wehub-resource-sync
122 lines
4.0 KiB
Markdown
122 lines
4.0 KiB
Markdown
---
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name: error-handling-patterns
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description: Master error handling patterns across languages including exceptions, Result types, error propagation, and graceful degradation to build resilient applications. Use when implementing error handling, designing APIs, or improving application reliability.
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---
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# Error Handling Patterns
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Build resilient applications with robust error handling strategies that gracefully handle failures and provide excellent debugging experiences.
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## When to Use This Skill
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- Implementing error handling in new features
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- Designing error-resilient APIs
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- Debugging production issues
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- Improving application reliability
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- Creating better error messages for users and developers
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- Implementing retry and circuit breaker patterns
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- Handling async/concurrent errors
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- Building fault-tolerant distributed systems
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## Core Concepts
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### 1. Error Handling Philosophies
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**Exceptions vs Result Types:**
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- **Exceptions**: Traditional try-catch, disrupts control flow
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- **Result Types**: Explicit success/failure, functional approach
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- **Error Codes**: C-style, requires discipline
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- **Option/Maybe Types**: For nullable values
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**When to Use Each:**
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- Exceptions: Unexpected errors, exceptional conditions
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- Result Types: Expected errors, validation failures
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- Panics/Crashes: Unrecoverable errors, programming bugs
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### 2. Error Categories
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**Recoverable Errors:**
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- Network timeouts
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- Missing files
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- Invalid user input
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- API rate limits
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**Unrecoverable Errors:**
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- Out of memory
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- Stack overflow
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- Programming bugs (null pointer, etc.)
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## Detailed patterns and worked examples
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Detailed pattern documentation lives in `references/details.md`. Read that file when the navigation tier above is insufficient.
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## Best Practices
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1. **Fail Fast**: Validate input early, fail quickly
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2. **Preserve Context**: Include stack traces, metadata, timestamps
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3. **Meaningful Messages**: Explain what happened and how to fix it
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4. **Log Appropriately**: Error = log, expected failure = don't spam logs
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5. **Handle at Right Level**: Catch where you can meaningfully handle
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6. **Clean Up Resources**: Use try-finally, context managers, defer
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7. **Don't Swallow Errors**: Log or re-throw, don't silently ignore
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8. **Type-Safe Errors**: Use typed errors when possible
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```python
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# Good error handling example
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def process_order(order_id: str) -> Order:
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"""Process order with comprehensive error handling."""
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try:
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# Validate input
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if not order_id:
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raise ValidationError("Order ID is required")
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# Fetch order
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order = db.get_order(order_id)
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if not order:
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raise NotFoundError("Order", order_id)
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# Process payment
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try:
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payment_result = payment_service.charge(order.total)
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except PaymentServiceError as e:
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# Log and wrap external service error
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logger.error(f"Payment failed for order {order_id}: {e}")
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raise ExternalServiceError(
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f"Payment processing failed",
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service="payment_service",
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details={"order_id": order_id, "amount": order.total}
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) from e
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# Update order
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order.status = "completed"
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order.payment_id = payment_result.id
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db.save(order)
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return order
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except ApplicationError:
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# Re-raise known application errors
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raise
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except Exception as e:
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# Log unexpected errors
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logger.exception(f"Unexpected error processing order {order_id}")
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raise ApplicationError(
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"Order processing failed",
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code="INTERNAL_ERROR"
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) from e
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```
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## Common Pitfalls
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- **Catching Too Broadly**: `except Exception` hides bugs
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- **Empty Catch Blocks**: Silently swallowing errors
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- **Logging and Re-throwing**: Creates duplicate log entries
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- **Not Cleaning Up**: Forgetting to close files, connections
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- **Poor Error Messages**: "Error occurred" is not helpful
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- **Returning Error Codes**: Use exceptions or Result types
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- **Ignoring Async Errors**: Unhandled promise rejections
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