iOS - UIWebView (NSURLProtocol)拦

2016-08-10 本文已影响3689人态度哥

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：

NSURLProtocol

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... ...

如何使用NSURLProtocol

<br >

创建

#import <Foundation/Foundation.h>

@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copy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) id <NSURLProtocolClient> client;

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:

我是原图

- 这是运行后打印的log
运行ing

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

我是最终效果图

- 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

注意点:

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。

后记:

我在开发中发现 http 转 https 的时候会有错误,有哪位大神指导下改如何去改,多谢.

iOS - UIWebView (NSURLProtocol)拦

NSURLProtocol

如何使用NSURLProtocol

注意点:

后记:

相关链接:

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