#import <Foundation/Foundation.h>
 
@interface CustomURLProtocol : NSURLProtocol
 
@end

+ canInitWithRequest: 
//抽象方法，子类给出是否能相应该请求。如果响应YES，说明自己的CustomURLProtocol实现该请求。
 
+ canonicalRequestForRequest:
//抽象方法，重写该方法，可以对请求进行修改，例如添加新的头部信息，修改，修改url等，返回修改后的请求。
 
+ requestIsCacheEquivalent:toRequest:
//看都是缓存了
 
- startLoading:
//开始下载，需要在该方法中发起一个请求，对于NSURLConnection来说，就是创建一个NSURLConnection，对于NSURLSession，就是发起一个NSURLSessionTask 。一般下载前需要设置该请求正在进行下载，防止多次下载的情况发生
 
- stopLoading:
//停止相应请求，清空请求Connection 或 Task

//导入自定义NSURLProtocol类
#import "CustomURLProtocol.h"
//在ViewDidLoad中添加拦截网络请求的代码
//注册网络请求拦截
[NSURLProtocol registerClass:[CustomURLProtocol class]];
//在ViewWillDisappear中添加取消网络拦截的代码
//取消注册网络请求拦截
[NSURLProtocol unregisterClass:[CustomURLProtocol class]];

//直接在AppDelegate中的didFinishLaunchingWithOptions注册网络拦截代码
//注册Protocol
[NSURLProtocol registerClass:[CustomURLProtocol class]];
NSURLProtocol使用实例

#define URLProtocolHandledKey @"URLProtocolHandledKey"
 
+ (BOOL)canInitWithRequest:(NSURLRequest *)request{
 //只处理http和https请求
  NSString *scheme = [[request URL] scheme];
  if ( ([scheme caseInsensitiveCompare:@"http"] == NSOrderedSame ||
   [scheme caseInsensitiveCompare:@"https"] == NSOrderedSame)){
    //看看是否已经处理过了，防止无限循环
    if ([NSURLProtocol propertyForKey:URLProtocolHandledKey inRequest:request]) {
      return NO;
    }
    return YES;
  }
  return NO;
}
 
+ (NSURLRequest *) canonicalRequestForRequest:(NSURLRequest *)request {
   /** 可以在此处添加头等信息 */
  NSMutableURLRequest *mutableReqeust = [request mutableCopy];
  mutableReqeust = [self redirectHostInRequset:mutableReqeust];
  return mutableReqeust;
}
 
+(NSMutableURLRequest*)redirectHostInRequset:(NSMutableURLRequest*)request{
  if ([request.URL host].length == 0) {
    return request;
  }
 
  NSString *originUrlString = [request.URL absoluteString];
  NSString *originHostString = [request.URL host];
  NSRange hostRange = [originUrlString rangeOfString:originHostString];
  if (hostRange.location == NSNotFound) {
    return request;
  }
  //定向薄荷喵到主页
  NSString *ip = @"bohemiao.com";
 
  // 替换域名
  NSString *urlString = [originUrlString stringByReplacingCharactersInRange:hostRange withString:ip];
  NSURL *url = [NSURL URLWithString:urlString];
  request.URL = url;
 
  return request;
}
 
+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b{
  return [super requestIsCacheEquivalent:a toRequest:b];
}
 
- (void)startLoading{
  NSMutableURLRequest *mutableReqeust = [[self request] mutableCopy];
  //标示该request已经处理过了，防止无限循环
  [NSURLProtocol setProperty:@YES forKey:URLProtocolHandledKey inRequest:mutableReqeust];
  self.connection = [NSURLConnection connectionWithRequest:mutableReqeust delegate:self];
  //使用NSURLSession也是一样的
}
 
- (void)stopLoading{
  [self.connection cancel];
}
 
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
  [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
}
 
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
  [self.client URLProtocol:self didLoadData:data];
}
 
- (void) connectionDidFinishLoading:(NSURLConnection *)connection {
  [self.client URLProtocolDidFinishLoading:self];
}
 
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
  [self.client URLProtocol:self didFailWithError:error];
}

@protocol NSURLProtocolClient <NSObject>
 
//请求重定向
- (void)URLProtocol:(NSURLProtocol *)protocol wasRedirectedToRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse;
 
// 响应缓存是否合法
- (void)URLProtocol:(NSURLProtocol *)protocol cachedResponseIsValid:(NSCachedURLResponse *)cachedResponse;
 
//刚接收到Response信息
- (void)URLProtocol:(NSURLProtocol *)protocol didReceiveResponse:(NSURLResponse *)response cacheStoragePolicy:(NSURLCacheStoragePolicy)policy;
 
//数据加载成功
- (void)URLProtocol:(NSURLProtocol *)protocol didLoadData:(NSData *)data;
 
//数据完成加载
- (void)URLProtocolDidFinishLoading:(NSURLProtocol *)protocol;
 
//数据加载失败
- (void)URLProtocol:(NSURLProtocol *)protocol didFailWithError:(NSError *)error;
 
//为指定的请求启动验证
- (void)URLProtocol:(NSURLProtocol *)protocol didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;
 
//为指定的请求取消验证
- (void)URLProtocol:(NSURLProtocol *)protocol didCancelAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;
 
@end