Merge pull request #3 from ing-bank/v2

Add DefaultHandler as an option

errors.go

@@ -7,7 +7,6 @@ import (
 
 const defaultCode = http.StatusInternalServerError
 
-// DefaultErrorRegistry is the default ErrorRegistry for the application, can be overridden for rare use-cases.
 var DefaultErrorRegistry = NewErrorRegistry()
 
 type internalHandler func(err error) (int, any)
@@ -25,7 +24,6 @@ type ErrorStringHandler[R any] func(err string) (int, R)
 // the handler is registered for. The R type is the type of the response body.
 type ErrorHandler[E error, R any] func(E) (int, R)
 
-// NewErrorRegistry is ideal for testing or overriding the default one.
 func NewErrorRegistry() *ErrorRegistry {
 	registry := &ErrorRegistry{
 		handlers:       make(map[string]internalHandler),
@@ -46,7 +44,6 @@ func NewErrorRegistry() *ErrorRegistry {
 	return registry
 }
 
-// ErrorRegistry contains a map of ErrorHandlers.
 type ErrorRegistry struct {
 	// handlers are used when we know the type of the error
 	handlers map[string]internalHandler

v2/errors.go

@@ -8,13 +8,11 @@ import (
 
 const defaultCode = http.StatusInternalServerError
 
-// DefaultErrorRegistry is the default ErrorRegistry for the application, can be overridden for rare use-cases.
 var DefaultErrorRegistry = NewErrorRegistry()
 
 type internalHandler func(ctx context.Context, err error) (int, any)
 type internalStringHandler func(ctx context.Context, err string) (int, any)
 
-// NewErrorRegistry is ideal for testing or overriding the default one.
 func NewErrorRegistry() *ErrorRegistry {
 	registry := &ErrorRegistry{
 		handlers:       make(map[string]internalHandler),
@@ -29,32 +27,49 @@ func NewErrorRegistry() *ErrorRegistry {
 			return handler(ctx, err.Error())
 		}
 
-		return registry.DefaultCode, registry.DefaultResponse
+		return registry.defaultResponse(ctx, err)
 	}
 
 	return registry
 }
 
-// ErrorRegistry contains a map of ErrorHandlers.
 type ErrorRegistry struct {
 	// handlers are used when we know the type of the error
 	handlers map[string]internalHandler
 
 	// stringHandlers are used when the error is only a string
 	stringHandlers map[string]internalStringHandler
 
-	// DefaultCode to return when no handler is found
+	// DefaultHandler takes precedent over DefaultCode and DefaultResponse
+	DefaultHandler func(ctx context.Context, err error) (int, any)
+
+	// DefaultCode to return when no handler is found. Deprecated: Prefer DefaultHandler
 	DefaultCode int
 
-	// DefaultResponse to return when no handler is found
+	// DefaultResponse to return when no handler is found. Deprecated: Prefer DefaultHandler
 	DefaultResponse any
 }
 
+// SetDefaultResponse is deprecated, prefer RegisterDefaultHandler
 func (e *ErrorRegistry) SetDefaultResponse(code int, response any) {
 	e.DefaultCode = code
 	e.DefaultResponse = response
 }
 
+func (e *ErrorRegistry) RegisterDefaultHandler(callback func(ctx context.Context, err error) (int, any)) {
+	e.DefaultHandler = callback
+}
+
+func (e *ErrorRegistry) defaultResponse(ctx context.Context, err error) (int, any) {
+	// In production, we should return a generic error message. If you want to know why, read this:
+	// https://owasp.org/www-community/Improper_Error_Handling
+	if e.DefaultHandler != nil {
+		return e.DefaultHandler(ctx, err)
+	}
+
+	return e.DefaultCode, e.DefaultResponse
+}
+
 // NewErrorResponse Returns an error response using the DefaultErrorRegistry. If no specific handler could be found,
 // it will return the defaults.
 func NewErrorResponse(ctx context.Context, err error) (int, any) {
@@ -71,9 +86,7 @@ func NewErrorResponseFrom(registry *ErrorRegistry, ctx context.Context, err erro
 		return entry(ctx, err)
 	}
 
-	// In production, we should return a generic error message. If you want to know why, read this:
-	// https://owasp.org/www-community/Improper_Error_Handling
-	return registry.DefaultCode, registry.DefaultResponse
+	return registry.defaultResponse(ctx, err)
 }
 
 // RegisterErrorHandler registers an error handler in DefaultErrorRegistry. The R type is the type of the response body.

v2/errors_test.go

@@ -128,6 +128,38 @@ func TestErrorResponseFrom_ReturnsGenericErrorOnNotFound(t *testing.T) {
 	assert.Equal(t, "test", response)
 }
 
+func TestErrorResponseFrom_UsesDefaultCallbackOnNotFound(t *testing.T) {
+	t.Parallel()
+	// Arrange
+	registry := NewErrorRegistry()
+
+	expectedResponse := Response{
+		Errors: map[string]any{"error": "internal server error"},
+	}
+
+	var calledWithErr error
+	var calledWithCtx context.Context
+	callback := func(ctx context.Context, err error) (int, any) {
+		calledWithErr = err
+		calledWithCtx = ctx
+		return http.StatusInternalServerError, expectedResponse
+	}
+
+	registry.RegisterDefaultHandler(callback)
+
+	ctx := context.WithValue(context.Background(), ErrorA{}, "good")
+
+	// Act
+	code, response := NewErrorResponseFrom(registry, ctx, assert.AnError)
+
+	// Assert
+	assert.Equal(t, expectedResponse, response)
+	assert.Equal(t, code, http.StatusInternalServerError)
+
+	assert.Equal(t, ctx, calledWithCtx)
+	assert.Equal(t, assert.AnError, calledWithErr)
+}
+
 func TestErrorResponseFrom_ReturnsErrorAWithContext(t *testing.T) {
 	t.Parallel()
 	// Arrange
@@ -141,7 +173,7 @@ func TestErrorResponseFrom_ReturnsErrorAWithContext(t *testing.T) {
 	callback := func(ctx context.Context, err *ErrorA) (int, any) {
 		calledWithErr = err
 		calledWithCtx = ctx
-		return 500, expectedResponse
+		return http.StatusInternalServerError, expectedResponse
 	}
 
 	err := &ErrorA{message: "It was the man with one hand!"}
@@ -172,7 +204,7 @@ func TestErrorResponseFrom_ReturnsErrorB(t *testing.T) {
 	var calledWithErr *ErrorB
 	callback := func(ctx context.Context, err *ErrorB) (int, any) {
 		calledWithErr = err
-		return 500, expectedResponse
+		return http.StatusInternalServerError, expectedResponse
 	}
 
 	err := &ErrorB{message: "It was the man with one hand!"}
@@ -200,7 +232,7 @@ func TestErrorResponseFrom_ReturnsErrorBInInterface(t *testing.T) {
 	var calledWithErr error
 	callback := func(ctx context.Context, err *ErrorB) (int, any) {
 		calledWithErr = err
-		return 500, expectedResponse
+		return http.StatusInternalServerError, expectedResponse
 	}
 
 	var err error = &ErrorB{message: "It was the man with one hand!"}