handle FeedMessage without FeetEntitys 🐛💥✅

cli.js

@@ -78,8 +78,14 @@ const bindings = argv['gtfs-rt-bindings']
 const {FeedMessage} = bindings.transit_realtime || bindings
 const onFeedMessage = (buf) => {
 	const data = FeedMessage.toObject(FeedMessage.decode(buf))
-	if (!data || !data.header || !Array.isArray(data.entity)) {
-		throw new Error('invalid feed')
+	if (!data) throw new Error('invalid feed')
+	if (!data.header) throw new Error('invalid feed: missing header')
+
+	// Protocol buffers don't encode empty arrays, so .entity is missing with 0 FeedEntitys.
+	if (!('entity' in data)) {
+		data.entity = []
+	} else if (!Array.isArray(data.entity)) {
+		throw new Error('invalid feed: missing entity[]')
 	}
 
 	if (printAsJSON) {

package.json

@@ -31,7 +31,7 @@
 		"mri": "^1.1.1"
 	},
 	"scripts": {
-		"test": "cat example-feed.pbf | ./cli.js --json | wc -l",
+		"test": "./test.sh",
 		"prepublishOnly": "npm test"
 	}
 }

test.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+set -e
+set -o pipefail
+
+cd "$(dirname $0)"
+
+set -x
+
+cat example-feed.pbf | ./cli.js --json | wc -l
+
+# FeedMessage with valid FeedHeader but 0 FeedEntitys
+empty="$(echo '0a 0d 0a 03 32 2e 30 10 00 18 9d ce c4 91 06' | xxd -r -p | ./cli.js)"
+if [ "$empty" != '' ]; then
+	1>&2 echo "FeedMessage with valid FeedHeader but 0 FeedEntitys: unexpected output \`$health_status\`"
+	exit 1
+fi