v2 to v3 conversion: avoid json-in-json for metadata

pmtiles/convert.go

@@ -481,6 +481,18 @@ func v2_to_header_json(v2_json_metadata map[string]interface{}, first4 []byte) (
 		}
 	}
 
+	// deserialize embedded JSON and lift keys to top-level
+	// to avoid "json-in-json"
+	if val, ok := v2_json_metadata["json"]; ok {
+		string_val := val.(string)
+		var inside map[string]interface{}
+		json.Unmarshal([]byte(string_val), &inside)
+		for k, v := range inside {
+			v2_json_metadata[k] = v
+		}
+		delete(v2_json_metadata, "json")
+	}
+
 	return header, v2_json_metadata, nil
 }
 

pmtiles/convert_test.go

@@ -73,6 +73,7 @@ func TestV2UpgradeExtra(t *testing.T) {
 		"center":      "-122.1906,37.7599,11",
 		"format":      "pbf",
 		"compression": "gzip",
+		"json": "{\"abc\":\"def\"}",
 	}, []byte{0x0, 0x0, 0x0, 0x0})
 	if err != nil {
 		t.Fatalf("parsing error %s", err)
@@ -89,6 +90,9 @@ func TestV2UpgradeExtra(t *testing.T) {
 	if _, ok := json_metadata["center"]; ok {
 		t.Fatalf("expected center not in result")
 	}
+	if _, ok := json_metadata["abc"]; !ok {
+		t.Fatalf("expected abc in result")
+	}
 }
 
 func TestZoomCenterDefaults(t *testing.T) {