网络编程学习笔记（一）-----socket

今天开始学习Linux的C++网络编程。

 

以前也用过一点socket，但是没有总结过，今天重新复习，然后总结之。

 

首先介绍一些数据类型：

 

sockaddr_in

sockaddr_un

sockaddr

 

struct sockaddr { __SOCKADDR_COMMON (sa_); /* Common data: address family and length. */ char sa_data[14]; /* Address data. */ }; struct sockaddr_un { sa_family_t sun_family; /* AF_UNIX */ char sun_path[UNIX_PATH_MAX]; /* pathname */ }; /* Structure describing an Internet (IP) socket address. */ #define __SOCK_SIZE__ 16 /* sizeof(struct sockaddr) */ struct sockaddr_in { sa_family_t sin_family; /* Address family */ __be16 sin_port; /* Port number */ struct in_addr sin_addr; /* Internet address */ /* Pad to size of `struct sockaddr'. */ unsigned char __pad[__SOCK_SIZE__ - sizeof(short int) - sizeof(unsigned short int) - sizeof(struct in_addr)]; };

 

这些结构体的定义虽然看起来不同，但是长度是相同的，而且对于处理而言，sockaddr_in显得最为方便，但是为了兼容链接，bind等函数的接口，需要做一个安全的强制类型转换 ：

 

（struct sockaddr*）&some_sockaddr_in_definition

 

剩下一个要点就是理解网络连接的基本过程：

对于服务器端，首先创建socket，然后填写socketaddr_in的内容，这里需要注意的是sin_port的填写需要通过htons()函数对port进行转换。

//htons函数将一个16位数从主机字节顺序转换成网络字节顺序

 

1 bind（）绑定端口

 

2 listen（）

 

3 accept（）等待client的连接

 

4 解析用户的数据

 

5 send()发送给用户数据

 

循环执行3-5

 

代码如下：

#include<sys/types.h> #include<sys/socket.h> #include<stdio.h> #include<sys/un.h> #include<unistd.h> #include<stdlib.h> #include<errno.h> #include<netinet/in.h> #include<sys/wait.h> #include<arpa/inet.h> const int BACKLOG = 10;//接受的没有accept的链接 const int PORT = 8611; int main() { int server_sockfd,client_sockfd; struct sockaddr_in sever_addr,client_addr; if( (server_sockfd = socket(AF_INET,SOCK_STREAM,0))==-1) { perror("initialize sever socket failed"); exit(1); } //set the type of net and the listen port sever_addr.sin_family = AF_INET; sever_addr.sin_port = htons(PORT); sever_addr.sin_addr.s_addr = INADDR_ANY; //set the other bits to zero bzero(&(sever_addr.sin_addr),8); //bind if(bind(server_sockfd,(struct sockaddr*)&sever_addr, sizeof(struct sockaddr_in)) == -1) { perror("bind failed"); exit(-1); } //listen if(listen(server_sockfd,BACKLOG) == -1) { perror("listen failed"); exit(-1); } while(1) { int sin_size = sizeof(struct sockaddr_in); if((client_sockfd = accept(server_sockfd,(struct sockaddr*)&client_addr,(socklen_t*)&sin_size) ) == -1) { perror("accept"); continue; } printf("server get connect from %s/n", inet_ntoa(client_addr.sin_addr)); if(!fork()) { if(send(client_sockfd,"Hello world/n",13,0) == -1) { perror("send"); close(client_sockfd); exit(-1); } close (client_sockfd); } } while( waitpid(-1,NULL,WNOHANG)>0); return 0; }

 

对于客户端来说，情况要更简单一些：

 

1 构造socket，socketaddr_in，这些是和server相同的，不同的是需要构造一个hostent类型的数据

/* Description of data base entry for a single host. */ struct hostent { char *h_name; /* Official name of host. */ char **h_aliases; /* Alias list. */ int h_addrtype; /* Host address type. */ int h_length; /* Length of address. */ char **h_addr_list; /* List of addresses from name server. */ #if defined __USE_MISC || defined __USE_GNU # define h_addr h_addr_list[0] /* Address, for backward compatibility.*/ #endif };

 

该实体的构造可以调用函数gethostbyname()（或者为gethostbyaddr()）函数来实现。

 

 

2 connect()

 

3 sent()

 

4 recv()

 

#include<stdio.h> #include<unistd.h> #include<stdlib.h> #include<errno.h> #include<string.h> #include<netdb.h> #include<sys/socket.h> #include<netinet/in.h> #include<sys/types.h> const int PORT = 8611; const int MAX_PACK_LEN = 100; int main(int argc, char **argv) { if(argc!=2) { printf("Usage : Client hostname/n"); exit(-1); } int sockfd,num; char buf[MAX_PACK_LEN]; struct hostent *he; struct sockaddr_in client_addr; //get the host information if( (he =gethostbyname(argv[1]) ) == NULL) { herror("gethostbyname"); exit(-1); } //creat socket if((sockfd = socket(AF_INET,SOCK_STREAM,0)) == -1) { perror("Client socket"); exit(-1); } //initialize the sockaddr_in client_addr.sin_family = AF_INET; client_addr.sin_port = htons(PORT); client_addr.sin_addr = *((struct in_addr*)he->h_addr); bzero(&(client_addr.sin_zero),8); //connect if(-1 == connect(sockfd,(struct sockaddr*)&client_addr,sizeof(sockaddr))) { perror("client connection"); exit(-1); } //receive the data if( (num = recv(sockfd,buf,MAX_PACK_LEN,0)) == -1) { perror("client receive data failed"); exit(-1); } //it's the safe method to output the data received! buf[num] = '/0'; printf("Received :%s/n",buf); close(sockfd); return 0; }