Firebase存储：child（）不适用于iOS App

Question

I'm getting the following error when trying to download an image from my Firebase Storage:

Error Domain=FIRStorageErrorDomain Code=-13010 "Object 2xxxxxxx8/profile_pic does not exist."

(I obviously put the x's up there to mask private info.)

I'm adding a path reference to my Firebase Storage using the following code:

let storage = FIRStorage.storage()
let storageRef = storage.referenceForURL("gs://project-4xxxxxxxxxxxxx.appspot.com")
let profilePicReference = storageRef.child(signedInUser.uid + "/profile_pic")

I know the code above is good cause everything was working correctly: I could see a folder was added in my Storage space, and an image was uploaded into that folder - all directly from my iOS App.

The problems started when I manually deleted said folder from my Firebase Storage (I did this through the Firebase web portal) - just cause I wanted verify everything was working, so I deleted the folder to start fresh - expecting the code above would recreate it once I ran the App again - and since then I'm getting this error over and over again.

Really makes no sense.

Are there any quirks or issues with Firebase Storage? Some sort of caching that has to be addressed?

Any tips would be greatly appreciated!

Answer 1

Are there any quirks or issues with Firebase Storage? Some sort of caching that has to be addressed?

An UploadTask executes asynchronously . If I try downloading an image immediately after uploading an image, I can reproduce your error. What's happening is that the download code executes before the image finishes uploading, producing the image-does-not-exist error. You can see that the download code executes too early by printing out some messages in the callbacks:

    let storage = FIRStorage.storage()
    let storageRef = storage.reference() //You don't need to explicitly write the url in your code.
                                         //The config file GoogleService-Info.plist will handle that.

    let imageRef = storageRef.child("images/align_menu.tiff")

    let localURL =  NSBundle.mainBundle().URLForResource(
        "align_menu",
        withExtension: "tiff"
    )!

    //Upload the image:
    let uploadTask = imageRef.putFile(localURL, metadata: nil) { (metadata, error) -> Void in
        if let returnedError = error {
            // Uh-oh, an error occurred!
            print("[My Upload Error]: \(returnedError)")
        } else {
            // Metadata contains file metadata such as size, content-type, and download URL.
            print("[My Upload Success]:")
            let downloadURL = metadata!.downloadURL()!
            print("[URL for download]: \(downloadURL)")
        }

    }

    //Download the image:
    imageRef.dataWithMaxSize(1 * 1024 * 1024) { (data, error) -> Void in
        if let returnedError = error {
            // Uh-oh, an error occurred!
            print("[My Download Error]: \(returnedError)")
        }
        else {
            print("[My Download Success]:")

            if let validImage = UIImage(data: data!) {
                NSOperationQueue.mainQueue().addOperationWithBlock() {
                    self.imageView.image = validImage
                }
            }
        }

    }

That code produces the output:

[My Download Error]: ...."Object images/align_menu.tiff does not exist."... 

and then after a few seconds I see the output:

[My Upload Success]:
[URL for download]: ... 

which demonstrates that the download callback is executing before the upload callback. I can't quite figure out the details of why that happens--but obviously the callbacks are not added to a serial queue. *

To cure the asynchronous problem, you have several options:

1) Put the download code inside the callback for the upload code.

That way, the download won't start executing until after the image has successfully uploaded. After I did that, deleting the image using the Firebase Storage webpage before running the app had no deleterious effect on my upload/download, and the messages were output in the expected order:

[My Upload Success]:
[URL for download]: ...
[My Download Success]:

2) Attach a .Success observer to the uploadTask.

As described in the Firebase docs, in the Monitor Upload Progress section , you can get notified if the uploadTask successfully uploads the image:

    let storage = FIRStorage.storage()
    let storageRef = storage.reference() //You don't need to explicitly write the url in your code.
                                         //The config file GoogleService-Info.plist will handle that.

    let imageRef = storageRef.child("images/align_menu.tiff")

    let localURL =  NSBundle.mainBundle().URLForResource(
        "align_menu",
        withExtension: "tiff"
    )!

    //Upload the image:
    let uploadTask = imageRef.putFile(localURL, metadata: nil) { (metadata, error) -> Void in
        if let returnedError = error {
            // Uh-oh, an error occurred!
            print("[My Upload Error]: \(returnedError)")
        } else {
            // Metadata contains file metadata such as size, content-type, and download URL.
            print("[My Upload Success]:")
            let downloadURL = metadata!.downloadURL()!
            print("[URL for download]: \(downloadURL)")
        }

    }


    let observer = uploadTask.observeStatus(.Success) { (snapshot) -> Void in

        //Download the image:
        imageRef.dataWithMaxSize(1 * 1024 * 1024) { (data, error) -> Void in
            if let returnedError = error {
                // Uh-oh, an error occurred!
                print("[My Download Error]: \(returnedError)")
            }
            else {
                print("[My Download Success]:")

                if let validImage = UIImage(data: data!) {
                    NSOperationQueue.mainQueue().addOperationWithBlock() {
                        self.imageView.image = validImage
                    }
                }
            }

        }

    }

3) Use Grand Central Dispatch to notify you when the upload is successful.

You don't have control over what queues the callbacks get added to (the Firebase method implementations decide that), but you can use Grand Central Dispatch to notify you when arbitrary code finishes executing. The following works for me:

    let storage = FIRStorage.storage()
    let storageRef = storage.reference() //You don't need to explicitly write the url in your code.
                                         //The config file GoogleService-Info.plist will handle that.

    let imageRef = storageRef.child("images/align_menu.tiff")

    let localURL =  NSBundle.mainBundle().URLForResource(
        "align_menu",
        withExtension: "tiff"
    )!

    let myExecutionGroup = dispatch_group_create()

    dispatch_group_enter(myExecutionGroup)
    //Upload the image:
    let _ = imageRef.putFile(localURL, metadata: nil) { (metadata, error) -> Void in
        if let returnedError = error {
            // Uh-oh, an error occurred!
            print("[My Upload Error]: \(returnedError)")
        } else {
            // Metadata contains file metadata such as size, content-type, and download URL.
            print("[My Upload Success]:")
            let downloadURL = metadata!.downloadURL()!
            print("[URL for download]: \(downloadURL)")

            dispatch_group_leave(myExecutionGroup)
        }

    }

    let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)

    dispatch_group_notify(myExecutionGroup, queue) {
        //This callback executes for every dispatch_group_leave().

        //Download the image:
        imageRef.dataWithMaxSize(1 * 1024 * 1024) { (data, error) -> Void in
            if let returnedError = error {
                // Uh-oh, an error occurred!
                print("[My Download Error]: \(returnedError)")
            }
            else {
                print("[My Download Success]:")

                if let validImage = UIImage(data: data!) {
                    NSOperationQueue.mainQueue().addOperationWithBlock() {
                        self.imageView.image = validImage
                    }
                }
            }

        }

    }

---

* I tried putting a sleep(10) between the original upload code and download code, and that did not alleviate the problem. I thought that if the upload callback was executing on a background thread, then the upload callback would have time to complete while the main thread was sleeping, then after the sleep finished the download code would execute and the download callback would be added to a queue somewhere, then the download callback would execute. Because the sleep(10) didn't solve the problem, that meant the upload callback had to have been added to an execution queue for the main thread, and the sleep halted the main thread and anything in the queue from executing.

That leads me to believe that the upload and download callbacks are added to an asynchronous queue on the main thread (it's not a synchronous queue otherwise the callbacks would execute in order). I think an asynchronous queue on the main thread means that when there is dead time on the main thread, the tasks in the queue will execute, and you also get rapid switching between the various tasks when there is dead time in a particular task, like waiting for an HTTP response. For example, if there are two tasks in an asynchronous queue on the main thread, then there is rapid switching between the main thread, task1, and task2 whenever there is dead time in any one of them.