有时候我们调试两个不同内网的设备时，网络通信是一件比较麻烦的事。而且现在许多地方的宽带拨号获取的已然是服务商提供的大内网IP段了。
我们知道，不同内网间是不通的，虽然可以在两个网络内通过端口映射来实现，但实现难度较大，并且不一定拥有主路由的控制权限。
为此，依据对socket的学习，特意写了一个基于外网服务器转发的两客户端通信程序，将该代码编译后在服务器上执行即可，要通信的两个设备都以客户端的形式连接到服务器，客户端便能实现通信。
/*
C socket server example
*/
#include<stdio.h>
#include<string.h>
#include <sys/types.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#include<unistd.h>
#include <pthread.h>
#define BUFSIZE 2000
void* client1fun(void*);
int socket_desc, client_sock1, client_sock2, c1, c2, read_size;
struct sockaddr_in server, client1,client2;
char client_message[BUFSIZE];
int clientn;
int main(int argc, char *argv[])
{
clientn = 0;
int portno = atoi(argv[1]);
pthread_t sender, client1, client2;
pthread_create(&client1, NULL, client1fun, NULL);
//Create socket
socket_desc = socket(AF_INET, SOCK_STREAM, 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
puts("Socket created");
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons((unsigned short)portno);
//Bind
if (bind(socket_desc, (struct sockaddr *)&server, sizeof(server)) < 0)
{
//print the error message
perror("bind failed. Error");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc, 2);
//Accept and incoming connection
puts("Waiting for incoming connections...");
while (1)
{
int n;
char buf[BUFSIZE];
bzero(buf, BUFSIZE);
printf("client2:\n");
//accept connection from an incoming client
client_sock2 = accept(socket_desc, (struct sockaddr *)&client2, (socklen_t*)&c2);
if (client_sock2 < 0)
{
perror("accept failed");
exit(1);
}
clientn++;
puts("Connection accepted");
//write(client_sock2, "Welecom!\n", strlen("Welecom!\n"));
while (1)
{
n = read(client_sock2, buf, BUFSIZE);
if (n < 0)
{
perror("recv failed");
exit(1);
}
if (n == 0)
{
clientn--;
break;
}
printf("%s", buf);
if (clientn < 2)
{
//write(client_sock2, "No respond!\n", strlen("No respond!\n"));
}
if (clientn == 2)
{
write(client_sock1, buf, strlen(buf));
}
}
close(client_sock2);
}
pthread_join(client1, NULL);
return 0;
}
void* client1fun(void* client_sock)
{
while (1)
{
int n;
char buf[BUFSIZE];
bzero(buf, BUFSIZE);
sleep(1);
printf("client1");
//accept connection from an incoming client
client_sock1 = accept(socket_desc, (struct sockaddr *)&client1, (socklen_t*)&c1);
if (client_sock1 < 0)
{
perror("accept failed");
exit(1);
}
clientn++;
puts("Connection accepted");
//write(client_sock1, "Welecom!\n", strlen("Welecom!\n"));
while (1)
{
n = read(client_sock1, buf, BUFSIZE);
if (n < 0)
{
perror("recv failed");
exit(1);
}
if (n == 0)
{
clientn--;
break;
}
printf("%s", buf);
if (clientn < 2)
{
//write(client_sock1, "No respond!\n", strlen("No respond!\n"));
}
if (clientn == 2)
{
write(client_sock2, buf, strlen(buf));
}
}
close(client_sock1);
}
}
注意：编译请加参数 -pthread 。
上个版本存在许多问题，现在修正部分BUG并增加用户友好性，代码如下：
/*
C socket server example
*/
#include<stdio.h>
#include<string.h>
#include <sys/types.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#include<unistd.h>
#include <pthread.h>
#define BUFSIZE 2000
void* client1fun(void*);
int socket_desc, client_sock1, client_sock2, c1, c2;
struct sockaddr_in server, client, client2;
int clientn;
int main(int argc, char *argv[])
{
clientn = 0;
int portno = atoi(argv[1]);
pthread_t sender, client1;
pthread_create(&client1, NULL, client1fun, NULL);
//Create socket
socket_desc = socket(AF_INET, SOCK_STREAM, 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
puts("Socket created");
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons(portno);
//Bind
if (bind(socket_desc, (struct sockaddr *)&server, sizeof(server)) < 0)
{
//print the error message
perror("bind failed. Error");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc, 2);
//Accept and incoming connection
puts("Waiting for incoming connections...");
while (1)
{
int n;
char buf[BUFSIZE];
bzero(buf, BUFSIZE);
int ss = sizeof(client2);
//accept connection from an incoming client
client_sock2 = accept(socket_desc, (struct sockaddr *)&client2, (socklen_t*)&ss);
if (client_sock2 < 0)
{
perror("accept failed");
exit(1);
}
clientn++;
printf("Connection accepted fron %s:%d\n", inet_ntoa(client2.sin_addr), client2.sin_port);
//write(client_sock2, "Welecom!\n", strlen("Welecom!\n"));
while (n = read(client_sock2, buf, BUFSIZE))
{
printf("[%s:%d]: %s\n", inet_ntoa(client2.sin_addr), client2.sin_port, buf);
if (clientn == 2)
{
write(client_sock1, buf, strlen(buf));
}
}
clientn--;
printf("Client [%s:%d] ofline\n",inet_ntoa(client2.sin_addr), client2.sin_port);
close(client_sock2);
}
pthread_join(client1, NULL);
return 0;
}
void* client1fun(void* client_sock)
{
while (1)
{
int n;
char buf[BUFSIZE];
bzero(buf, BUFSIZE);
sleep(1);
int ss = sizeof(client);
//accept connection from an incoming client
client_sock1 = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&ss);
if (client_sock1 < 0)
{
perror("accept failed");
exit(1);
}
clientn++;
printf("Connection accepted fron %s:%d\n", inet_ntoa(client.sin_addr), client.sin_port);
//write(client_sock1, "Welecom,1!\n", strlen("Welecom!\n"));
while (n = read(client_sock1, buf, BUFSIZE))
{
//n = read(client_sock1, buf, BUFSIZE);
printf("[%s:%d]: %s\n", inet_ntoa(client.sin_addr), client.sin_port, buf);
if (clientn == 2)
{
write(client_sock2, buf, strlen(buf));
}
}
clientn--;
printf("Client [%s:%d] ofline\n", inet_ntoa(client.sin_addr), client.sin_port);
close(client_sock1);
}
}