8.1 Client-Server Model

• 8.1.1 gethostbyname
• 8.1.2 getservbyname
• 8.1.3 socket and bind
• 8.1.4 listen and accept

 CLIENT---------------------SERVER
-------------------------------------------

socket() -----------------------socket()

(bind()) -----------------------bind()

----------------------------------listen()

connect()--------------->

<-------------- -----------------accept()

send()------------------>
 

<-------------- -----------------recv()
send() ------------------>

---------------------------------recv()

close()

Communication addresses:

struct sockaddr_in myaddr; /* for local socket address */
struct sockaddr_in peeraddr; /* for peer socket address */

8.1.1 gethostbyname

struct hostent *gethostbyname(name)
char *name;

Example:

struct hostent *hp; /*ptr to host info for remote*/
--------------
peeraddr.sin_family = AF_INET;
hp = gethostbyname(argv[1])
peeraddr_in.sin_addr.s_addr
= ((struct in_addr *)(hp->h_addr))->s_addr;

8.1.2 getservbyname

struct servent *getservbyname(name,proto)
char *name, *proto;

Example:

struct servent *sp /* pointer to service info */
-----
sp = getservbyname ( "example", "tpc" );
peeraddr.sin_port = sp->s_port;

8.1.3 socket and bind

s = socket ( af, type, protocol );
int af,type,protocol;

bind(s,addr,addrlen)
int s
struct sockaddr *addr;
int addrlen;

Example:

struct sockaddr_in sin;
s = socket(AF_INET,SOCK_STREAM,0);
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = INADDR_ANY;
sin.sin_port = MYPORT;
bind ( s, &sin, sizeof(sin) );

8.1.4 listen and accept

listen(s, maxrequests)
int s, maxrequests;
..........
s=accept(ls,addr,addrlen)
int s;
int ls;
struct sockaddr *addr;
int *addrlen;

Example:

listen (ls,5);
....................

addrlen = sizeof(sockaddr_in);
s = accept( ls, &peeraddr, &addrlen );

SOCKET s IS NOW READY TO RECEIVE DATA FROM CLIENT

recv (s, &buffer, len, 0);
............................
send (s, &buff2, len2,0);

CLIENT:

connect ( s, addr, addrlen)
int s;
struct sockaddr *addr;
int addrlen;

count = send(s,msg,flags)
int s;
char *msg;
int len,flags;