Copy save if the save to start is an autosave

Prevent potential data loss when starting an autosave by copying it
first.  This avoids overwriting a random autosave slot when the server
shuts down after having loaded an autosave.

packages/slave/slave.js

@@ -461,6 +461,23 @@ class Instance extends libLink.Link {
 			saveName = "world.zip";
 		}
 
+		// Load a copy if it's autosave to prevent overwriting the autosave
+		if (saveName.startsWith("_autosave")) {
+			this.logger.info("Copying autosave");
+			let now = new Date();
+			let newName = util.format(
+				"%s-%s-%s %s%s %s",
+				now.getUTCFullYear(),
+				(now.getUTCMonth() + 1).toLocaleString("en", { minimumIntegerDigits: 2 }),
+				now.getUTCDate().toLocaleString("en", { minimumIntegerDigits: 2 }),
+				now.getUTCHours().toLocaleString("en", { minimumIntegerDigits: 2 }),
+				now.getUTCMinutes().toLocaleString("en", { minimumIntegerDigits: 2 }),
+				saveName,
+			);
+			await fs.copy(this.path("saves", saveName), this.path("saves", newName));
+			saveName = newName;
+		}
+
 		if (!this.config.get("factorio.enable_save_patching")) {
 			return saveName;
 		}

test/integration/clusterio.js

@@ -173,11 +173,21 @@ describe("Integration of Clusterio", function() {
 		});
 
 		describe("instance start", function() {
-			it("starts the instance", async function() {
+			it("starts the given save", async function() {
 				slowTest(this);
-				await execCtl("instance start test");
+				await execCtl("instance start test --save world.zip");
 				await checkInstanceStatus(44, "running");
 			});
+			it("copies the save if an autosave is the target", async function() {
+				slowTest(this);
+				await execCtl("instance stop 44");
+				let savesDir = path.join("temp", "test", "instances", "test", "saves");
+				await fs.copy(path.join(savesDir, "world.zip"), path.join(savesDir, "_autosave1.zip"));
+				await execCtl("instance start test");
+				let result = await libLink.messages.listSaves.send(getControl(), { instance_id: 44 });
+				let running = result.list.find(s => s.loaded);
+				assert(running.name !== "_autosave1.zip");
+			});
 		});
 
 		describe("instance send-rcon", function() {