简单的网络编程———TCP/UDP

定义
TCP (Transmission Control Protocol)和UDP(User Datagram Protocol)协议属于传输层协议。其中TCP提供IP环境下的数据可靠传输，它提供的服务包括数据流传送、可靠性、有效流控、全双工操作和多路复用。通过面向连接、端到端和可靠的数据包发送。通俗说，它是事先为所发送的数据开辟出连接好的通道，然后再进行数据发送；

UDP则不为IP提供可靠性、流控或差错恢复功能。
一般来说，TCP对应的是可靠性要求高的应用，而UDP对应的则是可靠性要求低、传输经济的应用。TCP支持的应用协议主要有：Telnet、FTP、SMTP等；UDP支持的应用层协议主要有：NFS（网络文件系统）、SNMP（简单网络管理协议）、DNS（主域名称系统）、TFTP（通用文件传输协议）等。

TCP：“面向连接”就是在正式通信前必须要与对方建立起连接。
UDP（User Data Protocol，用户数据报协议）是与TCP相对应的协议。它是面向非连接的协议，它不与对方建立连接，而是直接就把数据包发送过去！“面向非连接”就是在正式通信前不必与对方先建立连接，不管对方状态就直接发送。

TCP服务端程序

#include <sys/types.h>        
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>


/* socket	创建
 * bind		绑定ip、端口
 * listen	监听
 * accept	接收客户端连接
 * send/recv	发送接收
 */

#define SERVER_PORT 8888
#define BACKLOG     10		//监听路数

int main(int argc, char **argv)
{
	int iSocketServer;
	int iSocketClient;
	struct sockaddr_in tSocketServerAddr;
	struct sockaddr_in tSocketClientAddr;
	int iRet;
	int iAddrLen;

	int iRecvLen;
	unsigned char ucRecvBuf[1000];

	int iClientNum = -1;

	signal(SIGCHLD,SIG_IGN);//清理子进程（僵尸进程）
	
							/*IPV4，TCP*/
	iSocketServer = socket(AF_INET, SOCK_STREAM, 0);
	if (-1 == iSocketServer)
	{
		printf("socket error!\n");
		return -1;
	}

	tSocketServerAddr.sin_family      = AF_INET;
	tSocketServerAddr.sin_port        = htons(SERVER_PORT);  /* 监测端口 */
 	tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;/*本机所有ip*/
	memset(tSocketServerAddr.sin_zero, 0, 8);
		
		/*绑定IP地址、端口等信息到socket上*/
	iRet = bind(iSocketServer, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
	if (-1 == iRet)
	{
		printf("bind error!\n");
		return -1;
	}

	iRet = listen(iSocketServer, BACKLOG);//可监听10个客户端
	if (-1 == iRet)
	{
		printf("listen error!\n");
		return -1;
	}

	while (1)
	{
		iAddrLen = sizeof(struct sockaddr);
		
			/* 等待客户端连接												保存客户端地址 			地址长度*/
		iSocketClient = accept(iSocketServer, (struct sockaddr *)&tSocketClientAddr, &iAddrLen);
		if (-1 != iSocketClient)//有客户端连接
		{
			iClientNum++;												/* 得到ip*/
			printf("Get connect from client %d : %s\n",  iClientNum, inet_ntoa(tSocketClientAddr.sin_addr));

			/*对每一个客户端连接创建子进程*/
			if (!fork())
			{
				/* 子进程的源码 */
				while (1)
				{
					/* 接收客户端发来的数据并打印出来 */
					iRecvLen = recv(iSocketClient, ucRecvBuf, 999, 0);
					if (iRecvLen <= 0)
					{
						close(iSocketClient);
						return -1;
					}
					else
					{
						ucRecvBuf[iRecvLen] = '\0';
						printf("Get Msg From Client %d: %s\n", iClientNum, ucRecvBuf);
					}
				}				
			}
		}
	}
	
	close(iSocketServer);
	return 0;
}

TCP客户端程序

#include <sys/types.h>         
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>

/* socket
 * connect
 * send/recv
 */

#define SERVER_PORT 8888

/*输入服务器ip：192.168.1.11*/
int main(int argc, char **argv)
{
	int iSocketClient;
	struct sockaddr_in tSocketServerAddr;
	
	int iRet;
	unsigned char ucSendBuf[1000];
	int iSendLen;

	if (argc != 2)
	{
		printf("Usage:\n");
		printf("%s <server_ip>\n", argv[0]);
		return -1;
	}

	iSocketClient = socket(AF_INET, SOCK_STREAM, 0);

	tSocketServerAddr.sin_family      = AF_INET;
	tSocketServerAddr.sin_port        = htons(SERVER_PORT);  /* host to net, short */
 	//tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
 	if (0 == inet_aton(argv[1], &tSocketServerAddr.sin_addr))//传入服务器ip
 	{
		printf("invalid server_ip\n");
		return -1;
	}
	memset(tSocketServerAddr.sin_zero, 0, 8);

		/*连接到服务器*/
	iRet = connect(iSocketClient, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));	
	if (-1 == iRet)
	{
		printf("connect error!\n");
		return -1;
	}

	while (1)
	{
		if (fgets(ucSendBuf, 999, stdin))//从标准输入获得数据，以回车结束
		{
			iSendLen = send(iSocketClient, ucSendBuf, strlen(ucSendBuf), 0);
			if (iSendLen <= 0)
			{
				close(iSocketClient);
				return -1;
			}
		}
	}
	
	return 0;
}

SOCK_STREAM这种的特点是面向连接的，即每次收发数据之前必须通过connect建立连接；
SOCK_DGRAM这种是User Datagram Protocol协议的网络通讯，它是无连接的，不可靠的。

UDP服务端程序

#include <sys/types.h>       
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>


/* socket
 * bind
 * sendto/recvfrom
 */
#define SERVER_PORT 8888

int main(int argc, char **argv)
{
	int iSocketServer;
	int iSocketClient;
	struct sockaddr_in tSocketServerAddr;
	struct sockaddr_in tSocketClientAddr;
	int iRet;
	int iAddrLen;
	int iRecvLen;
	unsigned char ucRecvBuf[1000];
	int iClientNum = -1;
															/*UDP连接*/
	iSocketServer = socket(AF_INET, SOCK_DGRAM, 0);
	if (-1 == iSocketServer)
	{
		printf("socket error!\n");
		return -1;
	}

	tSocketServerAddr.sin_family      = AF_INET;
	tSocketServerAddr.sin_port        = htons(SERVER_PORT);  /* host to net, short */
 	tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
	memset(tSocketServerAddr.sin_zero, 0, 8);
	
	iRet = bind(iSocketServer, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));
	if (-1 == iRet)
	{
		printf("bind error!\n");
		return -1;
	}

	while (1)
	{
		iAddrLen = sizeof(struct sockaddr);
		iRecvLen = recvfrom(iSocketServer, ucRecvBuf, 999, 0, (struct sockaddr *)&tSocketClientAddr, &iAddrLen);
		if (iRecvLen > 0)
		{
			ucRecvBuf[iRecvLen] = '\0';
			printf("Get Msg From %s : %s\n", inet_ntoa(tSocketClientAddr.sin_addr), ucRecvBuf);
		}
	}
	close(iSocketServer);
	return 0;
}

UDP客户端程序

#include <sys/types.h>          /* See NOTES */
#include <sys/socket.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>

/* socket
 * sendto/recvfrom
 * 
 *	使用connect，使用send/recv进行收发
 *不是使用connect，使用sendto/recvfrom进行收发
 */


#define SERVER_PORT 8888

int main(int argc, char **argv)
{
	int iSocketClient;
	struct sockaddr_in tSocketServerAddr;
	
	int iRet;
	unsigned char ucSendBuf[1000];
	int iSendLen;

	if (argc != 2)
	{
		printf("Usage:\n");
		printf("%s <server_ip>\n", argv[0]);
		return -1;
	}

	iSocketClient = socket(AF_INET, SOCK_DGRAM, 0);

	tSocketServerAddr.sin_family      = AF_INET;
	tSocketServerAddr.sin_port        = htons(SERVER_PORT);  /* host to net, short */
 	//tSocketServerAddr.sin_addr.s_addr = INADDR_ANY;
 	if (0 == inet_aton(argv[1], &tSocketServerAddr.sin_addr))
 	{
		printf("invalid server_ip\n");
		return -1;
	}
	memset(tSocketServerAddr.sin_zero, 0, 8);

/*
	iRet = connect(iSocketClient, (const struct sockaddr *)&tSocketServerAddr, sizeof(struct sockaddr));	
	if (-1 == iRet)
	{
		printf("connect error!\n");
		return -1;
	}
*/
	while (1)
	{
		if (fgets(ucSendBuf, 999, stdin))
		{
			//iSendLen = send(iSocketClient, ucSendBuf, strlen(ucSendBuf), 0);
			iSendLen = sendto(iSocketClient, ucSendBuf, strlen(ucSendBuf), 0, (const struct sockaddr *)&tSocketServerAddr, iAddrLen);
			if (iSendLen <= 0)
			{
				close(iSocketClient);
				return -1;
			}
		}
	}
	return 0;
}

实验现象
虚拟机上

开发板上