Upload Files with Cloud Storage for C++

Cloud Storage allows developers to quickly and easily upload files to a Google Cloud Storage bucket provided and managed by Firebase.

Create a Reference

To upload a file, first create a Cloud Storage reference to the location in Cloud Storage you want to upload the file to.

You can create a reference by appending child paths to the storage root:

// Create a root reference
StorageReference storage_ref = storage->GetReference();

// Create a reference to "mountains.jpg"
StorageReference mountains_ref = storage_ref.Child("mountains.jpg");

// Create a reference to 'images/mountains.jpg'
StorageReference mountain_images_ref = storage_ref.Child("images/mountains.jpg");

// While the file names are the same, the references point to different files
mountains_ref.name() == mountain_images_ref.name();           // true
mountains_ref.full_path() == mountain_images_ref.full_path(); // false

You cannot upload data with a reference to the root of your Google Cloud Storage bucket. Your reference must point to a child URL.

Upload Files

Once you have a reference, you can upload files to Cloud Storage in two ways:

  1. Upload from a byte buffer in memory
  2. Upload from a file path representing a file on device

Upload from data in memory

The PutData() method is the simplest way to upload a file to Cloud Storage. PutData() takes a byte buffer and returns a Future<Metadata> which will contain information about the file when the Future completes. You can use a Controller to manage your upload and monitor its status.

// Data in memory
const size_t kByteBufferSize = ...
uint8_t byte_buffer[kByteBufferSize] = { ... };

// Create a reference to the file you want to upload
StorageReference rivers_ref = storage_ref.Child("images/rivers.jpg");

// Upload the file to the path "images/rivers.jpg"
Future future = rivers_ref.PutBytes(byte_buffer, kByteBufferSize);

At the point the request has been made but we have to wait for the Future to complete before the file is uploaded. Since games typically run in a loop, and are less callback driven than other applications, you'll typically poll for completion.

if (future.status() != firebase::kFutureStatusPending) {
  if (future.status() != firebase::kFutureStatusComplete) {
    LogMessage("ERROR: GetData() returned an invalid future.");
    // Handle the error...
  } else if (future.Error() != firebase::storage::kErrorNone) {
    LogMessage("ERROR: GetData() returned error %d: %s", future.Error(),
               future.error_message());
    // Handle the error...
    }
  } else {
    // Metadata contains file metadata such as size, content-type, and download URL.
    Metadata* metadata = future.Result();
    std::string download_url = metadata->download_url();
  }
}

Upload from a local file

You can upload local files on the devices, such as photos and videos from the camera, with the PutFile() method. PutFile() takes a std::string representing the path to the file and returns a Future<Metadata> which will contain information about the file when the Future completes. You can use a Controller to manage your upload and monitor its status.

// File located on disk
std::string local_file = ...

// Create a reference to the file you want to upload
StorageReference rivers_ref = storage_ref.Child("images/rivers.jpg");

// Upload the file to the path "images/rivers.jpg"
Future future = rivers_ref.PutFile(localFile);

// Wait for Future to complete...

if (future.Error() != firebase::storage::kErrorNone) {
  // Uh-oh, an error occurred!
} else {
  // Metadata contains file metadata such as size, content-type, and download URL.
  Metadata* metadata = future.Result();
  std::string download_url = metadata->download_url();
}

If you want to actively manage your upload, you can supply a Controller to the PutFile() or PutBytes() methods. This allows you to use the controller to observe the ongoing upload operation. See Manage Uploads for more information.

Add File Metadata

You can also include metadata when you upload files. This metadata contains typical file metadata properties such as name, size, and content_type (commonly referred to as MIME type). The PutFile() method automatically infers the content type from the filename extension, but you can override the auto-detected type by specifying content_type in the metadata. If you do not provide a content_type and Cloud Storage cannot infer a default from the file extension, Cloud Storage uses application/octet-stream. See the Use File Metadata section for more information about file metadata.

// Create storage reference
StorageReference mountains_ref = storage_ref.Child("images/mountains.jpg");

// Create file metadata including the content type
StorageMetadata metadata;
metadata.set_content_type("image/jpeg");

// Upload data and metadata
mountains_ref.PutBytes(data, metadata);

// Upload file and metadata
mountains_ref.PutFile(local_file, metadata);

Manage Uploads

In addition to starting uploads, you can pause, resume, and cancel uploads using the Pause(), Resume(), and Cancel() methods on Controller, which you may optionally pass to the PutBytes() or PutFile() methods.

// Start uploading a file
firebase::storage::Controller controller;
storage_ref.Child("images/mountains.jpg").PutFile(local_file, nullptr, &controller);

// Pause the upload
controller.Pause();

// Resume the upload
controller.Resume();

// Cancel the upload
controller.Cancel();

Monitor Upload Progress

You can attach listeners to uploads in order to monitor the progress of the upload.

class MyListener : public firebase::storage::Listener {
 public:
  virtual void OnProgress(firebase::storage::Controller* controller) {
    // A progress event occurred
  }
};

{
  // Start uploading a file
  MyEventListener my_listener;
  storage_ref.Child("images/mountains.jpg").PutFile(local_file, my_listener);
}

Error Handling

There are a number of reasons why errors may occur on upload, including the local file not existing, or the user not having permission to upload the desired file. You can find more information about errors in the Handle Errors section of the docs.

Next Steps

Now that you've uploaded files, let's learn how to download them from Cloud Storage.

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