Buffer IPC sends to avoid crashes

Workaround for nodejs/node#34797

lib/fork.js

@@ -3,6 +3,7 @@ const childProcess = require('child_process');
 const path = require('path');
 const fs = require('fs');
 const Emittery = require('emittery');
+const {controlFlow} = require('./ipc-flow-control');
 
 if (fs.realpathSync(__filename) !== __filename) {
 	console.warn('WARNING: `npm link ava` and the `--preserve-symlink` flag are incompatible. We have detected that AVA is linked via `npm link`, and that you are using either an early version of Node 6, or the `--preserve-symlink` flag. This breaks AVA. You should upgrade to Node 6.2.0+, avoid the `--preserve-symlink` flag, or avoid using `npm link ava`.');
@@ -52,12 +53,12 @@ module.exports = (file, options, execArgv = process.execArgv) => {
 		emitStateChange({type: 'worker-stderr', chunk});
 	});
 
+	const bufferedSend = controlFlow(subprocess);
+
 	let forcedExit = false;
 	const send = evt => {
-		if (subprocess.connected && !finished && !forcedExit) {
-			subprocess.send({ava: evt}, () => {
-				// Disregard errors.
-			});
+		if (!finished && !forcedExit) {
+			bufferedSend({ava: evt});
 		}
 	};
 

lib/ipc-flow-control.js

@@ -0,0 +1,40 @@
+// Manage how quickly messages are delivered to the channel. In theory, we
+// should be able to call `send()` until it returns `false` but this leads to
+// crashes with advanced serialization, see
+// <https://github.com/nodejs/node/issues/34797>.
+//
+// Even if that's fixed (and the Node.js versions with the fixes are the
+// minimally supported versions) we need flow control based on `send()`'s return
+// value.
+
+function controlFlow(channel) {
+	let sending = false;
+
+	const buffer = [];
+	const deliverNext = () => {
+		if (!channel.connected) {
+			buffer.length = 0;
+		}
+
+		if (buffer.length === 0) {
+			sending = false;
+			return;
+		}
+
+		channel.send(buffer.shift(), deliverNext);
+	};
+
+	return message => {
+		if (!channel.connected) {
+			return;
+		}
+
+		buffer.push(message);
+		if (!sending) {
+			sending = true;
+			setImmediate(deliverNext);
+		}
+	};
+}
+
+exports.controlFlow = controlFlow;

lib/worker/ipc.js

@@ -1,5 +1,6 @@
 'use strict';
 const Emittery = require('emittery');
+const {controlFlow} = require('../ipc-flow-control');
 
 const emitter = new Emittery();
 process.on('message', message => {
@@ -25,10 +26,9 @@ process.on('message', message => {
 exports.options = emitter.once('options');
 exports.peerFailed = emitter.once('peerFailed');
 
+const bufferedSend = controlFlow(process);
 function send(evt) {
-	if (process.connected) {
-		process.send({ava: evt});
-	}
+	bufferedSend({ava: evt});
 }
 
 exports.send = send;