From 610859eb3b2fcdd017f8d000e859f23439ee6181 Mon Sep 17 00:00:00 2001
From: Hornwitser <github@hornwitser.no>
Date: Sun, 29 Dec 2019 04:22:04 +0100
Subject: [PATCH] Improve error message from statistics_exporter

If the JSON parse failed it will usually be because Factorio returned an
error message instead of JSON, pass this along for easier debugging.
---
 plugins/statistics_exporter/instance.js    |  7 ++++++-
 plugins/statistics_exporter/test/plugin.js | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/plugins/statistics_exporter/instance.js b/plugins/statistics_exporter/instance.js
index ff6644b8..d9b74927 100644
--- a/plugins/statistics_exporter/instance.js
+++ b/plugins/statistics_exporter/instance.js
@@ -23,7 +23,12 @@ const instanceGameFlowStatistics = new Gauge(
 class InstancePlugin extends plugin.BaseInstancePlugin {
 	async onMetrics() {
 		let string = await this.instance.server.sendRcon('/sc remote.call("statistics_exporter", "export")');
-		let stats =  JSON.parse(string);
+		let stats;
+		try {
+			stats = JSON.parse(string);
+		} catch (err) {
+			throw new Error(`Error parsing statistics JSON: ${err.message}, content "${string}"`);
+		}
 
 		let instanceId = this.instance.config.id;
 		instanceGameTicksTotal.labels(String(instanceId)).set(stats.game_tick);
diff --git a/plugins/statistics_exporter/test/plugin.js b/plugins/statistics_exporter/test/plugin.js
index 8d76d798..2716e7b8 100644
--- a/plugins/statistics_exporter/test/plugin.js
+++ b/plugins/statistics_exporter/test/plugin.js
@@ -48,6 +48,24 @@ describe("statistics_exporter plugin", function() {
 					'7357', 'pollution_statistics', 'input', 'boiler').get(),
 				2000);
 			});
+			it("should pass on JSON parse errors", async function() {
+				let string = 'An error occured\n';
+				instancePlugin.instance.server.rconCommandResults.set(
+					'/sc remote.call("statistics_exporter", "export")', string
+				);
+
+				let errorMessage;
+				try {
+					JSON.parse(string);
+				} catch (err) {
+					errorMessage = err.message;
+				}
+
+				await assert.rejects(
+					instancePlugin.onMetrics(),
+					new Error(`Error parsing statistics JSON: ${errorMessage}, content "${string}"`)
+				);
+			});
 		});
 	});
 });