Error Handling

Properly handling errors in JSON operations.

Error Types

Standard Errors

var (
    ErrPathNotFound       = errors.New("path not found")
    ErrInvalidPath        = errors.New("invalid path format")
    ErrTypeMismatch       = errors.New("type mismatch")
    ErrInvalidJSON        = errors.New("invalid JSON format")
    ErrDepthLimit         = errors.New("depth limit exceeded")
    ErrSizeLimit          = errors.New("size limit exceeded")
    ErrSecurityViolation  = errors.New("security violation detected")
    ErrProcessorClosed    = errors.New("processor is closed")
    ErrConcurrencyLimit   = errors.New("concurrency limit exceeded")
    ErrUnsupportedPath    = errors.New("unsupported path operation")
    ErrOperationTimeout   = errors.New("operation timeout")           // Deprecated
    ErrResourceExhausted  = errors.New("system resources exhausted")  // Deprecated
)

Error Checking

val, err := json.Get(data, "user.name")
if err != nil {
    if errors.Is(err, json.ErrPathNotFound) {
        // Path not found
        return defaultName
    }
    if errors.Is(err, json.ErrTypeMismatch) {
        // Type mismatch
        return "", fmt.Errorf("field type error: %w", err)
    }
    return "", err
}

JsonsError

Structure

JsonsError is the library's primary error type, containing operation context information:

type JsonsError struct {
    Op      string `json:"op"`      // Operation type: "get", "set", "delete", "marshal", etc.
    Path    string `json:"path"`    // JSON path (if any)
    Message string `json:"message"` // Human-readable error message
    Err     error  `json:"err"`     // Underlying error
}

func (e *JsonsError) Error() string
func (e *JsonsError) Unwrap() error
func (e *JsonsError) Is(target error) bool

Usage

val, err := json.Get(data, "user.name")
if err != nil {
    // Use errors.Is to check error type
    if errors.Is(err, json.ErrPathNotFound) {
        // Path not found
    }
    if errors.Is(err, json.ErrTypeMismatch) {
        // Type mismatch
    }

    // Use errors.As to get detailed context
    var jsonErr *json.JsonsError
    if errors.As(err, &jsonErr) {
        fmt.Printf("Operation: %s\n", jsonErr.Op)
        fmt.Printf("Path: %s\n", jsonErr.Path)
        fmt.Printf("Message: %s\n", jsonErr.Message)
    }
}

Error Handling Patterns

Provide Default Values

// Type-safe getter functions have built-in default value support
name := json.GetString(data, "user.name", "anonymous")
age := json.GetInt(data, "user.age", 0)
active := json.GetBool(data, "user.active", false)

Collect Multiple Errors

type MultiError struct {
    Errors []error
}

func (e *MultiError) Add(err error) {
    e.Errors = append(e.Errors, err)
}

func (e *MultiError) HasError() bool {
    return len(e.Errors) > 0
}

func (e *MultiError) Error() string {
    msgs := make([]string, len(e.Errors))
    for i, err := range e.Errors {
        msgs[i] = err.Error()
    }
    return strings.Join(msgs, "; ")
}

// Usage
var multiErr MultiError
for _, path := range requiredPaths {
    if _, err := json.Get(data, path); err != nil {
        multiErr.Add(fmt.Errorf("%s: %w", path, err))
    }
}
if multiErr.HasError() {
    return multiErr.Error()
}

Error Wrapping

val, err := json.Get(data, "config.api_key")
if err != nil {
    return fmt.Errorf("failed to read API key: %w", err)
}

Custom Errors

Business Errors

type ValidationError struct {
    Field   string
    Message string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("validation failed %s: %s", e.Field, e.Message)
}

// Usage
func validateUser(data string) error {
    name := json.GetString(data, "name")
    if name == "" {
        return &ValidationError{Field: "name", Message: "required"}
    }
    if len(name) < 2 {
        return &ValidationError{Field: "name", Message: "must be at least 2 characters"}
    }
    return nil
}

Logging

Structured Logging

val, err := json.Get(data, path)
if err != nil {
    log.Error("JSON operation failed",
        "path", path,
        "error", err,
        "error_type", fmt.Sprintf("%T", err),
    )
    return err
}

Audit Logging

func auditLog(op string, path string, err error) {
    if err != nil {
        log.Warn("Operation failed",
            "operation", op,
            "path", path,
            "error", err,
        )
    } else {
        log.Info("Operation succeeded",
            "operation", op,
            "path", path,
        )
    }
}

Recovery Strategies

SafeError Safe Output

SafeError returns a client-safe error message, stripping internal context information:

// Signature: func SafeError(err error) string

val, err := json.Get(untrustedInput, "data")
if err != nil {
    // SafeError strips internal details like paths and operation context
    safeMsg := json.SafeError(err)
    http.Error(w, safeMsg, http.StatusBadRequest)
    return
}

Retry

func withRetry(fn func() error, maxRetries int) error {
    var err error
    for i := 0; i < maxRetries; i++ {
        if err = fn(); err == nil {
            return nil
        }
        time.Sleep(time.Second * time.Duration(i+1))
    }
    return err
}

// Usage
err := withRetry(func() error {
    return processData(data)
}, 3)

Degradation

func getConfig(data string) Config {
    cfg := json.DefaultConfig()

    // Use type-safe getter functions with built-in default values
    cfg.StrictMode = json.GetBool(data, "config.strict", true)

    return cfg
}

Error Classification

User Input Errors

Caused by user-provided JSON data or paths:

val, err := json.Get(data, "user.name")
if err != nil {
    switch {
    case errors.Is(err, json.ErrInvalidJSON):
        // JSON format error
        return fmt.Errorf("data format error: %w", err)
    case errors.Is(err, json.ErrPathNotFound):
        // Path not found
        return fmt.Errorf("field not found: %w", err)
    case errors.Is(err, json.ErrTypeMismatch):
        // Type mismatch
        return fmt.Errorf("type error: %w", err)
    case errors.Is(err, json.ErrInvalidPath):
        // Path syntax error
        return fmt.Errorf("path syntax error: %w", err)
    case errors.Is(err, json.ErrUnsupportedPath):
        // Unsupported path operation
        return fmt.Errorf("unsupported operation: %w", err)
    }
}

Security-Related Errors

Potential security threats detected:

val, err := json.Get(untrustedInput, "data")
if err != nil {
    if errors.Is(err, json.ErrSecurityViolation) {
        // Security violation, log and reject
        log.Warn("Security violation", "error", err)
        return errors.New("invalid input")
    }
    if errors.Is(err, json.ErrSizeLimit) {
        return fmt.Errorf("data exceeds size limit: %w", err)
    }
    if errors.Is(err, json.ErrDepthLimit) {
        return fmt.Errorf("nesting depth exceeded: %w", err)
    }
    return err
}

System Errors

System-level transient errors:

val, err := json.Get(data, "user.name")
if err != nil {
    if errors.Is(err, json.ErrOperationTimeout) {
        // Operation timeout, retryable <Badge type="danger" text="Deprecated" />
        return fmt.Errorf("transient error, please retry: %w", err)
    }
    if errors.Is(err, json.ErrConcurrencyLimit) {
        // Concurrency limit (returned when MaxConcurrency is reached, retryable)
        return fmt.Errorf("system busy, please try later: %w", err)
    }
    if errors.Is(err, json.ErrResourceExhausted) {
        // Resource exhausted <Badge type="danger" text="Deprecated" />
        return fmt.Errorf("insufficient system resources: %w", err)
    }
    if errors.Is(err, json.ErrProcessorClosed) {
        // Processor is closed
        return fmt.Errorf("processor unavailable: %w", err)
    }
    return err
}

Error Handling Best Practices

1. Distinguish Error Types

func processJSON(data string) error {
    val, err := json.Get(data, "user.name")
    if err != nil {
        // Use errors.Is to distinguish error types
        switch {
        case errors.Is(err, json.ErrInvalidJSON),
            errors.Is(err, json.ErrPathNotFound),
            errors.Is(err, json.ErrTypeMismatch),
            errors.Is(err, json.ErrInvalidPath):
            // User input error, return friendly message
            return fmt.Errorf("data format error: %w", err)
        case errors.Is(err, json.ErrSecurityViolation):
            // Security error, log and reject
            log.Warn("Security violation", "error", err)
            return errors.New("invalid input")
        case errors.Is(err, json.ErrConcurrencyLimit):
            // Concurrency limit, can retry later
            return fmt.Errorf("system busy, please retry later: %w", err)
        case errors.Is(err, json.ErrOperationTimeout): // Deprecated (not returned currently, kept for compatibility)
            return fmt.Errorf("transient error, please retry: %w", err)
        default:
            // System error
            log.Error("System error", "error", err)
            return errors.New("internal error")
        }
    }
    return nil
}

2. Use errors.As for Context

func handleWithDetail(data string, path string) error {
    val, err := json.Get(data, path)
    if err != nil {
        var jsonErr *json.JsonsError
        if errors.As(err, &jsonErr) {
            return fmt.Errorf("operation %s failed (path: %s): %w",
                jsonErr.Op, jsonErr.Path, jsonErr.Err)
        }
        return fmt.Errorf("operation failed: %w", err)
    }
    return nil
}

3. Error Chain Tracing

func deepProcess(data string) error {
    if err := processLevel1(data); err != nil {
        return fmt.Errorf("deep processing failed: %w", err)
    }
    return nil
}

func processLevel1(data string) error {
    if err := processLevel2(data); err != nil {
        return fmt.Errorf("level 1 failed (path data.field): %w", err)
    }
    return nil
}

func processLevel2(data string) error {
    _, err := json.Get(data, "data.field")
    return err
}

// Error chain example:
// Deep processing failed: level 1 failed (path data.field): path not found

See Also

• Constants and Errors
• Security Overview
• Performance Optimization