sockets programming in unix

CSTP FS97 CS490D (cotter) 1

Sockets Programming in UNIX

References:

Internetworking with TCP/IP Vol III - BSD version

UNIX Network Programming - W. Richard Stevens

CSTP WS01 CS423 (cotter) 2

Sockets Programming in UNIX

• UNIX Socket API functions• Example TCP / UDP Clients• Example TCP / UDP Servers


Basic Socket FunctionsServer(UNIX)

• Create a socket of a particular type– retcode = socket (family, type, protocol )

– s = socket (PF_INET, SOCK_STREAM, 0)

– returns socket number or -1 on error

• Bind that socket to a specific port– retcode = bind (socket, localaddr, addrlen )

– n = bind (s, (struct sockaddr *)myaddr, sizeof(myaddr))

– returns 0 on success, -1 on fail


Basic Socket FunctionsServer(UNIX)

• Wait for an incoming message– retcode = listen (socket, queuelen)

– ans = listen(s, 0) /* queuelen max ~ 5*/

– return value 0 = success, -1 = fail

• Create a new socket and return new socket ID to client– retcode = accept (socket, addr, addrlen)

– ans = accept (s, (struct sockaddr *)cl_addr, sizeof(cl_addr))

– return value socket number = success, -1 = fail


Basic Socket Functions Server (UNIX)

• Read / send a message– retcode = read [write] (socket, buff, bufflen)– ans = read (s, buf, sizeof(buf))– ans = write (s, buf, sizeof(buf))– return value word count = success, -1 = fail

• Close the socket– retcode = shutdown (socket , direction)

• direction: 0 means input, 1 means output, 2 means both

– retcode = close (socket )– return value 0 = success, -1 = fail


Basic Socket FunctionsClient (UNIX)

• Create a socket of a particular type– Socket ( )

• Establish a connection to a remote Port/Socket– retcode = connect (socket, addr, addrlen)– ans = connect (s, (struct sockaddr *)&svr, sizeof(svr))– return value 0 = success, -1 = fail

• Send and receive messages to/from remote socket– Read ( ) / Write ( )

• Close the socket– Close ( )


Additional Socket Functions(UNIX)

• Byte ordering functions– servaddr.sin_port = htons (SERV_PORT)– myaddr.sin_addr.s_addr = htonl (INADDR_ANY)

• Name resolution functions– host / protocol / service, by name / address / port

• Other Stuff– zero out memory blocks

• bzero ((char *)&myaddr, sizeof(myaddr));

– copy memory blocks• bcopy (hp->h_addr, (caddr_T)&svaddr.sin_addr, hp->h_length)


Example UNIX Client

• Develop a set of procedures that can be used by other programs to implement client / server.

int connectTCP (host, service)

int connectsock(host, service, “tcp”)

[identify service, host, port]

[get a socket]

[connect to service / host / port]

[return socket number]


Example UNIX ClientconnectTCP.c

int connectTCP (char *host, char *service)

{

return connectsock (host, service, “tcp”);

}


Example UNIX Clientconnectsock.c

#include <sys/types.h>, <sys/socket.h>, <netinet/in.h>,<netdb.h>

int connectsock (char *host, char *service, char *protocol)

{

struct hostent *phe;

struct servent *pse;

struct protoent *ppe;

struct sockaddr_in sin;

int s, type;



bzero ((char *)&sin, sizeof (sin));

sin.sin_family = AF_INET;

if (pse = getservbyname (service, protocol) )

sin.sin_port = pse ->s_port;

else if ( (sin.sin_port = htons((u_short)atoi(service))) == 0)

error_exit (“can’t get %s service\n”, service);

if (phe = gethostbyname (host) )

bcopy(phe->h_addr, (char *)&sin.sin_addr, phe->h_length);

else if ((sin.sin_addr.s_addr = inet_addr(host)) == INADDR_NONE)

error_exit (“can’t get %s host\n”, host);



if ( (ppe = getprotobyname (protocol) == 0)error_exit (“can’t get %s host\n”, host);

if (strcmp (protocol, “tcp”) == 0) type = SOCK_STREAM;

else type = SOCK_DGRAM;if (s = socket (PF_INET, type, ppe->p_proto)) < 0)

error_exit (“Can’t create a socket\n”);if (connect (s, (struct sockaddr *)&sin, sizeof(sin)) < 0)

error_exit (“can’t connect to remote socket\n”);return s;}


Example UNIX ClientTCPecho.c

#include <stdio.h>

#define LINELEN 128

int main (argc, argv)

{

host = argv[1];

service = argv[2];

TCPecho (host, service);

exit (0);

}



int TCPecho (char *host, char *service) {char buf[LINELEN+1];int s, n, outchars, inchars;s = connectTCP (host, service);while (fgets (buf, sizeof(buf), stdin))

{buf[LINELEN] = ‘\0’;outchars = strlen(buf);(void) write (s, buf, outchars);



for (inchars = 0; inchars < outchars; inchars +=n) {n = read (s, &buf[inchars], outchars -

inchars);if (n < 0)

error_exit(“socket read failed\n”);}

fputs (buf, stdout);}

}


TCP Client Algorithm

• Client / Server Communications– request / response interaction

– write / read (send / recv)

• Single write may require multiple reads– response may be segmented

– continue appending reads until return length = 0


Example UNIX ClientUDPecho.c

#include <stdio.h>

#define LINELEN 128

int main (argc, argv)

{

host = argv[1];

service = argv[2];

UDPecho (host, service);

exit (0);

}



int UDPecho (char *host, char *service) {char buf[LINELEN+1];int s, n, outchars, inchars;s = connectUDP (host, service);while (fgets (buf, sizeof(buf), stdin))

{buf[LINELEN] = ‘\0’;outchars = strlen(buf);(void) write (s, buf, outchars);



if (read (s, buf, nchars) < 0)

error_exit (“Socket read failed \n”);

fputs (buf, stdout);

}

}


Iterative Connectionless ServersTIME Server

/* UDPtimed.c - main */

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <stdio.h>

#include <time.h>

#include <string.h>

extern int errno;

int passiveUDP(const char *service);

int errexit(const char *format, ...);

#define UNIXEPOCH 2208988800 /* UNIX epoch, in UCT secs*/



int main(int argc, char *argv[])

{

struct sockaddr_in fsin; /* the from address of a client */

char *service = "time"; /* service name or port number */

char buf[1]; /* "input" buffer; any size > 0 */

int sock; /* server socket */

time_t now; /* current time */

int alen; /* from-address length */

switch (argc) {

case 1: break;

case 2: service = argv[1];

break;

default: errexit("usage: UDPtimed [port]\n");

}



sock = passiveUDP(service);

while (1) {

alen = sizeof(fsin);

if (recvfrom(sock, buf, sizeof(buf), 0,

(struct sockaddr *)&fsin, &alen) < 0)

errexit("recvfrom: %s\n", strerror(errno));

(void) time(&now);

now = htonl((u_long)(now + UNIXEPOCH));

(void) sendto(sock, (char *)&now, sizeof(now), 0,

(struct sockaddr *)&fsin, sizeof(fsin));

}

}


Concurrent Connection-OrientedTCPechod.c

#include <sys/types.h>,<sys/signal.h>,<sys/socket.h>, <sys/time.h>,<sys/wait.h>,<sys/resource.h>,<sys/errno.h>, <netinet/in.h>,<unistd.h>,<stdlib.h>,<stdio.h>,<string.h>

#define QLEN 5 /* maximum connection queue length */

#define BUFSIZE 4096

extern int errno;

void reaper(int);

int TCPechod(int fd);

int errexit(const char *format, ...);

int passiveTCP(const char *service, int qlen);



int main(int argc, char *argv[ ])

{

char *service = "echo"; /* service name or port number*/

struct sockaddr_in fsin; /* the address of a client */

int alen; /* length of client's address*/

int msock; /* master server socket */

int ssock; /* slave server socket */

switch (argc) {

case 1: break;

case 2: service = argv[1];

break;

default: errexit("usage: TCPechod [port]\n");

}



msock = passiveTCP(service, QLEN);

(void) signal(SIGCHLD, reaper);

while (1) {

alen = sizeof(fsin);

ssock = accept(msock, (struct sockaddr *)&fsin, &alen);

if (ssock < 0) {

if (errno == EINTR)

continue;

errexit("accept: %s\n", strerror(errno));

}



switch (fork()) {

case 0: /* child */

(void) close(msock);

exit(TCPechod(ssock));

default: /* parent */

(void) close(ssock);

break;

case -1:

errexit("fork: %s\n", strerror(errno));

}

}

}



int TCPechod(int fd)

{

char buf[BUFSIZ];

int cc;

while (cc = read(fd, buf, sizeof buf)) {

if (cc < 0)

errexit("echo read: %s\n", strerror(errno));

if (write(fd, buf, cc) < 0)

errexit("echo write: %s\n", strerror(errno));

}

return 0;

}



/*---------------------------------------------------

* reaper - clean up zombie children

*--------------------------------------------------*/

/*ARGSUSED*/

void

reaper(int sig)

{

int status;

while (wait3(&status, WNOHANG, (struct rusage *)0) >= 0)

/* empty */;

}

sockets programming in unix

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