使用自定义 NSURLProtocol 时 UIWebView 不加载重定向页面的内容

Question

我注册了一个 UIWebView 和一个自定义 NSURLProtocol class 来代理 HTTP 请求。我在加载 github.com 时遇到问题。如果我浏览到 https://github.com then it loads the page and its contents just fine. However, if I browse to http://github.com，它会正确加载 HTML，但不会加载图像或 CSS。这是我加载 https 版本时的样子：

这是我加载 http 版本时的样子：

这是我用来重现此问题的视图控制器的代码：

@interface ViewController ()
{
    UIWebView *aWebView;
}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    [NSURLProtocol registerClass:[WebViewProxyURLProtocol class]];

    aWebView = [[UIWebView alloc] initWithFrame:self.view.frame];
    aWebView.delegate = self;
    [self.view addSubview:aWebView];

    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://github.com"]];
    [aWebView loadRequest:request];
}

@end

这是 NSURLProtocol 的实现：

@interface WebViewProxyURLProtocol : NSURLProtocol <NSURLConnectionDataDelegate>

@end

@implementation WebViewProxyURLProtocol {
    NSMutableURLRequest* correctedRequest;
}

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    return ([[request allHTTPHeaderFields] objectForKey:@"X-WebViewProxy"] == nil);
}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request {
    return request;
}

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b {
    return NO;
}

- (id)initWithRequest:(NSURLRequest *)request cachedResponse:(NSCachedURLResponse *)cachedResponse client:(id<NSURLProtocolClient>)client {
    if (self = [super initWithRequest:request cachedResponse:cachedResponse client:client]) {
        // Add header to prevent loop in proxy
        correctedRequest = request.mutableCopy;
        [correctedRequest addValue:@"True" forHTTPHeaderField:@"X-WebViewProxy"];
    }
    return self;
}

- (void)startLoading {
    [NSURLConnection connectionWithRequest:correctedRequest delegate:self];
}

- (void)stopLoading {
    correctedRequest = nil;
}

- (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];
}

- (NSURLRequest *)connection:(NSURLConnection *)connection
             willSendRequest:(NSURLRequest *)request
            redirectResponse:(NSURLResponse *)redirectResponse
{
    return request;
}

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection
                  willCacheResponse:(NSCachedURLResponse *)cachedResponse
{
    return nil;
}

@end

如果我禁用自定义 NSURLProtocol class，它工作正常。我使用 Charles 检查 HTTP 请求和响应，无论是否使用 NSURLProtocol，它们看起来都一样。

那么问题来了：为什么UIWebView在使用NSURLConnection获取页面数据时，没有请求到网页内容呢？

Answer 1

我终于想通了。当我在 connection:didReceiveResponse 中收到重定向响应 (HTTP 3xx) 时：我不得不调用 [self.client URLProtocol:self wasRedirectedToRequest:redirectRequest redirectResponse:response].

Answer 2

我们有同样的工作 - 重定向有效但内容未加载。

在 Apple doc 之后，他们提到应该使用 NSURLProtocol 子类中的 connection:willSendRequest:redirectResponse 委托方法处理重定向。

我们的解决方案最终看起来像这样：

- (NSURLRequest *)connection:(NSURLConnection *)connection willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)response {
  if (response) {
    NSMutableURLRequest *redirect = [request mutableCopy];
    [NSURLProtocol removePropertyForKey:kFlagRequestHandled inRequest:redirect];
    [RequestHelper addWebViewHeadersToRequest:redirect];

    // THE IMPORTANT PART
    [self.client URLProtocol:self wasRedirectedToRequest:redirect redirectResponse:response];

    return redirect;
  }

return request;

}

Answer 3

对于那些寻找 Swift 解决方案的人，我采用了@micmdk 所做的并对其进行了调整。

在我的例子中，我拦截了带有 URLProtocol class 的请求。在 override func startLoading() 方法中，我根据请求设置了属性：

override func startLoading() {
    ...
    guard let mutableRequest = request as? NSMutableURLRequest else {
        exit(0)
    }

    URLProtocol.setProperty("true", forKey:"requestHasBeenHandled", in: mutableRequest)

    return mutableRequest as URLRequest
}

这会阻止处理重定向。所以我删除了属性，像这样：

func urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void) {
    guard let redirect = request as? NSMutableURLRequest else {
        exit(0)
    }

    URLProtocol.removeProperty(forKey: "requestHasBeenHandled", in: redirect)

    self.client?.urlProtocol(self, wasRedirectedTo: redirect as URLRequest, redirectResponse: response)
}

已确认有效。图片和资产正确加载。

使用自定义 NSURLProtocol 时 UIWebView 不加载重定向页面的内容

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