Fall 2000Datacom 11 Socket Programming Review Examples: Client and Server-Diagnostics UDP versus TCP Echo

Fall 2000Datacom 12 Socket Interface-an Application Programming Interface (API) Create the Socket for a specific transport layer protocol s=socket(PF_INET,SOCK_STREAM,0) or s=socket(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

Fall 2000Datacom 13 Data structures: hostent *hp hp->h_name (character) contains host name hp->h_length number of bytes in IP address hp->h_addr[4] contains IP address byte1:byte2:byte3:byte4 A.B.C.D 0<A,B,C,D< is address of localhost or loop-back address

Fall 2000Datacom 14 Data structures: sockaddr_in sin sin.sin_family AF_INET sin.sin_addr.s_addr IP address in reverse byte order DCBA is address of localhost or loop-back address sin.sin_port Server port number in some strange format

Fall 2000Datacom 15 Socket Interface: Server (a) Creating socket s=socket(PF_INET,SOCK_STREAM,0) Binding a Socket to a Port Number—this 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 client’s IP address—it cannot be specified until connection is accepted.

Fall 2000Datacom 16 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) –Sender’s IP address is returned as sin.sin_addr.s_addr –New socket is created and its number is returned

Fall 2000Datacom 17 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)

Fall 2000Datacom 18 Socket Interface: Client (a) Create a socket s=socket(PF_INET,SOCK_STREAM,0) Connecting to a server-active open connect (s, (struct sockaddr*) &sin, sizeof(sin)) Server’s IP address is stored in sin.sin_addr.s_addr Server’s Port is stored in sin.sin_port Returns accept or not accepted

Fall 2000Datacom 19 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