CSAPP 网络编程部分 查询域名IP

查询域名IP

调用Linux系统的库函数, 实现对某一域名的解析, 使用命令行进行参数的输入.f

/* $begin hostinfo */
// #include "csapp.h"
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXLINE 8192 /* Max text line length */

void Freeaddrinfo(struct addrinfo* res) {
    freeaddrinfo(res);
}

/* Getaddrinfo-style error */
void gai_error(int code, char* msg) {
    fprintf(stderr, "%s: %s\n", msg, gai_strerror(code));
    exit(0);
}

void Getnameinfo(const struct sockaddr* sa, socklen_t salen, char* host,
                 size_t hostlen, char* serv, size_t servlen, int flags) {
    int rc;

    if ((rc = getnameinfo(sa, salen, host, hostlen, serv, servlen, flags)) != 0)
        gai_error(rc, "Getnameinfo error");
}


int main(int argc, char** argv) {
    struct addrinfo *p, *listp, hints;
    char buf[MAXLINE];
    int rc, flags;

    if (argc != 2) {
        fprintf(stderr, "usage: %s <domain name>\n", argv[0]);
        exit(0);
    }

    /* Get a list of addrinfo records */
    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_INET; /* IPv4 only */                // line:netp:hostinfo:family
    hints.ai_socktype = SOCK_STREAM; /* Connections only */   // line:netp:hostinfo:socktype
    if ((rc = getaddrinfo(argv[1], NULL, &hints, &listp)) != 0) {
        fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(rc));
        exit(1);
    }

    /* Walk the list and display each IP address */
    flags = NI_NUMERICHOST; /* Display address string instead of domain name */
    for (p = listp; p; p = p->ai_next) {
        Getnameinfo(p->ai_addr, p->ai_addrlen, buf, MAXLINE, NULL, 0, flags);
        printf("%s\n", buf);
    }

    /* Clean up */
    Freeaddrinfo(listp);

    exit(0);
}
/* $end hostinfo */