Use File Metadata on iOS

After uploading a file to Firebase 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, 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 Firebase Storage reference using the metadataWithCompletion: method.

// Create reference to the file whose metadata we want to retrieve
FIRStorageReference *forestRef = [storageRef child:@"images/forest.jpg"];

// Get metadata properties
[forestRef metadataWithCompletion:^(FIRStorageMetadata *metadata, NSError *error){
  if (error != nil) {
    // Uh-oh, an error occurred!
  } else {
    // Metadata now contains the metadata for 'images/forest.jpg'
  }
}];
  

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

// Get metadata properties
forestRef.metadataWithCompletion { (metadata, error) -> Void in
  if (error != nil) {
    // Uh-oh, an error occurred!
  } else {
    // 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:withCompletion: 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
FIRStorage *forestRef = [storageRef child:@"images/forest.jpg"];

// Create file metadata to update
FIRStorageMetadata *newMetadata = [[FIRStorageMetadata alloc] init];
newMetadata.cacheControl = @"public,max-age=300";
newMetadata.contentType = @"image/jpeg";

// Update metadata properties
[forestRef updateMetadata:newMetadata completion:^(FIRStorageMetadata *metadata, NSError *error){
  if (error != nil) {
    // Uh-oh, an error occurred!
  } else {
    // Updated metadata for 'images/forest.jpg' is returned
  }
}];
  

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

// Create file metadata to update
let newMetadata = FIRStorageMetadata()
newMetadata.cacheControl = "public,max-age=300"
newMetadata.contentType = "image/jpeg"

// Update metadata properties
forestRef.updateMetadata(metadata) { (metadata, error) -> Void in
  if (error != nil) {
    // Uh-oh, an error occurred!
  } else {
    // Updated metadata for 'images/forest.jpg' is returned
  }
}
    

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

// Create file metadata with property to delete
FIRStorageMetadata *newMetadata = [[FIRStorageMetadata alloc] init];
newMetadata.contentType = @"";
// Delete the metadata property
[forestRef updateMetadata:newMetadata completion:^(FIRStorageMetadata metadata, NSError error){
  if (error != nil) {
    // Uh-oh, an error occurred!
  } else {
    // metadata.contentType should be nil
  }
}];

// Create file metadata with property to delete
let newMetadata = FIRStorageMetadata()
newMetadata.contentType = ""
// Delete the metadata property
forestRef.updateMetadata(metadata) { (metadata, error) -> Void in
  if (error != nil) {
    // Uh-oh, an error occurred!
  } else {
    // metadata.contentType should be nil
  }
}

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 NSDictionary containing NSString properties.

NSDictionary *metadata = @{
  @"customMetadata": @{
    @"location": @"Yosemite, CA, USA",
    @"activity": @"Hiking"
  }
}

var metadata = [
  "customMetadata": [
    "location": "Yosemite, CA, USA",
    "activity": "Hiking"
  ]
]
    

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:

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