Use file metadata with Cloud Storage for Unity

After uploading a file to Cloud Storage reference, you can also get and update the file metadata, for example to update the content type. Files can also store custom key/value pairs with additional file metadata.

Get File Metadata

File metadata contains common properties such as Name, SizeBytes, and ContentType (often referred to as MIME type) in addition to some less common ones like ContentDisposition and CreationTimeMillis. This metadata can be retrieved from a Cloud Storage reference using the GetMetadataAsync method.

// Create reference to the file whose metadata we want to retrieve
StorageReference forestRef =
    storageRef.Child("images/forest.jpg");

// Get metadata properties
forestRef.GetMetadataAsync().ContinueWithOnMainThread(task => {
    if (!task.IsFaulted && !task.IsCanceled) {
        StorageMetadata meta = task.Result;
        // do stuff with meta
    }
});

Update File Metadata

You can update file metadata at any time after the file upload completes by using the UpdateMetadataAsync method which takes a MetadataChange object. Refer to the full list for more information on what properties can be updated. Only the properties specified in the metadata are updated, all others are left unmodified.

// Create reference to the file whose metadata we want to change
StorageReference forestRef = storageRef.Child("images/forest.jpg");

// Create file metadata to update
var newMetadata = new MetadataChange();
newMetadata.CacheControl = "public,max-age=300";
newMetadata.ContentType = "image/jpeg";

// Update metadata properties
forestRef.UpdateMetadataAsync(newMetadata).ContinueWithOnMainThread(task => {
    if (!task.IsFaulted && !task.IsCanceled) {
        // access the updated meta data
        StorageMetadata meta = task.Result;
    }
});

You can delete writable metadata properties by passing the empty string:

// Create file metadata to update
var newMetadata = new MetadataChange();
newMetadata.ContentType = "";

// Update metadata properties
forestRef.UpdateMetadataAsync(newMetadata).ContinueWithOnMainThread(task => {
    if (!task.IsFaulted && !task.IsCanceled) {
        StorageMetadata meta = task.Result;
        // meta.ContentType should be an empty string now
    }
});

Handle Errors

There are a number of reasons why errors may occur on getting or updating metadata, including the file not existing, or the user not having permission to access the desired file. More information on errors can be found in the Handle Errors section of the docs.

Custom Metadata

You can specify custom metadata as a Dictionary<string, string>.

var newMetadata = new MetadataChange {
    CustomMetadata = new Dictionary<string, string> {
        {"location", "Yosemite, CA, USA"},
        {"activity", "Hiking"}
    }
};

// UpdateMetadataAsync

You can store app-specific data for each file in custom metadata, but we highly recommend using a database (such as the Firebase Realtime Database) to store and synchronize this type of data.

File Metadata Properties

A full list of metadata properties on a file is available below:

Property	Type	Modifyable in MetadataChange
Bucket	string	NO
Generation	string	NO
MetadataGeneration	string	NO
Path	string	NO
Name	string	NO
SizeBytes	long	NO
CreationTimeMillis	long	NO
UpdatedTimeMillis	long	NO
CacheControl	string	YES
ContentDisposition	string	YES
ContentEncoding	string	YES
ContentLanguage	string	YES
ContentType	string	YES
DownloadUrl	Uri	NO
DownloadUrls	IList<Uri>	NO
CustomMetadataKeys	IEnumerable<string>	YES

Next Steps

Uploading, downloading, and updating files is important, but so is being able to remove them. Let's learn how to delete files from Cloud Storage.