From 4fdf3e9d7229d0e0aaeab1203c2a678e55506d35 Mon Sep 17 00:00:00 2001
From: Charles Samborski <demurgos@demurgos.net>
Date: Wed, 19 Sep 2018 09:07:53 +0200
Subject: [PATCH] refactor: IPC message forwarding

# Why

`foregroundChild` is currently hard-coded to only support forwarding with the root process. To support a general `proxy` function between any two objects behaving like processes, we can begin by refactoring the internals to be more parametrized.

# What

Move the start of the IPC message forwarding to its own function.
---
 index.js | 44 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/index.js b/index.js
index cda9a2e..a866d5e 100644
--- a/index.js
+++ b/index.js
@@ -4,6 +4,9 @@ if (process.platform === 'win32') {
   spawn = require('cross-spawn')
 }
 
+function noop() {
+}
+
 /**
  * Normalizes the arguments passed to `foregroundChild`.
  *
@@ -90,14 +93,7 @@ module.exports = function (/* program, args, cb */) {
 
   if (process.send) {
     process.removeAllListeners('message')
-
-    child.on('message', function (message, sendHandle) {
-      process.send(message, sendHandle)
-    })
-
-    process.on('message', function (message, sendHandle) {
-      child.send(message, sendHandle)
-    })
+    proxyMessages(process, child)
   }
 
   return child
@@ -120,3 +116,35 @@ function proxySignals (child) {
     }
   }
 }
+
+/**
+ * Starts forwarding IPC messages to `child` through `parent`.
+ *
+ * @param parent Parent process.
+ * @param child Child Process.
+ * @return `unproxy` function to stop the forwarding.
+ * @internal
+ */
+function proxyMessages(parent, child) {
+  if (parent.send === undefined) {
+    return noop
+  }
+
+  function childListener(message, handle) {
+    parent.send(message, handle)
+  }
+
+  function parentListener(message, handle) {
+    child.send(message, handle)
+  }
+
+  child.on('message', childListener)
+  parent.on('message', parentListener)
+
+  return unproxySignals;
+
+  function unproxySignals() {
+    child.removeListener('message', childListener)
+    parent.removeListener('message', parentListener)
+  }
+}