Port Succo's fix to cache decodeHooks

decode_hooks.go

@@ -36,6 +36,30 @@ func typedDecodeHook(h DecodeHookFunc) DecodeHookFunc {
 	return nil
 }
 
+// cachedDecodeHook takes a raw DecodeHookFunc (an interface{}) and turns
+// it into a closure to be used directly
+// if the type fails to convert we return a closure always erroring to keep the previous behaviour
+func cachedDecodeHook(raw DecodeHookFunc) func(from reflect.Value, to reflect.Value) (interface{}, error) {
+	switch f := typedDecodeHook(raw).(type) {
+	case DecodeHookFuncType:
+		return func(from reflect.Value, to reflect.Value) (interface{}, error) {
+			return f(from.Type(), to.Type(), from.Interface())
+		}
+	case DecodeHookFuncKind:
+		return func(from reflect.Value, to reflect.Value) (interface{}, error) {
+			return f(from.Kind(), to.Kind(), from.Interface())
+		}
+	case DecodeHookFuncValue:
+		return func(from reflect.Value, to reflect.Value) (interface{}, error) {
+			return f(from, to)
+		}
+	default:
+		return func(from reflect.Value, to reflect.Value) (interface{}, error) {
+			return nil, errors.New("invalid decode hook signature")
+		}
+	}
+}
+
 // DecodeHookExec executes the given decode hook. This should be used
 // since it'll naturally degrade to the older backwards compatible DecodeHookFunc
 // that took reflect.Kind instead of reflect.Type.
@@ -61,13 +85,17 @@ func DecodeHookExec(
 // The composed funcs are called in order, with the result of the
 // previous transformation.
 func ComposeDecodeHookFunc(fs ...DecodeHookFunc) DecodeHookFunc {
+	cached := make([]func(from reflect.Value, to reflect.Value) (interface{}, error), 0, len(fs))
+	for _, f := range fs {
+		cached = append(cached, cachedDecodeHook(f))
+	}
 	return func(f reflect.Value, t reflect.Value) (interface{}, error) {
 		var err error
 		data := f.Interface()
 
 		newFrom := f
-		for _, f1 := range fs {
-			data, err = DecodeHookExec(f1, newFrom, t)
+		for _, c := range cached {
+			data, err = c(newFrom, t)
 			if err != nil {
 				return nil, err
 			}
@@ -81,13 +109,17 @@ func ComposeDecodeHookFunc(fs ...DecodeHookFunc) DecodeHookFunc {
 // OrComposeDecodeHookFunc executes all input hook functions until one of them returns no error. In that case its value is returned.
 // If all hooks return an error, OrComposeDecodeHookFunc returns an error concatenating all error messages.
 func OrComposeDecodeHookFunc(ff ...DecodeHookFunc) DecodeHookFunc {
+	cached := make([]func(from reflect.Value, to reflect.Value) (interface{}, error), 0, len(ff))
+	for _, f := range ff {
+		cached = append(cached, cachedDecodeHook(f))
+	}
 	return func(a, b reflect.Value) (interface{}, error) {
 		var allErrs string
 		var out interface{}
 		var err error
 
-		for _, f := range ff {
-			out, err = DecodeHookExec(f, a, b)
+		for _, c := range cached {
+			out, err = c(a, b)
 			if err != nil {
 				allErrs += err.Error() + "\n"
 				continue

mapstructure.go

@@ -283,7 +283,8 @@ type DecoderConfig struct {
 // structure. The top-level Decode method is just a convenience that sets
 // up the most basic Decoder.
 type Decoder struct {
-	config *DecoderConfig
+	config           *DecoderConfig
+	cachedDecodeHook func(from reflect.Value, to reflect.Value) (interface{}, error)
 }
 
 // Metadata contains information about decoding a structure that
@@ -408,6 +409,9 @@ func NewDecoder(config *DecoderConfig) (*Decoder, error) {
 	result := &Decoder{
 		config: config,
 	}
+	if config.DecodeHook != nil {
+		result.cachedDecodeHook = cachedDecodeHook(config.DecodeHook)
+	}
 
 	return result, nil
 }
@@ -462,10 +466,10 @@ func (d *Decoder) decode(name string, input interface{}, outVal reflect.Value) e
 		return nil
 	}
 
-	if d.config.DecodeHook != nil {
+	if d.cachedDecodeHook != nil {
 		// We have a DecodeHook, so let's pre-process the input.
 		var err error
-		input, err = DecodeHookExec(d.config.DecodeHook, inputVal, outVal)
+		input, err = d.cachedDecodeHook(inputVal, outVal)
 		if err != nil {
 			return fmt.Errorf("error decoding '%s': %w", name, err)
 		}