Form reader support for encoding.TextUnmarshaler

This allows Context.Read to read components that support the text unmarshaler interface, like UUID libraries

reader.go

@@ -1,6 +1,7 @@
 package routing
 
 import (
+	"encoding"
 	"encoding/json"
 	"encoding/xml"
 	"errors"
@@ -19,6 +20,10 @@ const (
 	MIME_MULTIPART_FORM = "multipart/form-data"
 )
 
+var (
+	textUnmarshalerType = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+)
+
 // DataReader is used by Context.Read() to read data from an HTTP request.
 type DataReader interface {
 	// Read reads from the given HTTP request and populate the specified data.
@@ -107,6 +112,13 @@ func readForm(form map[string][]string, prefix string, rv reflect.Value) error {
 			name = prefix + "." + name
 		}
 
+		// check if type implements a known type, like encoding.TextUnmarshaler
+		if ok, err := readFormFieldKnownType(form, name, rv.Field(i)); err != nil {
+			return err
+		} else if ok {
+			continue
+		}
+
 		if ft.Kind() != reflect.Struct {
 			if err := readFormField(form, name, rv.Field(i)); err != nil {
 				return err
@@ -124,6 +136,23 @@ func readForm(form map[string][]string, prefix string, rv reflect.Value) error {
 	return nil
 }
 
+func readFormFieldKnownType(form map[string][]string, name string, rv reflect.Value) (bool, error) {
+	value, ok := form[name]
+	if !ok {
+		return false, nil
+	}
+	rv = indirect(rv)
+	rt := rv.Type()
+
+	// check if type implements encoding.TextUnmarshaler
+	if rt.Implements(textUnmarshalerType) {
+		return true, rv.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(value[0]))
+	} else if reflect.PtrTo(rt).Implements(textUnmarshalerType) {
+		return true, rv.Addr().Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(value[0]))
+	}
+	return false, nil
+}
+
 func readFormField(form map[string][]string, name string, rv reflect.Value) error {
 	value, ok := form[name]
 	if !ok {

reader_test.go

@@ -84,3 +84,27 @@ func TestDefaultDataReader(t *testing.T) {
 		assert.Equal(t, expected, data, test.tag)
 	}
 }
+
+type TU struct {
+	UValue string
+}
+
+func (tu *TU) UnmarshalText(text []byte) error {
+	tu.UValue = "TU_" + string(text[:])
+	return nil
+}
+
+func TestTextUnmarshaler(t *testing.T) {
+	var a struct {
+		ATU TU     `form:"atu"`
+		NTU string `form:"ntu"`
+	}
+	values := map[string][]string{
+		"atu": []string{"ORIGINAL"},
+		"ntu": []string{"ORIGINAL"},
+	}
+	err := ReadFormData(values, &a)
+	assert.Nil(t, err)
+	assert.Equal(t, "TU_ORIGINAL", a.ATU.UValue)
+	assert.Equal(t, "ORIGINAL", a.NTU)
+}