[第四版]用getaddrinfo设置tcp基本连接属性

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);
    }
}