[HIGH] Standardize error handling patterns across all packages

[claranceliberi]

Problem Statement

Error handling throughout the codebase is inconsistent, with different patterns used across packages. Some errors are logged but not properly handled, others are ignored, and there's no standardized approach for error classification, recovery, or user feedback.

Impact Assessment

• Severity: High
• Impact: Difficult debugging, inconsistent behavior, poor error recovery
• Affected Components: All packages, error propagation, user experience
• Reliability Risk: Medium - Inconsistent error handling affects system stability
• Maintainability: High - Difficult to debug and maintain

Technical Details

Inconsistent Error Handling Patterns

1. Pipeline Processing:

   • File: pkg/pipeline/processor.go
   • Lines: 115-122 - Continues execution after pipeline failures
   • Issue: Should implement circuit breaker pattern

2. Configuration Loading:

   • File: pkg/config/config.go
   • Lines: 125-163 - Partial failure handling
   • Issue: Inconsistent error propagation

3. HTTP Client:

   • File: pkg/clients/tsclient/client.go
   • Lines: Multiple locations - Mixed error handling styles
   • Issue: No standardized retry or recovery logic

Current Problems

// Inconsistent error handling examples:

// pkg/pipeline/processor.go:115-122
if err := pipelineProcessor.Process(ctx); err \!= nil {
    logger.Error("Failed to process metrics pipeline", zap.Error(err))
    // Continues execution - should implement circuit breaker
}

// pkg/config/config.go:147
log.Printf("Error getting VM ID: %v", err)  // Printf instead of structured logging
return ""  // Silent failure

// pkg/clients/tsclient/client.go - Multiple patterns
return nil, err  // Direct propagation
return nil, fmt.Errorf("failed to X: %w", err)  // Wrapped error
logger.Error(...); return err  // Log and return

Acceptance Criteria

• Define standard error types and classifications
• Implement consistent error wrapping and context
• Add structured error logging with correlation IDs
• Implement retry mechanisms with exponential backoff
• Add circuit breaker patterns for external dependencies
• Create error recovery strategies
• Add error metrics and monitoring
• Implement user-friendly error messages

Implementation Guidelines

1. Error Type System:

type ErrorType string

const (
    ErrorTypeValidation    ErrorType = "validation"
    ErrorTypeConfiguration ErrorType = "configuration"
    ErrorTypeNetwork       ErrorType = "network"
    ErrorTypeStorage       ErrorType = "storage"
    ErrorTypeAuth          ErrorType = "authentication"
    ErrorTypeInternal      ErrorType = "internal"
)

type AppError struct {
    Type        ErrorType         `json:"type"`
    Code        string           `json:"code"`
    Message     string           `json:"message"`
    Details     map[string]interface{} `json:"details,omitempty"`
    Cause       error            `json:"-"`
    Timestamp   time.Time        `json:"timestamp"`
    RequestID   string           `json:"request_id,omitempty"`
    Retryable   bool             `json:"retryable"`
}

2. Error Handling Middleware:

type ErrorHandler interface {
    Handle(ctx context.Context, err error) error
    ShouldRetry(err error) bool
    GetRetryDelay(attempt int) time.Duration
}

type CircuitBreaker interface {
    Execute(ctx context.Context, fn func() error) error
    State() CircuitState
    Reset()
}

3. Standard Error Patterns:

// Validation errors
func ValidateConfig(cfg *Config) error {
    if cfg.Endpoint == "" {
        return NewAppError(ErrorTypeValidation, "INVALID_ENDPOINT", 
            "endpoint cannot be empty", nil, false)
    }
    return nil
}

// Network errors with retry
func (c *Client) sendWithRetry(ctx context.Context, req *http.Request) error {
    return c.retryHandler.Execute(ctx, func() error {
        return c.send(ctx, req)
    })
}

Error Classification System

Error Categories

1. Transient Errors: Network timeouts, temporary service unavailability
2. Permanent Errors: Configuration issues, authentication failures
3. Validation Errors: Input validation, format errors
4. System Errors: Out of memory, disk full, permission denied

Retry Strategies

• Exponential Backoff: For network and service errors
• Circuit Breaker: For failing external services
• Immediate Retry: For transient local errors
• No Retry: For validation and authentication errors

Standard Error Responses

// User-facing error messages
type ErrorResponse struct {
    Error     string                 `json:"error"`
    Code      string                 `json:"code"`
    Message   string                 `json:"message"`
    Details   map[string]interface{} `json:"details,omitempty"`
    RequestID string                 `json:"request_id,omitempty"`
}

// Internal error context
type ErrorContext struct {
    Component   string            `json:"component"`
    Operation   string            `json:"operation"`
    UserID      string            `json:"user_id,omitempty"`
    RequestID   string            `json:"request_id,omitempty"`
    Metadata    map[string]string `json:"metadata,omitempty"`
}

Testing Requirements

• Unit tests for error handling scenarios
• Integration tests for error propagation
• Chaos engineering tests for failure scenarios
• Error rate monitoring and alerting
• Recovery time measurement

Implementation Phases

1. Phase 1: Define error types and standards
2. Phase 2: Implement error handling middleware
3. Phase 3: Update all packages to use standards
4. Phase 4: Add monitoring and observability

Related Issues

• Enables: Better monitoring and alerting ([TESTING] Add comprehensive security and integration test coverage #12)
• Depends on: Logging security improvements ([HIGH] Fix information leakage in logging and debug output #6)
• Blocks: Production readiness
• Related to: Authentication framework error handling ([CRITICAL] Implement authentication and authorization framework #3)

Definition of Done

• Standard error types defined and documented
• All packages use consistent error handling
• Retry mechanisms implemented where appropriate
• Circuit breaker patterns for external dependencies
• Error monitoring and metrics in place
• Documentation for error handling guidelines
• Tests covering error scenarios