feat: Support decoding protobuf without defaults

The protobuf specification demands type-specific default values such as
0 for numbers when decoding. That is quite weird for TypeScript code
which usually uses null or undefined for missing values. Let's create an
alternative way to decode without defaults.

Maybe the following issue will be resolved at some point so we would not
need our own workaround:
protobufjs/protobuf.js#1572

src/util/protobufUtil.ts

@@ -0,0 +1,31 @@
+import type protobufjs from "protobufjs/minimal";
+
+/**
+ * The protobuf specification demands type-specific default values such as 0 for
+ * numbers when decoding. That is quite weird for TypeScript code which usually
+ * uses null or undefined for missing values. Let's create an alternative way to
+ * decode without defaults.
+ *
+ * Maybe the following issue will be resolved at some point so we would not need
+ * our own workaround:
+ * https://github.com/protobufjs/protobuf.js/issues/1572
+ */
+
+interface ProtobufMessageType<T> {
+  decode: (reader: protobufjs.Reader | Uint8Array, length?: number) => T;
+  toObject: (
+    message: T,
+    options?: protobufjs.IConversionOptions,
+  ) => Record<string, unknown>;
+}
+
+const decodeWithoutDefaults = <T>(
+  messageType: ProtobufMessageType<T>,
+  payload: Uint8Array,
+): T =>
+  messageType.toObject(messageType.decode(payload), {
+    longs: Number,
+    defaults: false,
+  }) as T;
+
+export default decodeWithoutDefaults;

tests/util/protobufUtil.unit.test.ts

@@ -0,0 +1,97 @@
+import { hfp } from "../../src/protobuf/hfp";
+import { mqtt } from "../../src/protobuf/mqtt";
+import decodeWithoutDefaults from "../../src/util/protobufUtil";
+
+describe("decodeWithoutDefaults", () => {
+  test("decode HFP message with payload stop 'null'", () => {
+    const hfpData = {
+      SchemaVersion: 1,
+      topic: {
+        SchemaVersion: 1,
+        receivedAt: new Date("2023-10-23T13:42:42.794243Z").getTime(),
+        topicPrefix: "/hfp/",
+        topicVersion: "v2",
+        journeyType: hfp.Topic.JourneyType.journey,
+        temporalType: hfp.Topic.TemporalType.ongoing,
+        eventType: hfp.Topic.EventType.VP,
+        transportMode: hfp.Topic.TransportMode.bus,
+        operatorId: 18,
+        vehicleNumber: 1003,
+        uniqueVehicleId: "18/1003",
+        routeId: "5520",
+        directionId: 2,
+        headsign: "Matinkylä (M)",
+        startTime: "15:56",
+        nextStop: "2323253",
+        geohashLevel: 4,
+        latitude: 60.168,
+        longitude: 24.734,
+      },
+      payload: {
+        SchemaVersion: 1,
+        desi: "520",
+        dir: "2",
+        oper: 6,
+        veh: 1003,
+        tst: "2023-10-23T13:42:42.728Z",
+        tsi: 1698068562,
+        spd: 8.49,
+        hdg: 156,
+        lat: 60.168786,
+        long: 24.734465,
+        acc: -1.29,
+        dl: -101,
+        odo: 20729,
+        drst: 0,
+        oday: "2023-10-23",
+        jrn: 812,
+        line: 1110,
+        start: "15:56",
+        loc: hfp.Payload.LocationQualityMethod.GPS,
+        stop: null,
+        route: "5520",
+        occu: 0,
+      },
+    };
+    const verificationErrorMessage = hfp.Data.verify(hfpData);
+    expect(verificationErrorMessage).toBeNull();
+    const encoded = hfp.Data.encode(hfp.Data.create(hfpData)).finish();
+    const withDefaults = hfp.Data.decode(encoded);
+    const noDefaults = decodeWithoutDefaults(hfp.Data, encoded);
+    expect(withDefaults.payload).toHaveProperty("stop");
+    expect(withDefaults.payload.stop).toBeDefined();
+    expect(withDefaults.payload.stop).toStrictEqual(0);
+    expect(withDefaults.payload.loc).toStrictEqual(expect.any(Number));
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
+    expect(noDefaults.payload.stop).toBeUndefined();
+    expect(noDefaults.payload).not.toHaveProperty("stop");
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
+    expect(noDefaults.payload.loc).toStrictEqual(expect.any(Number));
+    // Change Longs to Numbers so that toMatchObject succeeds.
+    withDefaults.payload.tsi = Number(withDefaults.payload.tsi);
+    if (withDefaults.topic?.receivedAt != null) {
+      withDefaults.topic.receivedAt = Number(withDefaults.topic.receivedAt);
+    }
+    expect(withDefaults).toMatchObject(noDefaults);
+  });
+
+  test("decode MQTT message with missing topic", () => {
+    const mqttMessage = {
+      SchemaVersion: 1,
+      payload: Buffer.from("foo", "utf8"),
+    };
+    const verificationErrorMessage = mqtt.RawMessage.verify(mqttMessage);
+    expect(verificationErrorMessage).toBeNull();
+    const encoded = mqtt.RawMessage.encode(
+      mqtt.RawMessage.create(mqttMessage),
+    ).finish();
+    const withDefaults = mqtt.RawMessage.decode(encoded);
+    const noDefaults = decodeWithoutDefaults(mqtt.RawMessage, encoded);
+    expect(withDefaults).toHaveProperty("topic");
+    expect(withDefaults.topic).toBeDefined();
+    expect(withDefaults.topic).toStrictEqual("");
+    expect(noDefaults).not.toHaveProperty("topic");
+    expect(noDefaults.topic).toBeUndefined();
+    expect(withDefaults).toMatchObject(noDefaults);
+  });
+});