ipv6 适配

参考链接：

苹果新闻：Supporting IPv6-only Networks

适配参考：Supporting IPv6 DNS64/NAT64 Networks
苹果的Reachability:About Reachability

Revision_Image.png

适配的工作多集中在 Reachability 和 SCNetworkReachability 两个地方.疑问也大多出自于此；

Connect Without Preflight
The Reachability APIs (see SCNetworkReachability Reference) are intended for diagnostic purposes after identifying a connectivity issue. Many apps incorrectly use these APIs to proactively check for an Internet connection by calling the SCNetworkReachabilityCreateWithAddress
method and passing it an IPv4 address of 0.0.0.0
, which indicates that there is a router on the network. However, the presence of a router doesn’t guarantee that an Internet connection exists. In general, avoid preflighting network reachability. Just try to make a connection and gracefully handle failures. If you must check for network availability, avoid calling the SCNetworkReachabilityCreateWithAddress
method. Call the SCNetworkReachabilityCreateWithName
method and pass it a hostname instead.
Some apps also pass the SCNetworkReachabilityCreateWithAddress
method an IPv4 address of 169.254.0.0
, a self-assigned link-local address, to check for an active Wi-Fi connection. To check for Wi-Fi or cellular connectivity, look for the network reachability flagkSCNetworkReachabilityFlagsIsWWAN
instead.

根据上文所述，苹果应该是禁止使用
SCNetworkReachabilityCreateWithAddress
方法，而是应该用SCNetworkReachabilityCreateWithName
代替，但是再看苹果官方的 Reachability 最新适配 IPv6 的版本发现，依然在使用 SCNetworkReachabilityCreateWithAddress.
而且已经适配了 IPv6 的 AFNetWorking 也使用了此方法，所以至少可以确定，使用SCNetworkReachabilityCreateWithAddress是不会存在问题，如下图，参考Reachability 与 AF，至少使用 sockaddr_in
结合 SCNetworkReachabilityCreateWithAddress 是不会有问题的。我猜测苹果所说可能是禁止使用 169.254.0.0 这样的 ip 地址吧.
此处有个疑问是为什么AF做两部判断，而 Reachability 不做判断，这个问题在 issue 中也可以找到，下面自己可能需要对不同设备不同版本进行测试，确认下.

Reachability_Code_Image.png

AF_Image1.png

AF_Image2.png

总结下我最终适配方案：
AF首先更新到最新；
Reachability 更换为苹果最新的适配 IPv6 的版本；
判断网络使用 Reachability 中的 reachabilityWithHostName 方法；
此方法我是针对非 iOS9 和 iOS8 的设备在 IPv6 网和正常网络下都进行了测试可以正常使用的；
而对于 Reachability 中 reachabilityForInternetConnection 方法在非 iOS9 下有bug的问题，我就参考了AF的处理方法，进行系统版本判断，经过测试，可以正常使用；

相关链接：
preflight check with SCNetworkReachabilityCreateWithAddress using a zero IPv6 address
[转自GeekerProbe]-Support for IPv6