仅在IPv6上使用iOS的DNS解析同步？

Question

(这是一项正在进行的工作。我想知道是否有人能改进它)

在目标C中，使用NSHost很容易解析主机名。

[[NSHost hostWithName:@"www.google.com"] address]

可悲的是，iOS (iPhone)只包含NSHost的一个私有版本。

我在其他对象或方法中找到了许多方法来实现这一点，但是所有这些方法都只在结果中获得了IPv4地址。所以现在我发现的唯一有效的方法就是。

我第一次尝试使用异步CFHostStartInfoResolution，就像布杜纳根一样，但未能使其适应IPv6。

你们中的一些人会感激得到一个方法的工作，所以这里有一个，但如果你们知道一种方式将是异步的，我会很感激了解它。因为目前，我使用弹出窗口来警告下一次由于缓慢的细胞连接可能发生的冻结。

/**
 Give the IPs corresponding to a Hostname

 Sometime only 1 IPv4 is shown even if there's more.
 Sometime only 1 IPv6 is shown even if there's more.
 Certainly due to iOS Memory optimisation when locally cached

 @author Christian Gonzalvez, http://wiki.gonzofamily.com
 @param hostName A hostname
 @return an Array of NSString of all the corresponding IP addresses. The first
 is the Canonical name, the following are IPs (all NSString)
 */
+ (NSArray *)addressesForHostname:(NSString *)hostname
{
    const char* hostnameC = [hostname UTF8String];

    struct addrinfo hints, *res;
    struct sockaddr_in *s4;
    struct sockaddr_in6 *s6;
    int retval;
    char buf[64];
    NSMutableArray *result; //the array which will be return
    NSMutableArray *result4; //the array of IPv4, to order them at the end
    NSString *previousIP = nil;

    memset (&hints, 0, sizeof (struct addrinfo));
    hints.ai_family = PF_UNSPEC;//AF_INET6;
    hints.ai_flags = AI_CANONNAME;
        //AI_ADDRCONFIG, AI_ALL, AI_CANONNAME,  AI_NUMERICHOST
        //AI_NUMERICSERV, AI_PASSIVE, OR AI_V4MAPPED

    retval = getaddrinfo(hostnameC, NULL, &hints, &res);
    if (retval == 0)
      {

        if (res->ai_canonname)
          {
            result = [NSMutableArray arrayWithObject:[NSString stringWithUTF8String:res->ai_canonname]];
          }
        else
          {
                //it means the DNS didn't know this host
            return nil;
          }
        result4= [NSMutableArray array];
        while (res) {
            switch (res->ai_family){
                case AF_INET6:              
                    s6 = (struct sockaddr_in6 *)res->ai_addr;
                    if(inet_ntop(res->ai_family, (void *)&(s6->sin6_addr), buf, sizeof(buf))
                       == NULL)
                      {
                        NSLog(@"inet_ntop failed for v6!\n");
                      }
                    else
                      {
                            //surprisingly every address is in double, let's add this test
                        if (![previousIP isEqualToString:[NSString stringWithUTF8String:buf]]) {
                            [result addObject:[NSString stringWithUTF8String:buf]];
                        }
                      }
                    break;

                case AF_INET:               
                    s4 = (struct sockaddr_in *)res->ai_addr;
                    if(inet_ntop(res->ai_family, (void *)&(s4->sin_addr), buf, sizeof(buf))
                       == NULL)
                      {
                        NSLog(@"inet_ntop failed for v4!\n");
                      }
                    else
                      {
                            //surprisingly every address is in double, let's add this test
                        if (![previousIP isEqualToString:[NSString stringWithUTF8String:buf]]) {
                            [result4 addObject:[NSString stringWithUTF8String:buf]];
                        }
                      }
                    break;
                default:
                    NSLog(@"Neither IPv4 nor IPv6!");

            }
                //surprisingly every address is in double, let's add this test
            previousIP = [NSString stringWithUTF8String:buf];

            res = res->ai_next;
        }
      }else{
          NSLog(@"no IP found");
          return nil;
      }

    return [result arrayByAddingObjectsFromArray:result4];
}

注意:我注意到大多数情况下只返回一个IPv6，我怀疑这是由于本地缓存时iOS内存优化所致。如果您一次又一次地运行此方法，有时您有3 IPv6，但是只有1 IPv4。

Answer 1

如果希望在后台线程上运行方法，最简单的方法是使用performSelectorInBackground:withObject:；这是NSObject的实例方法，因此任何对象都可以使用它而不需要任何额外的工作(有趣的是，包括类对象，这在本例中是很好的，因为这是一个类方法)：

[[self class] performSelectorInBackground:@selector(addressesForHostName:) 
                               withObject:theHostName];

在该方法中，您需要为线程设置一个自动释放池。您还需要设置某种回调方法来将返回值返回到主线程。确保不尝试在后台线程上执行任何GUI活动。在主线程上这样做是安全的。

+ (NSArray *)addressesForHostname:(NSString *)hostname
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    // Do your stuff...

    // Wait until done to allow memory to be managed properly
    // If we did not do this, the array might be deallocated
    // before the main thread had a chance to retain it
    [self performSelectorOnMainThread:@selector(addressesCallback:)
                              withObject:[result arrayByAddingObjectsFromArray:result4]
                           waitUntilDone:YES];
    // Inside a class method, self refers to the class object.

    [pool drain];
}

如果您一开始没有在主线程上，或者如果您需要更多的控制，您也可以查看NSOperation，它更强大，因此需要更多的工作。不过，它仍然比显式线程管理更容易！

希望这能解决你的问题。听起来就像让这个方法做你需要的，你只需要它不阻塞主线程。

Answer 2

多亏了乔什，我才能做到，但以下是我必须做的：

而不是直接调用

self.ipAddressesString = [CJGIpAddress addressesForHostname:@"www.google.com"];

我打电话

[self resolveNow:@"www.google.com"];

并创建3种新方法：

- (void)resolveNow:(NSString *)hostname
{
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
    [self performSelectorInBackground:@selector(hostname2ipAddresses:) 
                                   withObject:hostname];
}

- (void)hostname2ipAddresses:(NSString *)hostname
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
      //Here is my previous lonely line !! safely started in an other thread
    self.ipAddressesString = [CJGIpAddress addressesForHostname:hostname];
    [self performSelectorOnMainThread:@selector(resolutionDidFinish)
                           withObject:nil
                        waitUntilDone:YES];
    [pool drain];
}

- (void)resolutionDidFinish
{
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
    //My STUFF with self.ipAddressesString (now filled)
}

编辑:在实践中，我在一个模型中使用了所有这些，所以当我在解析结束之前关闭视图时，我就崩溃了

因此，在视图中，我添加了dealloc，这是避免崩溃的必要条件。

- (void)dealloc
{
    self.model.delegate = nil;
    [super dealloc];
}

然后-在模型中-我在做任何事情之前测试委托。