公司最近有个需求,去除h5页面的广告,最后实现的方式是后台去过滤,移动端这里只需要拦截里面的一个css地址重定向就可以.开会的时候以为很简单,毕竟
UIWebView
协议方法里面有个每次请求都会走的协议方法- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
实际开发的过程当中才发现这是行不通的.
中间过程就不说了.结果肯定是可以做到的,用到了神奇的 NSURLProtocol
这里主要做下笔记:
它是干什么的呢,是一个挺牛逼的类,它是一个抽象类,不能去实例化它,只能子类化NSURLProtocol
,
每次在对一个 URL 进行请求的时候 URL Loading System
都会向 已经注册的 Protocol
询问是否可以处理该请求。这里就看出他的作用来了. 比如: 拦截UIWebView的请求,忽略请求,重定向... ...
创建
#import@interface FilteredProtocol : NSURLProtocol @end
在合适的地方注册(demo是在appdelegate
类中)
[NSURLProtocol registerClass:[FilteredProtocol class]];
取消注册,一般在加载完成或dealloc
方法里面取消
[NSURLProtocol unregisterClass:[FilteredProtocol class]];
重写父类方法
+ (BOOL)canInitWithRequest:(NSURLRequest *)request; + (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request; + (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b; - (void)startLoading; - (void)stopLoading;
一个个的说
+ (BOOL)canInitWithRequest:(NSURLRequest *)request;
这个方法是决定这个 protocol 是否可以处理传入的 request 的如是返回 true 就代表可以处理,如果返回 false 那么就不处理这个 request 。
+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request;
这个方法主要是用来返回格式化好的request
,如果自己没有特殊需求的话,直接返回当前的request就好了。如果你想做些其他的,比如地址重定向,或者请求头的重新设置,你可以cop
y下这个request
然后进行设置。
+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b;
该方法主要是判断两个请求是否为同一个请求,如果为同一个请求那么就会使用缓存数据。通常都是调用父类的该方法。
- (void)startLoading;- (void)stopLoading;
开始处理这个请求和结束处理这个请求
我们处理(拦截)好请求之后,就要开始对他经常处理,这个时候就用到了父类里面的client
对象.
/*! @method client @abstract Returns the NSURLProtocolClient of the receiver. @result The NSURLProtocolClient of the receiver. */ @property (nullable, readonly, retain) idclient;
他是一个协议,里面的方法和NSURLConnection
差不多
- (void)URLProtocol:(NSURLProtocol *)protocol wasRedirectedToRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse; - (void)URLProtocol:(NSURLProtocol *)protocol cachedResponseIsValid:(NSCachedURLResponse *)cachedResponse; - (void)URLProtocol:(NSURLProtocol *)protocol didReceiveResponse:(NSURLResponse *)response cacheStoragePolicy:(NSURLCacheStoragePolicy)policy; - (void)URLProtocol:(NSURLProtocol *)protocol didLoadData:(NSData *)data; - (void)URLProtocolDidFinishLoading:(NSURLProtocol *)protocol; - (void)URLProtocol:(NSURLProtocol *)protocol didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge; - (void)URLProtocol:(NSURLProtocol *)protocol didCancelAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;
实际应用(拿我拦截css为例子)
需求是要去掉下面图片上立刻下载
的广告:
这是运行后打印的log
上图可以看到截获的所有的请求地址,不管是js,css还是png图片都有
这是代码运行后的效果
代码如下:
static NSString*const sourUrl = @"http://cdn.web.chelaile.net.cn/ch5/styles/main-1cb999d572.css"; static NSString*const localUrl = @"http://h5apps.scity.cn/hack/cdn.web.chelaile.net.cn/ch5/styles/main-1cb999d572.css"; static NSString*const FilteredCssKey = @"filteredCssKey"; @interface FilteredProtocol () @property (nonatomic, strong) NSMutableData *responseData; @property (nonatomic, strong) NSURLConnection *connection; @end
@implementation FilteredProtocol + (BOOL)canInitWithRequest:(NSURLRequest *)request { NSLog(@"request.URL.absoluteString = %@",request.URL.absoluteString); //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:FilteredCssKey inRequest:request]) return NO; return YES; } return NO; }
+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request { NSMutableURLRequest *mutableReqeust = [request mutableCopy]; //截取重定向 if ([request.URL.absoluteString isEqualToString:sourUrl]) { NSURL* url1 = [NSURL URLWithString:localUrl]; mutableReqeust = [NSMutableURLRequest requestWithURL:url1]; } return mutableReqeust; }
+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b { return [super requestIsCacheEquivalent:a toRequest:b]; }
- (void)startLoading { NSMutableURLRequest *mutableReqeust = [[self request] mutableCopy]; //给我们处理过的请求设置一个标识符, 防止无限循环, [NSURLProtocol setProperty:@YES forKey:FilteredCssKey inRequest:mutableReqeust]; BOOL enableDebug = NO; //这里最好加上缓存判断 if (enableDebug) { NSString *str = @"写代码是一门艺术"; NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding]; NSURLResponse *response = [[NSURLResponse alloc] initWithURL:mutableReqeust.URL MIMEType:@"text/plain" expectedContentLength:data.length textEncodingName:nil]; [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed]; [self.client URLProtocol:self didLoadData:data]; [self.client URLProtocolDidFinishLoading:self]; } else { self.connection = [NSURLConnection connectionWithRequest:mutableReqeust delegate:self]; } }
- (void)stopLoading { if (self.connection != nil) { [self.connection cancel]; self.connection = nil; } }
#pragma mark- NSURLConnectionDelegate - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error { [self.client URLProtocol:self didFailWithError:error]; } #pragma mark - NSURLConnectionDataDelegate - (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response { self.responseData = [[NSMutableData alloc] init]; [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed]; } - (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data { [self.responseData appendData:data]; [self.client URLProtocol:self didLoadData:data]; } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { [self.client URLProtocolDidFinishLoading:self]; } @end
Protocols的
遍历是反向的,也就是最后注册的Protocol会被优先判断。就是先注册A再注册B ,优先判断B
一定要注意标记请求,不然你会无限的循环下去。。。因为一旦你需要处理这个请求,那么系统会创建你这个protocol
的实例,然后你自己又开启了connection
进行请求的话,又会触发URL Loading system
的回调。系统给我们提供了+ (void)setProperty:(id)value forKey:(NSString *)key inRequest:(NSMutableURLRequest *)request;
和+ (id)propertyForKey:(NSString *)key inRequest:(NSURLRequest *)request;
这两个方法进行标记和区分。