RF: Packet type assertion

index.ts

@@ -27,6 +27,11 @@ import { validNmeaChecksum } from "./helpers";
 export type Packet = APBPacket | BWCPacket | DBTPacket | DTMPacket | GGAPacket | GLLPacket | GNSPacket | GSAPacket | GSTPacket | GSVPacket | HDGPacket | HDMPacket | HDTPacket | MTKPacket | MWVPacket | RDIDPacket | RMCPacket | VHWPacket | VTGPacket | ZDAPacket;
 export { APBPacket, BWCPacket, DBTPacket, DTMPacket, GGAPacket, GLLPacket, GNSPacket, GSAPacket, GSTPacket, GSVPacket, HDGPacket, HDMPacket, HDTPacket, MTKPacket, MWVPacket, RDIDPacket, RMCPacket, VHWPacket, VTGPacket, ZDAPacket };
 
+export function assertPacketIs<IdType extends string, PacketType extends PacketStub = Packet>(packetId: IdType, packet: PacketType): asserts packet is (PacketType & { sentenceId: IdType }) {
+    if (packet.sentenceId !== packetId) {
+        throw new Error(`Was expecting packetId of '${packetId}'. Found '${packet.sentenceId}' instead.`);
+    }
+}
 
 type Decoder = (stub: PacketStub, parts: string[]) => Packet;
 

tests/CustomPacketsTest.ts

@@ -2,7 +2,7 @@ import "should";
 
 import { initStubFields, PacketStub } from "../codecs/PacketStub";
 import { appendChecksumFooter } from "../helpers";
-import { parseGenericPacket, DefaultPacketFactory } from "../index";
+import { assertPacketIs, parseGenericPacket, DefaultPacketFactory } from "../index";
 
 
 
@@ -61,9 +61,7 @@ describe("CustomPackets", (): void => {
     it("Log", (): void => {
         const packet = parseGenericPacket(appendChecksumFooter("$P_LOG,5,everything is ok"), CUSTOM_PACKET_FACTORY);
 
-        if (packet.sentenceId !== logSentenceId) {
-            throw Error("Bad packet type");
-        }
+        assertPacketIs(logSentenceId, packet);
 
         packet.logNum.should.equal(5);
         packet.logMsg.should.equal("everything is ok");
@@ -72,9 +70,7 @@ describe("CustomPackets", (): void => {
     it("Btn", (): void => {
         const packet = parseGenericPacket(appendChecksumFooter("$P_BTN,0,L"), CUSTOM_PACKET_FACTORY);
 
-        if (packet.sentenceId !== buttonPressSentenceId) {
-            throw Error("Bad packet type");
-        }
+        assertPacketIs(buttonPressSentenceId, packet);
 
         packet.buttonId.should.equal(0);
         packet.longPress.should.equal(true);

tests/UnsafePacketsTest.ts

@@ -1,24 +1,20 @@
 import "should";
 
-import { getUnsafePacketId, parseUnsafeNmeaSentence } from "../index";
+import { assertPacketIs, getUnsafePacketId, parseUnsafeNmeaSentence } from "../index";
 
 describe("UnsafeParsing", (): void => {
     it("Built in NMEA sentence", (): void => {
         const packet = parseUnsafeNmeaSentence("$GPZDA,160012.71,11,03,2004,-1,00*7D");
 
-        if (packet.sentenceId !== "ZDA") {
-            throw Error("sentenceId should be \"ZDA\"");
-        }
+        assertPacketIs("ZDA", packet);
 
         packet.localZoneHours.should.equal(-1);
     });
 
     it("Unknown sentence", (): void => {
         const packet = parseUnsafeNmeaSentence("$GPTXT,01,01,02,ANTSTATUS=OPEN*2B");
 
-        if (packet.sentenceId !== "?") {
-            throw Error("sentenceId should be \"?\"");
-        }
+        assertPacketIs("?", packet);
 
         packet.dataFields.length.should.equal(4);
         (packet.talkerId === "GP").should.equal(true);