TCP服务器端默认函数调用顺序
- socket():创建socket
- bind():分配socket地址
- listen():等待连接请求状态
- accept():允许连接
- read() / write():数据交换
- close():断开连接
等待连接请求状态
int listen(int sock, int backlog);
- 成功时返回0, 失败时返回-1
- sock:服务器端套接字
- backlog:连接请求等待队列的长度
受理客户端连接请求
服务器端套接字是做门卫的,与客户端交换数据需要另外一个套接字,这个套接字由accept()函数自动创建。
int accept(int sock, struct sockaddr *addr, socklen_t *addrlen);
- 成功时返回创建的套接字文件描述符,失败时返回-1
- sock:服务器端套接字的文件描述符
- addr:发起连接的客户端的地址信息
- addrlen:addr的长度地址
TCP客户端默认函数调用顺序
- socket():创建套接字
- connect():请求连接
- read() / write():交换数据
- close():断开连接
请求连接
int connect(int sock, struct sockaddr *servaddr, socklen_t addrlen);
- 客户端的IP地址和端口在调用connect()自动分配;
- 客户端调用connect()后,只有在服务器端接受连接请求或者发生断网等异常情况时才会返回;
- 服务器端接受到了客户端的connect信息,并不会立即进行数据交换,而是把连接请求信息记录到等待队列;
- 客户端只有等到服务器端调用listen()后才能调用connect()函数;
- 在客户端调用connect()前,如果服务器端调用accept()函数,则进入阻塞(blocking)状态,直到客户端调用connect为止。
实现迭代服务器端/客户端
服务器端/客户端源码
echo_server.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
void error_handling(char* message);
int main(int argc, char* argv[]) {
int serv_sock, clnt_sock;
char message[BUF_SIZE];
int str_len, i;
struct sockaddr_in serv_adr, clnt_adr;
socklen_t clnt_adr_sz;
if (argc != 2) {
printf("Usage: %s <port> \n", argv[0]);
exit(1);
}
serv_sock = socket(PF_INET, SOCK_STREAM, 0);
if (serv_sock == -1) {
error_handling("socket() error");
}
memset(&serv_adr, 0, sizeof(serv_adr));
serv_adr.sin_family = AF_INET;
serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_adr.sin_port = htons(atoi(argv[1]));
if (bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1) {
error_handling("bind() error");
}
if (listen(serv_sock, 5) == -1) {
error_handling("listen() error");
}
clnt_adr_sz = sizeof(clnt_adr);
for (i = 0; i < 5; ++i) {
clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &clnt_adr_sz);
if (clnt_sock == -1) {
error_handling("accept() error");
}
else {
printf("Connected client %d \n", i + 1);
}
while ((str_len = read(clnt_sock, message, BUF_SIZE)) != 0) {
write(clnt_sock, message, str_len);
}
close(clnt_sock);
}
close(serv_sock);
return 0;
}
void error_handling(char* message) {
fputs(message, stderr);
fputc('\n', stderr);
exit(1);
}
echo_client.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
void error_handling(char* message);
int main(int argc, char* argv[]) {
int sock;
char message[BUF_SIZE];
int str_len, recv_len, recv_cnt;
struct sockaddr_in serv_adr;
if (argc != 3) {
printf("Usage: %s <IP> <port> \n", argv[0]);
exit(1);
}
sock = socket(PF_INET, SOCK_STREAM, 0);
if (sock == -1) {
error_handling("socket() error");
}
memset(&serv_adr, 0, sizeof(serv_adr));
serv_adr.sin_family = AF_INET;
serv_adr.sin_addr.s_addr = inet_addr(argv[1]);
serv_adr.sin_port = htons(atoi(argv[2]));
if (connect(sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr)) == -1) {
error_handling("connect() error");
}
else {
puts("Connected...............");
}
while (1)
{
fputs("Input message(Q to quit): ", stdout);
fgets(message, BUF_SIZE, stdin);
if (!strcmp(message, "q\n") || !strcmp(message, "Q\n")) {
break;
}
str_len = write(sock, message, strlen(message));
recv_len = 0;
while (recv_len < str_len) {
recv_cnt = read(sock, &message[recv_len], BUF_SIZE - 1);
if (recv_cnt == -1) {
error_handling("read() error!");
}
recv_len += recv_cnt;
}
message[recv_len] = 0;
printf("Message from server: %s", message);
}
close(sock);
return 0;
}
void error_handling(char* message) {
fputs(message, stderr);
fputc('\n', stderr);
exit(1);
}
运行命令
// run echo_server.c
gcc echo_server.c -o eserver
./eserver 9190
// run echo_cient.c
gcc echo_client.c -o eclient
./eclient 127.0.0.1 9190