AFNetworking 原作者都无法解决的问题: 如何使用ip直接访问https网站?

背景

最近App似乎有报异常是DNS无法解析,尝试解决此问题.搜集到的资料很少,甚至连AFN原作者都判定这可能是一个无解的问题,参见: https://github.com/AFNetworking/AFNetworking/issues/2954,不过最终还是靠着stackoverflow上的一丁点提示,顺利找到并汇集成了一个可用的解决方案.大喜,与君共享!

问题描述

通过IP直接访问网站,可以解决DNS劫持问题.DNS劫持,可以通过修改电脑的host文件模拟.如果是HTTP请求,使用ip地址直接访问接口,配合header中Host字段带上原来的域名信息即可;如果是 https请求,会很麻烦,需要 Overriding TLS Chain Validation Correctly;curl 中有一个 -resolve 方法可以实现使用指定ip访问https网站,iOS中集成curl库应该也可以,不过改动太大,未验证;对于服务器IP经常变的情况,可能需要使用httpDNS服务,参见:https://www.dnspod.cn/httpdns.

解决方案讨论

1. 最直接的方式是允许无效的SSL证书,生产环境不建议使用;

2.一个需要部分重写AFN源码的方法.

在Info.plist中添加NSAppTransportSecurity类型Dictionary,在NSAppTransportSecurity下添加NSAllowsArbitraryLoads类型Boolean,值设为YES.这些本来是用来解决iOS9下,允许HTTP请求访问网络的,当然作用不止这些.具体原因感兴趣的自行google.
给 AFURLConnectionOperation 类添加新属性:

/** 可信任的域名,用于支持通过ip访问此域名下的https链接.Trusted domain, this domain for support via IP access HTTPS links.*/
@property(nonatomic, strong) NSMutableArray * trustHostnames;

给 AFURLConnectionOperation 实现的代理方法: - (void)connection:(NSURLConnection *)connection
willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge 添加添加可信任的域名的相关逻辑代码:

- (void)connection:(NSURLConnection *)connection
willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge
{if (self.authenticationChallenge) {self.authenticationChallenge(connection, challenge);return;}if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {SecTrustRef serverTrust = challenge.protectionSpace.serverTrust;/* 添加可信任的域名,以支持:直接使用ip访问特定https服务器.Add trusted domain name to support: direct use of IP access specific HTTPS server.*/for (NSString * trustHostname  in [self trustHostnames]) {serverTrust = AFChangeHostForTrust(serverTrust, trustHostname);}....

参考Apple官方文档,实现自定义的添加可信域名的函数: AFChangeHostForTrust

static inline SecTrustRef AFChangeHostForTrust(SecTrustRef trust, NSString * trustHostname)
{if ( ! trustHostname || [trustHostname isEqualToString:@""]) {return trust;}CFMutableArrayRef newTrustPolicies = CFArrayCreateMutable(kCFAllocatorDefault, 0, &kCFTypeArrayCallBacks);SecPolicyRef sslPolicy = SecPolicyCreateSSL(true, (CFStringRef)trustHostname);CFArrayAppendValue(newTrustPolicies, sslPolicy);#ifdef MAC_BACKWARDS_COMPATIBILITY/* This technique works in OS X (v10.5 and later) */SecTrustSetPolicies(trust, newTrustPolicies);CFRelease(oldTrustPolicies);return trust;
#else/* This technique works in iOS 2 and later, orOS X v10.7 and later */CFMutableArrayRef certificates = CFArrayCreateMutable(kCFAllocatorDefault, 0, &kCFTypeArrayCallBacks);/* Copy the certificates from the original trust object */CFIndex count = SecTrustGetCertificateCount(trust);CFIndex i=0;for (i = 0; i < count; i++) {SecCertificateRef item = SecTrustGetCertificateAtIndex(trust, i);CFArrayAppendValue(certificates, item);}/* Create a new trust object */SecTrustRef newtrust = NULL;if (SecTrustCreateWithCertificates(certificates, newTrustPolicies, &newtrust) != errSecSuccess) {/* Probably a good spot to log something. */return NULL;}return newtrust;
#endif
}

使用AOP方法,重写 AFURLConnectionOperation 的trustHostnames属性:

    /* 使用AOP方式,指定可信任的域名, 以支持:直接使用ip访问特定https服务器.*/[AFURLConnectionOperation aspect_hookSelector:@selector(trustHostnames) withOptions:AspectPositionInstead usingBlock: ^(id<AspectInfo> info){__autoreleasing NSArray * trustHostnames = @[@"www.example.com"];NSInvocation *invocation = info.originalInvocation;[invocation setReturnValue:&trustHostnames];}error:NULL];

此处用到的是一个 iOS AOP库,不熟悉的点这里: http://www.ios122.com/2015/08/aspects/.