Add SIGKILL detection to lib/factorio/server

Check if Factorio terminated as a result of SIGKILL and throw an error
suggesting the system may be low on memory as a cause.  Also print exit
code if the unexpected shutdown occured without a signal.

lib/errors.js

@@ -12,9 +12,13 @@ class InvalidMessage extends Error { }
 // Errror class for known errors occuring during startup
 class StartupError extends Error { }
 
+// Errors outside of our control.
+class EnvironmentError extends Error { }
+
 module.exports = {
 	CommandError,
 	RequestError,
 	InvalidMessage,
 	StartupError,
+	EnvironmentError,
 }

lib/factorio/server.js

@@ -14,6 +14,8 @@ const crypto = require("crypto");
 
 const ini = require("ini");
 const rconClient = require("rcon-client");
+const errors = require("lib/errors");
+
 
 /**
  * Determines the version of Factorio the datadir is pointing to by
@@ -461,7 +463,21 @@ class FactorioServer extends events.EventEmitter {
 		this._server.on('exit', (code, signal) => {
 			if (this._state !== "stopping") {
 				if (this._unexpected.length === 0) {
-					this.emit('error', new Error("Factorio server unexpectedly shut down"));
+					if (signal === 'SIGKILL') {
+						this.emit('error', new errors.EnvironmentError(
+							"Factorio server was unexpectedly killed, is the system low on memory?"
+						));
+
+					} else {
+						let msg;
+						if (code !== null) {
+							msg = `Factorio server unexpectedly shut down with code ${code}`
+						} else {
+							msg = `Factorio server was unexpectedly shut by down by signal ${signal}`;
+						}
+
+						this.emit('error', new Error(msg));
+					}
 
 				} else if (this._unexpected.length === 1) {
 					this.emit('error', new Error(this._unexpected[0]));

test/integration/server.js

@@ -4,6 +4,7 @@ const fs = require("fs-extra");
 const path = require("path");
 
 const factorio = require("lib/factorio");
+const errors = require("lib/errors");
 
 
 describe("Integration of lib/factorio/server", function() {
@@ -182,5 +183,34 @@ describe("Integration of lib/factorio/server", function() {
 				await server.stop();
 			});
 		});
+
+		describe(".start() termination detection", function() {
+			it("should tell if Factorio got killed", async function() {
+				// This does not work on Windows
+				if (process.platform == "win32") {
+					this.skip();
+				}
+				slowTest(this);
+				log(".start() for kill detection");
+
+				let startPromise = server.start("test.zip");
+				server.once('output', () => server._server.kill('SIGKILL'));
+
+				await assert.rejects(
+					startPromise,
+					new errors.EnvironmentError("Factorio server was unexpectedly killed, is the system low on memory?")
+				);
+			});
+
+			it("should tell if Factorio unexpectedly closed with a code", async function() {
+				slowTest(this);
+				log(".start() for unexpected close detection");
+
+				await assert.rejects(
+					server.start("does-not-exist.zip"),
+					new errors.EnvironmentError("Factorio server unexpectedly shut down with code 1")
+				);
+			});
+		});
 	});
 });