获取主机信息,网络信息AIP,getsockname,getpeername,getservbyname,getservbyport,inet_ntop,inet_pton

获取主机信息

1.ip地址转换，主机字节序 <---> 网络字节序

#include <arpa/inet.h>

int inet_pton(int af, const char* src, void* dst);

const char* inet_ntop(int af, const void* src, char* dst, socklen_t cnt)

inet_pton函数将用字符串表示的IP地址src（用淀粉十进制字符串表示的IPv4地址或用十六进制字符串表示的IPv6地址）转换成用网络字节序整数表示的IP地址，并把转换结果存储于dst指向的内存中。

其中，af 参数指定地址族，可以使AF_INET或者AF_INET6.inet_pton成功时返回1，失败时返回0，病设置errno。

inet_ntop函数进行相反的转换，前3个参数含义与inet_pton的参数相同，最后一个参数cnt指定目标存储单元的大小。成功时返回目标存储单元的地址，失败则返回NULL并设置errno。

这个头文件里面定义了“目标存储单元的大小”

#include <netinet/in.h>
#define  INET_ADDRESSLEN    16
#define  INET6_ADDRESSLEN  46

2.地址信息函数：

#include <sys/socket.h>
int getsockname(int sockfd, struct sockaddr* address, socklen_t* address_len);
int getpeername(int sockfd, struct slckaddr* address, socklen_t* address_len);

     getsockanme获取sockfd对应的本端socket地址，并将其存储于address参数指定的内存中，该socket地址的长度则存储于address_len参数指向的变量中。如果实际socket地址的长度大于address所指内存区的大小，那么该socket地址将被截断。getsocketname成功时返回0，失败则返回-1，并设置errno。

    getpeername获取sockfd对应的远端socket地址，其参数及返回值的含义与getsockname的参数及返回值相同。

3.网络信息AIP

#include <netdb.h>
struct hostent* gethostbyname(const char* name);
struct hostent* gethostbyaddr(const void* addr, size_t len, int type);

struct hostent
{
    char* h_name;
    char** h_aliases;
    int h_addrtype;
    int h_length;
    char** h_addr_list;//按网络字节序列出的主机IP地址列表
};

gethostbyname 函数根据主机名称获取主机的完整信息，
gethostbyaddr函数根据IP地址获取主机的完整信息。
gethostbyname函数通常先在本地的 /etc/hsots配置的文件中查找主机，
如果没有找到，再去访问DNS服务器。

#include <netdb.h>
struct servent* getservbyname(const char* name, const char* proto);
struct servent* getsrvbyport(int port, const char* proto);

struct servent
{
    char* s_name;
    char** s_aliases;
    int s_port;
    char* s_proto;
};

getservbyname函数根据名称获取某个服务的完整信息，
getsrvbyport函数根据端口号获取某个服务的完整信息。
他们实际上都是通过读取 /etc/services 文件来获取服务信息的

#include <netdb.h>
int getaddrinfo(const char* hostname, const char* service, const struct addrinfo* hints, struct addrinfo** result)

struct addrinfo
{
    int ai_flags;
    int ai_family;
    int ai_socktype;
    int ai_protocol;
    socklent_t ai_addrlen;
    char* ai_canonname;
    struct sockaddr* ai_addr;
    struct addrinfo* ai_next;
};

getaddrinfo函数既能通过主机名获取ip地址也能通过服务名获得端口号。

#include <netdb.h>
int getnameinfo(const struct sockaddr* sockaddr, socklen_t addrlen, char* host, socklen_t hostlen, char* serv, socklen_t servlen, int flags);

getnameinfo函数能通过socket地址同时获得以字符串表示的主机名和服务名。

4.举例说明：

举个例子A：

    const char* ip = argv[1];
    int port = atoi(argv[2]);
    int backlog = atoi(argv[3]);

    int sock = socket(PF_INET, SOCK_STREAM, 0);
    assert(socket >= 0);

    // create a ipv4 socket address
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    inet_pton(AF_INET, ip, &address.sin_addr);
    address.sin_port = htons(port);

举个例子B：

if(connect(sock, (struct sockaddr*)&serverSocket, sizeof(serverSocket)) != -1)
    {
        char buffer[BUFFER_SIZE];
        memset(buffer, '', sizeof(buffer));
        send(sock, buffer, BUFFER_SIZE, 0);
                        
        //client get server(peer) name
        struct sockaddr_in peerHost;
        socklen_t client_addrlength = sizeof(peerHost);
        getpeername(sock, (struct sockaddr*)&peerHost, &client_addrlength );
        char dest[100] ;
        inet_ntop(AF_INET, &peerHost.sin_addr,dest,100);
        int peerPort=ntohs(peerHost.sin_port);
        printf("dest ip : %s, port:%d", dest, peerPort);
    }

举个例子C：（完整版. 客户端）

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

#define BUFFER_SIZE  512

int main(int argc, char* argv[])
{
    if(argc<=2)
    {
        printf("usage: %s ip_address, port_number send_buffer_size 
", basename(argv[0]));
        return 1;
    }
    
    char* ip = argv[1];
    int port = atoi(argv[2]);

    struct sockaddr_in serverSocket;
    bzero(&serverSocket, sizeof(serverSocket));

    serverSocket.sin_port = htons(port);
    serverSocket.sin_family = AF_INET;
    inet_pton(AF_INET, ip , &serverSocket.sin_addr);
    
    int sock = socket(PF_INET, SOCK_STREAM, 0);
    assert(sock>=0);
    
    int sendBuf =atoi(argv[3]);
    int len = sizeof(sendBuf);
    //set tcp buff ,and read
    setsockopt(sock, SOL_SOCKET, SO_SNDBUF, &sendBuf, sizeof(sendBuf));
    getsockopt(sock, SOL_SOCKET, SO_SNDBUF, &sendBuf, (socklen_t*)&len);
    printf("the tcp send buffer size after setting is %d.
", sendBuf);
    
    if(connect(sock, (struct sockaddr*)&serverSocket, sizeof(serverSocket)) != -1)
    {
        char buffer[BUFFER_SIZE];
        memset(buffer, '', sizeof(buffer));
        send(sock, buffer, BUFFER_SIZE, 0);
        
        
        
        //client get server(peer) name
        struct sockaddr_in peerHost;
        socklen_t client_addrlength = sizeof(peerHost);
        getpeername(sock, (struct sockaddr*)&peerHost, &client_addrlength );
        char dest[100] ;
        inet_ntop(AF_INET, &peerHost.sin_addr,dest,100);
        int peerPort=ntohs(peerHost.sin_port);
        printf("dest ip : %s, port:%d", dest, peerPort);
    }
    
    close(sock);    

    return 0;
}

举个例子D：完整版（服务器）

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

#define BUFFER_SIZE 1024

int main(int argc, char* argv[])
{
    if(argc<=2)
    {
        printf("suage:%s IP_number port_number recv_buffer.
", basename(argv[0]));
        return 1;
    }

    char* ip = argv[1];
    int port = atoi(argv[2]);
    
    struct sockaddr_in serverAddr;
    bzero(&serverAddr,sizeof(serverAddr));
    
    serverAddr.sin_family = AF_INET;
    serverAddr.sin_port = htons(port);
    inet_pton(AF_INET,ip, &serverAddr.sin_addr);
    
    int sockfd = socket(PF_INET, SOCK_STREAM,0);
    assert(sockfd>=0);
    
    int recvbuf = atoi(argv[3]);
    int len = sizeof(recvbuf);
    //set tcp bufsize,then read it.
    setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &recvbuf, sizeof(recvbuf));
    getsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &recvbuf, (socklen_t*)&len);
    printf("The tcp receive buffer size after setting is %d.
", recvbuf);

    int ret = bind(sockfd, (struct sockaddr*)&serverAddr,sizeof(serverAddr));
    assert(ret>=0);
    
    ret = listen(sockfd, 5);
    assert(ret>=0);

    struct sockaddr_in client;
    socklen_t client_addrlength = sizeof(client);
    int connfd = accept(sockfd, (struct sockaddr*)&client, &client_addrlength);
    if(connfd < 0)
    {
        printf("errno is:%d 
", errno);
    }
    else
    {
        char buffer[BUFFER_SIZE];
        memset(buffer,'', sizeof(buffer));
        while(recv(connfd, buffer, BUFFER_SIZE-1, 0) > 0)
        {
           printf("recv success...");
        }
        
        close(connfd);
    }    
    
    close(sockfd);

    return 0;
}

举个例子E：完整版（访问某个开启了daytime的主机）

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

int main(int argc, char* argv[])
{
    assert(argc ==2);
    char* host = argv[1];
    //get dest host ip info
    struct hostent* hostinfo = gethostbyname(host);
    assert(hostinfo);
    
    //get daytime info
    struct servent* servinfo = getservbyname("daytime", "tcp");
    assert(servinfo);

//// attention the struct convert
    struct in_addr pNetIp = *(struct in_addr*)*hostinfo->h_addr_list;  
    char serverHostIp[100] ;
    inet_ntop(AF_INET, &pNetIp, serverHostIp, 100);
        
    printf("server host ip:[%s].daytime port is %d.
",serverHostIp, ntohs(servinfo->s_port));
    
    struct sockaddr_in address;
    bzero(&address, sizeof(address));
    address.sin_family = AF_INET;
    address.sin_port = servinfo->s_port;
    
    // Attention! directly use servent 
    address.sin_addr = *(struct in_addr*)*hostinfo->h_addr_list;
    
    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
    int result = connect(sockfd, (struct sockaddr*)&address, sizeof(address));
    assert(result != -1);
    
    char buffer[128];
    result = read(sockfd, buffer, sizeof(buffer));
    assert(result > 0);
    buffer[result] = '';
    printf("the day time is: %s", buffer);

    close(sockfd);
    return 0;
}