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网络编程——TCP的半关闭

程序员文章站 2022-06-30 18:21:10
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参考

  1. 《TCP/IP网络编程》 尹圣雨

TCP的半关闭

一旦两台主机间建立了套接字连接,每个主机就会拥有单独的输入流和输出流。其中一个主机的输入流与另一主机的输出流相连,而输出流则与另一主机的输入流相连

Linux的close函数和Windows的closesocket函数会同时断开两个流。即主机无法传输数据,也无法接收数据。导致另一台主机正在发送的数据无法再接收了。因此,我们需要半关闭状态,只关闭其中的一个流

假设服务器端想半关闭自己的输出流,一方面需要让客户端知道数据已经传输完毕,另一方面要保留输入流。要实现第一点,服务器端应最后向客户端传递EOF表示文件传输结束;要实现第二点,就使用shutdown函数代替close或closesocket函数

shutdown函数

#include <sys/socket.h>
int shutdown(int sock, int howto);

成功时返回0,失败时返回-1。其中,sock为需要断开的套接字文件描述符;howto为传递断开方式信息

howto有三种可能值:

  1. SHUT_RD:断开输入流
  2. SHUT_WR:断开输出流
  3. SHUT_RDWR:同时断开I/O流

实现

服务器端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30
void error_handling(char* message);

int main(int argc, char* argv[])
{
    int serv_sd, clnt_sd;
    FILE* fp;
    char buf[BUF_SIZE];
    int read_cnt;

    struct sockaddr_in serv_adr, clnt_adr;
    socklen_t clnt_adr_sz;
    
    if (argc != 2)
    {
        printf("Usage : %s <port>\n", argv[0]);
        exit(1);
    }
    
    fp = fopen("file_server.c", "rb");
    serv_sd = socket(PF_INET, SOCK_STREAM, 0);

    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]));

    bind(serv_sd, (struct sockaddr*)&serv_adr, sizeof(serv_adr));
    listen(serv_sd, 5);

    clnt_adr_sz = sizeof(clnt_adr);
    clnt_sd = accept(serv_sd, (struct sockaddr*)&clnt_adr, &clnt_adr_sz);

    while (1)
    {
        read_cnt = fread((void*)buf, 1, BUF_SIZE, fp);
        if(read_cnt < BUF_SIZE)
        {
            write(clnt_sd, buf, read_cnt);
            break;
        }
        write(clnt_sd, buf, BUF_SIZE);
    }

    shutdown(clnt_sd, SHUT_WR);                       // 半关闭
    read(clnt_sd, buf, BUF_SIZE);
    printf("Message from client: %s \n", buf);

    fclose(fp);
    close(clnt_sd);
    close(serv_sd);
    return 0;
}

void error_handling(char* message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

客户端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30
void error_handling(char* message);

int main(int argc, char* argv[])
{
    int sd;
    FILE* fp;
    char buf[BUF_SIZE];
    int read_cnt;
    struct sockaddr_in serv_adr;
    if (argc != 3)
    {
        printf("Usage : %s <IP> <port>\n", argv[0]);
        exit(1);
    }

    fp = fopen("receive.dat", "wb");
    sd = socket(PF_INET, SOCK_STREAM, 0);
    
    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]));

    connect(sd, (struct sockaddr*)&serv_adr, sizeof(serv_adr));

    while ((read_cnt = read(sd, buf, BUF_SIZE)) != 0)
    {
        fwrite((void*)buf, 1, read_cnt, fp);
    }

    puts("Received file data");
    write(sd, "Thank you", 10);
    fclose(fp);
    close(sd);
    return 0;
}

void error_handling(char* message)
{
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

基于Windows实现

Windows平台没有太大区别,知识shutdown的参数名略有不同

#include <WinSock2.h>

int shutdown(SOCKET sock, int howto);

成功时返回0,失败时返回SOCKET_ERROR

howto有三种可能值:

  1. SD_RECEIVE:断开输入流
  2. SD_SEND:断开输出流
  3. SD_BOTH:同时断开I/O流

服务器端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <WinSock2.h>

#define BUF_SIZE 30
void ErrorHandling(char* message);

int main(int argc, char* argv[])
{
	WSADATA wsaData;
	SOCKET hServSock, hClntSock;
	FILE* fp;
	char buf[BUF_SIZE];
	int readCnt;
	errno_t error;

	SOCKADDR_IN servAdr, clntAdr;
	int clntAdrSz;
	
	if (argc != 2)
	{
		printf("Usage : %s <port> \n", argv[0]);
		exit(1);
	}
	if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
	{
		ErrorHandling("WSAStartup() error!");
	}

	error = fopen_s(&fp, "file_server_win.c", "rb");
	hServSock = socket(PF_INET, SOCK_STREAM, 0);

	memset(&servAdr, 0, sizeof(servAdr));
	servAdr.sin_family = AF_INET;
	servAdr.sin_addr.s_addr = htonl(INADDR_ANY);
	servAdr.sin_port = htons(atoi(argv[1]));

	bind(hServSock, (SOCKADDR*)&servAdr, sizeof(servAdr));
	listen(hServSock, 5);

	clntAdrSz = sizeof(clntAdr);
	hClntSock = accept(hServSock, (SOCKADDR*)&clntAdr, &clntAdrSz);

	while (1)
	{
		readCnt = fread((void*)buf, 1, BUF_SIZE, fp);
		if (readCnt < BUF_SIZE)
		{
			send(hClntSock, (char*)&buf, readCnt, 0);
			break;
		}
		send(hClntSock, (char*)&buf, BUF_SIZE, 0);
	}
	
	shutdown(hClntSock, SD_SEND);
	recv(hClntSock, (char*)buf, BUF_SIZE, 0);
	printf("Message from client: %s \n", buf);

	fclose(fp);
	closesocket(hClntSock);
	closesocket(hServSock);
	WSACleanup();
	return 0;
}

void ErrorHandling(char* message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

客户端

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <WinSock2.h>
#include <WS2tcpip.h>

#define BUF_SIZE 30
void ErrorHandling(char* message);

int main(int argc, char* argv[])
{
	WSADATA wsaData;
	SOCKET hSocket;
	FILE* fp;
	errno_t error;
	
	char buf[BUF_SIZE];
	int readCnt;
	SOCKADDR_IN servAdr;

	if (argc != 3)
	{
		printf("Usage: %s <IP> <port>\n", argv[0]);
		exit(1);
	}
	if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0)
	{
		ErrorHandling("WSAStartup() error!");
	}

	error = fopen_s(&fp, "receive.dat", "wb");
	hSocket = socket(PF_INET, SOCK_STREAM, 0);

	memset(&servAdr, 0, sizeof(servAdr));
	servAdr.sin_family = AF_INET;
	inet_pton(AF_INET, argv[1], &servAdr.sin_addr);
	servAdr.sin_port = htons(atoi(argv[2]));

	connect(hSocket, (SOCKADDR*)&servAdr, sizeof(servAdr));

	while ((readCnt = recv(hSocket, buf, BUF_SIZE, 0)) != 0)
	{
		fwrite((void*)buf, 1, readCnt, fp);
	}

	puts("Received file data");
	send(hSocket, "Thank you", 10, 0);
	fclose(fp);
	closesocket(hSocket);
	WSACleanup();
	return 0;
}

void ErrorHandling(char* message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}