响应为 header `Cache-Control:Private` 的文件是否会被阻止缓存在 NSURLCache 中？

Question

是否会阻止响应为 header Cache-Control:Private 的文件缓存在 NSURLCache 中？共享缓存（如 setSharedCache 和 NSURLCache.sharedCache() ）或自定义缓存？

为了扩展，我需要在离线时访问 UIWebView。这个 WebView 的来源有多个外部 CSS 和与之关联的 JS 文件。我可以缓存网站的大部分内容（CSS 等看起来就位），但它似乎没有缓存为网站提供重要信息的特定 JavaScript 文件。我注意到不会缓存的文件与其余文件之间的区别是它的 Cache-Control 设置为私有（其他是 public）。但是，根据我的阅读，将缓存控制设置为私有是为了防止在代理上进行缓存。它会影响 iOS 上的缓存吗？

设置缓存

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {

    let URLCache: NSURLCache = NSURLCache(memoryCapacity: 10 * 1024 * 1024,
                                            diskCapacity: 50 * 1024 * 1024,
                                                diskPath: nil)

    NSURLCache.setSharedURLCache(URLCache)

    println("Disk cache usage: \(NSURLCache.sharedURLCache().currentDiskUsage)")

    // 
    sleep(1)

    return true
}

使用缓存

func getWebPage(onCompletion: (NSString, NSURL) -> Void) {

    let url = getApplicationSelectorURL()

    let request = NSURLRequest(URL: url, cachePolicy: .ReturnCacheDataElseLoad, timeoutInterval: 10.0)

    let queue = NSOperationQueue()

    NSURLConnection.sendAsynchronousRequest(request, queue: queue, completionHandler: { response, data, error in
        println("Web page task completed")

        var cachedResponse: NSCachedURLResponse

        if (error != nil) {
            println("NSURLConnection error: \(error.localizedDescription)")
            if let cachedResponse = NSURLCache.sharedURLCache().cachedResponseForRequest(request) {
                if let htmlString = NSString(data: cachedResponse.data, encoding: NSUTF8StringEncoding) {
                    onCompletion(htmlString, url)
                } else {
                    println("htmlString nil")
                }
            } else {
                println("cacheResponse nil")
            }
        } else {
            cachedResponse = NSCachedURLResponse(response: response, data: data, userInfo: nil, storagePolicy: .Allowed)
            NSURLCache.sharedURLCache().storeCachedResponse(cachedResponse, forRequest: request)
            if let htmlString = NSString(data: data, encoding: NSUTF8StringEncoding) {
                onCompletion(htmlString, url)
            } else {
                println("htmlString nil")
            }
        }
    })
}

填充 UIWebView

APICommunicator.sharedInstance.getWebPage({ htmlString, url in

    dispatch_async(dispatch_get_main_queue(),{
        self.webView.loadHTMLString(htmlString, baseURL: url)
    })

})

Answer 1

是的，NSURLCache 不缓存具有私有缓存控制策略的响应。 RFC #2616 表示

private: Indicates that all or part of the response message is intended for a single user and MUST NOT be cached by a shared cache. This allows an origin server to state that the specified parts of the response are intended for only one user and are not a valid response for requests by other users. A private (non-shared) cache MAY cache the response.

嗯，NSURLCache 使用 sharedCache，您甚至在发布的代码中设置了它。我想它几乎解释了一切。

解决方案是更改服务器行为，或者覆盖 NSURLCache class 的某些方法。（例如，您可以重写 header client-side，但这应该是一个非常糟糕的 hack。）

Answer 2

我最终创建了一个类似于 NSURLConnectionDelegate 方法 willCacheResponse 的方法，并替换了 Cache-Control:private header.

willCacheResponse 方法

func willCacheResponse(cachedResponse: NSCachedURLResponse) -> NSCachedURLResponse?
{        
    let response = cachedResponse.response

    let HTTPresponse: NSHTTPURLResponse = response as NSHTTPURLResponse

    let headers: NSDictionary = HTTPresponse.allHeaderFields

    var modifiedHeaders: NSMutableDictionary = headers.mutableCopy() as NSMutableDictionary

    modifiedHeaders["Cache-Control"] = "max-age=604800"

    let modifiedResponse: NSHTTPURLResponse = NSHTTPURLResponse(
            URL: HTTPresponse.URL!,
            statusCode: HTTPresponse.statusCode,
            HTTPVersion: "HTTP/1.1",
            headerFields: modifiedHeaders)!

    let modifiedCachedResponse = NSCachedURLResponse(
            response: modifiedResponse,
            data: cachedResponse.data,
            userInfo: cachedResponse.userInfo,
            storagePolicy: cachedResponse.storagePolicy)

    return modifiedCachedResponse
}

调用方法

if let cachedResponse = self.willCacheResponse(
        NSCachedURLResponse(response: response,
                                data: data,
                            userInfo: nil,
                       storagePolicy: .Allowed)) {

    NSURLCache.sharedURLCache().storeCachedResponse(cachedResponse, forRequest: request)
}

现在离线时也能正确显示。真是一段旅程。

响应为 header `Cache-Control:Private` 的文件是否会被阻止缓存在 NSURLCache 中？

Would a file with a response header `Cache-Control:Private` be prevented from being cached in a NSURLCache?

caching

uiwebview

nsurlcache

ios