TextUnmarshaler support for binding

README.md

@@ -2080,6 +2080,67 @@ func ListHandler(s *Service) func(ctx *gin.Context) {
 }
 ```
 
+### Bind form-data request with custom field type
+
+Gin can support the encoding.TextUnmarshaler interface for non-struct types
+
+```go
+type HexInteger int
+
+func (f *HexInteger) UnmarshalText(text []byte) error {
+	v, err := strconv.ParseInt(string(text), 16, 64)
+	if err != nil {
+		return err
+	}
+	*f = HexInteger(v)
+	return nil
+}
+
+type FormA struct {
+	FieldA HexInteger `form:"field_a"`
+}
+
+// query with field_a = "0f"
+func GetDataA(c *gin.Context) {
+	var a FormA
+	c.Bind(&a)
+	// a.FieldA == 15
+}
+```
+
+For struct types, you can implement your own custom Unmarshaler using the `binding.BindUnmarshaler` 
+interface, which has the interface signature of `UnmarshalParam(param string) error`.
+
+```go
+type customType struct {
+	Protocol string
+	Path     string
+	Name     string
+}
+
+func (f *customType) UnmarshalParam(param string) error {
+	parts := strings.Split(param, ":")
+	if len(parts) != 3 {
+		return fmt.Errorf("invalid format")
+	}
+	f.Protocol = parts[0]
+	f.Path = parts[1]
+	f.Name = parts[2]
+	return nil
+}
+
+type FormA struct {
+	FieldA customType `form:"field_a"`
+}
+
+// query with field_a = "file:/:foo"
+func GetDataA(c *gin.Context) {
+	var a FormA
+	c.Bind(&a)
+	// a.FieldA.Protocol == "file", a.FieldA.Path == "/", and a.FieldA.Name == "foo"
+}
+```
+
 ### http2 server push
 
 http.Pusher is supported only **go1.8+**. See the [golang blog](https://blog.golang.org/h2push) for detail information.

binding/binding.go

@@ -46,6 +46,10 @@ type BindingUri interface {
 	BindUri(map[string][]string, any) error
 }
 
+type BindUnmarshaler interface {
+	UnmarshalParam(param string) error
+}
+
 // StructValidator is the minimal interface which needs to be implemented in
 // order for it to be used as the validator engine for ensuring the correctness
 // of the request. Gin provides a default implementation for this using

binding/form_mapping.go

@@ -5,6 +5,7 @@
 package binding
 
 import (
+	"encoding"
 	"errors"
 	"fmt"
 	"reflect"
@@ -175,11 +176,17 @@ func setByForm(value reflect.Value, field reflect.StructField, form map[string][
 		if !ok {
 			vs = []string{opt.defaultValue}
 		}
+		if ok, err := trySetCustom(vs[0], value); ok || err != nil {
+			return ok, err
+		}
 		return true, setSlice(vs, value, field)
 	case reflect.Array:
 		if !ok {
 			vs = []string{opt.defaultValue}
 		}
+		if ok, err := trySetCustom(vs[0], value); ok || err != nil {
+			return ok, err
+		}
 		if len(vs) != value.Len() {
 			return false, fmt.Errorf("%q is not valid value for %s", vs, value.Type().String())
 		}
@@ -193,10 +200,26 @@ func setByForm(value reflect.Value, field reflect.StructField, form map[string][
 		if len(vs) > 0 {
 			val = vs[0]
 		}
+		if ok, err := trySetCustom(val, value); ok || err != nil {
+			return ok, err
+		}
 		return true, setWithProperType(val, value, field)
 	}
 }
 
+func trySetCustom(val string, value reflect.Value) (isSet bool, err error) {
+	switch v := value.Addr().Interface().(type) {
+	case encoding.TextUnmarshaler:
+		if value.Kind() != reflect.Struct {
+			return true, v.UnmarshalText([]byte(val))
+		}
+	case BindUnmarshaler:
+		return true, v.UnmarshalParam(val)
+	}
+
+	return false, nil
+}
+
 func setWithProperType(val string, value reflect.Value, field reflect.StructField) error {
 	switch value.Kind() {
 	case reflect.Int:

binding/form_mapping_test.go

@@ -5,7 +5,10 @@
 package binding
 
 import (
+	"fmt"
 	"reflect"
+	"strconv"
+	"strings"
 	"testing"
 	"time"
 
@@ -288,3 +291,110 @@ func TestMappingIgnoredCircularRef(t *testing.T) {
 	err := mappingByPtr(&s, formSource{}, "form")
 	assert.NoError(t, err)
 }
+
+type foohex int
+
+func (f *foohex) UnmarshalText(text []byte) error {
+	v, err := strconv.ParseInt(string(text), 16, 64)
+	if err != nil {
+		return err
+	}
+	*f = foohex(v)
+	return nil
+}
+
+func TestMappingCustomFieldType(t *testing.T) {
+	var s struct {
+		Foo foohex `form:"foo"`
+	}
+	err := mappingByPtr(&s, formSource{"foo": {`f5`}}, "form")
+	assert.NoError(t, err)
+
+	assert.EqualValues(t, 245, s.Foo)
+}
+
+func TestMappingCustomFieldTypeWithURI(t *testing.T) {
+	var s struct {
+		Foo foohex `uri:"foo"`
+	}
+	err := mappingByPtr(&s, formSource{"foo": {`f5`}}, "uri")
+	assert.NoError(t, err)
+
+	assert.EqualValues(t, 245, s.Foo)
+}
+
+type customType struct {
+	Protocol string
+	Path     string
+	Name     string
+}
+
+func (f *customType) UnmarshalParam(param string) error {
+	parts := strings.Split(param, ":")
+	if len(parts) != 3 {
+		return fmt.Errorf("invalid format")
+	}
+	f.Protocol = parts[0]
+	f.Path = parts[1]
+	f.Name = parts[2]
+	return nil
+}
+
+func TestMappingCustomStructType(t *testing.T) {
+	var s struct {
+		FileData customType `form:"data"`
+	}
+	err := mappingByPtr(&s, formSource{"data": {`file:/foo:happiness`}}, "form")
+	assert.NoError(t, err)
+
+	assert.EqualValues(t, "file", s.FileData.Protocol)
+	assert.EqualValues(t, "/foo", s.FileData.Path)
+	assert.EqualValues(t, "happiness", s.FileData.Name)
+}
+
+func TestMappingCustomPointerStructType(t *testing.T) {
+	var s struct {
+		FileData *customType `form:"data"`
+	}
+	err := mappingByPtr(&s, formSource{"data": {`file:/foo:happiness`}}, "form")
+	assert.NoError(t, err)
+
+	assert.EqualValues(t, "file", s.FileData.Protocol)
+	assert.EqualValues(t, "/foo", s.FileData.Path)
+	assert.EqualValues(t, "happiness", s.FileData.Name)
+}
+
+type MySlice []string
+
+func (s *MySlice) UnmarshalParam(param string) error {
+	*s = MySlice(strings.Split(param, ","))
+	return nil
+}
+
+func TestMappingCustomSliceType(t *testing.T) {
+	var s struct {
+		Permissions MySlice `form:"permissions"`
+	}
+	err := mappingByPtr(&s, formSource{"permissions": {"read,write,delete"}}, "form")
+	assert.NoError(t, err)
+
+	assert.EqualValues(t, []string{"read", "write", "delete"}, s.Permissions)
+}
+
+type MyArray [3]string
+
+func (s *MyArray) UnmarshalParam(param string) error {
+	parts := strings.Split(param, ",")
+	*s = MyArray([3]string{parts[0], parts[1], parts[2]})
+	return nil
+}
+
+func TestMappingCustomArrayType(t *testing.T) {
+	var s struct {
+		Permissions MyArray `form:"permissions"`
+	}
+	err := mappingByPtr(&s, formSource{"permissions": {"read,write,delete"}}, "form")
+	assert.NoError(t, err)
+
+	assert.EqualValues(t, [3]string{"read", "write", "delete"}, s.Permissions)
+}