How to Use SwiftyDropbox's "destination" with a Download - dropbox-api

Question

In reviewing the SwiftyDropbox tutorial in the v2 Dropbox API, it shows how to perform a download:
// Download a file
let destination : (NSURL, NSHTTPURLResponse) -> NSURL = { temporaryURL, response in
let fileManager = NSFileManager.defaultManager()
let directoryURL = fileManager.URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
// generate a unique name for this file in case we've seen it before
let UUID = NSUUID().UUIDString
let pathComponent = "\(UUID)-\(response.suggestedFilename!)"
return directoryURL.URLByAppendingPathComponent(pathComponent)
}
client.files.download(path: "/MyFile.db", destination: destination).response { response, error in
if let (metadata, url) = response {
print("*** Download file ***")
let data = NSData(contentsOfURL: url)
print("Downloaded file name: \(metadata.name)")
print("Downloaded file url: \(url)")
print("Downloaded file data: \(data)")
} else {
print(error!)
}
}
I'm unclear what's going on with the destination part. Why do I need to generate a random string for the filename?
When I try to specify my own filename, the download doesn't seem to work:
let destination : (NSURL, NSHTTPURLResponse) -> NSURL = { temporaryURL, response in
let directoryURL = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
return directoryURL.URLByAppendingPathComponent("MyFile.db")
}
I want to download a file from Dropbox named MyFile.db and I want to put it in my device's documents directory with the name MyFile.db and overwrite it if it's already there.
How can I do that?

Answer 1

When you say it doesn't seem to work, I expect you mean you get an error like this:
Error Domain=NSCocoaErrorDomain Code=516 "“CFNetworkDownload_bPYhu1.tmp” couldn’t be moved to “Documents” because an item with the same name already exists." UserInfo={NSSourceFilePathErrorKey=..., NSUserStringVariant=(
Move
), NSDestinationFilePath=..., NSUnderlyingError=0x7fda0a67cea0 {Error Domain=NSPOSIXErrorDomain Code=17 "File exists"}}
SwiftyDropbox, by virtue of using AlamoFire, doesn't currently let you overwrite files using the download function.
Specifically, SwiftyDropbox calls download in AlamoFire, and AlamoFire calls NSFileManager.moveItemAtURL. The documentation for NSFileManager.moveItemAtURL says:
If an item with the same name already exists at dstURL, this method aborts the move attempt and returns an appropriate error.
So, it seems like it's just being cautious, and making it hard for your app to accidentally overwrite (ad potentially lose) data. If you definitely know you want to overwrite a particular file, you'll need to do so explicitly, after the Dropbox API call. We'll consider this a feature request though.
Update: SwiftyDropbox now offers the ability to overwrite the files directly as of version 3.1.0, e.g., using download(path:rev:overwrite:destination:).