Use file metadata with Cloud Storage on Flutter

Notice

This page is archived and might not reflect the latest version of the FlutterFire plugins. You can find the latest information on firebase.google.com:

https://firebase.google.com/docs/storage/flutter/file-metadata

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

note

By default, a Cloud Storage bucket requires Firebase Authentication to perform any action on the bucket's data or files. You can change your Firebase Security Rules for Cloud Storage to allow unauthenticated access. Since Firebase and your project's default App Engine app share this bucket, configuring public access may make newly uploaded App Engine files publicly accessible, as well. Be sure to restrict access to your Cloud Storage bucket again when you set up Authentication.

Get File Metadata#

File metadata contains common properties such as name, size, and contentType (often referred to as MIME type) in addition to some less common ones like contentDisposition and timeCreated. This metadata can be retrieved from a Cloud Storage reference using the getMetadata() method.

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

// Get metadata properties
final metadata = await forestRef.getMetadata();

// Metadata now contains the metadata for 'images/forest.jpg'

Update File Metadata#

You can update file metadata at any time after the file upload completes by using the updateMetadata() method. 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
final forestRef = storageRef.child("images/forest.jpg");

// Create file metadata to update
final newMetadata = SettableMetadata(
  cacheControl: "public,max-age=300",
  contentType: "image/jpeg",
);

// Update metadata properties
final metadata = await forestRef.updateMetadata(newMetadata);

// Updated metadata for 'images/forest.jpg' is returned

You can delete writable metadata properties by passing null:

// Delete the cacheControl property
final newMetadata = SettableMetadata(cacheControl: null);
final metadata = await forestRef.updateMetadata(newMetadata);

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 using the customMetadata parameter of the SettableMetadata constructor:

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

// Create file metadata to update
final newCustomMetadata = SettableMetadata(
  customMetadata: {
    "location": "Yosemite, CA, USA",
    "activity": "Hiking",
  },
);

// Update metadata properties
final metadata = await forestRef.updateMetadata(newCustomMetadata);

// Updated metadata for 'images/forest.jpg' is returned

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	Settable?
`bucket`	`String`	No
`generation`	`String`	No
`metageneration`	`String`	No
`metadataGeneration`	`String`	No
`fullPath`	`String`	No
`name`	`String`	No
`size`	`int`	No
`timeCreated`	`DateTime`	No
`updated`	`DateTime`	No
`md5Hash`	`String`	No
`cacheControl`	`String`	Yes
`contentDisposition`	`String`	Yes
`contentEncoding`	`String`	Yes
`contentLanguage`	`String`	Yes
`contentType`	`String`	Yes
`customMetadata`	`Map<String, String>`	Yes

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.