linux学习笔记（三）——一个例子了解linux网络编程之认识API

一个简单的C/S模型，TCP链接，客户端发送消息，服务端展示到标准输出。通过这个例子，完整的将socket api，多线程/多进程模型，epoll/select，以及并发编程reactor和proactor设计模式。

先来认识API。对于一个建立TCP链接的过程，先对于CS模型来说，Server端：建立socket->绑定端口->监听请求->接受请求。Client端：建立socket->发起连接请求。

这些过程都有对应的api提供。通过例程和注释来看。

SimpleServer.cpp

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

using namespace std;


int main(int argc,char** argv)
{
    int socketfd,readfd;
    struct sockaddr_in server_addr;
    struct sockaddr_in client_addr;
    socklen_t addr_size;
    char buffer[1024];


    int port = atoi(argv[1]);

    //new fd
    if ((socketfd = socket(AF_INET,SOCK_STREAM,0)) == -1)
    {
	printf("Socket Error:%s\n",strerror(errno));
	exit(-1);
    }

    //init server addr
    bzero(&server_addr,sizeof(struct sockaddr_in));
    server_addr.sin_family=AF_INET;
    server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    server_addr.sin_port = htons(port);
    
    //bind port
    if(bind(socketfd,(struct sockaddr*)(&server_addr),sizeof(struct sockaddr)) == -1)
    {
	printf("Bind Error:%s\n",strerror(errno));
	exit(-1);
    }	

    //listend the port
    if (listen(socketfd,5))
    {
	printf("Listen Error:%s\n",strerror(errno));
	exit(-1);
    }

    while(1)//handler client one by one
    {
    	//server for accept
    	if ((readfd = accept(socketfd,(struct sockaddr*)(&client_addr),&addr_size)) == -1)
    	{
	    printf("Accept Error:%s\n",strerror(errno));
            exit(-1);
    	}
	printf("Accept Client Address:%s\n",inet_ntoa(client_addr.sin_addr));
        int readbytes = 0;

        //read until end
	//int number = 0;
	while((readbytes = read(readfd,buffer,1024))>0)
	{
	    //printf("Recived Content:%s\n",buffer);
	    write(STDOUT_FILENO,buffer,strlen(buffer));
	    fflush(stdout);
	    memset(buffer,0,1024);
	}
        
	if (readbytes == 0)
        {
	    printf("Read Finished!\n");
	}else{
	    printf("Read Terminate Error:%s\n",strerror(errno));
            exit(-1);
	}; 
	
	close(readfd);
    }
    close(socketfd);
    exit(0);
}

SimpleClient.cpp

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

using namespace std;

int main(int argc,char **argv)
{
    int socketfd;
    struct in_addr server_ip;
    struct sockaddr_in server_addr;
    struct hostent *host;
    char buffer[1024];

    if ((socketfd = socket(AF_INET,SOCK_STREAM,0)) == -1)
    {
	printf("Socket Error:%s\n",strerror(errno));
        exit(-1);
    }   
    inet_aton(argv[1],&server_ip);
    //init server address
    bzero(&server_addr,sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(atoi(argv[2]));
    server_addr.sin_addr = server_ip;
    
    if (connect(socketfd,(struct sockaddr*)&server_addr,sizeof(sockaddr_in)) == -1)
    {
	printf("Connect Server Error:%s\n",strerror(errno));
        exit(-1);
    }

    while(fgets(buffer,1024,stdin) != NULL)
    {
//	int number = htonl(atoi(buffer));
//	write(socketfd,&number,sizeof(int));
//	if (strlen(buffer) != (sizeof(buffer)-1))
//	{
//	    buffer[strlen(buffer)-1] = '\0';
//	}	
	write(socketfd,buffer,strlen(buffer));
	printf("Send Message:%s",buffer);
        if (strcmp(buffer,"exit\n")==0)
        {
	    printf("Exit Client!\n");
            close(socketfd);
            exit(0);
        }
	
    };
    close(socketfd);
    exit(0);   	
}

总结知识点：

1、socket\bind\listen\accept\connect的调用方式

2、网络字节序和主机字节序的转换（只有数字型需要转换，char等字符串型不需要转换；由于需要三次握手，端口等需要字节序换转）