Support for unmarshalling custom geometry types

Author: tschaub

item.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"reflect"
 	"regexp"
 
 	"github.com/go-viper/mapstructure/v2"
@@ -122,6 +123,14 @@ func (item Item) MarshalJSON() ([]byte, error) {
 	return json.Marshal(itemMap)
 }
 
+var geometryUnmarshaler json.Unmarshaler
+
+// GeometryUnmarshaler allows a custom geometry type that satisfies the json.Unmarshaler interface to be provided.
+// If not set, item geometries will be unmarshaled as a map[string]any.
+func GeometryUnmarshaler(g json.Unmarshaler) {
+	geometryUnmarshaler = g
+}
+
 func (item *Item) UnmarshalJSON(data []byte) error {
 	itemMap := map[string]any{}
 	if err := json.Unmarshal(data, &itemMap); err != nil {
@@ -166,6 +175,33 @@ func (item *Item) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
+	if geometryUnmarshaler != nil {
+		geometryMap, ok := itemMap["geometry"]
+		if ok {
+			geometryData, err := json.Marshal(geometryMap)
+			if err != nil {
+				return err
+			}
+
+			var gv any
+			gvt := reflect.TypeOf(geometryUnmarshaler)
+			if gvt.Kind() == reflect.Pointer {
+				gv = reflect.New(gvt.Elem()).Interface()
+			} else {
+				gv = reflect.New(gvt).Elem().Interface()
+			}
+			g, ok := gv.(json.Unmarshaler)
+			if !ok {
+				return fmt.Errorf("expected %#v to satisfy the json.Unmarshaler interface", gv)
+			}
+			if err := g.UnmarshalJSON(geometryData); err != nil {
+				return err
+			}
+
+			item.Geometry = g
+		}
+	}
+
 	return nil
 }
 

item_test.go

@@ -63,3 +63,97 @@ func TestItemMarshal(t *testing.T) {
 
 	assert.JSONEq(t, expected, string(data))
 }
+
+func TestItemUnmarshal(t *testing.T) {
+	data := `{
+		"type": "Feature",
+		"stac_version": "1.0.0",
+		"id": "item-id",
+		"geometry": {
+			"type": "Point",
+			"coordinates": [1, 2]
+		},
+		"properties": {
+			"test": "value"
+		},
+		"links": [
+			{
+				"rel": "self",
+				"href": "https://example.com/stac/item-id"
+			}
+		],
+		"assets": {
+			"thumbnail": {
+				"title": "Thumbnail",
+				"href": "https://example.com/stac/item-id/thumb.png",
+				"type": "image/png"
+			}
+		}
+	}`
+
+	item := &stac.Item{}
+	require.NoError(t, json.Unmarshal([]byte(data), item))
+
+	assert.Equal(t, "item-id", item.Id)
+
+	require.NotNil(t, item.Geometry)
+
+	g, ok := item.Geometry.(map[string]any)
+	require.True(t, ok)
+	geometryType, ok := g["type"].(string)
+	require.True(t, ok)
+	assert.Equal(t, "Point", geometryType)
+}
+
+type TestGeometry struct {
+	data []byte
+}
+
+func (g *TestGeometry) UnmarshalJSON(data []byte) error {
+	g.data = data
+	return nil
+}
+
+func TestGeometryUnmarshal(t *testing.T) {
+	original := &TestGeometry{}
+	stac.GeometryUnmarshaler(original)
+	defer stac.GeometryUnmarshaler(nil)
+
+	data := `{
+		"type": "Feature",
+		"stac_version": "1.0.0",
+		"id": "item-id",
+		"geometry": {
+			"type": "Point",
+			"coordinates": [1, 2]
+		},
+		"properties": {
+			"test": "value"
+		},
+		"links": [
+			{
+				"rel": "self",
+				"href": "https://example.com/stac/item-id"
+			}
+		],
+		"assets": {
+			"thumbnail": {
+				"title": "Thumbnail",
+				"href": "https://example.com/stac/item-id/thumb.png",
+				"type": "image/png"
+			}
+		}
+	}`
+
+	item := &stac.Item{}
+	require.NoError(t, json.Unmarshal([]byte(data), item))
+
+	assert.Equal(t, "item-id", item.Id)
+
+	assert.Nil(t, original.data)
+	require.NotNil(t, item.Geometry)
+
+	g, ok := item.Geometry.(*TestGeometry)
+	require.True(t, ok)
+	assert.NotNil(t, g.data)
+}