UIWebView兼容Webp格式图片

最近项目需要WebView能够兼容Webp格式的图片，节省用户的流量。

具体实现是通过NSURLProtocol拦截WebView的网络请求，筛选出请求Webp图片的网络请求，下载完Webp图片后使用谷歌的WebP解析库解析图片，转换成Jpg格式图片,传给网页。

代码如下:

+ (BOOL)canInitWithRequest:(NSURLRequest *)request
{
    if ([NSURLProtocol propertyForKey:TTWebPProtocolHandledKey inRequest:request]) {
        return NO;
    }
    
    NSURL *url = [request URL];
    NSString *userAgent = [request allHTTPHeaderFields][@"User-Agent"];
    if (![[userAgent lowercaseString] containsString:@"applewebkit"]) {
        return  NO;
    }
    
    NSString* const requestFiletype = [[url pathExtension] lowercaseString];
    
    return [@"webp" isEqualToString:requestFiletype];
}

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

- (void)startLoading
{
    NSMutableURLRequest *mutableReqeust = [[self request] mutableCopy];
    [NSURLProtocol setProperty:@YES forKey:TTWebPProtocolHandledKey inRequest:mutableReqeust];

    self.sessionTask = [self.session dataTaskWithRequest:self.request];
    [self.sessionTask resume];
}

- (void)stopLoading
{
    [self.sessionTask cancel];
    self.sessionTask = nil;
}


#pragma mark -- NSURLSessionTaskDelegate
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
 completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler
{
    self.imgData = [[NSMutableData alloc] init];
    [self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];
    
    if (completionHandler) {
        completionHandler(NSURLSessionResponseAllow);
    }
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
    didReceiveData:(NSData *)data
{
    [self.imgData appendData:data];
}

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
    didCompleteWithError:(nullable NSError *)error
{
    if (error) {
        [self.client URLProtocol:self didFailWithError:error];
        return;
    }
    
    UIImage *webpImg = [UIImage sd_imageWithData:self.imgData];
    NSData *imgData  = UIImageJPEGRepresentation(webpImg, 1);
    
    [self.client URLProtocol:self didLoadData:imgData];
    [self.client URLProtocolDidFinishLoading:self];

}

#pragma mark -- Setter && Getter
- (NSURLSession *)session
{
    if (!_session) {
        
        NSURLSessionConfiguration *sessonConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
        _session = [NSURLSession sessionWithConfiguration:sessonConfig delegate:self delegateQueue:nil];
    }
    return _session;
}

Demo链接