Socket Programming
2005/03/16
Reference
W. Richard Stevens, “Unix Network Programming 2/e Volume 1” ,1998
James F. Kurose and Keith W. Ross,
"Computer Networks: A Top-Down Approach
Featuring the Internet 3/e“, 2002.
Server & Client
TCP/UDP
IP
Ethernet Adapter Server
TCP/UDP
IP
Ethernet Adapter Clients
Socket API
hardware kernel space user space
ports
Server & Client
What is Socket?
Service access point of TCP/IP protocol stacks
Socket is an interface between Application
layer and Transport layer
What is Socket?
A socket is a file descriptor that lets an application read/write data from/to the network
Once configured the application can
pass data to the socket for network transmission
receive data from the socket (transmitted through the network by some other host)
TCP Client & Server
socket() bind() listen() accept()
write() read()
read() TCP Server
close() socket()
TCP Client
connect() write()
read() close()
connection establishment data request
data reply
end-of-file notification
socket()
int s = socket(domain, type, protocol);
s: socket descriptor
domain: integer, communication domain
e.g., AF_INET (IPv4 protocol) – typically used
type: communication type
SOCK_STREAM: reliable, 2-way, connection-based service (TCP)
SOCK_DGRAM: unreliable, connectionless (UDP)
protocol: specifies protocol (see file /etc/protocols for a list of options) - usually set to 0
socket()
Ex.
int s; /* socket descriptor */
if((s = socket(AF_INET, SOCK_STREAM, 0)) < 0) { perror(“socket”);
exit(1);
}
bind()
int status = bind(sockid, &addrport, size);
status: error status, = -1 if bind failed
sockid: integer, socket descriptor
addrport: struct sockaddr, the (IP) address and port of the machine (address usually set to
INADDR_ANY – chooses a local address)
size: the size (in bytes) of the addrport structure
bind()
Ex.
int s; /* socket descriptor */
struct sockaddr_in srv; /* used by bind() */
/* create the socket */
srv.sin_family = AF_INET; /* use the Internet addr family */
srv.sin_port = htons(8888); /* bind socket ‘fd’ to port 8888*/
/* bind: a client may connect to any of my addresses */
srv.sin_addr.s_addr = htonl(INADDR_ANY);
if(bind(s, (struct sockaddr*) &srv, sizeof(srv)) < 0) { perror("bind"); exit(1);
}
listen()
int status = listen(sock, queuelen);
status: 0 if listening, -1 if error
sock: integer, socket descriptor
queuelen: integer, # of active participants that can
“wait” for a connection
listen is non-blocking: returns immediately
listen()
Ex.
int s; /* socket descriptor */
struct sockaddr_in srv; /* used by bind() */
/* 1) create the socket */
/* 2) bind the socket to a port */
if(listen(s, 5) < 0) { perror(“listen”);
exit(1);
}
accept()
int s = accept(sock, &name, &namelen);
s: integer, the new socket (used for data-transfer)
sock: integer, the orig. socket (being listened on)
name: struct sockaddr, address of the active participant
namelen: sizeof(name): value/result parameter
must be set appropriately before call
adjusted by OS upon return
accept is blocking: waits for connection before returning
accept()
Ex.
int s; /* socket descriptor */
struct sockaddr_in srv; /* used by bind() */
struct sockaddr_in cli; /* used by accept() */
int newfd; /* returned by accept() */
int cli_len = sizeof(cli); /* used by accept() */
/* 1) create the socket */
/* 2) bind the socket to a port */
/* 3) listen on the socket */
newfd = accept(s, (struct sockaddr*) &cli, &cli_len);
if(newfd < 0) {
perror("accept"); exit(1);
}
connect()
int status = connect(sock, &name, namelen);
status: 0 if successful connect, -1 otherwise
sock: integer, socket to be used in connection
name: struct sockaddr: address of passive participant
namelen: integer, sizeof(name)
connect is blocking
connect()
Ex.
int s; /* socket descriptor */
struct sockaddr_in srv; /* used by connect() */
/* create the socket */
/* connect: use the Internet address family */
srv.sin_family = AF_INET;
/* connect: socket ‘s’ to port 8888 */
srv.sin_port = htons(8888);
/* connect: connect to IP Address “140.112.1.1” */
srv.sin_addr.s_addr = inet_addr(“140.112.1.1”);
if(connect(s, (struct sockaddr*) &srv, sizeof(srv)) < 0) { perror(”connect"); exit(1);
}
read()
Ex.
read blocks waiting for data from the client but does not guarantee that sizeof(buf) is read
int s; /* socket descriptor */
char buf[512]; /* used by read() */
int nbytes; /* used by read() */
/* 1) create the socket */
/* 2) bind the socket to a port */
/* 3) listen on the socket */
/* 4) accept the incoming connection */
if((nbytes = read(s, buf, sizeof(buf))) < 0) { perror(“read”); exit(1);
}
write()
Ex.
int s; /* socket descriptor */
char buf[512]; /* used by write() */
int nbytes; /* used by write() */
/* 1) create the socket */
/* 2) bind the socket to a port */
/* 3) listen on the socket */
/* 4) accept the incoming connection */
if((nbytes = write(s, buf, sizeof(buf))) < 0) { perror(“write”);
exit(1);
}
Address & Port Byte Ordering
Address and port are stored as integers
Problem:
different machines / OS’s use different word orderings
little-endian: lower bytes first
big-endian: higher bytes first
these machines may communicate with one another over the network
128.119.40.12
128 119 40 12
12.40.119.128 128 119 40 12
Big-Endian machine
Little-Endian machine
WR ON G!!!
Byte Ordering Solution
htons(): “Host to Network Short”
htonl(): “Host to Network Long”
ntohs(): “Network to Host Short”
ntohl(): “Network to Host Long”
Other Useful Function
void bzero(void *dest, size_tnbytes);
void bcopy(const void *src, void *dest, size_tnbytes);
int bcmp(const void *ptr1, const void *ptr2, size_tnbytes);
void *memset(void *dest, intc, size_tnbytes);
void *memcpy(void *dest, const void *src, size_tnbytes);
int memcmp(const void *ptr1, const void *ptr2, size_tnbytes);
Other Useful Function
int gethostname(char *name, int len)
struct hostent * gethostbyaddr(char *addr, int len, int type):
in_addr_t inet_addr(const char *cp)
char * inet_ntoa(const struct in_addr in)
Make sure to #include the header files, check
it yourself !!
HW1:Echo Server & Client
Your job is to implement an Echo Server which will send back whatever it receives
You also have to write a program which will send message to the Echo Server
Client Server
Establish TCP Connection
Terminate Connection
“Hello World”
“Hello World”
HW1:Echo Server & Client
Echo Server execution format
While someone connects to the server, server should output some information
EchoServer server_port
Client execution format
EchoClient server_ip server_port message Client_IP[140.112.30.1]
Client_Port[54321]
Message_Received[Hello World]
Message_Sendback[Hello World]
HW1:Echo Server & Client
Your program must be gcc 3.3.1 compatible
Name your program in this way
b91902xxx_s.cc for Echo Server
b91902xxx_c.cc for Client
Make your program as a tarball
Email the tarball to
network_hw@voip.csie.ntu.edu.tw
Subject:[network hw1]b91902xxx name
Due after two weeks (3/30 PM2:20)
tar zcvf b91902xxx_hw1.tar.gz b91902xxx_s.cc b91902xxx_c.cc
