Mini Wallet

A full-stack digital wallet application that enables users to securely register, authenticate, manage wallet balances, transfer funds, and track transaction history.

Built to explore fintech system fundamentals, secure authentication, transaction processing, database transactions, REST API design, and cloud deployment using modern technologies.

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Features

Authentication

• User Registration
• User Login
• JWT Authentication
• Protected API Routes
• Password Hashing using bcrypt

Wallet Management

• Wallet Creation
• Wallet Balance Tracking
• Wallet Top-Up

Transactions

• Peer-to-Peer Transfers
• Transaction History
• Atomic Database Transactions
• Transfer Validation

Deployment

• Frontend deployed on Vercel
• Backend deployed on Render
• PostgreSQL hosted on Neon

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Application Preview

Dashboard Overview

Displays wallet balance, account information, and current wallet status.

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Wallet Operations

Users can top up their wallet balance and transfer funds to other registered users.

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Transaction History

Tracks wallet activity including transfers and top-ups with transaction status information.

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Tech Stack

Category	Technology
Frontend	Next.js, React, TypeScript, Tailwind CSS
Backend	Go, Gin
Database	PostgreSQL, GORM
Authentication	JWT, bcrypt
Hosting	Vercel, Render, Neon

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System Architecture

Architecture Overview

The application follows a monolithic architecture consisting of a Next.js frontend, a Go backend built with Gin, and a PostgreSQL database hosted on Neon.

Flow

1. Users interact with the Next.js frontend.
2. The frontend communicates with the backend using REST APIs.
3. JWT middleware protects secured endpoints.
4. Business logic is handled by Go services and route handlers.
5. Data is stored in PostgreSQL through GORM.
6. Services are deployed on Vercel, Render, and Neon.

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Authentication Flow

Registration Process

1. User submits registration details.
2. Password is hashed using bcrypt.
3. User information is stored in PostgreSQL.
4. A wallet is automatically created.

Login Process

1. User submits credentials.
2. Credentials are validated.
3. JWT token is generated.
4. Token is returned to the client.
5. Protected endpoints require the token.

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Transfer Processing

Transfer Validation

Before executing a transfer, the system verifies:

• User authentication
• Recipient existence
• Valid transfer amount
• Sufficient sender balance

Atomic Transactions

Transfers are executed inside a database transaction to ensure consistency.

The system:

1. Debits the sender wallet.
2. Credits the receiver wallet.
3. Creates a transaction record.
4. Commits all changes together.

This prevents partial updates and maintains financial consistency.

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Database Schema

Core Entities

Users

Stores account information and authentication credentials.

Wallets

Maintains wallet balances linked to individual users.

Transactions

Stores transfer and wallet activity records.

Relationships

• One User owns one Wallet.
• One Wallet can participate in many Transactions.
• Transactions track both sender and receiver wallets.

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Deployment Architecture

Infrastructure

Component	Provider
Frontend	Vercel
Backend	Render
Database	Neon PostgreSQL

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Project Structure

.
├── cmd/
│   └── server/
│       └── main.go
│
├── config/
│   └── config.go
│
├── internal/
│   ├── constants/
│   │   └── transaction.go
│   │
│   ├── database/
│   │   └── db.go
│   │
│   ├── handlers/
│   │   ├── auth.go
│   │   ├── health.go
│   │   ├── transaction.go
│   │   ├── user.go
│   │   └── wallet.go
│   │
│   ├── middleware/
│   │   └── jwt.go
│   │
│   ├── models/
│   │
│   ├── routes/
│   │   └── routes.go
│   │
│   └── utils/
│
├── go.mod
├── go.sum
└── README.md

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API Endpoints

Authentication

Method	Endpoint
POST	/register
POST	/login

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User

Method	Endpoint
GET	/me

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Wallet

Method	Endpoint
GET	/wallet
POST	/wallet/topup
POST	/wallet/transfer

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Transactions

Method	Endpoint
GET	/transactions

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Health

Method	Endpoint
GET	/health

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Local Development Setup

Prerequisites

• Go 1.24+
• PostgreSQL
• Node.js
• npm

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Clone Repository

git clone <repository-url>

cd mini-wallet

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Install Dependencies

go mod tidy

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Configure Environment Variables

Create a .env file:

DB_HOST=
DB_PORT=
DB_USER=
DB_PASSWORD=
DB_NAME=

JWT_SECRET=

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Run Backend

go run cmd/server/main.go

Server starts on:

http://localhost:8080

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Challenges & Learnings

During development, several real-world engineering challenges were addressed:

• Designing secure JWT authentication workflows
• Implementing password hashing with bcrypt
• Managing wallet balances safely
• Executing atomic money transfers using database transactions
• Structuring a scalable Go backend
• Connecting cloud-hosted PostgreSQL databases
• Deploying services across Render, Neon, and Vercel
• Managing environment variables across environments

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Future Improvements

• Refresh Tokens
• Email Verification
• Rate Limiting
• Two-Factor Authentication
• Pagination
• Transaction Export (CSV/PDF)
• Audit Logs
• Admin Dashboard
• Real-Time Notifications
• Multi-Currency Support

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Author

Farhan

B.Tech Computer Science Engineering

Built as a portfolio project to explore backend engineering, fintech systems, secure authentication, database transactions, and cloud-native deployment.