Socket 101 Excerpt from Network Programming

Transcription

1 Socket 101 Excerpt from Network Programming EDA095 Nätverksprogrammering Originals by Roger Henriksson Computer Science Lund University

2 Java I/O Streams Stream (swe. Ström) - A stream is a sequential ordering of bytes (chars) - Input/output is mostly done by streams, examples include keyboard input, terminal window, files, and network communication - Bytes are written to streams and read from streams 2

3 InputStream Represents an incoming stream public int abstract read() throws IOException; public int read(byte[] input) throws IOException; public int read(byte[] input,int offset,int length) throws IOException; public long skip(long n) throws IOException; public int available() throws IOException; public void close() throws IOException; 3

4 OutputStream Represents an outgoing stream public abstract void write(int b) throws IOException; public void write(byte[] data) throws IOException; public void write(byte[] data, int offset, int length) throws IOException; public void flush() throws IOException; public void close() throws IOException; 4

5 Socket end point for network communication - The socket object handles connection to other sockets - The stream objects handle read/write of bytes (created by the socket upon connection) - Two variants, UDP and TCP 5

6 TCP transmission control protocol Connection between two ports on (usually) two different computers. Keeps connection. Less efficient than UDP, but: Automatic resending / sorting of messages No size limit TCP-connection works as two streams (in/out) 6

7 Socket Constructors public Socket(String host, int port) throws UnknownHostException, IOException; public Socket(InetAddress host,int port) throws IOException; Get-methods public InputStream getinputstream() throws IOException; public OutputStream getoutputstream() throws IOException; public InetAddress getinetaddress(); public int getport(); public InetAddress getlocaladdress(); public int getlocalport(); 7

8 Socket, cont d Settings public void settcpnodelay(boolean on) throws SocketException; public boolean gettcpnodelay() throws SocketException; public void setsotimeout(int milliseconds) throws SocketException; public int getsotimeout() throws SocketException; Disconnect public void close() throws IOException; 8

9 Create a socket (client) Socket socket = null; InputStream input = null; OutputStream output = null; try { socket = new Socket( argus-7.student.lth.se",80); input = socket.getinputstream(); output = socket.getoutputstream(); } catch (UnknownHostException e) { System.out.println(e); System.exit(1); } catch (IOException e) { System.out.println(e); System.exit(1); } 9

10 Reading blocks public int read(byte[] input,int offset,int length) throws IOException; No guarantee that length number of bytes is read! Example: how to read exact 100 bytes byte[] buffer = new byte[100]; int read = 0; int result = 0; while (read<100 && result!=-1) { result = input.read(buffer,read,100-read); if (result!=-1) read = read+result; } 10

11 ServerSocket Receiver for connection requests from sockets. Upon connection creates a socket object Server life cycle 1. Instantiate ServerSocket. 2. Wait for connection (accept()). Socket is created. 3. Fetch streams, getinputstream() and getoutputstream(). 4. Communicate by reading and writing bytes. 5. Disconnect 6. Go to step 2 and wait for new connection. 11

12 ServerSocket, cont d Constructors public ServerSocket(int port) throws IOException; public ServerSocket(int port, int queuelength) throws IOException; Wait for connection (blocking) public Socket accept() throws IOException; Disconnect server public void close() throws IOException; 12

13 ServerSocket, cont d Get-methods public InetAddress getinetaddress(); public int getlocalport(); public int getsotimeout() throws IOException; Set-methods public void setsotimeout(int timeout) throws IOException; 13

14 UDP user datagram protocol Protocol for sending packages. Efficient (for media), but Limited package size large messages must be divided No guarantee that packages arrive at destination No guarantee that packages arrive in order Unconnected protocol 14