1、在一次性能优化中突然发现一个svg矢量图动画导致CPU持续占用的问题，该svg在web中使用，

　　即使webview释放之后，CPU依然占用达到10%，6s+上测试结果

　　svg如下所示：

　　

　　注意该动画的时间是无限长，指定时间结束之后，CPU将不再占用，因此这可能是webkit中的bug。

　　svg是HTML5中的标准，每个webview都应该支持。未测试WKWebView兼容情况

2、问题解决　　

　　可以看到该svg是由web中的css文件引用，真正的请求是：https://egame.gtimg.cn/club/pgg/v2.5/v2/img/global/loading-fecf2b8eea.svg

　　为了可以将这个问题解决掉，在前端暂无法修复的情况下，我选择使用NSURLProtocol中的方法，hook该请求，并返回404

　　具体操作使用了一个OHHTTPStubs的框架，代码如下：

　　

+ (void)addLoadingSVG_Patch{    [OHHTTPStubs stubRequestsPassingTest:^BOOL(NSURLRequest *request) {                NSString *url = [request.URL description];        if([url hasSuffix:@"svg"] && [[url lastPathComponent] hasPrefix:@"loading"])        {            QG_Event(MODULE_LIVE_ASS, @"patch fuck loading animated svg request!!! = %@", request);            return YES;        }        return NO;    } withStubResponse:^OHHTTPStubsResponse*(NSURLRequest *request) {                return [OHHTTPStubsResponse responseWithFileAtPath:@""                                                statusCode:404 headers:@{@"Content-Type":@"image/jpeg"}];    }];}

　　问题解决

3、NSURLProtocol是苹果的一个协议，其中通过 + (BOOL)canInitWithRequest:(NSURLRequest *)request; 这个方法返回是否要手动接管这个请求

　　通常web的离线缓存基于此实现，接管请求之后，需要自己实现请求的代码，并将返回结果通过NSURLProtocol的client对象回调给上层，例如：

　　在startLoading方法中，实现请求，并返回结果。

- (void)startLoading{    self.clientRunLoop = CFRunLoopGetCurrent();    NSURLRequest* request = self.request;    id
     
       client = self.client;        if (!self.stub)    {        NSDictionary* userInfo = [NSDictionary dictionaryWithObjectsAndKeys:                                  @"It seems like the stub has been removed BEFORE the response had time to be sent.",                                  NSLocalizedFailureReasonErrorKey,                                  @"For more info, see https://github.com/AliSoftware/OHHTTPStubs/wiki/OHHTTPStubs-and-asynchronous-tests",                                  NSLocalizedRecoverySuggestionErrorKey,                                  request.URL, // Stop right here if request.URL is nil                                  NSURLErrorFailingURLErrorKey,                                  nil];        NSError* error = [NSError errorWithDomain:@"OHHTTPStubs" code:500 userInfo:userInfo];        [client URLProtocol:self didFailWithError:error];        if (OHHTTPStubs.sharedInstance.afterStubFinishBlock)        {            OHHTTPStubs.sharedInstance.afterStubFinishBlock(request, self.stub, nil, error);        }        return;    }        OHHTTPStubsResponse* responseStub = self.stub.responseBlock(request);        if (OHHTTPStubs.sharedInstance.onStubActivationBlock)    {        OHHTTPStubs.sharedInstance.onStubActivationBlock(request, self.stub, responseStub);    }        if (responseStub.error == nil)    {        NSHTTPURLResponse* urlResponse = [[NSHTTPURLResponse alloc] initWithURL:request.URL                                                                     statusCode:responseStub.statusCode                                                                    HTTPVersion:@"HTTP/1.1"                                                                   headerFields:responseStub.httpHeaders];                // Cookies handling        if (request.HTTPShouldHandleCookies && request.URL)        {            NSArray* cookies = [NSHTTPCookie cookiesWithResponseHeaderFields:responseStub.httpHeaders forURL:request.URL];            if (cookies)            {                [NSHTTPCookieStorage.sharedHTTPCookieStorage setCookies:cookies forURL:request.URL mainDocumentURL:request.mainDocumentURL];            }        }                        NSString* redirectLocation = (responseStub.httpHeaders)[@"Location"];        NSURL* redirectLocationURL;        if (redirectLocation)        {            redirectLocationURL = [NSURL URLWithString:redirectLocation];        }        else        {            redirectLocationURL = nil;        }        [self executeOnClientRunLoopAfterDelay:responseStub.requestTime block:^{            if (!self.stopped)            {                // Notify if a redirection occurred                if (((responseStub.statusCode > 300) && (responseStub.statusCode < 400)) && redirectLocationURL)                {                    NSURLRequest* redirectRequest = [NSURLRequest requestWithURL:redirectLocationURL];                    [client URLProtocol:self wasRedirectedToRequest:redirectRequest redirectResponse:urlResponse];                    if (OHHTTPStubs.sharedInstance.onStubRedirectBlock)                    {                        OHHTTPStubs.sharedInstance.onStubRedirectBlock(request, redirectRequest, self.stub, responseStub);                    }                }                                // Send the response (even for redirections)                [client URLProtocol:self didReceiveResponse:urlResponse cacheStoragePolicy:NSURLCacheStorageNotAllowed];                if(responseStub.inputStream.streamStatus == NSStreamStatusNotOpen)                {                    [responseStub.inputStream open];                }                [self streamDataForClient:client                         withStubResponse:responseStub                               completion:^(NSError * error)                 {                     [responseStub.inputStream close];                     NSError *blockError = nil;                     if (error==nil)                     {                         [client URLProtocolDidFinishLoading:self];                     }                     else                     {                         [client URLProtocol:self didFailWithError:responseStub.error];                         blockError = responseStub.error;                     }                     if (OHHTTPStubs.sharedInstance.afterStubFinishBlock)                     {                         OHHTTPStubs.sharedInstance.afterStubFinishBlock(request, self.stub, responseStub, blockError);                     }                 }];            }        }];    } else {        // Send the canned error        [self executeOnClientRunLoopAfterDelay:responseStub.responseTime block:^{            if (!self.stopped)            {                [client URLProtocol:self didFailWithError:responseStub.error];                if (OHHTTPStubs.sharedInstance.afterStubFinishBlock)                {                    OHHTTPStubs.sharedInstance.afterStubFinishBlock(request, self.stub, responseStub, responseStub.error);                }            }        }];    }}- (void)stopLoading{    self.stopped = YES;}