File metadata in Firebase - Commands & Configuration

Introduction

File metadata stores extra information about files in Firebase Storage. It helps you keep track of details like file type, size, and custom tags without changing the file itself.

When you want to know the type of a file before downloading it to show the right icon.

When you need to store who uploaded a file or when it was uploaded.

When you want to add custom tags to files for easier searching later.

When you want to control file caching behavior by setting cache control headers.

When you want to update file information without re-uploading the whole file.

Commands

Uploads a file named photo.jpg to Firebase Storage and sets metadata for content type and a custom uploader tag.

Terminal

firebase storage:upload ./images/photo.jpg --metadata contentType=image/jpeg,customMetadata.uploader=alice

Expected Output

✔  Uploaded ./images/photo.jpg to gs://your-project.appspot.com/images/photo.jpg

Metadata set: contentType=image/jpeg, customMetadata.uploader=alice

→

--metadata - Sets metadata properties like content type and custom tags during upload

Retrieves and shows the metadata of the uploaded photo.jpg file to verify the stored information.

Terminal

firebase storage:metadata images/photo.jpg

Expected Output

File: images/photo.jpg

Content-Type: image/jpeg

Custom Metadata:

  uploader: alice

Size: 204800 bytes

Updated: 2024-06-01T12:00:00Z

Updates the metadata of photo.jpg to add a description without changing the file content.

Terminal

firebase storage:metadata:update images/photo.jpg --metadata customMetadata.description='Vacation photo'

Expected Output

✔  Metadata updated for images/photo.jpg

Custom Metadata:

  uploader: alice

  description: Vacation photo

→

--metadata - Updates or adds metadata properties without re-uploading the file

Checks the updated metadata to confirm the new description tag was added successfully.

Terminal

firebase storage:metadata images/photo.jpg

Expected Output

File: images/photo.jpg

Content-Type: image/jpeg

Custom Metadata:

  uploader: alice

  description: Vacation photo

Size: 204800 bytes

Updated: 2024-06-01T12:05:00Z

Key Concept

If you remember nothing else from this pattern, remember: file metadata lets you store and update extra information about files without changing the files themselves.

Common Mistakes

Trying to update metadata by re-uploading the whole file instead of using metadata update commands.

This wastes bandwidth and time because the file content does not need to change to update metadata.

Use the metadata update command to change metadata without re-uploading the file.

Not setting the correct content type metadata when uploading files.

Without the right content type, browsers or apps may not handle the file correctly, causing display or download issues.

Always set the contentType metadata to match the file type during upload.

Using unsupported characters or formats in custom metadata keys or values.

Firebase Storage requires metadata keys and values to follow specific rules; invalid formats cause errors.

Use only letters, numbers, hyphens, and underscores in keys and simple string values.

Summary

Upload files with metadata to store extra information like content type and custom tags.

Use metadata commands to view and update file metadata without re-uploading files.

Proper metadata helps apps handle files correctly and adds useful searchable information.