the input stream for this socket.
• Returnsan input stream for reading bytes from
  this socket.
• public OutputStream getOutputStream()
• Get the output stream for this socket.
• Returnsan output stream for writing bytes to
  this socket.

13
Socket Information

• Example 10-4 (Daytime Protocol Client) on page
  314
• Daytime protocol Connect to 140.129.20.87 and
  port 13
• Use getInputStream to read the daytime
• Outputs
• It is Tue Mar 27 094543 2001 at 140.129.20.87

14
Socket Information

• Example 10-4 (Daytime Protocol Client) on page
  314
• Daytime protocol Connect to 140.129.20.87 and
  port 13
• Use getInputStream to read the daytime
• Outputs
• It is Tue Mar 27 094543 2001 at 140.129.20.87
• More complicate sample Time protocol on page 317

15
Socket Information

• Example 10-6 (Echo Protocol Client) on page 321
• Echo protocol Connect to 140.129.20.87 and port
  7
• You may try telnet 140.129.20.87 7
• Use getInputStream to read the echo string from
  server
• Use getOutputStream to write string to server

16
Closing the Socket

• It is very good practice to close sockets.
• System may hit max number of sockets before GC
  kicks in. (Especially for Browser app.)
• public void close()
• Closes this socket.
• public void shutdownInput()
• Places the input stream for this socket at "end
  of stream".
• Any data sent to the input stream side of the
  socket is acknowledged and then silently
  discarded.
• If you read from a socket input stream after
  invoking shutdownInput() on the socket, the
  stream will return EOF.

17
Closing the Socket

• public void shutdownOutput()
• Disables the output stream for this socket.
• For a TCP socket, any previously written data
  will be sent followed by TCP's normal connection
  termination sequence.
• If you write to a socket output stream after
  invoking shutdownOutput() on the socket, the
  stream will throw an IOException.

18
Closing the Socket

• Example PortScan on page 323
• Code sample close a socket
• finally
• try
• if (connection ! null)
  connection.close()
• catch (IOException e)

19
Socket Options

• public void setTcpNoDelay(boolean on)
• Enable/disable TCP_NODELAY (disable/enable
  Nagle's algorithm).
• Parameterson - true to enable TCP_NODELAY, false
  to disable
• public boolean getTcpNoDelay()
• Tests if TCP_NODELAY is enabled.
• Returnsa boolean indicating whether or not
  TCP_NODELAY is enabled.

20
Socket Options

• Datagrams not yet been sent but Socket is closed
• public void setSoLinger(boolean on, int linger)
• Enable/disable SO_LINGER with the specified
  linger time in seconds.
• The maximum timeout value is platform specific.
• The setting only affects socket close.
• public int getSoLinger()
• Returns setting for SO_LINGER.
• -1 returns implies that the option is disabled.
• Example
• If (s.getSoLinger() -1) s.setSoLinger(true,
  240)

21
Socket Options

• public void setSoTimeout(int timeout)
• Enable/disable SO_TIMEOUT with the specified
  timeout, in milliseconds.
• With this option set to a non-zero timeout, a
  read() call on the InputStream associated with
  this Socket will block for only this amount of
  time.
• If the timeout expires, a java.io.InterruptedIOExc
  eption is raised, though the Socket is still
  valid.
• The option must be enabled prior to entering the
  blocking operation to have effect.
• The timeout must be gt 0.
• A timeout of zero is interpreted as an infinite
  timeout.

22
Socket Options

• public int getSoTimeout()
• Returns setting for SO_TIMEOUT.
• 0 returns implies that the option is disabled
  (i.e., timeout of infinity).
• Example
• If (s.getSoTimeout() 0) s.setSoTimeout(180000)

23
Socket Options

• public void setSendBufferSize(int size)
• Sets the SO_SNDBUF option to the specified value
  for this Socket.
• The SO_SNDBUF option is used by the platform's
  networking code as a hint for the size to set the
  underlying network I/O buffers.
• Increasing buffer size can increase the
  performance of network I/O for high-volume
  connection, while decreasing it can help reduce
  the backlog of incoming data.
• Because SO_SNDBUF is a hint, applications that
  want to verify what size the buffers were set to
  should call getSendBufferSize()

24
Socket Options

• public int getSendBufferSize()
• Get value of the SO_SNDBUF option for this
  Socket, that is the buffer size used by the
  platform for output on this Socket

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Socket Options

• public void setReceiveBufferSize(int size)
• Sets the SO_RCVBUF option to the specified value
  for this Socket.
• The SO_RCVBUF option is used by the platform's
  networking code as a hint for the size to set the
  underlying network I/O buffers.
• Increasing buffer size can increase the
  performance of network I/O for high-volume
  connection, while decreasing it can help reduce
  the backlog of incoming data.
• Because SO_RCVBUF is a hint, applications that
  want to verify what size the buffers were set to
  should call getReceiveBufferSize()

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Socket Options

• public int getReceiveBufferSize()
• Gets the value of the SO_RCVBUF option for this
  Socket, that is the buffer size used by the
  platform for input on this Socket

27
Socket Options

• If SO_KEEPALIVE is turned on, then the client
  will occasionally send a data packet over an idle
  connection (once every two hours) just to make
  sure the server hasnt crashed.
• public void setKeepAlive(boolean on)
• Enable/disable SO_KEEPALIVE.
• Parameterson - whether or not to have socket
  keep alive turned on.
• public boolean getKeepAlive()
• Tests if SO_KEEPALIVE is enabled.

28
InetAddress Class

• public static InetAddress getByName(String host)
• Determines the IP address of a host, given the
  host's name.
• The host name can either be a machine name, such
  as "java.sun.com", or a string representing its
  IP address, such as "206.26.48.100".
• public static InetAddress getAllByName(String ho
  st)
• Determines all the IP addresses of a host, given
  the host's name.
• public static InetAddress getLocalHost()
• Returns the local host.

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InetAddress Class

• public InetAddress(String host)
• Create a InetAddress of a host, given the host's
  name.
• public public byte getAddress()
• Returns the raw IP address of this InetAddress
  object.
• The result is in network byte order the highest
  order byte of the address is in getAddress()0.
• public String getHostAddress()
• Returns the IP address string "d.d.d.d".

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InetAddress Class

• public String getHostName()
• Gets the host name for this IP address.
• public boolean isMulticastAddress()
• Utility routine to check if the InetAddress is an
  IP multicast address.
• IP multicast address is a Class D address i.e
  first four bits of the address are 1110.