/* This page contains the client program. The following one contains the * server program. Once the server has been compiled and started, clients * anywhere on the Internet can send commands (file names) to the server. * The server responds by opening and returning the entire file requested. */#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <netdb.h>#define SERVER_PORT 12345		/* arbitrary, but client and server must agree */#define BUF_SIZE 4096			/* block transfer size */int main(int argc, char **argv){  int c, s, bytes;  char buf[BUF_SIZE];			/* buffer for incoming file */  struct hostent *h;			/* info about server */  struct sockaddr_in channel;		/* holds IP address */  if (argc != 3) fatal("Usage: client server-name file-name");  h = gethostbyname(argv[1]);		/* look up host's IP address */  if (!h) fatal("gethostbyname failed");  s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);  if (s < 0) fatal("socket");  memset(&channel, 0, sizeof(channel));  channel.sin_family= AF_INET;  memcpy(&channel.sin_addr.s_addr, h->h_addr, h->h_length);  channel.sin_port= htons(SERVER_PORT);  c = connect(s, (struct sockaddr *) &channel, sizeof(channel));  if (c < 0) fatal("connect failed");  /* Connection is now established. Send file name including 0 byte at end. */  write(s, argv[2], strlen(argv[2])+1);  /* Go get the file and write it to standard output. */  while (1) {        bytes = read(s, buf, BUF_SIZE);	/* read from socket */        if (bytes <= 0) exit(0);	/* check for end of file */        write(1, buf, bytes);		/* write to standard output */  }}fatal(char *string){  printf("%s\n", string);  exit(1);}