如何使用AlamoFire下载blob

Question

我正试图在WKWebView中快速工作，目前有一个使用AlamoFire的下载引擎。我遇到了一个使用blob: url方案下载项目的站点。是否有一种一般使用AlamoFire或WKWebView下载blob文件的方法？

我的具体目标是将内容从这个blob下载到一个文件中。

我很感谢你的帮助。谢谢。

所有相关代码附后。

下面是我遇到问题的URL：

blob:https://cubari.moe/87d49857-dfef-4f0f-bb83-db8517fd3094

下面是我的日志中的错误：

2021-12-10 22:41:45.382527-0500 Asobi[14529:358202] -canOpenURL: failed for URL: "blob:https://cubari.moe/87d49857-dfef-4f0f-bb83-db8517fd3094" - error: "This app is not allowed to query for scheme blob"
2021-12-10 22:41:45.474214-0500 Asobi[14529:358357] Task <4B011CC1-60E9-4AAD-98F0-BB6A6D0C92FB>.<1> finished with error [-1002] Error Domain=NSURLErrorDomain Code=-1002 "unsupported URL" UserInfo={NSLocalizedDescription=unsupported URL, NSErrorFailingURLStringKey=blob:https://cubari.moe/87d49857-dfef-4f0f-bb83-db8517fd3094, NSErrorFailingURLKey=blob:https://cubari.moe/87d49857-dfef-4f0f-bb83-db8517fd3094, _NSURLErrorRelatedURLSessionTaskErrorKey=(
    "LocalDownloadTask <4B011CC1-60E9-4AAD-98F0-BB6A6D0C92FB>.<1>"
), _NSURLErrorFailingURLSessionTaskErrorKey=LocalDownloadTask <4B011CC1-60E9-4AAD-98F0-BB6A6D0C92FB>.<1>, NSUnderlyingError=0x6000017e99b0 {Error Domain=kCFErrorDomainCFNetwork Code=-1002 "(null)"}}
2021-12-10 22:41:45.476703-0500 Asobi[14529:358202] [Process] 0x124034e18 - [pageProxyID=6, webPageID=7, PID=14540] WebPageProxy::didFailProvisionalLoadForFrame: frameID=3, domain=WebKitErrorDomain, code=102
Failed provisional nav: Error Domain=WebKitErrorDomain Code=102 "Frame load interrupted" UserInfo={_WKRecoveryAttempterErrorKey=<WKReloadFrameErrorRecoveryAttempter: 0x6000019a88c0>, NSErrorFailingURLStringKey=blob:https://cubari.moe/87d49857-dfef-4f0f-bb83-db8517fd3094, NSErrorFailingURLKey=blob:https://cubari.moe/87d49857-dfef-4f0f-bb83-db8517fd3094, NSLocalizedDescription=Frame load interrupted}

下面是我在WKNavigation决策策略中下载决策处理程序的代码

// Check if a page can be downloaded
func webView(_ webView: WKWebView,
             decidePolicyFor navigationResponse: WKNavigationResponse,
             decisionHandler: @escaping (WKNavigationResponsePolicy) -> Void) {
    
    if navigationResponse.canShowMIMEType {
        decisionHandler(.allow)
    } else {
        let url = navigationResponse.response.url
        
        // Alternative to decisionHandler(.download) since that's iOS 15 and up
        //let documentUrl = url?.appendingPathComponent(navigationResponse.response.suggestedFilename!)
        parent.webModel.downloadDocumentFrom(url: url!)
        decisionHandler(.cancel)
    }
}

下面是我的下载数据函数的代码(它使用AF.download方法)

// Download file from page
func downloadDocumentFrom(url downloadUrl : URL) {
    if currentDownload != nil {
        showDuplicateDownloadAlert = true
        return
    }
    
    let queue = DispatchQueue(label: "download", qos: .userInitiated)
    var lastTime = Date()
    
    let destination: DownloadRequest.Destination = { tempUrl, response in
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
        let suggestedName = response.suggestedFilename ?? "unknown"
        
        let fileURL = documentsURL.appendingPathComponent(suggestedName)

        return (fileURL, [.removePreviousFile, .createIntermediateDirectories])
    }
    
    self.showDownloadProgress = true
    
    currentDownload = AF.download(downloadUrl, to: destination)
        .downloadProgress(queue: queue) { progress in
            if Date().timeIntervalSince(lastTime) > 1.5 {
                lastTime = Date()
                
                DispatchQueue.main.async {
                    self.downloadProgress = progress.fractionCompleted
                }
            }
        }
        .response { response in
            DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
                self.showDownloadProgress = false
                self.downloadProgress = 0.0
            }
            
            if response.error == nil, let currentPath = response.fileURL {
                self.downloadFileUrl = currentPath
                self.showFileMover = true
            }
            
            if let error = response.error {
                self.errorDescription = "Download could not be completed. \(error)"
                self.showError = true
            }
        }
}

Answer 1

几天后，我想出了如何在没有WKDownloadDelegate的情况下下载blob。下面的代码构建在this answer之上。

需要创建消息处理程序来响应JS消息。我在makeUIView函数中创建了这个

webModel.webView.configuration.userContentController.add(context.coordinator, name: "jsListener")

在您的WKNavigationDelegate中，您需要在导航操作中添加此代码。

注意:由于我使用SwiftUI，我的所有变量/模型都位于父类中(UIViewRepresentable协调器)。

func webView(_ webView: WKWebView,
             decidePolicyFor navigationAction: WKNavigationAction,
             decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    if let url = navigationAction.request.url, let scheme = url.scheme?.lowercased() {
        if scheme == "blob" {
            // Defer to JS handling
            parent.webModel.executeBlobDownloadJS(url: url)
            
            decisionHandler(.cancel)
        } else {
            decisionHandler(.allow)
        }
    }
}

以下是请求存储在浏览器内存中的blob的JS。我在包装器函数中添加了这个JS，该函数名为evaluateJavaScript，并为代码的整洁提供了url。

function blobToDataURL(blob, callback) {
    var reader = new FileReader()
    reader.onload = function(e) {callback(e.target.result.split(",")[1])}
    reader.readAsDataURL(blob)
}

async function run() {
    const url = "\(url)"
    const blob = await fetch(url).then(r => r.blob())

    blobToDataURL(blob, datauri => {
        const responseObj = {
            url: url,
            mimeType: blob.type,
            size: blob.size,
            dataString: datauri
        }
        window.webkit.messageHandlers.jsListener.postMessage(JSON.stringify(responseObj))
    })
}

run()

除了返回的JS对象之外，我还必须创建一个结构，以便反序列化JSON字符串：

struct BlobComponents: Codable {
    let url: String
    let mimeType: String
    let size: Int64
    let dataString: String
}

然后，我将发送到WKScriptMessageHandler的消息解释为保存到文件中。这里我使用了SwiftUI文件移动器，但是您可以对这个内容做任何您想做的事情。

func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
    guard let jsonString = message.body as? String else {
        return
    }
    
    parent.webModel.blobDownloadWith(jsonString: jsonString)
}

在我的web模型中(需要导入CoreServices)：

func blobDownloadWith(jsonString: String) {
    guard let jsonData = jsonString.data(using: .utf8) else {
        print("Cannot convert blob JSON into data!")
        return
    }

    let decoder = JSONDecoder()
    
    do {
        let file = try decoder.decode(BlobComponents.self, from: jsonData)
        
        guard let data = Data(base64Encoded: file.dataString),
            let uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassMIMEType, file.mimeType as CFString, nil),
            let ext = UTTypeCopyPreferredTagWithClass(uti.takeRetainedValue(), kUTTagClassFilenameExtension)
        else {
            print("Error! \(error)")
            return
        }
        
        let fileName = file.url.components(separatedBy: "/").last ?? "unknown"
        let path = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
        let url = path.appendingPathComponent("blobDownload-\(fileName).\(ext.takeRetainedValue())")
        
        try data.write(to: url)
        
        downloadFileUrl = url
        showFileMover = true
    } catch {
        print("Error! \(error)")
        return
    }
}