Error Handling

Understanding and handling API error responses

The PartsSource APIs use standard HTTP status codes and return detailed error information following RFC 7807 (Problem Details for HTTP APIs).

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HTTP Status Codes

Success Codes (2xx)

Code	Meaning	Usage
200 OK	Request succeeded	GET, POST search, successful mutations
201 Created	Resource created	POST that creates resources
204 No Content	Success with no body	DELETE operations

Client Error Codes (4xx)

Code	Meaning	Common Causes
400 Bad Request	Invalid request	Validation errors, malformed JSON
401 Unauthorized	Authentication required	Missing/invalid/expired token
403 Forbidden	Access denied	Valid token but insufficient permissions
404 Not Found	Resource not found	Invalid ID, resource doesn't exist
409 Conflict	State conflict	Idempotency conflict, concurrent update
422 Unprocessable	Semantic error	Valid format but business rule violation
429 Too Many Requests	Rate limited	Exceeded request quota

Server Error Codes (5xx)

Code	Meaning	Common Causes
500 Internal Server Error	Unexpected error	Bug, unhandled exception
502 Bad Gateway	Upstream failure	External service unavailable
503 Service Unavailable	Temporary outage	Maintenance, overload
504 Gateway Timeout	Upstream timeout	External service slow

---

Error Response Formats

The API returns errors in different formats depending on where the error occurs.

Standard Error Response

For errors handled at the controller level:

{
  "success": false,
  "errors": [
    "Customer not found",
    "Additional error message if applicable"
  ],
  "correlationId": "0HN7QJKV3QJ8K:00000001",
  "timestamp": "2025-10-21T14:30:00.000Z"
}

Field	Type	Description
success	boolean	Always false for errors
errors	string[]	Array of error messages
correlationId	string	Unique request identifier for debugging
timestamp	string	ISO 8601 timestamp

Problem Details Response (RFC 7807)

For errors handled at the exception/middleware level:

{
  "type": "https://tools.ietf.org/html/rfc7231#section-6.5.4",
  "title": "Resource Not Found",
  "status": 404,
  "detail": "Customer with ID '12345' was not found.",
  "correlationId": "0HN7QJKV3QJ8K:00000001",
  "timestamp": "2025-10-21T14:30:00.000Z",
  "service": "CustomerApi"
}

Field	Type	Description
type	string	URI reference identifying the error type
title	string	Short, human-readable summary
status	integer	HTTP status code
detail	string	Human-readable explanation
correlationId	string	Unique request identifier
timestamp	string	ISO 8601 timestamp
service	string	Which API returned the error

Validation Error Response

For request validation failures (400 Bad Request):

{
  "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
  "title": "Validation Failed",
  "status": 400,
  "detail": "One or more validation errors occurred.",
  "correlationId": "0HN7QJKV3QJ8K:00000001",
  "errors": {
    "email": ["Email address is required"],
    "firstName": ["First name must not exceed 50 characters"],
    "quoteItems": ["At least one item is required"]
  }
}

The errors object contains field-level validation messages:

• Keys are field names (using camelCase)

• Values are arrays of error messages for that field

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Common Error Scenarios

Authentication Errors (401)

{
  "type": "https://tools.ietf.org/html/rfc7235#section-3.1",
  "title": "Unauthorized",
  "status": 401,
  "detail": "Authentication is required to access this resource.",
  "correlationId": "0HN7QJKV3QJ8K:00000001"
}

Causes:

• Missing Authorization header

• Invalid or malformed token

• Expired token (tokens expire after 1 hour)

• Token signature validation failed

Solution: Obtain a new access token and retry.

Forbidden Errors (403)

{
  "type": "https://tools.ietf.org/html/rfc7231#section-6.5.3",
  "title": "Forbidden",
  "status": 403,
  "detail": "You do not have permission to access this resource.",
  "correlationId": "0HN7QJKV3QJ8K:00000001"
}

Causes:

• Attempting to access another tenant's data (CustomerApi)

• User doesn't have access to the requested facility

Solution: Verify your client credentials have the required permissions.

Not Found Errors (404)

{
  "success": false,
  "errors": ["Customer not found"],
  "correlationId": "0HN7QJKV3QJ8K:00000001",
  "timestamp": "2025-10-21T14:30:00.000Z"
}

Causes:

• Resource ID doesn't exist

• Resource was deleted

• Typo in the resource identifier

Idempotency Conflict (409)

{
  "error": "Request body does not match the original request for this idempotency key."
}

Causes:

• Reusing an idempotency key with different request body

• Request is still processing from a previous attempt

Solution: Wait and retry, or use a new idempotency key for a different operation.

---

Error Handling Best Practices

1. Always Check the success Field

var response = await httpClient.PostAsync("/api/orders", content);
var result = await response.Content.ReadFromJsonAsync<ApiResponse<Order>>();

if (!result.Success)
{
    foreach (var error in result.Errors)
    {
        Console.WriteLine($"Error: {error}");
    }
    return;
}

// Process result.Data

2. Log the Correlation ID

Always log the correlationId for debugging with support:

if (!response.IsSuccessStatusCode)
{
    var error = await response.Content.ReadFromJsonAsync<ProblemDetails>();
    _logger.LogError(
        "API error: {Title}. CorrelationId: {CorrelationId}",
        error.Title,
        error.CorrelationId);
}

3. Handle Validation Errors Gracefully

Parse field-level errors for user-friendly messages:

if (response.StatusCode == HttpStatusCode.BadRequest)
{
    var validation = await response.Content.ReadFromJsonAsync<ValidationProblemDetails>();

    foreach (var (field, messages) in validation.Errors)
    {
        foreach (var message in messages)
        {
            Console.WriteLine($"{field}: {message}");
        }
    }
}

4. Implement Retry Logic for 5xx Errors

Use exponential backoff for server errors:

public async Task<T> ExecuteWithRetry<T>(Func<Task<HttpResponseMessage>> action, int maxRetries = 3)
{
    for (int attempt = 1; attempt <= maxRetries; attempt++)
    {
        var response = await action();

        if (response.IsSuccessStatusCode)
        {
            return await response.Content.ReadFromJsonAsync<T>();
        }

        // Don't retry client errors (4xx) - they won't succeed without changes
        if ((int)response.StatusCode >= 400 && (int)response.StatusCode < 500)
        {
            throw new ApiException(await response.Content.ReadAsStringAsync());
        }

        // Retry server errors (5xx) with exponential backoff
        if (attempt < maxRetries)
        {
            var delay = TimeSpan.FromSeconds(Math.Pow(2, attempt));
            await Task.Delay(delay);
        }
    }

    throw new MaxRetriesExceededException();
}

5. Don't Retry 4xx Errors Without Changes

Client errors (4xx) indicate a problem with your request. Retrying without modification won't help.

Error	Action
400	Fix validation errors, then retry
401	Get new token, then retry
403	Check permissions - may not be retryable
404	Verify resource exists
409	Wait (if processing) or use new idempotency key
429	Wait for rate limit reset

---

Code Examples

TypeScript

interface ApiError {
  success: false;
  errors: string[];
  correlationId: string;
  timestamp: string;
}

interface ValidationError {
  type: string;
  title: string;
  status: number;
  detail: string;
  errors: Record<string, string[]>;
  correlationId: string;
}

async function handleApiResponse<T>(response: Response): Promise<T> {
  if (response.ok) {
    const data = await response.json();
    return data.data as T;
  }

  if (response.status === 400) {
    const validation: ValidationError = await response.json();
    console.error('Validation errors:', validation.errors);
    throw new ValidationException(validation);
  }

  const error: ApiError = await response.json();
  console.error(`API Error [${error.correlationId}]:`, error.errors);
  throw new ApiException(error);
}

Python

import requests
from typing import TypeVar, Generic

T = TypeVar('T')

def handle_response(response: requests.Response) -> dict:
    if response.ok:
        data = response.json()
        return data.get('data')

    error = response.json()
    correlation_id = error.get('correlationId', 'unknown')

    if response.status_code == 400:
        # Validation error
        errors = error.get('errors', {})
        for field, messages in errors.items():
            for msg in messages:
                print(f"Validation error - {field}: {msg}")
        raise ValidationError(errors, correlation_id)

    if response.status_code == 401:
        raise AuthenticationError("Token expired or invalid", correlation_id)

    if response.status_code >= 500:
        raise ServerError(f"Server error: {error.get('title')}", correlation_id)

    raise ApiError(error.get('errors', ['Unknown error']), correlation_id)

---

Troubleshooting

"Authentication is required"

1. Verify your Authorization header is present

2. Check token format: Bearer <token> (with space after "Bearer")

3. Verify token hasn't expired (1 hour lifetime)

4. Request a new token if expired

"Validation Failed" with empty errors

1. Check Content-Type header is application/json

2. Verify JSON body is properly formatted

3. Check for encoding issues in the request body

Receiving HTML instead of JSON

1. Verify the URL path is correct

2. Check you're using HTTPS (not HTTP)

3. Verify the base URL is correct for your environment

Getting 5xx errors consistently

1. Note the correlationId from the response

2. Contact support with the correlation ID

3. Check the health endpoints for service status