geojson: handle extra/foreign members in feature

geojson/README.md

@@ -47,7 +47,7 @@ rawJSON, _ := fc.MarshalJSON()
 blob, _ := json.Marshal(fc)
 ```
 
-## Foreign/extra members in a feature collection
+## Foreign/extra members in feature and feature collection
 
 ```go
 rawJSON := []byte(`

geojson/feature.go

@@ -15,6 +15,12 @@ type Feature struct {
 	BBox       BBox         `json:"bbox,omitempty"`
 	Geometry   orb.Geometry `json:"geometry"`
 	Properties Properties   `json:"properties"`
+
+	// ExtraMembers can be used to encoded/decode extra key/members in
+	// the base of the feature object. Note that keys of "id", "type", "bbox"
+	// "geometry" and "properties" will not work as those are reserved by the
+	// GeoJSON spec.
+	ExtraMembers Properties `json:"-"`
 }
 
 // NewFeature creates and initializes a GeoJSON feature given the required attributes.
@@ -38,31 +44,65 @@ var _ orb.Pointer = &Feature{}
 // MarshalJSON converts the feature object into the proper JSON.
 // It will handle the encoding of all the child geometries.
 // Alternately one can call json.Marshal(f) directly for the same result.
+// Items in the ExtraMembers map will be included in the base of the
+// feature object.
 func (f Feature) MarshalJSON() ([]byte, error) {
 	return marshalJSON(newFeatureDoc(&f))
 }
 
 // MarshalBSON converts the feature object into the proper JSON.
 // It will handle the encoding of all the child geometries.
 // Alternately one can call json.Marshal(f) directly for the same result.
+// Items in the ExtraMembers map will be included in the base of the
+// feature object.
 func (f Feature) MarshalBSON() ([]byte, error) {
 	return bson.Marshal(newFeatureDoc(&f))
 }
 
-func newFeatureDoc(f *Feature) *featureDoc {
-	doc := &featureDoc{
-		ID:         f.ID,
-		Type:       "Feature",
-		Properties: f.Properties,
-		BBox:       f.BBox,
-		Geometry:   NewGeometry(f.Geometry),
+func newFeatureDoc(f *Feature) interface{} {
+	if len(f.ExtraMembers) == 0 {
+		doc := &featureDoc{
+			ID:         f.ID,
+			Type:       "Feature",
+			Properties: f.Properties,
+			BBox:       f.BBox,
+			Geometry:   NewGeometry(f.Geometry),
+		}
+
+		if len(doc.Properties) == 0 {
+			doc.Properties = nil
+		}
+
+		return doc
 	}
 
-	if len(doc.Properties) == 0 {
-		doc.Properties = nil
+	var tmp map[string]interface{}
+	if f.ExtraMembers != nil {
+		tmp = f.ExtraMembers.Clone()
+	} else {
+		tmp = make(map[string]interface{}, 3)
+	}
+
+	delete(tmp, "id")
+	if f.ID != nil {
+		tmp["id"] = f.ID
+	}
+	tmp["type"] = "Feature"
+
+	delete(tmp, "bbox")
+	if f.BBox != nil {
+		tmp["bbox"] = f.BBox
+	}
+
+	tmp["geometry"] = NewGeometry(f.Geometry)
+
+	if len(f.Properties) == 0 {
+		tmp["properties"] = nil
+	} else {
+		tmp["properties"] = f.Properties
 	}
 
-	return doc
+	return tmp
 }
 
 // UnmarshalFeature decodes the data into a GeoJSON feature.
@@ -85,45 +125,122 @@ func (f *Feature) UnmarshalJSON(data []byte) error {
 		return nil
 	}
 
-	doc := &featureDoc{}
-	err := unmarshalJSON(data, &doc)
+	tmp := make(map[string]nocopyRawMessage, 4)
+
+	err := unmarshalJSON(data, &tmp)
 	if err != nil {
 		return err
 	}
 
-	return featureUnmarshalFinish(doc, f)
+	*f = Feature{}
+	for key, value := range tmp {
+		switch key {
+		case "id":
+			err := unmarshalJSON(value, &f.ID)
+			if err != nil {
+				return err
+			}
+		case "type":
+			err := unmarshalJSON(value, &f.Type)
+			if err != nil {
+				return err
+			}
+		case "bbox":
+			err := unmarshalJSON(value, &f.BBox)
+			if err != nil {
+				return err
+			}
+		case "geometry":
+			g := &Geometry{}
+			err := unmarshalJSON(value, &g)
+			if err != nil {
+				return err
+			}
+
+			if g != nil {
+				f.Geometry = g.Geometry()
+			}
+		case "properties":
+			err := unmarshalJSON(value, &f.Properties)
+			if err != nil {
+				return err
+			}
+		default:
+			if f.ExtraMembers == nil {
+				f.ExtraMembers = Properties{}
+			}
+
+			var val interface{}
+			err := unmarshalJSON(value, &val)
+			if err != nil {
+				return err
+			}
+			f.ExtraMembers[key] = val
+		}
+	}
+
+	if f.Type != "Feature" {
+		return fmt.Errorf("geojson: not a feature: type=%s", f.Type)
+	}
+
+	return nil
 }
 
 // UnmarshalBSON will unmarshal a BSON document created with bson.Marshal.
 func (f *Feature) UnmarshalBSON(data []byte) error {
-	doc := &featureDoc{}
-	err := bson.Unmarshal(data, &doc)
+	tmp := make(map[string]bson.RawValue, 4)
+
+	err := bson.Unmarshal(data, &tmp)
 	if err != nil {
 		return err
 	}
 
-	return featureUnmarshalFinish(doc, f)
-}
-
-func featureUnmarshalFinish(doc *featureDoc, f *Feature) error {
-	if doc.Type != "Feature" {
-		return fmt.Errorf("geojson: not a feature: type=%s", doc.Type)
-	}
-
-	var g orb.Geometry
-	if doc.Geometry != nil {
-		if doc.Geometry.Coordinates == nil && doc.Geometry.Geometries == nil {
-			return ErrInvalidGeometry
+	*f = Feature{}
+	for key, value := range tmp {
+		switch key {
+		case "id":
+			err := value.Unmarshal(&f.ID)
+			if err != nil {
+				return err
+			}
+		case "type":
+			f.Type, _ = bson.RawValue(value).StringValueOK()
+		case "bbox":
+			err := value.Unmarshal(&f.BBox)
+			if err != nil {
+				return err
+			}
+		case "geometry":
+			g := &Geometry{}
+			err := value.Unmarshal(&g)
+			if err != nil {
+				return err
+			}
+
+			if g != nil {
+				f.Geometry = g.Geometry()
+			}
+		case "properties":
+			err := value.Unmarshal(&f.Properties)
+			if err != nil {
+				return err
+			}
+		default:
+			if f.ExtraMembers == nil {
+				f.ExtraMembers = Properties{}
+			}
+
+			var val interface{}
+			err := value.Unmarshal(&val)
+			if err != nil {
+				return err
+			}
+			f.ExtraMembers[key] = val
 		}
-		g = doc.Geometry.Geometry()
 	}
 
-	*f = Feature{
-		ID:         doc.ID,
-		Type:       doc.Type,
-		Properties: doc.Properties,
-		BBox:       doc.BBox,
-		Geometry:   g,
+	if f.Type != "Feature" {
+		return fmt.Errorf("geojson: not a feature: type=%s", f.Type)
 	}
 
 	return nil

geojson/feature_test.go

@@ -236,6 +236,33 @@ func TestFeatureMarshalJSON_null(t *testing.T) {
 	})
 }
 
+func TestFeatureMarshalJSON_extraMembers(t *testing.T) {
+	rawJSON := `
+	  { "type": "Feature",
+		"geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
+		"properties": {"prop0": "value0"},
+		"foo": "bar"
+	  }`
+
+	f, err := UnmarshalFeature([]byte(rawJSON))
+	if err != nil {
+		t.Fatalf("should unmarshal feature collection without issue, err %v", err)
+	}
+
+	if v := f.ExtraMembers.MustString("foo", ""); v != "bar" {
+		t.Errorf("missing extra: foo: %v", v)
+	}
+
+	data, err := f.MarshalJSON()
+	if err != nil {
+		t.Fatalf("unable to marshal: %v", err)
+	}
+
+	if !bytes.Contains(data, []byte(`"foo":"bar"`)) {
+		t.Fatalf("extras not in marshalled data")
+	}
+}
+
 func TestUnmarshalBSON_missingGeometry(t *testing.T) {
 	t.Run("missing geometry", func(t *testing.T) {
 		f := NewFeature(nil)
@@ -355,6 +382,34 @@ func TestMarshalRing(t *testing.T) {
 	}
 }
 
+func TestFeature_MarshalBSON_extraMembers(t *testing.T) {
+	f := NewFeature(orb.Point{1, 2})
+
+	f.ExtraMembers = map[string]interface{}{
+		"a": 1.0,
+		"b": 2.0,
+	}
+
+	data, err := bson.Marshal(f)
+	if err != nil {
+		t.Fatalf("unable to marshal feature collection: %v", err)
+	}
+
+	nf := &Feature{}
+	err = bson.Unmarshal(data, &nf)
+	if err != nil {
+		t.Fatalf("unable to unmarshal feature collection: %v", err)
+	}
+
+	if v := nf.ExtraMembers["a"]; v != 1.0 {
+		t.Errorf("incorrect extra member: %v != %v", v, 1.0)
+	}
+
+	if v := nf.ExtraMembers["b"]; v != 2.0 {
+		t.Errorf("incorrect extra member: %v != %v", v, 2.0)
+	}
+}
+
 // uncomment to test/benchmark custom json marshalling
 // func init() {
 // 	var c = jsoniter.Config{