fix: do not zero the field if not tagged for query nor path (#29)

CHANGELOG.md

@@ -5,6 +5,10 @@ How to release a new version:
 
 ## [Unreleased]
 
+## [0.6.1] - 2022-03-28
+### Changed
+- package `http/param` does not zero the field if not tagged with any relevant tags
+
 ## [0.6.0] - 2023-03-03
 ### Added
 - package `http/signature` to simplify defining http handler functions
@@ -45,7 +49,8 @@ How to release a new version:
 ### Added
 - Added Changelog.
 
-[Unreleased]: https://github.com/strvcom/strv-backend-go-net/compare/v0.6.0...HEAD
+[Unreleased]: https://github.com/strvcom/strv-backend-go-net/compare/v0.6.1...HEAD
+[0.6.1]: https://github.com/strvcom/strv-backend-go-net/compare/v0.6.0...v0.6.1
 [0.6.0]: https://github.com/strvcom/strv-backend-go-net/compare/v0.5.0...v0.6.0
 [0.5.0]: https://github.com/strvcom/strv-backend-go-net/compare/v0.4.0...v0.5.0
 [0.4.0]: https://github.com/strvcom/strv-backend-go-net/compare/v0.3.0...v0.4.0

http/param/param.go

@@ -106,28 +106,46 @@ func (p Parser) Parse(r *http.Request, dest any) error {
 			continue
 		}
 		valueField := v.Field(i)
-		// Zero the value, even if it would not be set by following path or query parameter.
-		// This will cause potential partial result from previous parser (e.g. json.Unmarshal) to be discarded on
-		// fields that are tagged for path or query parameter.
-		valueField.Set(reflect.Zero(typeField.Type))
-		tag := typeField.Tag
-		err := p.parseQueryParam(r, tag, valueField)
+		err := p.parseParam(r, typeField, valueField)
 		if err != nil {
 			return err
 		}
-		err = p.parsePathParam(r, tag, valueField)
+	}
+	return nil
+}
+
+func (p Parser) parseParam(r *http.Request, typeField reflect.StructField, v reflect.Value) error {
+	tag := typeField.Tag
+	pathParamName, okPath := p.PathParamTagResolver(tag)
+	queryParamName, okQuery := p.QueryParamTagResolver(tag)
+	if !okPath && !okQuery {
+		// do nothing if tagged neither for query nor param
+		return nil
+	}
+
+	// Zero the value, even if it would not be set by following path or query parameter.
+	// This will cause potential partial result from previous parser (e.g. json.Unmarshal) to be discarded on
+	// fields that are tagged for path or query parameter.
+	v.Set(reflect.Zero(typeField.Type))
+
+	if okPath {
+		err := p.parsePathParam(r, pathParamName, v)
+		if err != nil {
+			return err
+		}
+	}
+
+	if okQuery {
+		err := p.parseQueryParam(r, queryParamName, v)
 		if err != nil {
 			return err
 		}
 	}
+
 	return nil
 }
 
-func (p Parser) parsePathParam(r *http.Request, tag reflect.StructTag, v reflect.Value) error {
-	paramName, ok := p.PathParamTagResolver(tag)
-	if !ok {
-		return nil
-	}
+func (p Parser) parsePathParam(r *http.Request, paramName string, v reflect.Value) error {
 	if p.PathParamFunc == nil {
 		return fmt.Errorf("struct's field was tagged for parsing the path parameter (%s) but PathParamFunc to get value of path parameter is not defined", paramName)
 	}
@@ -141,11 +159,7 @@ func (p Parser) parsePathParam(r *http.Request, tag reflect.StructTag, v reflect
 	return nil
 }
 
-func (p Parser) parseQueryParam(r *http.Request, tag reflect.StructTag, v reflect.Value) error {
-	paramName, ok := p.QueryParamTagResolver(tag)
-	if !ok {
-		return nil
-	}
+func (p Parser) parseQueryParam(r *http.Request, paramName string, v reflect.Value) error {
 	query := r.URL.Query()
 	if values, ok := query[paramName]; ok && len(values) > 0 {
 		err := unmarshalValueOrSlice(values, v)

http/param/param_test.go

@@ -451,6 +451,26 @@ func TestParser_Parse_PathParam_FuncNotDefinedError(t *testing.T) {
 	assert.Error(t, err)
 }
 
+type otherFieldsStruct struct {
+	Q     string `param:"query=q"`
+	Other string `json:"other"`
+}
+
+func TestParser_Parse_DoesNotOverwrite(t *testing.T) {
+	p := DefaultParser()
+	req := httptest.NewRequest(http.MethodGet, "https://test.com/hello?q=input", nil)
+	expected := otherFieldsStruct{
+		Q:     "input",
+		Other: "already filled",
+	}
+
+	result := otherFieldsStruct{Other: "already filled"}
+	err := p.Parse(req, &result)
+
+	assert.NoError(t, err)
+	assert.Equal(t, expected, result)
+}
+
 type variousTagsStruct struct {
 	A string `key:"location=val"`
 	B string `key:"location=val=excessive"`