Sockets Programming in Linux

1
Sockets Programming in Linux

• References
• Internetworking with TCP/IP Vol III - Linux
  version
• UNIX Network Programming - W. Richard Stevens

2
Sockets Programming in Linux

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

3
Basic Socket FunctionsServer(Linux / 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

4
Basic Socket FunctionsServer(Linux / 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

5
Basic Socket Functions Server (Linux / 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
• retcode recv send (socket, buff, bufflen, 0)
• ans recv (s, buf, sizeof(buf), 0)
• ans send (s, buf, sizeof(buf), 0)
• 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

6
Basic Socket FunctionsClient (Linux / 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( ) of recv( ) / send(
• Close the socket
• Close ( )

7
Additional Socket Functions(Linux / 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-gth_addr, (caddr_T)svaddr.sin_addr,
  hp-gth_length)

8
Example Linux 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

9
Linux Client - Connectsock.c

• int connectTCP (char host, char service)
• return connectsock (host, service, tcp)

10
Linux Client - Connectsock.c

• include ltsys/types.hgt, ltsys/socket.hgt,
  ltnetinet/in.hgt,ltnetdb.hgt
• int connectsock (char host, char service, char
  protocol)
• struct hostent phe
• struct servent pse
• struct protoent ppe
• struct sockaddr_in sin
• int s, type

11
Linux Client - Connectsock.c

• bzero ((char )sin, sizeof (sin))
• sin.sin_family AF_INET
• if (pse getservbyname (service, protocol) )
• sin.sin_port pse -gts_port
• else if ( (sin.sin_port htons((u_short)atoi(serv
  ice))) 0)
• error_exit (cant get s service\n, service)
• if (phe gethostbyname (host) )
• bcopy(phe-gth_addr, (char )sin.sin_addr,
  phe-gth_length)
• else if ((sin.sin_addr.s_addr inet_addr(host))
  INADDR_NONE)
• error_exit (cant get s host\n, host)

12
Linux Client - Connectsock.c

• if ( (ppe getprotobyname (protocol) 0)
• error_exit (cant get s host\n, host)
• if (strcmp (protocol, tcp) 0)
• type SOCK_STREAM
• else type SOCK_DGRAM
• if (s socket (PF_INET, type, ppe-gtp_proto)) lt
  0)
• error_exit (Cant create a socket\n)
• if (connect (s, (struct sockaddr )sin,
  sizeof(sin)) lt 0)
• error_exit (cant connect to remote socket\n)
• return s

13
Example Linux Client - TCPecho.c

• include ltstdio.hgt
• define LINELEN 128
• int main (argc, argv)
• host argv1
• service argv2
• TCPecho (host, service)
• exit (0)

14
Example Linux Client - TCPecho.c

• int TCPecho (char host, char service)
• char bufLINELEN1
• int s, n, outchars, inchars
• s connectTCP (host, service)
• while (fgets (buf, sizeof(buf), stdin))
• bufLINELEN \0
• outchars strlen(buf)
• (void) write (s, buf, outchars)

15
Example Linux Client - TCPecho.c

• for (inchars 0 inchars lt outchars inchars
  n)
• n read (s, bufinchars, outchars -
  inchars)
• if (n lt 0)
• error_exit(socket read failed\n)
• fputs (buf, stdout)

16
TCP Client Algorithm Issues

• 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

17
Example Linux Client - UDPecho.c

• include ltstdio.hgt
• define LINELEN 128
• int main (argc, argv)
• host argv1
• service argv2
• UDPecho (host, service)
• exit (0)

18
Example Linux Client - UDPecho.c

• int UDPecho (char host, char service)
• char bufLINELEN1
• int s, n, outchars, inchars
• s connectUDP (host, service)
• while (fgets (buf, sizeof(buf), stdin))
• bufLINELEN \0
• outchars strlen(buf)
• (void) write (s, buf, outchars)

19
Example Linux Client - UDPecho.c

• if (read (s, buf, nchars) lt 0)
• error_exit (Socket read failed \n)
• fputs (buf, stdout)

20
Iterative Connectionless ServerTIME Server

• / UDPtimed.c - main /
• include ltsys/types.hgt
• include ltsys/socket.hgt
• include ltnetinet/in.hgt
• include ltstdio.hgt
• include lttime.hgt
• include ltstring.hgt
• extern int errno
• int passiveUDP(const char service)
• int errexit(const char format, ...)
• define UNIXEPOCH 2208988800 / UNIX epoch, in
  secs/

21
Iterative Connectionless ServerTIME Server

• int main(int argc, char argv)
• struct sockaddr_in fsin / the address of a
  client /
• char service "time" / service name or port
  number /
• char buf1 / "input" buffer any size gt 0
  /
• int sock / server socket /
• time_t now / current time /
• int alen / from-address length /
• switch (argc)
• case 1 break
• case 2 service argv1
• break
• default errexit("usage UDPtimed port\n")

22
Iterative Connectionless ServerTIME Server

• sock passiveUDP(service)
• while (1)
• alen sizeof(fsin)
• if (recvfrom(sock, buf, sizeof(buf), 0,
• (struct sockaddr )fsin, alen) lt 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))

23
Concurrent Connection-OrientedTCPechod.c

• include ltsys/types.h, ltsys/signal.h,
  ltsys/socket.h, ltsys/time.h, ltsys/resource.h,
  ltsys/wait.h, ltsys/errno.h, ltnetinet/in.hgt,
  ltpthread.hgt, ltunistd.hgt, ltstdlib.hgt, ltstdio.hgt,
  ltstring.hgt, lterrno.hgt
• define QLEN 10 / max connect queue
  length/
• define BUFSIZE 4096
• extern int errno
• void TCPechod(void pfd)
• int errexit(const char format, ...)
• int passiveTCP(const char service, int qlen)

24
Concurrent Connection-OrientedTCPechod.c

• int main(int argc, char argv)
• char service "echo" / service name/port
  /
• struct sockaddr_in fsin / address of
  client/
• unsigned int alen / len of client addr/
• int msock / master server socket /
• int ssock / slave server socket /
• pthread_t tid
• switch (argc)
• case 1 break
• case 2 service argv1
• break
• default errexit("usage TCPechod
  port\n")

25
Concurrent Connection-OrientedTCPechod.c

• msock passiveTCP(service, QLEN)
• while (1)
• alen sizeof(fsin)
• ssock accept (msock, (struct sockaddr
  )fsin, alen)
• if (ssock lt 0)
• errexit("accept s\n", strerror(errno))
• //Now create a thread to handle client request
• pthread_create (tid, NULL, TCPechod, (void
  )ssock)
• //end of while
• //end of main

26
Concurrent Connection-OrientedTCPechod.c

• msock passiveTCP(service, QLEN)
• while (1)
• alen sizeof(fsin)
• ssock accept(msock, (struct sockaddr )fsin,
  alen)
• if (ssock lt 0)
• errexit("accept s\n", strerror(errno))
• //Now create a thread to handle client request
• pthread_create (tid, NULL, TCPechod, (void
  )ssock)
• //end of while
• //end of main

27
Concurrent Connection-OrientedTCPechod.c

• void TCPechod(void pfd)
• char bufBUFSIZE
• int cc, fd
• fd (int ) pfd
• while (cc recv(fd, buf, sizeof (buf), 0))
• if (cc lt 0)
• errexit("echo read s\n", strerror(errno))
• printf ("We got s\n", buf)
• if (send(fd, buf, cc, 0) lt 0)
• errexit("echo write s\n", strerror(errno))
• bzero (buf, sizeof(buf))

28
Summary

• Sockets API almost identical in Windows and Linux
• Linux does not use WSAStartup, WSACleanup
• Linux uses close(socket), Windows uses
  closesocket()
• Some differences in Operating System functions
• Multiple threads
• Windows - _beginthread ()
• Linux pthread_create ()
• Multiple Processes
• Windows CreateProcess()
• Linux Fork()