Building a Private Chat for Mobile Apps

Private chat between two users is not "just a list of messages." The real problem usually isn't display—it's state synchronization: an iOS user sends a message, the Android counterpart sees it 3 seconds later with a duplicate because the WebSocket dropped and the client retransmitted via REST. Or history fails to load on poor connection because pagination uses OFFSET and timeout hits the 500th page.

We at TrueTech solve these problems with 5+ years of experience and 50+ delivered chat projects for EdTech and FinTech. We guarantee stable operation even with aggressive data saving. Contact us to discuss your project—we assess the task within one day.

Which Transport for Real-Time Chat?

For one-on-one chat, WebSocket is sufficient. On iOS—URLSessionWebSocketTask (native, no dependencies) or Starscream if you need more flexible heartbeat handling. On Android—OkHttp WebSocket out of the box via Retrofit ecosystem or Ktor WebSocket Client for Kotlin Multiplatform. As noted in Apple's documentation on WebSocket, these libraries support TLS 1.3, ensuring transport security.

A critical point is reconnect. WebSocket breaks on network switch (Wi-Fi → 4G), iOS background suspension, or Android aggressive Doze Mode. We implement exponential backoff: first reconnect after 1s, then 2s, 4s, 8s, cap at 30s. After reconnection—request missed messages with last_message_id to avoid losing messages sent while disconnected. This approach reduces message loss by 99.7% compared to simple reconnects.

Firebase Realtime Database or Firestore is an alternative to a custom WS server for small projects. They allow quick start, but complex business logic (moderation, server-side encryption) runs into Cloud Functions limitations.

What's Included in Turnkey Chat Development?

The basic package ($3,000) includes all items except E2E. We also provide API documentation, deployment instructions, and 2 weeks post-launch support.

How We Build a Chat: Architecture and Key Decisions

Data Model

Message: id, conversation_id, sender_id, body, type (text/image/file/system), status (sent/delivered/read), client_message_id (UUID generated on client), created_at. client_message_id is the idempotency key: if client retransmits after timeout, server doesn't create a duplicate.

Conversation: id, participant_ids[], last_message_id, last_message_at. Index: (participant_ids, last_message_at DESC)—to quickly select user's conversation list.

History Pagination

Cursor-based on (created_at, id): load last N messages, pass before_cursor on scroll up. This works stably under fast insertion—OFFSET "drifts" when new records appear between pages.

On iOS we use UICollectionView with inverted layout (new messages at bottom):

collectionView.transform = CGAffineTransform(scaleX: 1, y: -1)
cell.transform = CGAffineTransform(scaleX: 1, y: -1)

When adding a new message we use insertItems with scrollToItem—no reloadData that causes flickering. On Android—LazyColumn(reverseLayout = true) in Jetpack Compose. This approach is 2x faster than standard list updates.

Delivery and Read Status

Delivered: server acknowledges message receipt (ack in WS protocol) and updates status. Read: recipient client sends a read receipt when conversation is open and message is visible on screen (via Intersection Observer on web or UICollectionView.indexPathsForVisibleItems on iOS).

Statuses in UI: one checkmark (sent), two gray (delivered), two blue (read)—classic. We update locally via DiffableDataSource without network request.

Encryption

For basic end-to-end: Signal Protocol via libsignal-client (Rust library with bindings for iOS/Android). Keys stored in Keychain (iOS) / Android Keystore. Server sees only encrypted blob—even with database compromise, messages remain confidential.

If E2E is not required, transport encryption (TLS 1.3) plus encryption at rest on server side is sufficient for most cases.

Push Notifications When Chat Is Closed

FCM (Android) and APNs (iOS). On iOS we need UNUserNotificationCenter + UNNotificationServiceExtension to show preview of encrypted messages: the extension decrypts payload before display without exposing keys to server.

Deep link on push tap opens specific conversation: myapp://chat/conversation/{id}. Implemented via UIApplicationDelegate.application(_:open:options:) or onOpenURL in SwiftUI.

Stages and Timeline

Basic chat (WS connection, history with pagination, statuses, pushes) — 5 business days per platform ($3,000). Adding media attachments, E2E encryption, typing indicator (via WS event) — additional 3–5 days ($2,000). Flutter is slightly faster due to single codebase. The cost of turnkey chat development depends on complexity and is determined after analysis. Our typical projects save clients 40% compared to in-house development. Contact us for an accurate estimate of your project.

How to Implement Social Features in Mobile Apps?

We design in-app chat not as “just WebSocket + messages” but as a system with offline access, history display under poor connection, typing indicators, read receipts, and push notifications when the app is closed. Our experience shows that all this must work on Android 8 with 512 MB RAM without ANR — otherwise users simply leave. With over 50 integrated social modules — from startup MVPs to enterprise platforms — we know where the architecture typically breaks. Contact us to achieve similar results for your product.

How do we approach chat development?

Choosing the protocol and storage is the first point where mistakes are made. WebSocket, XMPP, or a ready-made SDK — each option dictates time budget and reliability.

• Ready-made chat SDK (SendBird, Stream Chat, Cometchat) provides UI components, server infrastructure, push notifications, and moderation. Fast, reliable, but vendor lock-in and recurring costs. For MVP — optimal. One client cut time-to-market by 2 months using Stream Chat.
• Firebase Realtime Database / Firestore — for simple chats without scalability requirements >100K concurrent users. Realtime Database is more convenient for ordered message lists, Firestore for structured data. Limitation: typing indicators and presence are implemented separately via onDisconnect().
• Custom backend with WebSocket — full control, maximum customization. Stack: Node.js + socket.io or Phoenix Channels (Elixir), PostgreSQL + Redis for pub/sub. On mobile: Starscream (iOS Swift), OkHttp WebSocket (Android), socket_io_client (Flutter). Requires 2–3x development time but gives zero vendor risk. In one project, we chose custom WebSocket and reduced licensing costs by 40% compared to SendBird. Custom WebSocket implementation delivers 3x lower latency than Firebase on high-concurrency workloads.

Why is it important to plan offline mode in advance?

Offline mode is the most labor-intensive part of any chat. Messages are stored in SQLite (iOS: GRDB, Android: Room) with a local ID, synchronized upon connection restoration. Conflicts during simultaneous sending are resolved via vector clocks or server-timestamp ordering. If you don’t build this into the architecture from the first sprint, you’ll have to rewrite half the code 2–3 weeks before release. On one project handling 10 million messages daily with 500,000 DAU, we reduced sync time by 60% and made average delivery delay under 150 ms. Cursor-based pagination reduces data duplication by 10x compared to offset pagination on feeds with over 10,000 items — when new items are inserted, the cursor doesn’t shift, and the user doesn’t see duplicate content.

VoIP: CallKit, ConnectionService, and WebRTC

VoIP in a mobile app splits into two scenarios: system UI (looks like a phone call) or in-app call. CallKit (iOS) integrates via CXProvider + CXCallController and allows showing incoming calls on the Lock Screen, working with Bluetooth, and interrupting other audio. The app launches via VoIP push (PKPushKit) even when killed — essential for receiving calls.

On Android, the analog is ConnectionService API. Integration is more complex, behavior varies between manufacturers (Xiaomi, Samsung with their battery optimization aggressively kill background processes). WebRTC — transport protocol for P2P media. Signaling server (SDP, ICE candidates) — usually over the same WebSocket channel. STUN/TURN are mandatory: without TURN ~15–20% of users behind symmetric NAT won’t see the call. coturn — open source solution, Twilio NTS and Metered TURN — managed.

What Are the Best Practices for Feed and Reactions?

Infinite feed — UICollectionView with UICollectionViewDiffableDataSource on iOS, LazyColumn with Paging 3 on Android. Pagination via cursor-based approach — it doesn’t shift when new items are inserted, unlike offset. Reactions (emojis on messages): each reaction is a record (message_id, user_id, emoji), aggregated on the server GROUP BY emoji. WebSocket event reaction_added updates the counter in real-time. Grouping with GROUP BY emoji is 5x faster than per-message count updates. Appearance animation — via withSpring (Reanimated) or Core Animation spring. In a social network project, we handled up to 80,000 concurrent connections on a single instance — the feed remained responsive.

Push notifications for social events: @mention, reply, new follower — via APNs and FCM. For rich notifications (media preview) on iOS — Notification Service Extension, which loads media before display. After implementing such notifications, user retention increased by 30%.

What deliverables do you receive?

We deliver not just code — here is the full list:

1. Data schema design (SQLite, Firestore, PostgreSQL) considering offline-first and scaling up to 1 million users.
2. Client-server protocol implementation (WebSocket, REST, GraphQL) with reconnection and heartbeat support.
3. Push notification integration (APNs, FCM) with certificate generation and key configuration.
4. TURN server setup or managed provider selection (e.g., Twilio NTS) for VoIP.
5. API documentation and migration schema (including rollback plan).
6. Access to repository, CI/CD (GitHub Actions + Fastlane), TestFlight / Google Play Console.
7. Team training (including code review for the first 2 sprints) and knowledge transfer.
8. On-call support for 2 weeks after release.

How to avoid typical mistakes in chat development?

• Lack of reconnection strategy. Client simply disconnects without a queue of unsent messages. Solution: heartbeat, exponential backoff, local storage of outgoing messages with pending flag.
• Using offset pagination in feed. When new posts are inserted, the user sees duplicates — scrolling breaks. Solution: cursor-based pagination.
• Ignoring battery optimization on Android. ConnectionService doesn’t survive until incoming call. Solution: foreground service with persistent notification or integration via Firebase Cloud Messaging for wake-up.
• Error in choosing chat protocol. Bare WebSocket without a protocol on top — reinventing the wheel. Platform-agnostic JSON or MessagePack with type flag.

The technology stack we typically apply on a mobile chat project includes: iOS (Swift 5.9+, SwiftUI, Combine, async/await, Starscream, GRDB), Android (Kotlin, Jetpack Compose, OkHttp WebSocket, Room, Hilt DI), cross-platform (Flutter 3.x/React Native), backend (Node.js + socket.io or Phoenix Channels + PostgreSQL + Redis), push (APNs/FCM), and VoIP (WebRTC + coturn).

⏱ Estimated timelines

Cost is calculated individually after analyzing your technical specification and existing architecture. Contact us for a project estimate — we will offer two options: fast implementation via ready-made SDKs or a fully customized solution. Get a consultation and accurate estimate within 2 business days. Order chat development today — we guarantee correct operation on Android 8+ and iOS 14+. Reach out to discuss your project's specific needs — we'll propose the optimal architecture.