fix(Label_4A_DIS): guard against comma-less DIS payloads (#493)

lib/plugins/Label_4A_DIS.test.ts

@@ -39,9 +39,8 @@ describe('Label 4A preamble DIS', () => {
     expect(decodeResult.formatted.items[2].value).toBe('@HOLD CNX');
   });
 
-  // disabled because all messages should decode
-  test.skip('decodes Label 4A_DIS <invalid>', () => {
-    message.text = '4A_DIS Bogus message';
+  test('does not throw on comma-less DIS payload', () => {
+    message.text = 'DIS';
     const decodeResult = plugin.decode(message);
 
     expect(decodeResult.decoded).toBe(false);
@@ -50,4 +49,31 @@ describe('Label 4A preamble DIS', () => {
     expect(decodeResult.formatted.description).toBe('Latest New Format');
     expect(decodeResult.formatted.items.length).toBe(0);
   });
+
+  test('does not throw on DIS with empty field after comma', () => {
+    message.text = 'DIS,';
+    const decodeResult = plugin.decode(message);
+
+    expect(decodeResult.decoded).toBe(false);
+    expect(decodeResult.decoder.decodeLevel).toBe('none');
+    expect(decodeResult.formatted.items.length).toBe(0);
+  });
+
+  test('does not decode DIS payload without comma', () => {
+    message.text = 'DIS01';
+    const decodeResult = plugin.decode(message);
+
+    expect(decodeResult.decoded).toBe(false);
+    expect(decodeResult.decoder.decodeLevel).toBe('none');
+    expect(decodeResult.formatted.items.length).toBe(0);
+  });
+
+  test('does not decode DIS payload without callsign', () => {
+    message.text = 'DIS01,190009';
+    const decodeResult = plugin.decode(message);
+
+    expect(decodeResult.decoded).toBe(false);
+    expect(decodeResult.decoder.decodeLevel).toBe('none');
+    expect(decodeResult.formatted.items.length).toBe(0);
+  });
 });

lib/plugins/Label_4A_DIS.ts

@@ -16,8 +16,14 @@ export class Label_4A_DIS extends DecoderPlugin {
   decode(message: Message, options: Options = {}): DecodeResult {
     const decodeResult = this.initResult(message, 'Latest New Format');
 
-    decodeResult.decoded = true;
     const fields = message.text.split(',');
+    if (fields.length < 3 || !fields[1] || fields[1].length < 3 || !fields[2]) {
+      decodeResult.decoded = false;
+      this.setDecodeLevel(decodeResult, decodeResult.decoded);
+      return decodeResult;
+    }
+
+    decodeResult.decoded = true;
     ResultFormatter.timestamp(
       decodeResult,
       DateTimeUtils.convertHHMMSSToTod(fields[1].substring(2) + '00'),