Add Encoder type for custom encoding of values

Author: ftdave

query/encode.go

@@ -33,6 +33,14 @@ import (
 
 var timeType = reflect.TypeOf(time.Time{})
 
+var encoderType = reflect.TypeOf(new(Encoder)).Elem()
+
+// Encoder is an interface implemented by any type that wishes to encode
+// itself into URL values in a non-standard way.
+type Encoder interface {
+	EncodeValues(v *url.Values) error
+}
+
 // Values returns the url.Values encoding of v.
 //
 // Values expects to be passed a struct, and traverses it recursively using the
@@ -107,14 +115,14 @@ func Values(v interface{}) (url.Values, error) {
 	}
 
 	values := make(url.Values)
-	reflectValue(values, val)
-	return values, nil
+	err := reflectValue(values, val)
+	return values, err
 }
 
 // reflectValue populates the values parameter from the struct fields in val.
 // Embedded structs are followed recursively (using the rules defined in the
 // Values function documentation) breadth-first.
-func reflectValue(values url.Values, val reflect.Value) {
+func reflectValue(values url.Values, val reflect.Value) error {
 	var embedded []reflect.Value
 
 	typ := val.Type()
@@ -144,6 +152,14 @@ func reflectValue(values url.Values, val reflect.Value) {
 			continue
 		}
 
+		if sv.Type().Implements(encoderType) {
+			m := sv.Interface().(Encoder)
+			if err := m.EncodeValues(&values); err != nil {
+				return err
+			}
+			continue
+		}
+
 		if sv.Kind() == reflect.Slice || sv.Kind() == reflect.Array {
 			var del byte
 			if opts.Contains("comma") {
@@ -176,8 +192,12 @@ func reflectValue(values url.Values, val reflect.Value) {
 	}
 
 	for _, f := range embedded {
-		reflectValue(values, f)
+		if err := reflectValue(values, f); err != nil {
+			return err
+		}
 	}
+
+	return nil
 }
 
 // valueString returns the string representation of a value.

query/encode_test.go

@@ -5,6 +5,7 @@
 package query
 
 import (
+	"fmt"
 	"net/url"
 	"reflect"
 	"testing"
@@ -188,6 +189,34 @@ func TestValues_invalidInput(t *testing.T) {
 	}
 }
 
+type EncodedArgs []string
+
+func (m EncodedArgs) EncodeValues(v *url.Values) error {
+	for i, arg := range m {
+		v.Set(fmt.Sprintf("arg.%d", i), arg)
+	}
+	return nil
+}
+
+func TestValues_Marshaler(t *testing.T) {
+	s := struct {
+		Args EncodedArgs `url:"args"`
+	}{[]string{"a", "b", "c"}}
+	v, err := Values(s)
+	if err != nil {
+		t.Errorf("Values(%q) returned error: %v", s, err)
+	}
+
+	want := url.Values{
+		"arg.0": {"a"},
+		"arg.1": {"b"},
+		"arg.2": {"c"},
+	}
+	if !reflect.DeepEqual(want, v) {
+		t.Errorf("Values(%q) returned %v, want %v", s, v, want)
+	}
+}
+
 func TestTagParsing(t *testing.T) {
 	name, opts := parseTag("field,foobar,foo")
 	if name != "field" {