How to initialise an OutputStream with a Url?

Question

I try to create an OutputStream to an app group folder, which is created as follows:

 func createProjectDirectoryPath(path:String) -> String
    {
        let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.xyz")
        let logsPath = containerURL!.appendingPathComponent(path)
        NSLog("12345- folder path: %@", logsPath.path)

        do {
            try FileManager.default.createDirectory(atPath: logsPath.path, withIntermediateDirectories: true, attributes: nil)
        } catch let error as NSError {
            NSLog("12345- Unable to create directory %@", error.debugDescription)
        }
        return logsPath.path
    }

This function gives me a path like this

/private/var/mobile/Containers/Shared/AppGroup/40215F20-4713-4E23-87EF-1E21CCFB45DF/pcapFiles

This folder exists, because the line FileManager.default.fileExists(path) returns true. The next step is to append a generated filename to the path, which I am doing here

let urlToFile = URL(string: createProjectDirectoryPath(path: "pcapFiles").appending("/\(filename)"))

which gives me the correct new path

/private/var/mobile/Containers/Shared/AppGroup/40215F20-4713-4E23-87EF-1E21CCFB45DF/pcapFiles/39CC2DB4-A6D9-412E-BAAF-2FAA4AD70B22.pcap

If I call this line, ostream is always nil

let ostream = OutputStream(url: urlToFile!, append: false)

Do I miss something? The OutputStream should create the file on this path, but for unknown reason, it is not possible.

PS: AppGroup is enabled in Capabilities and in developers console.

score 1 · Accepted Answer · answered Jun 05 '17 at 10:05

Your createProjectDirectoryPath() function returns a file path, therefore you must use URL(fileURLWithPath:) to convert that to an URL. Alternatively, modify your function to return an URL instead:

func createProjectDirectoryPath(path:String) -> URL? {
    let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.xyz")
    let logsURL = containerURL!.appendingPathComponent(path)
    do {
        try FileManager.default.createDirectory(at: logsURL, withIntermediateDirectories: true)
    } catch let error as NSError {
        NSLog("Unable to create directory %@", error.debugDescription)
        return nil
    }
    return logsURL
}

In addition, you have to call open() on all Stream objects before they can be used, this will also create the file if it did not exist before:

guard let logsURL = createProjectDirectoryPath(path: "pcapFiles") else {
    fatalError("Cannot create directory")
}
let urlToFile = logsURL.appendingPathComponent(filename) 
guard let ostream = OutputStream(url: urlToFile, append: false) else {
    fatalError("Cannot open file")
}
ostream.open()

How to initialise an OutputStream with a Url?

1 Answers1