fixed decoding for "required" struct fields (#126)

* fixed decoding for "required" struct fields

* added optimization if key is not in dot notation

decoder.go

@@ -152,9 +152,15 @@ type fieldWithPrefix struct {
 func isEmptyFields(fields []fieldWithPrefix, src map[string][]string) bool {
 	for _, f := range fields {
 		for _, path := range f.paths(f.prefix) {
-			if !isEmpty(f.typ, src[path]) {
+			v, ok := src[path]
+			if ok && !isEmpty(f.typ, v) {
 				return false
 			}
+			for key := range src {
+				if !isEmpty(f.typ, src[key]) && strings.HasPrefix(key, path) {
+					return false
+				}
+			}
 		}
 	}
 	return true

decoder_test.go

@@ -1558,6 +1558,23 @@ func TestRequiredField(t *testing.T) {
 	}
 }
 
+type R2 struct {
+	A struct {
+		B int `schema:"b"`
+	} `schema:"a,required"`
+}
+
+func TestRequiredStructFiled(t *testing.T) {
+	v := map[string][]string{
+		"a.b": []string{"3"},
+	}
+	var a R2
+	err := NewDecoder().Decode(&a, v)
+	if err != nil {
+		t.Errorf("error: %v", err)
+	}
+}
+
 func TestRequiredFieldIsMissingCorrectError(t *testing.T) {
 	type RM1S struct {
 		A string `schema:"rm1aa,required"`