iOS 本地DNS解析方法

介紹兩種收集來的本地DNS解析的方式

- (NSArray*)DNSBySystem:(NSString *)dominName{
    Boolean result = '\0',bResolved;
    CFHostRef hostRef;
    CFArrayRef addresses = NULL;
    NSString *finalString = nil;
    char tempChar[1000];
    NSMutableArray *ipResults = [NSMutableArray arrayWithCapacity:10];
    strcpy(tempChar,(char *)[dominName UTF8String]);
    CFStringRef hostNameRef = CFStringCreateWithCString(kCFAllocatorDefault, tempChar, kCFStringEncodingASCII);
    hostRef = CFHostCreateWithName(kCFAllocatorDefault, hostNameRef);
    if (hostRef) {
        result = CFHostStartInfoResolution(hostRef, kCFHostAddresses, NULL);
        if (result == TRUE) {
            addresses = CFHostGetAddressing(hostRef, &result);
        }
    }
    bResolved = result == TRUE ? true : false;
    
    if(bResolved)
    {
        struct sockaddr_in* remoteAddr;
        for(int i = 0; i < CFArrayGetCount(addresses); i++)
        {
            CFDataRef saData = (CFDataRef)CFArrayGetValueAtIndex(addresses, i);
            remoteAddr = (struct sockaddr_in*)CFDataGetBytePtr(saData);
            if(remoteAddr != NULL)
            {
                //DNS解析結果cpy到char陣列裡
                char ip[16];
                strcpy(ip, inet_ntoa(remoteAddr->sin_addr));
                finalString = [NSString stringWithCString:ip encoding:NSUTF8StringEncoding];
                [ipResults addObject:finalString];
            }
        }
    }
    CFRelease(hostNameRef);
    CFRelease(hostRef);
    return ipResults;
}
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上面這種方法在IPv6環境下解析有點問題，IPv4下無問題。下面這種方法兩種環境下都適用

- (NSArray *)dnsByLocal:(NSString *)domain {
    if (domain.length == 0) {
        return nil;
    }
    struct addrinfo hints;
    memset(&hints, 0, sizeof(hints));
    hints.ai_family = PF_INET;
    hints.ai_protocol = IPPROTO_TCP;
    struct addrinfo *addrs, *addr;
    
    int getResult = getaddrinfo([domain UTF8String], NULL, &hints, &addrs);
    if (getResult || addrs == nil) {
        NSLog(@"Warn: DNS with domain:%@ failed:%d", domain, getResult);
        return nil;
    }
    addr = addrs;
    NSMutableArray *result = [NSMutableArray array];
    for (addr = addrs; addr; addr = addr->ai_next) {
        char host[NI_MAXHOST];
        memset(host, 0, NI_MAXHOST);
        getnameinfo(addr->ai_addr, addr->ai_addrlen, host, sizeof(host), NULL, 0, NI_NUMERICHOST);
        if (strlen(host) != 0) {
            [result addObject:[NSString stringWithUTF8String:host]];
        }
    }
    freeaddrinfo(addrs);
    NSLog(@"Info: DNS with domain:%@ -> %@", domain, result);
    return result;
}
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