网络编程学习笔记(TCP回射服务器程序修订版)

服务器端：

#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>#define SIN_PORT 9999
#define BUFLEN 256void str_echo(int fd);void sig_child(int signo)
{pid_t pid;int stat;while ((pid = waitpid(-1, &stat, WNOHANG)) > 0) {printf("pid %d terminated\n", pid);}}size_t readn(int fd, void *ptr, size_t n)
{char *p = ptr;size_t nleft = n;size_t nread;while (nleft > 0) {if ((nread = read(fd, p, nleft)) < 0) {if (errno == EINTR) nread = 0;else return -1;} else if (nread == 0) break;nleft -= nread;p += nread;}return n - nleft;
}size_t readline(int fd, void *ptr, size_t maxsize)
{char *p = ptr;size_t rc, n;char c;for (n = 1; n < maxsize; n++) {
again:if ((rc = read(fd, &c, 1)) == 1) {*p++ = c;if (c == '\n') break;} else if (rc == 0) {if (n == 1) return 0;else break;} else {if (errno == EINTR) goto again;return -1;}}*p = 0;return n;
}size_t writen(int fd, void *ptr, size_t n)
{char *p = ptr;size_t nleft = n,  nwriten;while (nleft > 0) {if ((nwriten = write(fd, p, nleft)) <= 0) {if (errno == EINTR) nwriten = 0;else return -1;}p += nwriten;nleft -= nwriten;}return n;
}void str_echo(int fd)
{char recvline[BUFLEN];int n;for (;;) {if ((n = readline(fd, recvline, BUFLEN)) == 0) return;printf("received buf=%s", recvline);writen(fd, recvline, n);}
}int main(int argc, char **argv)
{int listenfd, connfd, sockfd;int maxfd, i, maxi, n;int nready, client[FD_SETSIZE];pid_t child;struct sockaddr_in servaddr, clientaddr;char buf[BUFLEN];time_t ticks;fd_set rset, allset;int len;listenfd = socket(AF_INET, SOCK_STREAM, 0);if (listenfd < 0) {printf("socket error :%s\n", strerror(errno));        return -1;}servaddr.sin_family = AF_INET;servaddr.sin_port = htons(SIN_PORT);servaddr.sin_addr.s_addr = htonl(INADDR_ANY);signal(SIGCHLD, sig_child);if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0) {printf("bind error:%s\n", strerror(errno));close(listenfd);return -1;}if (listen(listenfd, 3) < 0) {printf("listen error:%s\n", strerror(errno));close(listenfd);return -1;}maxfd = listenfd;for (i = 0; i < FD_SETSIZE; i++) {client[i] = -1;}FD_ZERO(&allset);FD_SET(listenfd, &allset);for (;;) {rset = allset;nready = select(maxfd + 1, &rset, NULL, NULL, NULL);if (FD_ISSET(listenfd, &rset)) {len = sizeof(int);connfd = accept(listenfd, (struct sockaddr*)&clientaddr, &len);for (i = 0; i < FD_SETSIZE; i++) {if (client[i] < 0) {client[i] = connfd;break;}}if (i == FD_SETSIZE) {printf("too many client\n");return;}FD_SET(connfd, &allset);if (connfd > maxfd) maxfd = connfd;if (i > maxi) maxi = i;if (--nready <= 0) continue;}for (i = 0; i <= maxi; i++) {if ((sockfd = client[i]) < 0) continue;if (FD_ISSET(sockfd, &rset)) {if ((n = readline(sockfd, buf, BUFLEN)) == 0) {close(sockfd);FD_CLR(sockfd, &allset);client[i] = -1;} else {writen(sockfd, buf, n);}}if (--nready <= 0) break;}}return 0;
}

用一个client数组记录连接后的socket，同时将这个socket加入到描述字符集中。在监听到有连接请求后，遍历可用的字符集，因为readline是阻塞的，会出现拒绝式攻击。

可行的解决方法有如下三种：

（1）使用非阻塞I/O模型

（2）让每个客户由单独的控制线程提供服务（创建子进程或线程来为每个客户提供服务）

（3）对I/O设置超时

客户端：

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>#define SIN_PORT 9999
#define BUF_LEN 256
#define max(a, b) ((a) > (b) ? (a) : (b))size_t readline(int fd, void *ptr, int maxsize)
{char *p = ptr;char c;int rc;int n;for (n = 1; n < maxsize; n++) {again:if ((rc = read(fd, &c, 1)) == 1) {*p++ = c;if (c == '\n') break; } else if (rc == 0) {if (n == 1) return 0;else break;}else {if (errno == EINTR) goto again;else return -1;}}*p = 0;return n;
}size_t readn(int fd, void *ptr, size_t n)
{char *p = ptr;int nleft = n;int nread;while (nleft > 0) {if ((nread = read(fd, p, nleft)) < 0) {if (errno == EINTR) nread = 0;else return -1;} else if (nread == 0) break;nleft -= nread;p += nread;}return n - nleft;
}size_t writen(int fd, void *ptr, size_t n)
{size_t nwriten;size_t nleft = n;char *p = ptr;while (nleft > 0) {if ((nwriten = write(fd, p, nleft)) <= 0) {if (errno == EINTR) nwriten = 0;else return -1;}nleft -= nwriten;p += nwriten;}return n;
}void str_cli(FILE *file, int fd)
{char recvline[BUF_LEN], sendline[BUF_LEN];int maxfdp1;fd_set fdset;int ret;int stdineof = 0;FD_ZERO(&fdset);for(;;) {if (stdineof == 0)FD_SET(fileno(file), &fdset);FD_SET(fd, &fdset);maxfdp1 = max(fileno(file), fd) + 1;ret = select(maxfdp1, &fdset, NULL, NULL, NULL);   if (ret <= 0) {continue;}//printf("ret=%d\n", ret);if (FD_ISSET(fd, &fdset)) {if (readline(fd, recvline, BUF_LEN) == 0) {if (stdineof == 1)return;else {printf("readline error:%s\n", strerror(errno));return;}}fputs(recvline, stdout);} if (FD_ISSET(fileno(file), &fdset)) {memset(sendline, 0x00, sizeof(sendline));if (fgets(sendline, BUF_LEN, file) == NULL) {//printf("fgets error:%s\n", strerror(errno));stdineof = 1;shutdown(fd, SHUT_WR);FD_CLR(fileno(file), &fdset);continue;}//printf("len=%d\n", strlen(sendline));writen(fd, sendline, strlen(sendline));}   }
}int main(int argc, char** argv)
{struct sockaddr_in serveraddr;int sockfd;#ifndef ONLINE_JUDGE//freopen("6.4Client.c", "r", stdin);
#endifsockfd = socket(AF_INET, SOCK_STREAM, 0);if (sockfd < 0) {printf("socket error:%s\n", strerror(errno));return -1;}   serveraddr.sin_family = AF_INET;serveraddr.sin_port = htons(SIN_PORT);if (inet_pton(AF_INET, argv[1], &serveraddr.sin_addr) != 1) {printf("inet_pton error:%s\n", strerror(errno));close(sockfd);return -1;}if (connect(sockfd, (struct sockaddr*)&serveraddr, sizeof(serveraddr)) < 0) {printf("connect error:%s\n", strerror(errno));close(sockfd);return -1;}str_cli(stdin, sockfd);exit(0);}

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