Use File Metadata on Web

After uploading a file to Cloud Storage reference, you can also get or 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, 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. getMetadata() returns a Promise containing the complete metadata, or an error if the Promise rejects.

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

// Get metadata properties
forestRef.getMetadata().then(function(metadata) {
  // Metadata now contains the metadata for 'images/forest.jpg'
}).catch(function(error) {
  // Uh-oh, an error occurred!
});

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. updateMetadata() returns a Promise containing the complete metadata, or an error if the Promise rejects.

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

// Create file metadata to update
var newMetadata = {
  cacheControl: 'public,max-age=300',
  contentType: 'image/jpeg'
}

// Update metadata properties
forestRef.updateMetadata(newMetadata).then(function(metadata) {
  // Updated metadata for 'images/forest.jpg' is returned in the Promise
}).catch(function(error) {
  // Uh-oh, an error occurred!
});

You can delete a metadata property by setting it to null:

// Create file metadata with property to delete
var deleteMetadata = {
  contentType: null
}

// Delete the metadata property
forestRef.updateMetadata(deleteMetadata).then(function(metadata) {
  // metadata.contentType should be null
}).catch(function(error) {
  // Uh-oh, an error occurred!
});

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 an object containing String properties.

var metadata = {
  customMetadata: {
    'location': 'Yosemite, CA, USA',
    'activity': 'Hiking'
  }
}

You can use custom metadata for storing additional app specific data for each file, 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 Writable
bucket string NO
generation string NO
metageneration string NO
fullPath string NO
name string NO
size number NO
timeCreated string NO
updated string NO
md5Hash string YES on upload, NO on updateMetadata
cacheControl string YES
contentDisposition string YES
contentEncoding string YES
contentLanguage string YES
contentType string YES
downloadURLs Array of strings NO
customMetadata Object containing string->string mappings 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.

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