如何使用 AlamoFire 下载 blob URI

Question

我正在尝试快速使用 WKWebView，目前有一个使用 AlamoFire 的下载引擎。我遇到了一个使用 blob: url 方案来下载项目的站点。一般有没有办法使用 AlamoFire 或 WKWebView 下载 blob 文件？

我的具体目标是将此 blob URI 中的内容下载到文件中。

我将不胜感激。谢谢。

下面附上所有相关代码。

这是我遇到问题的网址：

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

这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}

这是我在 WKNavigation 决策策略中的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)
    }
}

这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，我能够弄清楚如何在没有 WKDownloadDelegate 的情况下下载 blob URL。以下代码基于this answer。

需要创建一个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，您需要将此代码添加到导航操作中。

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

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)
        }
    }
}

这是请求存储在浏览器内存中的 blob 的 JS。我将此 JS 添加到一个名为 evaluateJavaScript 的包装函数中，并带有 url 以使我的代码保持整洁。

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，我还必须创建一个可以反序列化 JSON 字符串的结构：

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

然后我将发送到 WKScriptMessageHandler 的消息并解释它们以保存到文件中。我在这里使用了 SwiftUI 文件移动器，但是你可以对这个内容做任何你想做的事情。

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

在我的网络模型中（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
    }
}