Light Chat Application System Design

Messaging applications are one of the most widely used software solutions today. Whether it is WhatsApp, Slack, or Microsoft Teams, the expectation is always the same: real-time, reliable, and efficient communication.

This article outlines the design considerations, component architecture, APIs, and optimization strategies needed to build a lightweight chat application that performs well across devices and networks.

General Requirements

A chat application should support the following features:

Sending and receiving messages in real time
Attaching media such as:
- Video
- Audio
- Pictures
- Location
Contact list management
Sharing messages with other users

Functional Requirements

Performance and device compatibility are critical. The application must satisfy:

Low latency (40–60 ms) for message delivery
Reliable operation in low bandwidth networks
Battery efficiency for extended background usage
Compatibility across a wide range of devices

Component Architecture

The system can be divided into the following components:

Frontend (Mobile/Web UI) – Renders chats, contacts, and media
Backend Services – Handles authentication, message delivery, and notifications
Database – Stores user information, contacts, and messages
Real-time Communication Layer – Ensures instant synchronization between clients
CDN/Media Layer – Optimizes and serves large file attachments

Communication Protocols

Real-time message delivery is a core feature. Below are the most common protocol options:

Long Polling

Advantages: Simple implementation, works with HTTP
Disadvantages: Higher latency, connection timeouts, traffic overhead

WebSockets

Advantages: Full-duplex communication, very fast
Disadvantages: Harder to load balance, potential firewall issues

Server-Sent Events (SSE)

Advantages: Built on HTTP/2, resource efficient, easy to scale
Disadvantages: Unidirectional, only supports text data

Recommendation: WebSockets are best suited for chat message delivery, while SSE can be used for lightweight event notifications.

API Design

Example APIs for a chat application:

// Subscribe to new messages
subscribeForMessages(api_key: string, user_id: string)

// Get contact list
getContacts(api_key: string, user_id: string)

// Attach media to a message
attachMedia(api_key: string, user_id: string, message_id: string, binary_data: Blob)

// Send a message
sendMessage(api_key: string, user_id: string, message: string)

Data Entities

type Contact = {
  id: string
  name: string
}

type Message = {
  id: string
  content: string
  attachments?: Attachment[]
  authorID: string
  receiverID: string
}

type Attachment = {
  id: string
  message_id: string
  type: 'link' | 'video' | 'audio' | 'image' | 'location'
  content: URL
}

Entities Call Example

// Get contacts for a user
const contacts = getContacts(api_key, user_id)

// Send a message
sendMessage(api_key, user_id, "Hello, how are you?")

// Attach media to a message
attachMedia(api_key, user_id, message_id, binaryFile)

// Subscribe for real-time messages
subscribeForMessages(api_key, user_id)

Optimization Strategies

Network Performance

Use GZIP or Brotli compression for text
Optimize images with WebP/PNG
Bundle splitting with HTTP/2 for faster loading
Lazy load non-critical resources
Serve images and media via CDN

Rendering Performance

Inline critical CSS, show skeleton screens during loading
Defer non-critical scripts
Avoid frequent DOM reflows and use CSS animations where possible

JavaScript Performance

Minify and bundle code efficiently
Use asynchronous and non-blocking operations
Minimize polyfill usage to reduce bundle size

Accessibility

Accessibility ensures inclusivity for all users. Key practices include:

Use rem units for scalable typography
Provide keyboard shortcuts for navigation
Offer multiple color schemes including color-blind friendly options
Announce live updates with aria-live attributes
Ensure images have descriptive alt attributes
Use semantic HTML5 for better screen reader compatibility

Conclusion

Designing a light chat application requires careful consideration of both functionality and performance. By focusing on:

Selecting the right real-time protocol
Designing clear APIs
Defining scalable data entities
Applying network and rendering optimizations
Enforcing accessibility standards

you can deliver a robust messaging experience that is fast, efficient, and user-friendly.

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