API Error Handling

Implement comprehensive, standardized error response system for PHP REST APIs with consistent JSON envelopes, specific error message extraction, and SweetAlert2 integration.

Core Principles:

•Consistent JSON envelope across all endpoints
•Specific error messages extracted from all exception types
•Appropriate HTTP status codes for all error categories
•Machine-readable error codes for programmatic handling
•Human-readable messages for SweetAlert2 display
•Secure error handling (no stack traces in production)
•Comprehensive logging with request IDs

See subdirectories for:

•references/ - Complete PHP classes (ApiResponse, ExceptionHandler, Exceptions)
•examples/ - Full endpoint implementation, frontend client

Response Envelope Standard

Success:

json

{
  "success": true,
  "data": { /* payload */ },
  "message": "Optional success message",
  "meta": {
    "timestamp": "2026-01-24T10:30:00Z",
    "request_id": "req_abc123"
  }
}

Error:

json

{
  "success": false,
  "message": "Human-readable error for SweetAlert2",
  "error": {
    "code": "ERROR_CODE",
    "type": "validation_error",
    "details": { /* field-specific errors */ }
  },
  "meta": {
    "timestamp": "2026-01-24T10:30:00Z",
    "request_id": "req_abc123"
  }
}

HTTP Status Codes

Status	Error Type	Use Case	Error Code Examples
400	Bad Request	Malformed JSON, missing params	INVALID_JSON, MISSING_PARAMETER
401	Unauthorized	Missing/invalid auth token	TOKEN_MISSING, TOKEN_EXPIRED
403	Forbidden	Valid auth but no permission	PERMISSION_DENIED, ACCESS_FORBIDDEN
404	Not Found	Resource doesn't exist	RESOURCE_NOT_FOUND, INVOICE_NOT_FOUND
405	Method Not Allowed	Wrong HTTP method	METHOD_NOT_ALLOWED
409	Conflict	Business rule violation	ALREADY_EXISTS, OVERPAYMENT
422	Unprocessable Entity	Validation errors	VALIDATION_FAILED, INVALID_EMAIL
429	Too Many Requests	Rate limiting	RATE_LIMIT_EXCEEDED
500	Internal Server Error	Unexpected errors	INTERNAL_ERROR, DATABASE_ERROR
503	Service Unavailable	Maintenance/overload	SERVICE_UNAVAILABLE, DEADLOCK

ApiResponse Helper (Quick Reference)

See references/ApiResponse.php for complete implementation

php

// Success responses
ApiResponse::success($data, $message, $status);
ApiResponse::created($data, $message);

// Error responses
ApiResponse::error($message, $code, $status, $type, $details);
ApiResponse::validationError($errors, $message);
ApiResponse::notFound($resource, $identifier);
ApiResponse::unauthorized($message);
ApiResponse::forbidden($permission);
ApiResponse::conflict($message, $code);
ApiResponse::methodNotAllowed($allowedMethods);
ApiResponse::rateLimited($retryAfter);
ApiResponse::serverError($message);
ApiResponse::serviceUnavailable($message);

Exception Handler (Quick Reference)

See references/ExceptionHandler.php for complete implementation

Key Features:

•Extracts specific messages from PDOException
•Parses SQLSTATE 45000 (user-defined exceptions from triggers)
•Extracts constraint violation messages
•Handles deadlocks gracefully
•Logs all errors with request ID
•Hides stack traces in production

PDOException Parsing:

php

// SQLSTATE 45000: Business rule from trigger
// "SQLSTATE[45000]: <<1>>: 1644 Overpayment not allowed"
// Extracted: "Overpayment not allowed"

// SQLSTATE 23000: Duplicate entry
// "Duplicate entry 'john@example.com' for key 'uk_email'"
// Extracted: "A record with this Email already exists: 'john@example.com'"

// SQLSTATE 23000: Foreign key violation
// "Cannot delete or update a parent row..."
// Extracted: "Referenced Customer does not exist or cannot be deleted"

Custom Exception Classes

See references/CustomExceptions.php for all classes

php

// Validation (422)
throw new ValidationException([
    'email' => 'Invalid email format',
    'phone' => 'Phone number required'
], 'Validation failed');

// Authentication (401)
throw new AuthenticationException('Token expired', 'expired');

// Authorization (403)
throw new AuthorizationException('MANAGE_USERS');

// Not Found (404)
throw new NotFoundException('Invoice', 'INV-123');

// Conflict (409)
throw new ConflictException('Already voided', 'ALREADY_VOIDED');

// Rate Limit (429)
throw new RateLimitException(60);

API Bootstrap Pattern

See references/bootstrap.php for complete file

Include at top of all API endpoints:

php

require_once __DIR__ . '/bootstrap.php';

// Helper functions available:
require_method(['POST', 'PUT']);
$data = read_json_body();
validate_required($data, ['customer_id', 'amount']);
$db = get_db();
$token = bearer_token();
require_auth();
require_permission('MANAGE_INVOICES');
handle_request(function() { /* endpoint logic */ });

Endpoint Implementation Pattern

See examples/InvoicesEndpoint.php for complete example

php

require_once __DIR__ . '/../bootstrap.php';
use App\Http\ApiResponse;
use App\Http\Exceptions\{NotFoundException, ValidationException};

require_auth();
handle_request(function() {
    $method = $_SERVER['REQUEST_METHOD'];
    match ($method) {
        'POST' => handlePost(),
        default => ApiResponse::methodNotAllowed('POST')
    };
});

function handlePost(): void {
    $data = read_json_body();
    validate_required($data, ['customer_id', 'items']);

    if (empty($data['items'])) {
        throw new ValidationException(['items' => 'Required']);
    }

    // Business logic...
    ApiResponse::created(['id' => $id], 'Created successfully');
}

Frontend Integration

See examples/ApiClient.js for complete implementation

javascript

const api = new ApiClient('./api');

// GET - Errors automatically shown via SweetAlert2
const response = await api.get('invoices.php', { status: 'pending' });
if (response) renderInvoices(response.data);

// POST - Validation errors highlight form fields
showLoading('Creating...');
const result = await api.post('invoices.php', formData);
hideLoading();
if (result) showSuccess('Created successfully');

// DELETE - With confirmation
const { value: reason } = await Swal.fire({
    title: 'Void?',
    input: 'textarea',
    showCancelButton: true
});
if (reason) {
    const res = await api.delete(`invoices.php?id=${id}`, { reason });
    if (res) showSuccess('Voided');
}

// Helpers: showSuccess/Error/Warning/Info, showConfirm, showLoading, hideLoading

Error Message Extraction

SQLSTATE 45000 (Trigger):

sql

SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Overpayment not allowed';
-- Extracted: "Overpayment not allowed" → Code: OVERPAYMENT_NOT_ALLOWED

SQLSTATE 23000 (Duplicate):

code

"Duplicate entry 'john@example.com' for key 'uk_email'"
-- Extracted: "A record with this Email already exists: 'john@example.com'"

SQLSTATE 23000 (Foreign Key):

code

"Cannot delete or update a parent row..."
-- Extracted: "Referenced Customer does not exist or cannot be deleted"

Deadlock:

code

"Deadlock found when trying to get lock..."
-- Extracted: "Database conflict. Please try again." → HTTP 503

Validation Pattern

Backend:

php

$errors = [];
if (empty($data['email'])) $errors['email'] = 'Email required';
elseif (!filter_var($data['email'], FILTER_VALIDATE_EMAIL))
    $errors['email'] = 'Invalid email';

if ($errors) ApiResponse::validationError($errors);

Frontend automatically:

•SweetAlert2 with formatted error list
•Highlights fields with .is-invalid
•Adds .invalid-feedback elements

Business Rule Pattern

php

$stmt = $db->prepare("SELECT status FROM invoices WHERE id = ? FOR UPDATE");
$stmt->execute([$id]);
$invoice = $stmt->fetch();

if (!$invoice) throw new NotFoundException('Invoice', $id);
if ($invoice['status'] === 'voided')
    throw new ConflictException('Already voided', 'ALREADY_VOIDED');
if ($invoice['status'] === 'paid')
    throw new ConflictException('Cannot void paid invoice', 'INVOICE_PAID');

Logging Pattern

All errors logged with context:

code

[req_abc123] PDOException: SQLSTATE[45000]: Overpayment not allowed in /api/payments.php:45
Context: {"user_id":123,"franchise_id":5,"url":"/api/payments.php","method":"POST"}

Implementation Checklist

Backend:

Frontend:

• All API calls use centralized ApiClient
• Errors displayed via SweetAlert2 only (no native alert/confirm)
• Validation errors highlight form fields
• Network errors handled gracefully
• Loading states shown during requests
• Error codes displayed in footer
• Offline state detected and handled
• Request IDs logged for debugging

Database:

• Triggers use SQLSTATE 45000 for business rules
• Clear, user-friendly error messages in triggers
• Constraints have descriptive names (uk_email_franchise)
• Foreign key errors give context

Quick Error Reference

php

// 400 - Bad Request
ApiResponse::error('Invalid request', 'BAD_REQUEST', 400);

// 401 - Unauthorized
ApiResponse::unauthorized('Session expired');

// 403 - Forbidden
ApiResponse::forbidden('MANAGE_USERS');

// 404 - Not Found
ApiResponse::notFound('Invoice', 'INV-123');

// 409 - Conflict
ApiResponse::conflict('Already voided', 'ALREADY_VOIDED');

// 422 - Validation
ApiResponse::validationError(['email' => 'Invalid format']);

// 500 - Server Error
ApiResponse::serverError('Unexpected error occurred');

Security Considerations

Production:

•Never expose stack traces
•Sanitize database error messages
•Log full errors server-side only
•Generic messages for unexpected errors

Development:

•Set APP_DEBUG=true for detailed errors
•Stack traces in logs
•Actual error messages displayed

Sensitive Data:

•Never include passwords in logs
•Sanitize SQL queries in error messages
•Remove file paths from production errors

Summary

Implementation:

•Include bootstrap.php at top of all endpoints
•Use ApiResponse helper for all responses
•Throw custom exceptions for specific errors
•Let ExceptionHandler convert to JSON
•Use ApiClient class on frontend
•Display all errors via SweetAlert2

Key Files:

•references/ApiResponse.php - Response helper
•references/ExceptionHandler.php - Exception converter
•references/CustomExceptions.php - Exception classes
•references/bootstrap.php - API setup
•examples/InvoicesEndpoint.php - Complete endpoint
•examples/ApiClient.js - Frontend client

Benefits:

•Consistent error format across all endpoints
•Specific messages from database exceptions
•Beautiful error display with SweetAlert2
•Easy debugging with request IDs
•Secure (no sensitive data exposure)
•Developer-friendly (clear patterns)

Remember: All error messages must be suitable for direct display in SweetAlert2. Write them for end users, not developers.