Linux网络编程——TCP和UDP通信

• TCP协议流程图、TCP建立即时聊天
• TCP即时聊天升级：服务器在客户端断开后不断开，客户端可以多次重连服务器进行即时聊天
• UDP协议流程图、UDP建立即时连接
• 如果在已经处于 ESTABLISHED状态下的socket(一般由端口号和标志符区分）需调用closesocket（一般不会立即关闭而经历TIME_WAIT的过程）后想继续重用该socket，但也可以直接用setsockopt和reuse。
• SO_RCVLOWAT设置接收缓冲区下限

1、TCP协议的流程图

服务端：socket---bind---listen---while(1){---accept---recv---send---close---}---close
客户端：socket----------------------------------connect---send---recv-----------------close

TCP建立即时聊天

tcp_client.c

#include <func.h>

int main(int argc,char* argv[])
{
	ARGS_CHECK(argc,3);
	int socketFd;
	socketFd=socket(AF_INET,SOCK_STREAM,0);
	ERROR_CHECK(socketFd,-1,"socket");
	struct sockaddr_in ser;
	bzero(&ser,sizeof(ser));
	ser.sin_family=AF_INET;
	ser.sin_port=htons(atoi(argv[2]));
	ser.sin_addr.s_addr=inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	int ret;
	ret=connect(socketFd,(struct sockaddr*)&ser,sizeof(ser));
	ERROR_CHECK(ret, -1, "connect");
	printf("connect success
");
	char buf[128]={0};
	fd_set rdset;
	while(1){
		FD_ZERO(&rdset);
		FD_SET(STDIN_FILENO, &rdset);
		FD_SET(socketFd, &rdset);
		ret = select(socketFd + 1, &rdset, NULL, NULL, NULL);
		if(FD_ISSET(socketFd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recv(socketFd, buf, sizeof(buf), 0);
			ERROR_CHECK(ret, -1, "recv");
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			memset(buf, 0, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			ret = send(socketFd, buf ,strlen(buf) - 1, 0);
			ERROR_CHECK(ret, -1, "send");
		}
	}
	close(socketFd);
}

tcp_server.c

#include <func.h>

int main(int argc,char* argv[])
{
	ARGS_CHECK(argc,3);
	int socketFd;
	socketFd = socket(AF_INET,SOCK_STREAM,0);
	ERROR_CHECK(socketFd, -1, "socket");
	struct sockaddr_in ser;
	bzero(&ser, sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	int ret;
	ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "bind");
	listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
	int new_fd;
	struct sockaddr_in client;
	bzero(&client, sizeof(client));
	int addrlen = sizeof(client);
	new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen);
	ERROR_CHECK(new_fd, -1, "accept");
	printf("client ip=%s, port=%d
", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
	fd_set rdset;
	char buf[128] = {0};
	while(1){
		FD_ZERO(&rdset);
		FD_SET(STDIN_FILENO, &rdset);
		FD_SET(new_fd, &rdset);
		ret = select(new_fd + 1, &rdset, NULL, NULL, NULL);
		if(FD_ISSET(new_fd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recv(new_fd, buf, sizeof(buf), 0);
			ERROR_CHECK(ret, -1, "recv");
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			memset(buf, 0, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			ret = send(new_fd, buf, strlen(buf) - 1, 0);
			ERROR_CHECK(ret, -1, "send");
		}
	}
	close(new_fd);
	close(socketFd);
	return 0;
}

2、TCP即时聊天升级：服务器在客户端断开后不断开，客户端可以多次重连服务器进行即时聊天

tcp_server.c

#include <func.h>

int main(int argc,char* argv[])
{
	ARGS_CHECK(argc,3);
	int socketFd;
	socketFd = socket(AF_INET,SOCK_STREAM,0);
	ERROR_CHECK(socketFd, -1, "socket");
	struct sockaddr_in ser;
	bzero(&ser, sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	int ret;
	ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "bind");
	listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
	int new_fd;
	struct sockaddr_in client;
	bzero(&client, sizeof(client));
	int addrlen = sizeof(client);
	char buf[128] = {0};
	fd_set rdset; 
	fd_set needMonitorSet; //需要监听的描述符集合
	FD_ZERO(&needMonitorSet);  
	FD_SET(STDIN_FILENO, &needMonitorSet);
	FD_SET(socketFd, &needMonitorSet);
	while(1){
		memcpy(&rdset, &needMonitorSet, sizeof(fd_set));
		ret = select(11, &rdset, NULL, NULL, NULL); //设最大监控描述符为10
		if(FD_ISSET(socketFd, &rdset)){ //如果监听到客户端则accept接受远程计算机的连接请求
			new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen); //accept函数接受一个连接时，会返回一个新的socket标识符，以后数据的数据传输和读取就要通过这个新的socket编号来处理，原来的socket继续监听其他客户机的连接请求。
			ERROR_CHECK(new_fd, -1, "accept");
			printf("client ip=%s, port=%d
", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
			FD_SET(new_fd, &needMonitorSet);	
		}
		if(FD_ISSET(new_fd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recv(new_fd, buf, sizeof(buf), 0);
			ERROR_CHECK(ret, -1, "recv");
			if(ret == 0){
				printf("byebye!
");
				FD_CLR(new_fd, &needMonitorSet);  //从needMonitorSet中删除new_fd
				close(new_fd);
				continue;
			}
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			memset(buf, 0, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			ret = send(new_fd, buf, strlen(buf) - 1, 0);
			ERROR_CHECK(ret, -1, "send");
		}
	}
	close(socketFd);
	return 0;
}

tcp_client.c和1同

3、使用UDP协议的流程图

服务端：socket---bind---recvfrom---sendto---close
客户端：socket----------sendto---recvfrom---close

• sendto()函数原型：
  **int sendto(int sockfd, const void msg,int len,unsigned int flags,const struct sockaddr to, int tolen);

  该函数比send()函数多了两个参数，to表示目地机的IP地址和端口号信息，而tolen常常被赋值为sizeof (struct sockaddr)。sendto 函数也返回实际发送的数据字节长度或在出现发送错误时返回-1。

• recvfrom()函数原型：

  **int recvfrom(int sockfd,void *buf,int len,unsigned int flags,struct sockaddr from,int fromlen);
  from是一个struct sockaddr类型的变量，该变量保存连接机的IP地址及端口号。fromlen常置为sizeof (struct sockaddr)。当recvfrom()返回时，fromlen包含实际存入from中的数据字节数。Recvfrom()函数返回接收到的字节数或当出现错误时返回-1，并置相应的errno。

  UDP传输一个数据报示例：

  udp_server.c

#include <func.h>

int main(int argc, char **argv){
	ARGS_CHECK(argc, 3);
	int socketFd;
	socketFd = socket(AF_INET, SOCK_DGRAM, 0);
	ERROR_CHECK(socketFd, -1, "socket");
	struct sockaddr_in ser;
	bzero(&ser,sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	int ret;
	ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "bind");
	char buf[128] = {0};
	struct sockaddr_in client;
	int addrlen = sizeof(client);
	ret = recvfrom(socketFd, buf, 5, 0, (struct sockaddr*)&client, &addrlen);
	ERROR_CHECK(ret, -1, "recvfrom");
	printf("client ip = %s, port = %d
", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
	printf("udp server gets %s
", buf);
	//bzero(buf, sizeof(buf));
	//ret = recvfrom(socketFd, buf, 5, 0, (struct sockaddr*)&client, &addrlen);
	//ERROR_CHECK(ret, -1, "recvfrom");
	//printf("udp server gets %s
", buf);
	ret = sendto(socketFd, "world", 5, 0, (struct sockaddr*)&client, sizeof(client));
	ERROR_CHECK(ret, -1, "sendto");
	close(socketFd);
	return 0;
}

udp_client.c

#include <func.h>

int main(int argc, char *argv[]){
	ARGS_CHECK(argc, 3);
	int socketFd;
	socketFd = socket(AF_INET, SOCK_DGRAM, 0);
	ERROR_CHECK(socketFd, -1, "socket");
	struct sockaddr_in ser;
	bzero(&ser, sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);
	int ret;
	ret = sendto(socketFd, "helloworld", 10, 0, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "sendto");
	char buf[128] = {0};
	ret = recvfrom(socketFd, buf, sizeof(buf), 0, NULL, NULL);
	ERROR_CHECK(ret, -1, "recvfrom");
	printf("udp client gets %s
", buf);
	close(socketFd);
	return 0;
}

4、使用UDP协议建立即时连接

udp_server.c

#include <func.h>

int main(int argc, char **argv){
	ARGS_CHECK(argc, 3);
	int socketFd;
	socketFd = socket(AF_INET, SOCK_DGRAM, 0);
	ERROR_CHECK(socketFd, -1, "socket");
	struct sockaddr_in ser;
	bzero(&ser,sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	int ret;
	ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "bind");
	char buf[128] = {0};
	struct sockaddr_in client;
	int addrlen = sizeof(client);
	printf("client ip = %s, port = %d
", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
	fd_set rdset;
	while(1){
		FD_ZERO(&rdset);
		FD_SET(STDIN_FILENO, &rdset);
		FD_SET(socketFd, &rdset);
		ret = select(socketFd + 1, &rdset, NULL, NULL, NULL);
		if(FD_ISSET(socketFd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recvfrom(socketFd, buf, sizeof(buf), 0, (struct sockaddr*)&client, &addrlen);
			ERROR_CHECK(ret, -1, "recvfrom");
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			bzero(buf, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(0 == ret){
				printf("byeybye
");
				break;
			}
			ret = sendto(socketFd, buf, strlen(buf) - 1, 0, (struct sockaddr*)&client, sizeof(client));
			ERROR_CHECK(ret, -1, "sendto");
		}
	}
	close(socketFd);
	return 0;
}

udp_client.c

#include <func.h>

int main(int argc, char *argv[]){
	ARGS_CHECK(argc, 3);
	int socketFd;
	socketFd = socket(AF_INET, SOCK_DGRAM, 0);
	ERROR_CHECK(socketFd, -1, "socket");
	struct sockaddr_in ser;
	bzero(&ser, sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);
	int ret;
	char buf[128] = {0};
	fd_set rdset;
	while(1){
		FD_ZERO(&rdset);
		FD_SET(STDIN_FILENO, &rdset);
		FD_SET(socketFd, &rdset);
		ret = select(socketFd + 1, &rdset, NULL, NULL, NULL);
		if(FD_ISSET(socketFd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recvfrom(socketFd, buf, sizeof(buf), 0, NULL, NULL);
			ERROR_CHECK(ret, -1, "recvfrom");
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			bzero(buf, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(0 == ret){
				printf("byeybye
");
				break;
			}
			ret = sendto(socketFd, buf, strlen(buf) - 1, 0, (struct sockaddr*)&ser, sizeof(ser));
			ERROR_CHECK(ret, -1, "sendto");
		}
	}
	close(socketFd);
	return 0;
}

5、如果在已经处于 ESTABLISHED状态下的socket(一般由端口号和标志符区分）需调用closesocket（一般不会立即关闭而经历TIME_WAIT的过程）后想继续重用该socket，但也可以直接用setsockopt和reuse。

int reuse=1;
setsockopt(s,SOL_SOCKET ,SO_REUSEADDR,(const char*)&reuse,sizeof(int));

tcp_server.c

#include <func.h>

int main(int argc,char* argv[])
{
	ARGS_CHECK(argc,3);
	int socketFd;
	socketFd = socket(AF_INET,SOCK_STREAM,0);
	ERROR_CHECK(socketFd, -1, "socket");
	int ret;
	int reuse = 1;
	ret = setsockopt(socketFd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int));
	ERROR_CHECK(ret, -1, "setsockopt");
	struct sockaddr_in ser;
	bzero(&ser, sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "bind");
	listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
	int new_fd;
	struct sockaddr_in client;
	bzero(&client, sizeof(client));
	int addrlen = sizeof(client);
	new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen);
	ERROR_CHECK(new_fd, -1, "accept");
	printf("client ip=%s, port=%d
", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
	fd_set rdset;
	char buf[128] = {0};
	while(1){
		FD_ZERO(&rdset);
		FD_SET(STDIN_FILENO, &rdset);
		FD_SET(new_fd, &rdset);
		ret = select(new_fd + 1, &rdset, NULL, NULL, NULL);
		if(FD_ISSET(new_fd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recv(new_fd, buf, sizeof(buf), 0);
			ERROR_CHECK(ret, -1, "recv");
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			memset(buf, 0, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			ret = send(new_fd, buf, strlen(buf) - 1, 0);
			ERROR_CHECK(ret, -1, "send");
		}
	}
	close(new_fd);
	close(socketFd);
	return 0;
}

tcp_client.c和1同

6、SO_RCVLOWAT：接收缓冲区下限

tcp_server_rcvlowat.c

#include <func.h>

int main(int argc,char* argv[])
{
	ARGS_CHECK(argc,3);
	int socketFd;
	socketFd = socket(AF_INET,SOCK_STREAM,0);
	ERROR_CHECK(socketFd, -1, "socket");
	int ret;
	int reuse = 1;
	ret = setsockopt(socketFd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(int));
	ERROR_CHECK(ret, -1, "setsockopt");
	struct sockaddr_in ser;
	bzero(&ser, sizeof(ser));
	ser.sin_family = AF_INET;
	ser.sin_port = htons(atoi(argv[2]));
	ser.sin_addr.s_addr = inet_addr(argv[1]);//点分十进制转为32位的网络字节序
	ret = bind(socketFd, (struct sockaddr*)&ser, sizeof(ser));
	ERROR_CHECK(ret, -1, "bind");
	listen(socketFd, 10);//缓冲区的大小，一瞬间能够放入的客户端连接信息
	int new_fd;
	struct sockaddr_in client;
	bzero(&client, sizeof(client));
	int addrlen = sizeof(client);
	new_fd = accept(socketFd, (struct sockaddr*)&client, &addrlen);
	ERROR_CHECK(new_fd, -1, "accept");
	printf("client ip=%s, port=%d
", inet_ntoa(client.sin_addr), ntohs(client.sin_port));
	fd_set rdset;
	char buf[128] = {0};
	int rcvLowAt = 10;
	ret=setsockopt(new_fd,SOL_SOCKET,SO_RCVLOWAT,&rcvLowAt,sizeof(int));

	ERROR_CHECK(ret, -1, "setsockopt");
	while(1){
		FD_ZERO(&rdset);
		FD_SET(STDIN_FILENO, &rdset);
		FD_SET(new_fd, &rdset);
		ret = select(new_fd + 1, &rdset, NULL, NULL, NULL);
		if(FD_ISSET(new_fd, &rdset)){
			bzero(buf, sizeof(buf));
			ret = recv(new_fd, buf, sizeof(buf), 0);
			ERROR_CHECK(ret, -1, "recv");
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			printf("%s
", buf);
		}
		if(FD_ISSET(STDIN_FILENO, &rdset)){
			memset(buf, 0, sizeof(buf));
			ret = read(STDIN_FILENO, buf, sizeof(buf));
			if(ret == 0){
				printf("byebye!
");
				break;
			}
			ret = send(new_fd, buf, strlen(buf) - 1, 0);
			ERROR_CHECK(ret, -1, "send");
		}
	}
	close(new_fd);
	close(socketFd);
	return 0;
}

tcp_client.c和1同