c - getaddrinfo 似乎在 Windows 和 Ubuntu 之间返回不同的结果？

Question

我有以下两组代码:

Windows

#undef UNICODE

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>

// link with Ws2_32.lib
#pragma comment (lib, "Ws2_32.lib")

int __cdecl main(int argc, char **argv)
{

    //-----------------------------------------
    // Declare and initialize variables
    WSADATA wsaData;
    int iResult;
    INT iRetval;

    DWORD dwRetval;
    argv[1] = "www.google.com";
    argv[2] = "80";
    int i = 1;

    struct addrinfo *result = NULL;
    struct addrinfo *ptr = NULL;
    struct addrinfo hints;

    struct sockaddr_in  *sockaddr_ipv4;
//    struct sockaddr_in6 *sockaddr_ipv6;
    LPSOCKADDR sockaddr_ip;

    char ipstringbuffer[46];
    DWORD ipbufferlength = 46;

    /*
    // Validate the parameters
    if (argc != 3) {
        printf("usage: %s <hostname> <servicename>\n", argv[0]);
        printf("getaddrinfo provides protocol-independent translation\n");
        printf("   from an ANSI host name to an IP address\n");
        printf("%s example usage\n", argv[0]);
        printf("   %s www.contoso.com 0\n", argv[0]);
        return 1;
    }
    */

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    //--------------------------------
    // Setup the hints address info structure
    // which is passed to the getaddrinfo() function
    ZeroMemory( &hints, sizeof(hints) );
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
  //  hints.ai_protocol = IPPROTO_TCP;

    printf("Calling getaddrinfo with following parameters:\n");
    printf("\tnodename = %s\n", argv[1]);
    printf("\tservname (or port) = %s\n\n", argv[2]);

//--------------------------------
// Call getaddrinfo(). If the call succeeds,
// the result variable will hold a linked list
// of addrinfo structures containing response
// information
    dwRetval = getaddrinfo(argv[1], argv[2], &hints, &result);
    if ( dwRetval != 0 ) {
        printf("getaddrinfo failed with error: %d\n", dwRetval);
        WSACleanup();
        return 1;
    }

    printf("getaddrinfo returned success\n");

    // Retrieve each address and print out the hex bytes
    for(ptr=result; ptr != NULL ;ptr=ptr->ai_next) {

        printf("getaddrinfo response %d\n", i++);
        printf("\tFlags: 0x%x\n", ptr->ai_flags);
        printf("\tFamily: ");
        switch (ptr->ai_family) {
            case AF_UNSPEC:
                printf("Unspecified\n");
                break;
            case AF_INET:
                printf("AF_INET (IPv4)\n");
                sockaddr_ipv4 = (struct sockaddr_in *) ptr->ai_addr;
                printf("\tIPv4 address %s\n",
                    inet_ntoa(sockaddr_ipv4->sin_addr) );
                break;
            case AF_INET6:
                printf("AF_INET6 (IPv6)\n");
                // the InetNtop function is available on Windows Vista and later
                // sockaddr_ipv6 = (struct sockaddr_in6 *) ptr->ai_addr;
                // printf("\tIPv6 address %s\n",
                //    InetNtop(AF_INET6, &sockaddr_ipv6->sin6_addr, ipstringbuffer, 46) );

                // We use WSAAddressToString since it is supported on Windows XP and later
                sockaddr_ip = (LPSOCKADDR) ptr->ai_addr;
                // The buffer length is changed by each call to WSAAddresstoString
                // So we need to set it for each iteration through the loop for safety
                ipbufferlength = 46;
                iRetval = WSAAddressToString(sockaddr_ip, (DWORD) ptr->ai_addrlen, NULL, 
                    ipstringbuffer, &ipbufferlength );
                if (iRetval)
                    printf("WSAAddressToString failed with %u\n", WSAGetLastError() );
                else    
                    printf("\tIPv6 address %s\n", ipstringbuffer);
                break;
            case AF_NETBIOS:
                printf("AF_NETBIOS (NetBIOS)\n");
                break;
            default:
                printf("Other %ld\n", ptr->ai_family);
                break;
        }
        printf("\tSocket type: ");
        switch (ptr->ai_socktype) {
            case 0:
                printf("Unspecified\n");
                break;
            case SOCK_STREAM:
                printf("SOCK_STREAM (stream)\n");
                break;
            case SOCK_DGRAM:
                printf("SOCK_DGRAM (datagram) \n");
                break;
            case SOCK_RAW:
                printf("SOCK_RAW (raw) \n");
                break;
            case SOCK_RDM:
                printf("SOCK_RDM (reliable message datagram)\n");
                break;
            case SOCK_SEQPACKET:
                printf("SOCK_SEQPACKET (pseudo-stream packet)\n");
                break;
            default:
                printf("Other %ld\n", ptr->ai_socktype);
                break;
        }
        printf("\tProtocol: ");
        switch (ptr->ai_protocol) {
            case 0:
                printf("Unspecified\n");
                break;
            case IPPROTO_TCP:
                printf("IPPROTO_TCP (TCP)\n");
                break;
            case IPPROTO_UDP:
                printf("IPPROTO_UDP (UDP) \n");
                break;
            default:
                printf("Other %ld\n", ptr->ai_protocol);
                break;
        }
        printf("\tLength of this sockaddr: %d\n", ptr->ai_addrlen);
        printf("\tCanonical name: %s\n", ptr->ai_canonname);
    }

    freeaddrinfo(result);
    WSACleanup();

    return 0;
}

Ubuntu

/*
** listener.c -- a datagram sockets "server" demo
*/

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

#define MYPORT "4950"   // the port users will be connecting to

#define MAXBUFLEN 100

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa)
{
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }

    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

int main(void)
{
    int sockfd;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    int numbytes;
    struct sockaddr_storage their_addr;
    char buf[MAXBUFLEN];
    socklen_t addr_len;
    char s[INET6_ADDRSTRLEN];

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
    hints.ai_socktype = SOCK_DGRAM;
    hints.ai_flags = AI_PASSIVE; // use my IP

    if ((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop through all the results and bind to the first we can
    for(p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("listener: socket");
            continue;
        }

        if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("listener: bind");
            continue;
        }

        break;
    }

    if (p == NULL) {
        fprintf(stderr, "listener: failed to bind socket\n");
        return 2;
    }

    freeaddrinfo(servinfo);

    printf("listener: waiting to recvfrom...\n");

    addr_len = sizeof their_addr;
    if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
        (struct sockaddr *)&their_addr, &addr_len)) == -1) {
        perror("recvfrom");
        exit(1);
    }

    printf("listener: got packet from %s\n",
        inet_ntop(their_addr.ss_family,
            get_in_addr((struct sockaddr *)&their_addr),
            s, sizeof s));
    printf("listener: packet is %d bytes long\n", numbytes);
    buf[numbytes] = '\0';
    printf("listener: packet contains \"%s\"\n", buf);

    close(sockfd);

    return 0;
}

当我尝试 www.google.com 时，我在 Windows 上没有返回 ipv6 套接字 - 这是为什么？

输出:(ubuntu)

caleb@ub1:~/Documents/dev/cs438/mp0/MP0$ ./a.out www.google.com
IP addresses for www.google.com:

 IPv4: 74.125.228.115
 IPv4: 74.125.228.116
 IPv4: 74.125.228.112
 IPv4: 74.125.228.113
 IPv4: 74.125.228.114
 IPv6: 2607:f8b0:4004:803::1010

输出:(获胜)

Calling getaddrinfo with following parameters:
        nodename = www.google.com
        servname (or port) = 80

getaddrinfo returned success
getaddrinfo response 1
        Flags: 0x0
        Family: AF_INET (IPv4)
        IPv4 address 74.125.228.114
        Socket type: SOCK_STREAM (stream)
        Protocol: Unspecified
        Length of this sockaddr: 16
        Canonical name: (null)
getaddrinfo response 2
        Flags: 0x0
        Family: AF_INET (IPv4)
        IPv4 address 74.125.228.115
        Socket type: SOCK_STREAM (stream)
        Protocol: Unspecified
        Length of this sockaddr: 16
        Canonical name: (null)
getaddrinfo response 3
        Flags: 0x0
        Family: AF_INET (IPv4)
        IPv4 address 74.125.228.116
        Socket type: SOCK_STREAM (stream)
        Protocol: Unspecified
        Length of this sockaddr: 16
        Canonical name: (null)
getaddrinfo response 4
        Flags: 0x0
        Family: AF_INET (IPv4)
        IPv4 address 74.125.228.112
        Socket type: SOCK_STREAM (stream)
        Protocol: Unspecified
        Length of this sockaddr: 16
        Canonical name: (null)
getaddrinfo response 5
        Flags: 0x0
        Family: AF_INET (IPv4)
        IPv4 address 74.125.228.113
        Socket type: SOCK_STREAM (stream)
        Protocol: Unspecified
        Length of this sockaddr: 16
        Canonical name: (null)

Answer 1

getaddrinfo 实际上返回从名称服务器获取的结构。此行为取决于操作系统。