Socket Programming Review

1
Socket Programming Review

• Examples
• Client and Server-Diagnostics
• UDP versus TCP
• Echo

2
Socket Interface-an Application Programming
Interface (API)

• Create the Socket for a specific transport layer
  protocol
• ssocket(PF_INET,SOCK_STREAM,0) or
• ssocket(PF_INET,SOCK_DGRAM,0)
• returned value is a handle e.g. 3,4 etc.
• PF_INET
• SOCK_STREAM means TCP 1 client/server
• SOCK_DGRAM means UDP multi-clients/server

3
Data structures hostent hp

• hp-gth_name (character) contains host name
• hp-gth_length number of bytes in IP address
• hp-gth_addr4 contains IP address
• byte1byte2byte3byte4
• A.B.C.D 0ltA,B,C,Dlt255
• 127.0.0.1 is address of localhost or loop-back
  address

4
Data structures sockaddr_in sin

• sin.sin_family AF_INET
• sin.sin_addr.s_addr IP address in reverse byte
  order DCBA
• 1.0.0.127 is address of localhost or loop-back
  address
• sin.sin_port Server port number in some strange
  format

5
Socket Interface Server (a)

• Creating socket
• ssocket(PF_INET,SOCK_STREAM,0)
• Binding a Socket to a Port Numberthis is the
  local address of this application
• bind (s, (struct sockaddr)sin, sizeof(sin))
• The entry for IP address in sin.sin_addr.s_addr
  will be the clients IP addressit cannot be
  specified until connection is accepted.

6
Socket Interface Server (b)

• Defining the queue length for the receiving
  socket
• int listen(s, MAX_PENDING)
• Specify max number of calls waiting
• Passive listening
• new_s accept (s, (struct sockaddr)sin,len)
• Senders IP address is returned as
  sin.sin_addr.s_addr
• New socket is created and its number is returned

7
Socket Interface Server (c)

• Receiving a message
• recv(new_s, buf, sizeof(buf),0)
• Receive message, store in buf
• Closing new socket
• close(new_s)

8
Socket Interface Client (a)

• Create a socket
• ssocket(PF_INET,SOCK_STREAM,0)
• Connecting to a server-active open
• connect (s, (struct sockaddr) sin, sizeof(sin))
• Servers IP address is stored in
  sin.sin_addr.s_addr
• Servers Port is stored in sin.sin_port
• Returns accept or not accepted

9
Socket Interface Client (b)

• Sending message to a server
• send(s, buf, len, 0)
• buf is a pointer to the message
• len is length of message string