formdata: handle optional fields correctly (#34)

Author: shoenig

formdata/data.go

@@ -24,11 +24,7 @@ var (
 
 func Parse(data url.Values, schema Schema) error {
 	for name, parser := range schema {
-		values, exists := data[name]
-		if !exists {
-			return ErrFieldNotPresent
-		}
-
+		values := data[name]
 		if err := parser.Parse(values); err != nil {
 			return fmt.Errorf("%s: %w", ErrParseFailure.Error(), err)
 		}

formdata/data_test.go

@@ -117,6 +117,28 @@ func Test_Parse_HTMLForm(t *testing.T) {
 	must.True(t, four)
 }
 
+func Test_Parse_HTMLForm_optional(t *testing.T) {
+	ctx := context.Background()
+	request, err := http.NewRequestWithContext(ctx, http.MethodPost, "/", nil)
+	must.NoError(t, err)
+
+	request.PostForm = make(url.Values)
+	request.PostForm.Set("one", "1")
+
+	var (
+		one string
+		two string
+	)
+
+	err2 := ParseForm(request, Schema{
+		"one": String(&one),
+		"two": StringOr(&two, "alternate"),
+	})
+	must.NoError(t, err2)
+	must.Eq(t, "1", one)
+	must.Eq(t, "alternate", two)
+}
+
 func Test_Parse_HTMLForm_not_ready(t *testing.T) {
 	ctx := context.Background()
 	request, err := http.NewRequestWithContext(ctx, http.MethodPost, "/", nil)