近期学习linux socket编程。看看unp那本书。顺便写了个类似最简单聊天功能的软件。界面是用qt写的。写下来总结总结吧，假设有问题。欢迎大家和我交流。

模式是C/S模式，server端等待请求。client发送后建立请求。连接用的是tcp不是udp，事实上udp实现更为简单。

一. 环境搭建

我用docker搭了几个虚拟机，详细搭建方式能够參考网上的或我之前写docker的总结：点击打开链接

docker还是非常轻量级的，比一般虚拟机起的快多了。

搭建好docker以后就是主要的先看网络是否联通，假设不连通看看链路。防火墙设置一下。

二.没有界面的代码实现：

这部分代码主要參考unp上的简单样例，当中肯定会有bug，由于没有考虑复杂的tcp环境，仅仅是单纯的先实现再说：

server端：

#include "unp.h"
#include <stdio.h>
#include <unistd.h>

void Answer(FILE *fop, FILE *fip, int sockfd) {
    int         maxfdp1, stdineof;
    fd_set      rset;
    char        buf[MAXLINE];
    int     n;

    stdineof = 0;
    FD_ZERO(&rset);
    for ( ; ; ) {
        if (stdineof == 0)
            FD_SET(fileno(fip), &rset);
        FD_SET(sockfd, &rset);
        maxfdp1 = max(fileno(fip), sockfd) + 1;
        Select(maxfdp1, &rset, NULL, NULL, NULL);

        if (FD_ISSET(sockfd, &rset)) {  /* socket is readable */
            if ( (n = Read(sockfd, buf, MAXLINE)) == 0) {
                if (stdineof == 1)
                    return;     /* normal termination */
                else
                    err_quit("client quit!");
            }

            Write(fileno(fop), buf, n);
        }

        if (FD_ISSET(fileno(fip), &rset)) {  /* input is readable */
            if ( (n = Read(fileno(fip), buf, MAXLINE)) == 0) {
                stdineof = 1;
                Shutdown(sockfd, SHUT_WR);  /* send FIN */
                FD_CLR(fileno(fip), &rset);
                continue;
            }

            Writen(sockfd, buf, n);
        }
    }
    
}

int main(int argc, char **argv)
{
    int                 listenfd, connfd;
    pid_t               childpid;
    socklen_t           clilen;
    struct sockaddr_in  cliaddr, servaddr;

    listenfd = Socket(AF_INET, SOCK_STREAM, 0);

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family      = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    //servaddr.sin_port        = htons(SERV_PORT);
    servaddr.sin_port        = htons(50001);

    Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));

    Listen(listenfd, LISTENQ);

    for ( ; ; ) {
        clilen = sizeof(cliaddr);
        if ( (connfd = accept(listenfd, (SA *) &cliaddr, &clilen)) < 0) {
            if (errno == EINTR)
                continue;       /* back to for() */
            else
                err_sys("accept error");
        }

        if ( (childpid = Fork()) == 0) {    /* child process */
            Close(listenfd);    /* close listening socket */
            Answer(stdout, stdin, connfd);
            printf("end of one connect!\n");
            exit(0);
        }
        Close(connfd);          /* parent closes connected socket */
    }
}

client代码：

#include	"unp.h"

const int SIZE = 1024;

void Input(FILE *fp, int sockfd) {
    int			maxfdp1, stdineof;
	fd_set		rset;
	char		buf[MAXLINE];
	int		n;

	stdineof = 0;
	FD_ZERO(&rset);
	for ( ; ; ) {
		if (stdineof == 0)
			FD_SET(fileno(fp), &rset);
		FD_SET(sockfd, &rset);
		maxfdp1 = max(fileno(fp), sockfd) + 1;
		Select(maxfdp1, &rset, NULL, NULL, NULL);

		if (FD_ISSET(sockfd, &rset)) {	/* socket is readable */
			if ( (n = Read(sockfd, buf, MAXLINE)) == 0) {
				if (stdineof == 1)
					return;		/* normal termination */
				else
					err_quit("str_cli: server terminated prematurely");
			}

			Write(fileno(stdout), buf, n);
		}

		if (FD_ISSET(fileno(fp), &rset)) {  /* input is readable */
			if ( (n = Read(fileno(fp), buf, MAXLINE)) == 0) {
				stdineof = 1;
				Shutdown(sockfd, SHUT_WR);	/* send FIN */
				FD_CLR(fileno(fp), &rset);
				continue;
			}

			Writen(sockfd, buf, n);
		}
	}
}

int main(int argc, char **argv)
{
	int					sockfd;
	struct sockaddr_in	servaddr;

	if (argc != 3)
		err_quit("usage: tcpcli <IPaddress>::<Port>");

	sockfd = Socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(atoi(argv[2]));
	Inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

	Connect(sockfd, (SA *) &servaddr, sizeof(servaddr));

	struct sockaddr_in ss;
    socklen_t len = sizeof(ss);
    if(getsockname(sockfd, (SA *)&ss, &len) < 0) return 0;
    int clientPort = ntohs(ss.sin_port);  //pay attention the translate n<->pstr_cli(stdin, sockfd);		/* do it all */
    
    printf("%d\n", clientPort);

    Input(stdin, sockfd);

	exit(0);
}

要想跑通这个代码还得配置unp的环境。

好吧。我以下有界面的代码能够不用配置unp环境

三.加界面

我抽象了几个基类。主要界面就4个，先来看看界面吧：

server端和client的聊天界面是一样的。server端我做了点小处理，拒绝多个客户的连接。当一个客户聊天时，监听的socket就被关闭了。

刚学qt就開始搞界面，真是太恶心了。

主要代码：

client登录：

#include "clientstart.h"
#include "chatclient.h"
#include <iostream>
#include <fstream>
#include <sstream>

using namespace std;

ClientStart::ClientStart(QWidget *parent) :
    StartBase(parent)
{
    this->className = "ClientStart";

    /*belong to first layout*/
    QLabel *labelOppositeIP = new QLabel("请输入服务器IP：");
    oppositeIP = new QLineEdit;
    QLabel *labelOppositePort = new QLabel("请输入服务器端口：");
    oppositePort = new QLineEdit;
    firstLayout->addWidget(labelOppositeIP, 2, 0, 1, 1);
    firstLayout->addWidget(oppositeIP, 2, 1, 1, 4);
    firstLayout->addWidget(labelOppositePort, 3, 0, 1, 1);
    firstLayout->addWidget(oppositePort, 3, 1, 1, 4);

    /*second layout*/
    secondLayout = new QHBoxLayout;
    secondLayout->setSpacing(60);
    secondLayout->addWidget(buttonSure);
    secondLayout->addWidget(buttonCancel);

    topLayout->addLayout(firstLayout);
    topLayout->addLayout(secondLayout);

    QWidget* widget = new QWidget(this);
    widget->setLayout(topLayout);  
    this->setCentralWidget(widget); //add the topLayout in current dialog

}

ClientStart::~ClientStart()
{
    //delete this;
}

void ClientStart::doOpen() {
    //QMessageBox::information(this, "success", QObject::tr("xxx"), QMessageBox::Ok);
    serverIP = (oppositeIP->text()).toStdString();
    serverPort = (oppositePort->text()).toStdString();

    /*start connect now*/
    bool isConnect = tryConnect();
    if(!isConnect) {
        errorCall(this, "连接失败");
        return ;
    }

    ChatClient cc(clientIP, clientPort, serverIP, serverPort, servaddr, clientSocketFd);
    cc.exec();
    //cc.show();
    this->close();
}

void ClientStart::doCancel() {
    QMessageBox::information(this, "failed", QObject::tr("请又一次设置"), QMessageBox::Ok);
    oppositeIP->setText("");
    oppositePort->setText("");
}

bool ClientStart::tryConnect() {
    clientSocketFd = socket(AF_INET, SOCK_STREAM, 0);

	bzero(&servaddr, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(atoi(serverPort.c_str()));
	inet_pton(AF_INET, serverIP.c_str(), &servaddr.sin_addr);

	if(::connect(clientSocketFd, (SA *) &servaddr, sizeof(servaddr)) < 0) return 0;

    /*get client port, ip has already got*/
    struct sockaddr_in ss;
    socklen_t len = sizeof(ss);
    if(getsockname(clientSocketFd, (SA *)&ss, &len) < 0) return 0;

    stringstream stmp; //change int to string
    stmp << ntohs(ss.sin_port);  //pay attention the translate n<->p
    clientPort = stmp.str();
    return 1;
}

#include "chatclient.h"
#include <iostream>
#include <fstream>

using namespace std;

ChatClient::ChatClient(std::string clientIP, std::string clientPort, std::string serverIP, std::string serverPort, struct sockaddr_in servaddr, int clientSocketFd) 
    : ChatBase(NULL) {
    this->clientIP = clientIP;
    this->clientPort = clientPort;
    this->serverIP = serverIP;
    this->serverPort = serverPort;
    this->servaddr = servaddr;
    this->clientSocketFd = clientSocketFd;

    this->lineLocalIP->setText(QString(clientIP.c_str()));
    this->lineLocalPort->setText(QString(clientPort.c_str()));
    this->lineOppositeIP->setText(QString(serverIP.c_str()));
    this->lineOppositePort->setText(QString(serverPort.c_str())); 
    
    this->secondLayout->setReadOnly(1);
    this->secondLayout->setText("start chatting now!\n");
    this->secondLayout->append(showTime());
    this->secondLayout->show();

    /*connect the socket and function*/
    stdineof = 0;
    FD_ZERO(&rset);
    revSN = new QSocketNotifier(clientSocketFd, QSocketNotifier::Read); 
    QObject::connect(revSN, SIGNAL(activated(int)), this, SLOT(doDataReceived()));
}

ChatClient::~ChatClient() {
    stdineof = 1;
    shutdown(clientSocketFd, SHUT_WR);	/* send FIN */
    FD_ZERO(&rset);
    
    this->close();
}

void ChatClient::doSendMsg() {
    std::string sent = (forthLayout->toPlainText()).toStdString();
    sent += ‘\n‘;
    if(write(clientSocketFd, sent.c_str(), sent.size()) < 0) {
        errorCall(this, "send message failed!");
        return ;
    }
    appendSecondLayout(sent);
    forthLayout->clear();
}

void ChatClient::doCancel() {
    forthLayout->clear();
}

void ChatClient::doSendFile() {}

void ChatClient::doVedio() {}

void ChatClient::doDataReceived() {
    int revLen;
    if ( (revLen = read(clientSocketFd, buf, MAXLINE)) == 0) {
	if (stdineof == 1)
		return;		/* normal termination */
	else {
            errorCall(this, "server terminated prematurely");
            this->close();
        }
    }
   
    buf[revLen] = ‘\0‘;
    appendSecondLayout(string(buf));

    return ;
}

我把所有代码上传到csdn了，链接：点击打开链接
安装时须要配置qt5，视频和传文件功能暂未实现

四.总结和未来展望

这个软件也就写着玩。肯定有Bug。

事实上之前的计划是作NAT转发，使得两台局域网之间的主机能够直接聊天，后来发现行不通，没有权限改动入网的路由NAT规则。

以后的计划例如以下：

1.是不用qt界面。直接命令行。

2.实现文件传输。

3.抛弃C/S架构，搞一台有公网ip的server，两台聊天的主机同一时候连到这个服务，server进行转发

假设大家有什么问题欢迎交流，希望能有小伙伴和我一起来搞～～。

代码虽不难，但也是自己倒腾的。转载请注明地址：http://blog.csdn.net/u011353822/article/details/41246277