通过URLProtocol拦截网络请求后进行ip替换或请求代理设置

一、关于 NSURLProtocol

NSURLProtocol作为URL Loading System中的一个独立部分存在，能够拦截所有的URL Loading System发出的网络请求，拦截之后便可根据需要做各种自定义处理，是iOS网络层的一个终极利器。虽然名叫NSURLProtocol，但它却不是协议。它是一个抽象类。我们要使用它的时候需要创建它的一个子类。
NSURLProtocol在iOS系统中大概处于这样一个位置：

Snip20181229_3.png

二、NSURLProtocol能拦截哪些网络请求

NSURLProtocol能拦截所有基于URL Loading System的网络请求。
URL Loading System的图如下：

872807-b7f17b6fbaf25831.png

所以，可以拦截的网络请求包括NSURLSession，NSURLConnection。现在主流的iOS网络库，例如AFNetworking，Alamofire等网络库都是基于NSURLSession或NSURLConnection的，所以这些网络库的网络请求都可以被NSURLProtocol所拦截。

PS：基于CFNetwork的网络请求，以及WKWebView的请求是无法拦截的。例如ASIHTTPRequest，MKNetwokit等网路库都是基于CFNetwork的，所以这些网络库的网络请求无法被NSURLProtocol拦截。

三、使用

使用NSURLProtocol的主要可以分为5个步骤：

Snip20181229_4.png

1、创建NSURLProtocol子类

由于NSURLProtocol是一个抽象类，要使用它的时候需要创建它的一个子类。.m文件如下：

#import "HJQURLProtocol.h"

static NSString * const URLProtocolHandledKey = @"URLProtocolHandledKey";

@interface HJQURLProtocol()
@property(nonatomic,strong)NSURLSession * session;
@end

@implementation HJQURLProtocol

+(BOOL)canInitWithRequest:(NSURLRequest *)request
{
  //是http或https则拦截处理
  NSString * scheme = [[request.URL scheme] lowercaseString];//获取URL转小写
  if ([scheme isEqualToString:@"http"] || [scheme isEqualToString:@"https"])
  {
    //有拦截处理过的则不再拦截,否则会在这死循环
    if ([NSURLProtocol propertyForKey:URLProtocolHandledKey inRequest:request])
    {
      return NO;
    }
    else
    {
      return YES;
    }
  }
  else
  {
    return NO;
  }
}

//改变请求request
+(NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
{
  return request;
}

//开始请求
-(void)startLoading
{
  NSMutableURLRequest * mutableRequest = [[self request] mutableCopy];
  //标识该request已经处理过了，防止无限循环
  [NSURLProtocol setProperty:@YES forKey:URLProtocolHandledKey inRequest:mutableRequest];
  
  
  //设置代理
  NSString * proxyHost = @"127.0.0.1";
  NSNumber * proxyPort = [NSNumber numberWithInt:8888];
  
  //创建一个代理服务器,包括HTTP或HTTPS代理,当然还可以添加SOCKS,FTP,RTSP等
  NSDictionary * proxyDic = @{
                              @"HTTPEnable": @YES,
                              @"HTTPProxy": proxyHost,
                              @"HTTPPort": proxyPort,
                              @"HTTPSEnable": @YES,
                              @"HTTPSProxy": proxyHost,
                              @"HTTPSPort": proxyPort
                              };
  
  NSURLSessionConfiguration * configuration = [NSURLSessionConfiguration ephemeralSessionConfiguration];//创建一个临时会话配置
  configuration.connectionProxyDictionary = proxyDic;
  
  //网络请求
  self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[[NSOperationQueue alloc] init]];
  NSURLSessionTask * task = [self.session dataTaskWithRequest:self.request];
  [task  resume];//开始任务
  
}

//停止请求
-(void)stopLoading
{
  [self.session invalidateAndCancel];
  self.session = nil;
}

#pragma mark ---- NSURLSessionDelegate
/*
  NSURLSessionDelegate接到数据后,通过URLProtocol传出去
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
  if (error)
  {
    [self.client URLProtocol:self didFailWithError:error];
  }
  else
  {
    [self.client URLProtocolDidFinishLoading:self];
  }
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler {
  
  [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
  completionHandler(NSURLSessionResponseAllow);
  
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
  [self.client URLProtocol:self didLoadData:data];
}

@end

2、注册protocol

基于NSURLConnection或[NSURLSession sharedSession]创建的网络请求，在AppDelegate的didFinishLaunchingWithOptions方法中调用registerClass方法即可。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  // Override point for customization after application launch.
  
  //注册protocol
  [NSURLProtocol registerClass:[HJQURLProtocol class]];
  
  return YES;
}

3、拦截用户的网络请求

首先，在拦截到网络请求后会先调用+(BOOL)canInitWithRequest:(NSURLRequest *)request方法。我们可以在该方法里进行是否处理这个拦截的逻辑。如设置只对拦截到的http或https请求进行处理。

+(BOOL)canInitWithRequest:(NSURLRequest *)request
{
  //是http或https则拦截处理
  NSString * scheme = [[request.URL scheme] lowercaseString];//获取URL转小写
  if ([scheme isEqualToString:@"http"] || [scheme isEqualToString:@"https"])
  {
    //有拦截处理过的则不再拦截,否则会在这死循环
    if ([NSURLProtocol propertyForKey:URLProtocolHandledKey inRequest:request])
    {
      return NO;
    }
    else
    {
      return YES;
    }
  }
  else
  {
    return NO;
  }
}

接着，会调用+(NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request在该方法中，我们可以对request进行处理。例如修改头部信息等。最后返回一个处理后的request实例。也可以在该方法里面将用户的请求域名替换成别的域名：

+(NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
{
  if ([request.URL host].length == 0)
  {
    return request;
  }

  NSString * originUrlStr = [request.URL absoluteString];
  NSString * originHostStr = [request.URL host];
  NSRange hostRange = [originUrlStr rangeOfString:originHostStr];
  
  if (hostRange.location == NSNotFound)
  {
    return request;
  }

  
  //定向到百度搜索
  NSString * ip = @"www.baidu.com";
  NSString * urlStr = [originUrlStr stringByReplacingCharactersInRange:hostRange withString:ip];
  NSURL * url = [NSURL URLWithString:urlStr];
  request.URL = url;

  return request;
}

4、转发

-(void)startLoading将处理过的request重新发送出去。发送的形式，可以是基于NSURLConnection，NSURLSession甚至CFNetwork。我们也可以在该方法里面设置网络代理，如下我们设置一个代理后，重新创建一个NSURLSession将网络请求发送出去：

//开始请求
-(void)startLoading
{
  NSMutableURLRequest * mutableRequest = [[self request] mutableCopy];
  //标识该request已经处理过了，防止无限循环
  [NSURLProtocol setProperty:@YES forKey:URLProtocolHandledKey inRequest:mutableRequest];
  
  //设置代理
  NSString * proxyHost = @"127.0.0.1";
  NSNumber * proxyPort = [NSNumber numberWithInt:8888];
  
  //创建一个代理服务器,包括HTTP或HTTPS代理,当然还可以添加SOCKS,FTP,RTSP等
  NSDictionary * proxyDic = @{
                              @"HTTPEnable": @YES,
                              @"HTTPProxy": proxyHost,
                              @"HTTPPort": proxyPort,
                              @"HTTPSEnable": @YES,
                              @"HTTPSProxy": proxyHost,
                              @"HTTPSPort": proxyPort
                              };
  
  NSURLSessionConfiguration * configuration = [NSURLSessionConfiguration ephemeralSessionConfiguration];//创建一个临时会话配置
  configuration.connectionProxyDictionary = proxyDic;
  
  //网络请求
  self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[[NSOperationQueue alloc] init]];
  NSURLSessionTask * task = [self.session dataTaskWithRequest:self.request];
  [task  resume];//开始任务
}

5、回调

上面使用的是NSURLSession请求，所以我们通过NSURLSessionDelegate来接收网络请求的数据(成功或失败等信息):

#pragma mark ---- NSURLSessionDelegate
/*
  NSURLSessionDelegate接到数据后,通过URLProtocol传出去
 */
//失败
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
  if (error)
  {
    [self.client URLProtocol:self didFailWithError:error]; //请求错误
  }
  else
  {
    [self.client URLProtocolDidFinishLoading:self]; //完成加载
  }
}
//接收到响应
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler {
  
  [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed]; //创建一个响应(缓存策略:不缓存)
  completionHandler(NSURLSessionResponseAllow);
  
}
//接收到数据
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
  [self.client URLProtocol:self didLoadData:data]; //接收到数据
}

然后再通过URLProtocol回调给外面用户发送网络请求的地方。不管外面用户是通过NSURLSession或NSURLConnection发起的网络请求，都可以收到URLProtocol的回调数据。URLProtocol回调的方法主要有以下几个：

[self.client URLProtocol:self didFailWithError:error]; //请求错误
[self.client URLProtocolDidFinishLoading:self]; //完成加载
[self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed]; //创建一个响应(缓存策略:不缓存)
[self.client URLProtocol:self didLoadData:data]; //接收到数据

6、结束

在-(void)stopLoading完成网络请求的操作

//结束请求
-(void)stopLoading
{
  [self.session invalidateAndCancel];
  self.session = nil;
}

四、代码

AppDelegate.m文件

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  // Override point for customization after application launch.
  
  //注册protocol
  [NSURLProtocol registerClass:[HJQURLProtocol class]];
  
  return YES;
}

ViewController.m文件

#import "ViewController.h"

@interface ViewController ()
@property(nonatomic,strong)NSMutableData *responseData;
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
 
  UIButton * btn = [UIButton buttonWithType:UIButtonTypeCustom];
  btn.frame = CGRectMake(0, 300, [UIScreen mainScreen].bounds.size.width, 50);
  [btn setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
  [btn setTitle:@"网络请求" forState:UIControlStateNormal];
  [btn addTarget:self action:@selector(buttonAction:) forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:btn];
}

#pragma mark ---- 按钮响应函数
-(void)buttonAction:(UIButton *)button
{
   [button setTitle:@"请求中..." forState:UIControlStateNormal];
  
  
//     //NSURLSession的网络请求
//    NSURLSession * session = [NSURLSession sharedSession];
//    NSURLRequest * request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"https://www.baidu.com"]];
//    NSURLSessionTask * task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
//        NSLog(@"NSURLSession got the response [%@]", response);
//        NSLog(@"NSURLSession got the data [%@]", data);
//    }];
//    [task resume];
  
  
   //NSURLConnection的网络请求
  NSURL * url = [NSURL URLWithString:@"https://www.baidu.com"];
  NSURLRequest * request = [NSURLRequest requestWithURL:url];
  NSURLConnection * connection = [NSURLConnection connectionWithRequest:request delegate:self];
  [connection start];
}

#pragma mark ---- NSURLConnectionDataDelegate代理方法
/*
 *当接收到服务器的响应（连通了服务器）时会调用
 */
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
  NSLog(@"接收到服务器的响应");
  //初始化数据
  self.responseData = [NSMutableData data];
}

/*
 *当接收到服务器的数据时会调用（可能会被调用多次，每次只传递部分数据）
 */
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
  NSLog(@"接收到服务器的数据");
  //拼接数据
  [self.responseData appendData:data];
}

/*
 *当服务器的数据加载完毕时就会调用
 */
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
  NSLog(@"服务器的数据加载完毕");
  //     NSLog(@"responseData:%@",self.responseData);
  
  NSString * jsonStr = [[NSString alloc] initWithData:self.responseData encoding:NSUTF8StringEncoding];
  
  NSLog(@"jsonStr:%@",jsonStr);
}

/*
 *请求错误（失败）的时候调用（请求超时\断网\没有网\，一般指客户端错误）
 */
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
  NSLog(@"请求错误:%@",error);
}
@end

HJQURLProtocol.m文件

#import "HJQURLProtocol.h"

static NSString * const URLProtocolHandledKey = @"URLProtocolHandledKey";

@interface HJQURLProtocol()
@property(nonatomic,strong)NSURLSession * session;
@end

@implementation HJQURLProtocol

+(BOOL)canInitWithRequest:(NSURLRequest *)request
{
  //是http或https则拦截处理
  NSString * scheme = [[request.URL scheme] lowercaseString];//获取URL转小写
  if ([scheme isEqualToString:@"http"] || [scheme isEqualToString:@"https"])
  {
    //有拦截处理过的则不再拦截,否则会在这死循环
    if ([NSURLProtocol propertyForKey:URLProtocolHandledKey inRequest:request])
    {
      return NO;
    }
    else
    {
      return YES;
    }
  }
  else
  {
    return NO;
  }
}

//改变请求request
+(NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request
{
  return request;
}

//开始请求
-(void)startLoading
{
  NSMutableURLRequest * mutableRequest = [[self request] mutableCopy];
  //标识该request已经处理过了，防止无限循环
  [NSURLProtocol setProperty:@YES forKey:URLProtocolHandledKey inRequest:mutableRequest];
  
  
  //设置代理
  NSString * proxyHost = @"127.0.0.1";
  NSNumber * proxyPort = [NSNumber numberWithInt:8888];
  
  //创建一个代理服务器,包括HTTP或HTTPS代理,当然还可以添加SOCKS,FTP,RTSP等
  NSDictionary * proxyDic = @{
                              @"HTTPEnable": @YES,
                              @"HTTPProxy": proxyHost,
                              @"HTTPPort": proxyPort,
                              @"HTTPSEnable": @YES,
                              @"HTTPSProxy": proxyHost,
                              @"HTTPSPort": proxyPort
                              };
  
  NSURLSessionConfiguration * configuration = [NSURLSessionConfiguration ephemeralSessionConfiguration];//创建一个临时会话配置
  configuration.connectionProxyDictionary = proxyDic;
  
  //网络请求
  self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[[NSOperationQueue alloc] init]];
  NSURLSessionTask * task = [self.session dataTaskWithRequest:self.request];
  [task  resume];//开始任务
  
}

//结束请求
-(void)stopLoading
{
  [self.session invalidateAndCancel];
  self.session = nil;
}

#pragma mark ---- NSURLSessionDelegate
/*
  NSURLSessionDelegate接到数据后,通过URLProtocol传出去
 */
//失败
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
  if (error)
  {
    [self.client URLProtocol:self didFailWithError:error]; //请求错误
  }
  else
  {
    [self.client URLProtocolDidFinishLoading:self]; //完成加载
  }
}
//接收到响应
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler {
  
  [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed]; //创建一个响应(缓存策略:不缓存)
  completionHandler(NSURLSessionResponseAllow);
  
}
//接收到数据
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
  [self.client URLProtocol:self didLoadData:data]; //接收到数据
}

@end

效果：你以为你请求的是https://www.baidu.com，但其实已经转到127.0.0.1代理服务器上了

Snip20181228_16.png