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Error Handling Implementation

This document describes the standard error handling middleware implemented for the TradeFlow-API project.

Overview

The application now includes comprehensive error handling that ensures:

  • All unexpected errors are caught and handled gracefully
  • API always responds with JSON format, even during errors
  • Errors are logged for debugging purposes
  • Consistent error response format across the application

Implementation Details

1. Global Exception Filter (AllExceptionsFilter)

Location: src/common/filters/all-exceptions.filter.ts

This NestJS exception filter catches all unhandled exceptions and formats them consistently:

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  // Catches all exceptions and returns standardized JSON responses
  // Logs errors for debugging
  // Returns { success: false, message: "Something went wrong" } for 500 errors
}

2. Express Error Handler Middleware

Location: src/common/middleware/errorHandler.ts

Traditional Express-style error handler that can be used with Express middleware:

export function errorHandler(err: Error, req: Request, res: Response, next: NextFunction): void {
  // Logs error to console
  // Returns 500 status with { success: false, message: "Something went wrong" }
}

3. Integration

The global exception filter is registered in src/app.module.ts using the APP_FILTER token, ensuring it catches all errors throughout the application.

Features

  • Automatic Error Logging: All errors are logged with timestamps and stack traces
  • Consistent JSON Responses: All errors return JSON with success: false format
  • Security: Internal error details are not exposed to clients
  • HTTP Status Codes: Appropriate status codes are maintained (500 for internal errors)
  • Request Context: Error responses include the request path for debugging

Testing

A test endpoint has been added to verify error handling:

GET /invoices/test-error

This endpoint deliberately throws an error to demonstrate the global error handling in action.

Error Response Format

All error responses follow this consistent format:

{
  "success": false,
  "message": "Something went wrong",
  "timestamp": "2023-XX-XXTXX:XX:XX.XXXZ",
  "path": "/invoices/test-error"
}

Benefits

  1. Prevents Server Crashes: Unhandled exceptions no longer crash the server
  2. Better User Experience: Clients receive structured error responses
  3. Improved Debugging: Errors are logged with full context
  4. Security: Internal error details are not exposed
  5. Consistency: All endpoints handle errors uniformly

Usage

The error handling is automatically active once the application starts. No additional configuration is required.

For custom error handling in specific controllers, you can still throw HttpException with specific status codes and messages, which will be properly formatted by the global filter.