Download And Save File From URL in Swift

Question

I'm trying to...

download a file (an MLModel) from a server
save that file to the device
re-launch the app
use the URL (path) that the file was saved to, to access the downloaded file.. so I don't have to re-download it every time the app launches

let download = URLSession.shared.downloadTask(with: url) { (urlOrNil, response, error) in

    if let error = error {
                print("❌ There was an error in \(#function) \(error)")
                completion(nil)
                return
            }


// the location the mlModel is saved at
            guard let fileURL = urlOrNil else {print("❇️>>>\(#file) \(#line)"); return  }
            do {
                //compiles the model
                let compiledUrl = try MLModel.compileModel(at: fileURL)

            //turns the model into an MLModel
            let model = try MLModel(contentsOf: compiledUrl)
            print("newModel Complete ")


            // find the app support directory
            let fileManager = FileManager.default
            // Finds a place to save the MLModel
            let appSupportDirectory = try! fileManager.url(for: .applicationSupportDirectory,
                                                           in: .userDomainMask, appropriateFor: compiledUrl, create: true)

            // create a permanent URL in the app support directory
            let permanentUrl = appSupportDirectory.appendingPathComponent(compiledUrl.lastPathComponent)



            print("\(permanentUrl)")


            // if the file exists, replace it. Otherwise, copy the file to the destination.
            if fileManager.fileExists(atPath: permanentUrl.absoluteString) {
                _ = try fileManager.replaceItemAt(permanentUrl, withItemAt: compiledUrl)
            } else {
                try fileManager.copyItem(at: compiledUrl, to: permanentUrl)
            }

            let newModel = try MLModel(contentsOf: permanentUrl)
            print("", newModel)



            completion(newModel)
        }catch{
            print("❌ There was an error in \(#function) \(error) : \(error.localizedDescription)")
        }
    }.resume()

From what I understand, this is saving my MLModel to the "permanentUrl". So I restart the app, I don't run downloadTask again (because the MLModel should be saved?), and I try to access the MLModel that I copied to the permanentURL with this code

let permanentUrl = URL(string:"file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application%20Support/CFNetworkDownload_v3EpLD.mlmodelc")

    do {
        let model = try MLModel(contentsOf: permanentUrl!)

        print(model)
    }catch{
        print("❌ There was an error in \(#function) \(error) : \(error.localizedDescription)")
    }

I get this Error

file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc does not exist" UserInfo={NSLocalizedDescription=file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc does not exist} : file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc does not exist

So I guess the MLModel wasn't saved? What am I missing here? I assume I saved the MLModel with downloadTask and I'm just not retrieving it the right way. How do I access the file that I had saved?

I saw many articles that seemed somewhat similar, but different enough to where the answers didn't work for me after many attempts and iterations. I might just not be smart/experienced enough to make up for the differing variables. I apologize if I should have been. — Ungraceful, Jan 08 '20 at 21:28

Ungraceful · Accepted Answer · 2020-01-13T23:39:33.733

This was the answer.

inside of the downloadTask function, I printed the compiledUrl.lastPathComponent and saved it. Then, when I re-ran the app I ran this code to find the URL of the file.

// saved compiledUrl.lastPathComponent
    let filename = "CFNetworkDownload_B9QvT1.mlmodelc"


    let fileManager = FileManager.default
    let appSupportDirectory = try! fileManager.url(for: .applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: true)

    let permanentUrl = appSupportDirectory.appendingPathComponent(filename)

    let model = try? MLModel(contentsOf: permanentUrl)
    print(model)

Download And Save File From URL in Swift

1 Answers1