Sockets For Clients Instructors: Fu-Chiung Cheng ( 鄭福炯 ) Associate Professor Computer Science & Engineering Tatung University

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

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

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

Telnet and Telnet Protocols Telnet command –%telnet localhost 25 or telnet 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 [ ], pleased to meet you

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 ". 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

Socket Class Client-side TCP operations URL, URLConnection, Applet and JEditorPane use Socket for client communication. Constructors: (page ) –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)

Socket Class Socket theSocket = new Socket(" ", 13); –Connect to host " “ and –use port 13 service InetAddress fddi = new InetAddress(“fddisunsie.oit.unc.edu”); Socket theSocket = new Socket( 80, fddi, 0) –Use fddi network interface –Local port 1024~65535

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. –Returns:the local address to which the socket is bound.

Socket Information public int getPort() –Returns the remote port to which this socket is connected. –Returns:the remote port number to which this socket is connected public int getLocalPort() –Returns the local port to which this socket is bound. –Returns:the local port number to which this socket is connected.

Socket Information Example 10-3 (SocketInfo) on page 313 Check and www.ttu.edu.tw Outputs: –Connected to / on port 80 from port 1118 of JAVA.ttu.edu.tw/ –Connected to on port 80 from port 1122 of JAVA.ttu.edu.tw/

Socket Information public InputStream getInputStream() –Get the input stream for this socket. –Returns:an input stream for reading bytes from this socket. public OutputStream getOutputStream() –Get the output stream for this socket. –Returns:an output stream for writing bytes to this socket.

Socket Information Example 10-4 (Daytime Protocol Client) on page 314 Daytime protocol: Connect to and port 13 Use getInputStream to read the daytime Outputs: –It is Tue Mar 27 09:45: at

Socket Information Example 10-4 (Daytime Protocol Client) on page 314 Daytime protocol: Connect to and port 13 Use getInputStream to read the daytime Outputs: –It is Tue Mar 27 09:45: at More complicate sample: Time protocol on page 317

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

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.

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.

Closing the Socket Example: PortScan on page 323 Code sample: close a socket finally { try { if (connection != null) connection.close(); } catch (IOException e) {} }

Socket Options public void setTcpNoDelay(boolean on) –Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm). –Parameters:on - true to enable TCP_NODELAY, false to disable public boolean getTcpNoDelay() –Tests if TCP_NODELAY is enabled. –Returns:a boolean indicating whether or not TCP_NODELAY is enabled.

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);

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.InterruptedIOException 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 > 0. –A timeout of zero is interpreted as an infinite timeout.

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);

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()

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

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()

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

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 hasn’t crashed. public void setKeepAlive(boolean on) –Enable/disable SO_KEEPALIVE. –Parameters:on - whether or not to have socket keep alive turned on. public boolean getKeepAlive() –Tests if SO_KEEPALIVE is enabled.

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 " ". public static InetAddress[] getAllByName(String host) –Determines all the IP addresses of a host, given the host's name. public static InetAddress getLocalHost() –Returns the local host.

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".

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.