网络编程
- 服务器端
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <string.h>
#include <strings.h>
#define SERVER_PORT 6666
#define SERVER_IP "127.0.0.1"
int main()
{
int lfd=socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in server_addr;
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family= AF_INET;
server_addr.sin_port=htons(6666);
server_addr.sin_addr.s_addr= htonl(INADDR_ANY);
bind(lfd,(struct sockaddr*) &server_addr, sizeof(server_addr));
listen(lfd,32);
int cfd;
struct sockaddr_in client_addr;
socklen_t client_addr_len=sizeof(client_addr);
cfd=accept(lfd,(struct sockaddr*) &client_addr, &client_addr_len);
char client_ip_buf[BUFSIZ];
inet_ntop(AF_INET,&client_addr.sin_addr.s_addr,client_ip_buf, sizeof(client_ip_buf));
printf("client ip: %s client port: %d\n", client_ip_buf, ntohs(client_addr.sin_port));
char buf[BUFSIZ];
while(1){
int n=read(cfd,buf,sizeof(buf));
int i;
for(i=0;i<n;i++){
buf[i]=toupper(buf[i]);
}
write(cfd,buf,n);
}
close(lfd);
close(cfd);
return 0;
}
- 客户端
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h> // struct sockaddr_in
#include <string.h>
#define SERVER_IP "127.0.0.1"
int main()
{
int cfd;
cfd=socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in server_addr;
memset(&server_addr,0,sizeof(server_addr));
server_addr.sin_family=AF_INET;
server_addr.sin_port=htons(6666);
inet_pton(AF_INET,SERVER_IP, &server_addr.sin_addr.s_addr);
connect(cfd,(struct sockaddr*) &server_addr, sizeof(server_addr));
char buf[BUFSIZ];
while(1){
fgets(buf,sizeof(buf),stdin);
write(cfd,buf,strlen(buf));
int n;
n=read(cfd,buf,sizeof(buf));
write(STDOUT_FILENO,buf,n);
}
close(cfd);
return 0;
}
如果先关server，再关client，则下次启动server时bind会报错，Address already in use.
关闭server后，端口并没有被释放。
代码改进，增加错误处理函数：
wrap.c
#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
void perr_exit(const char *s)
{
perror(s);
exit(1);
}
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr)
{
int n;
again:
if ( (n = accept(fd, sa, salenptr)) < 0) {
if ((errno == ECONNABORTED) || (errno == EINTR)) // accept为慢速系统调用。 EINTR The system call was interrupted by a signal that was caught before a valid connection arrived. CONNABORTED A connection has been aborted.
goto again;
else
perr_exit("accept error");
}
return n;
}
int Bind(int fd, const struct sockaddr *sa, socklen_t salen)
{
int n;
if ((n = bind(fd, sa, salen)) < 0)
perr_exit("bind error");
return n;
}
int Connect(int fd, const struct sockaddr *sa, socklen_t salen)
{
int n;
if ((n = connect(fd, sa, salen)) < 0)
perr_exit("connect error");
return n;
}
int Listen(int fd, int backlog)
{
int n;
if ((n = listen(fd, backlog)) < 0)
perr_exit("listen error");
return n;
}
int Socket(int family, int type, int protocol)
{
int n;
if ( (n = socket(family, type, protocol)) < 0)
perr_exit("socket error");
return n;
}
ssize_t Read(int fd, void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = read(fd, ptr, nbytes)) == -1) { //慢速系统调用，有可能造成进程永久阻塞。
// read 返回值： 1. >0 表示实际读到的字节数； 2. =0 数据读完，即读到文件，管道，socket末尾。 3. =-1 异常，通过errno细分， errno=EINTR 说明被信号中断，选择重启or退出；errno=EAGAIN (EWOULDBLOCK) 以非阻塞方式读并且没有数据。errno=其他值， 错误。
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
ssize_t n;
again:
if ( (n = write(fd, ptr, nbytes)) == -1) {
if (errno == EINTR)
goto again;
else
return -1;
}
return n;
}
int Close(int fd)
{
int n;
if ((n = close(fd)) == -1)
perr_exit("close error");
return n;
}
ssize_t Readn(int fd, void *vptr, size_t n) //需要读取n个字节，可能要分多次读
{
size_t nleft;
ssize_t nread;
char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nread = read(fd, ptr, nleft)) < 0) {
if (errno == EINTR)
nread = 0;
else
return -1;
} else if (nread == 0)
break;
nleft -= nread;
ptr += nread;
}
return n - nleft;
}
ssize_t Writen(int fd, const void *vptr, size_t n)
{
size_t nleft;
ssize_t nwritten;
const char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ( (nwritten = write(fd, ptr, nleft)) <= 0) {
if (nwritten < 0 && errno == EINTR)
nwritten = 0;
else
return -1;
}
nleft -= nwritten;
ptr += nwritten;
}
return n;
}
static ssize_t my_read(int fd, char *ptr)
{
static int read_cnt;
static char *read_ptr;
static char read_buf[100];
if (read_cnt <= 0) {
again:
if ((read_cnt = read(fd, read_buf, sizeof(read_buf))) < 0) {
if (errno == EINTR)
goto again;
return -1;
} else if (read_cnt == 0)
return 0;
read_ptr = read_buf;
}
read_cnt--;
*ptr = *read_ptr++;
return 1;
}
ssize_t Readline(int fd, void *vptr, size_t maxlen)
{
ssize_t n, rc;
char c, *ptr;
ptr = vptr;
for (n = 1; n < maxlen; n++) {
if ( (rc = my_read(fd, &c)) == 1) {
*ptr++ = c;
if (c == '\n')
break;
} else if (rc == 0) {
*ptr = 0;
return n - 1;
} else
return -1;
}
*ptr = 0;
return n;
}
多进程并发服务器：
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include "wrap.h"
#include <string.h>
#include <ctype.h>
#include <sys/wait.h>
#define SERVER_PORT 8888
void wait_child(int signo){
while(waitpid(0,NULL,WNOHANG)>0);
return;
}
int main()
{
int lfd,cfd;
lfd=Socket(AF_INET,SOCK_STREAM,0);
struct sockaddr_in serv_addr, client_addr;
bzero(&serv_addr,sizeof(serv_addr));
serv_addr.sin_family=AF_INET;
serv_addr.sin_port=htons(SERVER_PORT);
serv_addr.sin_addr.s_addr=htonl(INADDR_ANY);
//inet_pton(AF_INET,"127.0.0.1", &serv_addr.sin_addr.s_addr);
Bind(lfd,(struct sockaddr*)&serv_addr, sizeof(serv_addr));
Listen(lfd,128);
pid_t pid;
int n,i;
char buf[BUFSIZ];
char ip_buf[BUFSIZ];
while(1){
socklen_t client_addr_len=sizeof(client_addr);
cfd= Accept(lfd,(struct sockaddr*)&client_addr, &client_addr_len);
printf("client ip: %s-----client port: %d\n",
inet_ntop(AF_INET, &client_addr.sin_addr.s_addr, ip_buf, sizeof(ip_buf)),
ntohs(client_addr.sin_port));
pid=fork();
if(pid<0){
perror("fork error");
exit(1);
}
if(pid==0){
close(lfd);
break;
}
close(cfd);
signal(SIGCHLD,wait_child);
}
if(pid==0){
while(1){
n=Read(cfd,buf,sizeof(buf));
if(n==0){
close(cfd);
return 0;
}
if(n==-1){
perror("read err");
exit(1);
}
for(i=0;i<n;i++){
buf[i]=toupper(buf[i]);
}
Write(cfd,buf,n);
}
}
return 0;
}
多线程版：
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <ctype.h>
#include <unistd.h>
#include <fcntl.h>
#include "wrap.h"
#define MAXLINE 8192
#define SERV_PORT 8000
struct s_info { //定义一个结构体, 将地址结构跟cfd捆绑
struct sockaddr_in cliaddr;
int connfd;
};
void *do_work(void *arg)
{
int n,i;
struct s_info *ts = (struct s_info*)arg;
char buf[MAXLINE];
char str[INET_ADDRSTRLEN]; //#define INET_ADDRSTRLEN 16 可用"[+d"查看
while (1) {
n = Read(ts->connfd, buf, MAXLINE); //读客户端
if (n == 0) {
printf("the client %d closed...\n", ts->connfd);
break; //跳出循环,关闭cfd
}
printf("received from %s at PORT %d\n",
inet_ntop(AF_INET, &(*ts).cliaddr.sin_addr.s_addr, str, sizeof(str)),
ntohs((*ts).cliaddr.sin_port)); //打印客户端信息(IP/PORT)
for (i = 0; i < n; i++)
buf[i] = toupper(buf[i]); //小写-->大写
Write(STDOUT_FILENO, buf, n); //写出至屏幕
Write(ts->connfd, buf, n); //回写给客户端
}
Close(ts->connfd);
return (void *)0;
}
int main(void)
{
struct sockaddr_in servaddr, cliaddr;
socklen_t cliaddr_len;
int listenfd, connfd;
pthread_t tid;
struct s_info ts[256]; //根据最大线程数创建结构体数组.
int i = 0;
listenfd = Socket(AF_INET, SOCK_STREAM, 0); //创建一个socket, 得到lfd
bzero(&servaddr, sizeof(servaddr)); //地址结构清零
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY); //指定本地任意IP
servaddr.sin_port = htons(SERV_PORT); //指定端口号 8000
Bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)); //绑定
Listen(listenfd, 128); //设置同一时刻链接服务器上限数
printf("Accepting client connect ...\n");
while (1) {
cliaddr_len = sizeof(cliaddr);
connfd = Accept(listenfd, (struct sockaddr *)&cliaddr, &cliaddr_len); //阻塞监听客户端链接请求
ts[i].cliaddr = cliaddr;
ts[i].connfd = connfd;
/* 达到线程最大数时，pthread_create出错处理, 增加服务器稳定性 */
pthread_create(&tid, NULL, do_work, (void*)&ts[i]);
pthread_detach(tid); //子线程分离,防止僵线程产生.
i++;
}
return 0;
}
客户端发SYN，服务器端收到并回ACK后是SYN_RCVD状态，若客户端由于某种原因无法继续发送ack建立连接，则其操作系统会发送RST，服务器端收到后变回listen状态。
端口复用。
在server代码的socket()和bind()调用之间插入如下代码：
int opt = 1;
setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
