Swift - merge files

Question

How can I merge files in Swift / iOS ? The FileManager can move and copy items but I've seen nothing about merging files. I'd like to have something like

FileManager.default.merge(files: [URL], to location: URL) throws

Files can potentially be big, so I'd rather avoid having to pass their data in memory.

=== here is my own in memory merge:

let data = NSMutableData()
files.forEach({ partLocation in
  guard let partData = NSData(contentsOf: partLocation) else { return }
  data.append(partData as Data)
  do {
    try FileManager.default.removeItem(at: partLocation)
  } catch {
    print("error \(error)")
  }
})
data.write(to: destination, atomically: true)

Answer 1

Here is my own solution (thanks @Alexander for the guidance)

extension FileManager {
  func merge(files: [URL], to destination: URL, chunkSize: Int = 1000000) throws {
    try FileManager.default.createFile(atPath: destination.path, contents: nil, attributes: nil)
    let writer = try FileHandle(forWritingTo: destination)
    try files.forEach({ partLocation in
      let reader = try FileHandle(forReadingFrom: partLocation)
      var data = reader.readData(ofLength: chunkSize)
      while data.count > 0 {
        writer.write(data)
        data = reader.readData(ofLength: chunkSize)
      }
      reader.closeFile()
    })
    writer.closeFile()
  }
}

Answer 2

func merge(files: [URL], to destination: URL, chunkSize: Int = 100000000)  {
        for partLocation in files {
            // create a stream that reads the data above
            let stream: InputStream
            stream = InputStream.init(url: partLocation)!
            // begin reading
            stream.open()
            let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: chunkSize)
            //            var writeData : Data = Data()
            while stream.hasBytesAvailable {
                let read = stream.read(buffer, maxLength: chunkSize)  

                var writeData:Data = Data()
                writeData.append(buffer, count: read)    enter code here
                if let outputStream = OutputStream(url: destination, append: true) {
                    outputStream.open()
                    writeData.withUnsafeBytes { outputStream.write($0, maxLength: writeData.count) }
                    outputStream.close()
                    writeData.removeAll()
                }
            }
            stream.close()
            buffer.deallocate(capacity: chunkSize)

        }
    }