Firebase Security Rules: Syntax and Structure

1. Introduction

Firebase provides a set of Security Rules to secure your data in Firestore, Firebase Storage, and Firebase Realtime Database. These rules allow you to control who has access to your data and what they can do with it.

By the end of this tutorial, you will have learnt:

• The basic syntax and structure of Firebase Security Rules.
• How to write and structure your own security rules.

This tutorial assumes you have a basic understanding of Firebase. Knowledge about Firestore, Firebase Storage, or Realtime Database will be beneficial.

2. Step-by-Step Guide

Firebase Security Rules use a custom, JSON-like language. A rules file consists of service blocks, match blocks, and access control expressions.

Service Blocks: Defines which Firebase service the rules will apply to. Each service block contains one or more match blocks.

service cloud.firestore {
  // Match blocks go here
}

Match Blocks: Specifies the database paths that the rules will apply to. They can be nested to specify more specific paths.

match /databases/{database}/documents {
  // Access control expressions go here
}

Access Control Expressions: Determines who has read or write access to the matching path.

allow read, write: if request.auth != null;

3. Code Examples

Example 1: Allow all users to read, but only authenticated users to write.

service cloud.firestore {
  match /databases/{database}/documents {
    // Matches any document in the database
    match /{document=**} {
      allow read; // Everyone can read
      allow write: if request.auth != null; // Only authenticated users can write
    }
  }
}

In this example, the ** wildcard matches any document in any collection in the database. The request.auth != null condition checks if the user is authenticated.

Example 2: Allow users to read and write their own data.

service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow read, write: if request.auth != null && request.auth.uid == userId;
    }
  }
}

Here, the {userId} wildcard matches any document in the users collection. The condition checks if the user is authenticated and if the authenticated user's ID matches the document ID.

4. Summary

In this tutorial, we've covered:

• The basic syntax and structure of Firebase Security Rules.
• Writing rules that specify who can read and write data.

To continue your learning, try writing more complex rules and test them in the Firebase console. The Firebase documentation is a great resource for further reading.

5. Practice Exercises

1. Write a rule that allows users to read all documents, but only write to documents in a posts collection if the document's authorId field matches their user ID.

2. Write a rule that allows users to read a document in a privateMessages collection only if the document's recipientId field matches their user ID.

Solutions:

service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read;
      match /posts/{postId} {
        allow write: if request.auth != null && request.resource.data.authorId == request.auth.uid;
      }
    }
  }
}

service cloud.firestore {
  match /databases/{database}/documents {
    match /privateMessages/{messageId} {
      allow read: if request.auth != null && resource.data.recipientId == request.auth.uid;
    }
  }
}

Keep practicing! Writing effective security rules is a key skill in Firebase development.