ios - NSURLProtocol + UIWebView + 某些域 = 应用 UI 卡住
<p><p>我们正在为 iOS 构建一个浏览器。我们决定尝试使用自定义的 <code>NSURLProtocol</code> 子类来实现我们自己的缓存方案并执行用户代理欺骗。它在这两件事上都做得很好......问题是，导航到某些网站(msn.com 是最糟糕的)将导致 <em>整个应用程序的</em> UI 卡住长达 15 秒。显然有些东西阻塞了主线程，但它不在我们的代码中。</p>
<p>此问题仅在 <code>UIWebView</code> 和自定义协议(protocol)的组合中出现。如果我们换入 <code>WKWebView</code> (由于各种原因我们不能使用它)，问题就会消失。同样，如果我们不注册协议(protocol)以使其永远不会被使用，那么问题就会消失。</p>
<p>协议(protocol)的作用似乎也无关紧要<em></em>；我们编写了一个简单的虚拟协议(protocol)，除了转发响应之外什么都不做(帖子底部)。我们将该协议(protocol)放入没有任何其他代码的准系统测试浏览器中——结果相同。我们还尝试使用其他人的 (<code>RNCachingURLProtocol</code>) 并观察到相同的结果。似乎这两个组件与某些页面的简单组合会导致卡住。我无法尝试解决(甚至调查)这个问题，并且非常感谢任何指导或提示。谢谢!</p>
<pre><code>import UIKit
private let KEY_REQUEST_HANDLED = "REQUEST_HANDLED"
final class CustomURLProtocol: NSURLProtocol {
var connection: NSURLConnection!
override class func canInitWithRequest(request: NSURLRequest) -> Bool {
return NSURLProtocol.propertyForKey(KEY_REQUEST_HANDLED, inRequest: request) == nil
}
override class func canonicalRequestForRequest(request: NSURLRequest) -> NSURLRequest {
return request
}
override class func requestIsCacheEquivalent(aRequest: NSURLRequest, toRequest bRequest: NSURLRequest) -> Bool {
return super.requestIsCacheEquivalent(aRequest, toRequest:bRequest)
}
override func startLoading() {
var newRequest = self.request.mutableCopy() as! NSMutableURLRequest
NSURLProtocol.setProperty(true, forKey: KEY_REQUEST_HANDLED, inRequest: newRequest)
self.connection = NSURLConnection(request: newRequest, delegate: self)
}
override func stopLoading() {
connection?.cancel()
connection = nil
}
func connection(connection: NSURLConnection!, didReceiveResponse response: NSURLResponse!) {
self.client!.URLProtocol(self, didReceiveResponse: response, cacheStoragePolicy: .NotAllowed)
}
func connection(connection: NSURLConnection!, didReceiveData data: NSData!) {
self.client!.URLProtocol(self, didLoadData: data)
}
func connectionDidFinishLoading(connection: NSURLConnection!) {
self.client!.URLProtocolDidFinishLoading(self)
}
func connection(connection: NSURLConnection!, didFailWithError error: NSError!) {
self.client!.URLProtocol(self, didFailWithError: error)
}
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>我刚刚在 msn.com 上检查了 <code>NSURLProtocol</code> 的行为，发现在某个时候 <code>startLoading</code> 方法在 <code>WebCoreSynchronousLoaderRunLoopMode</code> 模式下被调用。这会导致主线程阻塞。</p>
<p>浏览<a href="https://developer.apple.com/library/ios/samplecode/CustomHTTPProtocol/Listings/CustomHTTPProtocol_Core_Code_CustomHTTPProtocol_m.html#//apple_ref/doc/uid/DTS40013653-CustomHTTPProtocol_Core_Code_CustomHTTPProtocol_m-DontLinkElementID_10" rel="noreferrer noopener nofollow">CustomHTTPProtocol Apple sample code</a> ，我找到了描述这个问题的评论。修复方式如下:</p>
<pre><code>@interface CustomHTTPProtocol () <NSURLSessionDataDelegate>
@property (atomic, strong, readwrite) NSThread * clientThread; ///< The thread on which we should call the client.
/*! The run loop modes in which to call the client.
*\details The concurrency control here is complex.It's set up on the client
*thread in -startLoading and then never modified.It is, however, read by code
*running on other threads (specifically the main thread), so we deallocate it in
*-dealloc rather than in -stopLoading.We can be sure that it's not read before
*it's set up because the main thread code that reads it can only be called after
*-startLoading has started the connection running.
*/
@property (atomic, copy, readwrite) NSArray * modes;
- (void)startLoading
{
NSMutableArray *calculatedModes;
NSString *currentMode;
// At this point we kick off the process of loading the URL via NSURLSession.
// The thread that calls this method becomes the client thread.
assert(self.clientThread == nil); // you can't call -startLoading twice
// Calculate our effective run loop modes.In some circumstances (yes I'm looking at
// you UIWebView!) we can be called from a non-standard thread which then runs a
// non-standard run loop mode waiting for the request to finish.We detect this
// non-standard mode and add it to the list of run loop modes we use when scheduling
// our callbacks.Exciting huh?
//
// For debugging purposes the non-standard mode is "WebCoreSynchronousLoaderRunLoopMode"
// but it's better not to hard-code that here.
assert(self.modes == nil);
calculatedModes = ;
;
currentMode = [ currentMode];
if ( (currentMode != nil) && ! ) {
;
}
self.modes = calculatedModes;
assert( > 0);
// Create new request that's a clone of the request we were initialised with,
// except that it has our 'recursive request flag' property set on it.
// ...
// Latch the thread we were called on, primarily for debugging purposes.
self.clientThread = ;
// Once everything is ready to go, create a data task with the new request.
self.task = [[ sharedDemux] dataTaskWithRequest:recursiveRequest delegate:self modes:self.modes];
assert(self.task != nil);
;
}
</code></pre>
<p>一些 Apple 工程师很有幽默感。</p>
<blockquote>
<p>Exciting huh?</p>
</blockquote>
<p>见 <a href="https://developer.apple.com/library/ios/samplecode/CustomHTTPProtocol/Listings/CustomHTTPProtocol_Core_Code_CustomHTTPProtocol_m.html#//apple_ref/doc/uid/DTS40013653-CustomHTTPProtocol_Core_Code_CustomHTTPProtocol_m-DontLinkElementID_10" rel="noreferrer noopener nofollow">full apple sample</a>了解详情。</p>
<p><code>WKWebView</code> 无法重现问题，因为 <code>NSURLProtocol</code> 不适用于它。见 <a href="https://stackoverflow.com/questions/24208229/wkwebview-and-nsurlprotocol-not-working" rel="noreferrer noopener nofollow">next question</a>了解详情。</p></p>
<p style="font-size: 20px;">关于ios - NSURLProtocol + UIWebView + 某些域 = 应用 UI 卡住，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/31327785/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/31327785/
</a>
</p>
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