Building Real-Time Mobile Features: WebSockets, SSE, and Firebase

Real-time features—live chat, presence indicators, collaborative editing, live dashboards, and instant notifications—have become baseline expectations for modern mobile applications. Implementing them reliably requires choosing the right transport protocol, managing connection lifecycle across mobile-specific challenges like backgrounding and network transitions, and designing data models optimized for real-time synchronization. This guide covers the three primary approaches: WebSockets, Server-Sent Events (SSE), and Firebase Realtime Database.

WebSockets: Full-Duplex Communication

WebSockets provide persistent, full-duplex communication channels between client and server over a single TCP connection. After an initial HTTP handshake, the connection upgrades to the WebSocket protocol, enabling both parties to send messages independently at any time. This makes WebSockets ideal for chat applications, multiplayer features, and any scenario requiring bidirectional real-time data flow.

On the server, libraries like Socket.IO (Node.js), Django Channels (Python), or Gorilla WebSocket (Go) manage WebSocket connections, rooms, and broadcasting. Socket.IO is particularly popular because it provides automatic reconnection, binary support, room-based broadcasting, and transparent fallback to HTTP long-polling when WebSocket connections are blocked by corporate firewalls or restrictive network configurations.

On the mobile client, use the native WebSocket API in React Native or the web_socket_channel package in Flutter. Implement a connection manager class that handles the complete lifecycle: initial connection, automatic reconnection with exponential backoff (starting at one second, doubling up to 30 seconds), heartbeat pings to detect stale connections, and message queuing during disconnection periods.

Server-Sent Events: Efficient One-Way Streaming

SSE provides a server-to-client streaming channel over standard HTTP. Unlike WebSockets, SSE is unidirectional—the server pushes events to the client, but the client communicates back through regular HTTP requests. This simplicity is an advantage for use cases like live feeds, dashboard updates, notification streams, and progress tracking where the server is the primary data source.

SSE connections automatically reconnect on failure, include a last-event-id mechanism for resuming streams without data loss, and work through standard HTTP infrastructure (proxies, load balancers, CDNs) without special configuration. The overhead is lower than WebSockets because SSE uses standard HTTP with chunked transfer encoding rather than a separate protocol.

In React Native, SSE can be consumed through the EventSource API (available via polyfills) or through libraries like react-native-sse. For scenarios where you need server-to-client streaming with occasional client-to-server requests, SSE often provides a simpler, more robust architecture than WebSockets.

Firebase Realtime Database and Firestore

Firebase provides managed real-time synchronization with zero server-side WebSocket infrastructure to maintain. The Realtime Database uses a JSON tree structure with real-time listeners that fire whenever data changes. Firestore, Firebase's newer database, provides richer querying capabilities, automatic scaling, and offline persistence out of the box.

Firebase's real-time listeners are remarkably efficient for mobile applications. They handle connection management, automatic reconnection, offline data caching, and conflict resolution transparently. For applications in the Bangladeshi market where connection quality varies, Firebase's built-in offline persistence means the app remains functional during connectivity drops and automatically syncs when the connection is restored.

Security rules defined in the Firebase console control read and write access at the document and field level. Structure security rules carefully—overly permissive rules expose user data, while overly restrictive rules break functionality. Use Firestore's collection group queries for scenarios like "retrieve all messages across all chat rooms sent by a specific user."

Presence Systems

User presence (online, offline, away) requires detecting both intentional disconnections (app closed) and unintentional disconnections (network failure, device sleep). Firebase's onDisconnect handler is purpose-built for this—it writes a specified value to the database when the server detects that the client has disconnected, regardless of the reason.

With WebSockets, implement presence through periodic heartbeat messages. The client sends a ping every 15 to 30 seconds, and the server marks users as offline if no heartbeat is received within the timeout window. Store the last-seen timestamp alongside the presence status so the client application can display contextual information like "last seen 5 minutes ago."

On mobile, background execution restrictions on both iOS and Android complicate presence accuracy. When the app enters the background, the OS may suspend network activity within seconds (iOS) or minutes (Android). Design your presence system to expect brief offline-online cycles during app backgrounding and set your timeout thresholds accordingly—a 60-second timeout avoids false offline indicators caused by brief backgrounding.

Typing Indicators and Ephemeral State

Typing indicators are a common real-time feature in chat applications. The implementation involves broadcasting a "typing" event when the user begins typing and a "stopped typing" event after a debounce period of inactivity (typically two to three seconds). To avoid excessive network traffic, throttle typing events to one per second maximum.

For ephemeral state like typing indicators, cursor positions, or draft content, consider whether persistence is necessary. Firebase Realtime Database is well-suited for ephemeral state due to its low latency and automatic cleanup via onDisconnect. With WebSockets, broadcast ephemeral state through socket events without persisting to your primary database.

Connection Management on Mobile

Mobile connections are inherently unstable. Devices move between Wi-Fi and cellular networks, enter tunnels and elevators, and have their network activity throttled by the operating system during low-power states. Your real-time connection layer must handle all of these scenarios gracefully.

Listen for network state changes using React Native's NetInfo or Flutter's connectivity_plus and proactively reconnect when connectivity is restored. Implement message ordering through sequence numbers or timestamps to handle out-of-order delivery after reconnection. Buffer outgoing messages during disconnection and flush the buffer upon reconnection, deduplicating any messages that may have been partially delivered.

Real-Time Expertise at Nexis Limited

We have implemented real-time features across chat applications, live dashboards, collaborative tools, and our own Digital Menu platform. Our mobile development services include real-time architecture design and implementation using the optimal technology for each use case. Contact us to discuss adding real-time capabilities to your mobile application.