getaddrinfo

getaddrinfo的一个重要功能, 很方便的构造struct sockaddr_in对象, 把繁琐的构造过程隐藏起来

getaddrinfo兼有gethostbyname和getservbyname等四个函数的功能

能传入ip/port, hostname/port, ip/service, hostname/service的组合

如127.0.0.1/13, www.abc.com/80, 127.0.0.1/daytime

#include <netdb.h>

/* 成功返回0, 出错返回非0 */

int getaddrinfo(const char *hostname,const char *service,

        const struct addrinfo *hints, struct addrinfo **result);

struct addrinfo{

    int ai_flags; /* AI_PASSIVE(用于server的bind), AI_CANONNAME(返回主机名www.abc.com) */

    int ai_family; /* AF_INET, AF_INET6, AF_UNSPEC*/

    int ai_socktype; /* SOCK_STREAM, SOCK_DGRAM */

    int ai_protocol; /* IPPROTO_[IP/IPV4/IPV6/UDP/TCP] */

    socklen_t ai_addrlen;  /* 下面ai_addr结构的长度 */

    char *ai_canonname; /* ai_flags选项返回的主机名 */

    struct sockaddr *ai_addr; /* 返回地址结构, 可直接用于connect函数 */

    struct addrinfo *ai_next; /* 当查询的主机存在多个地址时通过ai_next来遍历 */

}

hostname和serice就是上面讲的组合

hints是过滤条件, 这些过滤条件放在一个addrinfo的结构里, 通常用前四个成员作为过滤选项

result是过滤的结果, 也是存储在addrinfo结构里, 如果存在多个匹配项, 可通过ai_next来遍历

const char *gai_strerror(int error);

效果同error, 传入错误号返回字符串错误信息

不同的是gai_strerror传入的error是函数的返回值, 而不是全局变量errno

void freeaddrinfo(struct addrinfo *ai);

getaddrinfo的返回值是一个指针, 指向由系统malloc的内存区, 所以不用的时间需要freeaddrinfo

client

启动步骤:

先服务端 ./server13 或者 ./server 0::0 13

然后客户端 ./client 127.0.0.1 13 或者 ./client 0::0 13

#include "unp.h"

#include <netdb.h>

int tcp_connect(const char *host,const char *serv){

    int sockfd,n;

    struct addrinfo hints,*res,*ressave;

    bzero(&hints,sizeof(struct addrinfo));

    hints.ai_family=AF_UNSPEC;

    hints.ai_socktype=SOCK_STREAM;

    if((n=getaddrinfo(host,serv,&hints,&res)) != 0)

        err_quit("tcp_connect error for %s, %s: %s",

                host,serv,gai_strerror(n));

    ressave=res;

    do{

        sockfd=socket(res->ai_family,res->ai_socktype,res->ai_protocol);

        if(sockfd < 0)

            continue;

        if(connect(sockfd,res->ai_addr,res->ai_addrlen) == 0)

            break;

        Close(sockfd);

    }while((res=res->ai_next) != NULL);

    if(res == NULL)

        err_quit("tcp_connect error for %s, %s",host,serv);

    freeaddrinfo(ressave);

    return(sockfd);

}

int main(int argc, char *argv[]){

    int sockfd,n;

    char recvline[MAXLINE+1];

    socklen_t len;

    struct sockaddr_in addr;

    if(argc != 3)

        err_quit("usage: %s <www/ip> <http/80>",argv[0]);

    sockfd=tcp_connect(argv[1],argv[2]);

    len=sizeof(addr);

    getpeername(sockfd,(struct sockaddr *)&addr,&len);

    printf("connected to %s\n",sock_ntop((struct sockaddr *)&addr,len));

    while((n=Read(sockfd,recvline,MAXLINE)) >0){

        recvline[n]=0;

        Fputs(recvline,stdout);

    }

    return 0;

}

server

#include "unp.h"

#include <netdb.h>

#include <time.h>

int tcp_listen(const char *host,const char *service,socklen_t *addrlenp){

    int listenfd,n;

    const int on=1;

    struct addrinfo hints, *res,*ressave;

    bzero(&hints,sizeof(struct addrinfo));

    hints.ai_flags=AI_PASSIVE;

    hints.ai_family=AF_UNSPEC;

    hints.ai_socktype=SOCK_STREAM;

    if((n=getaddrinfo(host,service,&hints,&res)) != 0)

        err_quit("tcp_listen error for %s, %s: %s",host,service,gai_strerror(n));

    ressave=res;

    do{

        listenfd=socket(res->ai_family,res->ai_socktype,res->ai_protocol);

        if(listenfd < 0)

            continue;

        setsockopt(listenfd,SOL_SOCKET,SO_REUSEADDR,&on,sizeof(on));

        if(bind(listenfd,res->ai_addr,res->ai_addrlen) == 0)

            break;

        Close(listenfd);

    }while((res=res->ai_next) != NULL);

    if(res == NULL)

        err_quit("tcp_listen error for %s, %s",host,service);

    Listen(listenfd,10);

    if(addrlenp)

        *addrlenp=res->ai_addrlen;

    freeaddrinfo(ressave);

    return(listenfd);

}

int main(int argc, char *argv[]){

    int listenfd,connfd;

    socklen_t len;

    struct sockaddr_in cliaddr;

    char buff[MAXLINE];

    time_t ticks;

   if(argc == 2)

        listenfd=tcp_listen(NULL,argv[1],NULL);

    else if(argc == 3)

        listenfd=tcp_listen(argv[1],argv[2],NULL);

    else

        err_quit("usage: %s [<host>] <service/port>",argv[0]);

    for(;;){

        len=sizeof(cliaddr);

        connfd=Accept(listenfd,(struct sockaddr *)&cliaddr,&len);

        printf("connection from %s\n",sock_ntop((struct sockaddr *)&cliaddr,len));

        ticks=time(NULL);

        snprintf(buff,sizeof(buff),"%.24s\r\n",ctime(&ticks));

        Write(connfd,buff,strlen(buff));

        Close(connfd);

    }

}