server.c

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>

#define MAXLINE 256

fd_set all_set, ready_set;
int client[FD_SETSIZE];
int maxfd, max_client;

void add_new_client(int listenfd)
{
	struct sockaddr_in cli;
	socklen_t clilen = sizeof(cli);
	int i, fd;
	char str[INET_ADDRSTRLEN];

	fd = accept(listenfd, (struct sockaddr *)&cli, &clilen);
	for (i=0; i<FD_SETSIZE; i++) if (client[i]==-1) break;
	if (i==FD_SETSIZE) {
		printf("Too many clients.\n");
		exit(1);
	}
	client[i] = fd;
	if (fd>maxfd) maxfd = fd;
	if (i>max_client) max_client = i;
	FD_SET(fd, &all_set);
	printf("Client %d from %s at port %d connected\n", i,
			inet_ntop(PF_INET, &cli.sin_addr, str, sizeof(str)),
			ntohs(cli.sin_port));
}
void serve_client()
{
	int i, j, len, fd;
	char buf[MAXLINE];
	for (i=0; i<=max_client; i++) {
		if ((fd=client[i])==-1) continue;
		if (!FD_ISSET(fd, &ready_set)) continue;
		if (read(fd, buf, MAXLINE)) {
			printf("receive from client %d: %s", i, buf);
			len = strlen(buf);
			for (j=0; j<len; j++) buf[j] = toupper(buf[j]);
			write(fd, buf, len+1);
		} else {
			printf("client %d brocken\n", i);
			FD_CLR(fd, &all_set);
			client[i] = -1;
			close(fd);
		}
	}
}
int main()
{
	struct sockaddr_in serv;
	int i, nready, listenfd;

	bzero(&serv, sizeof(serv));
	serv.sin_family = PF_INET;
	serv.sin_port = htons(8000);
	serv.sin_addr.s_addr = htonl(INADDR_ANY);

	listenfd = socket(PF_INET, SOCK_STREAM, 0);
	bind(listenfd, (struct sockaddr *)&serv, sizeof(serv));
	listen(listenfd, 100);
	printf("Accepting connection...\n");

	FD_ZERO(&all_set);
	FD_SET(listenfd, &all_set);
	for (i=0; i<FD_SETSIZE; i++) client[i] = -1;
	maxfd = listenfd;
	max_client = -1;

	while (1) {
		ready_set = all_set;
		nready = select(maxfd+1, &ready_set, NULL, NULL, NULL);
		if (FD_ISSET(listenfd, &ready_set)) {
			add_new_client(listenfd);
			nready--;
		}
		while (nready) {
			serve_client();
			nready--;
		}
	}

	exit(0);
}