child_process: optimize IPC for large data

Squashed from:
- child_process: stop indexOf() on whole IPC buffer
- child_process: get rid of forEach() and slice() in IPC
- child_process: get rid of another forEach() in IPC

Fixes: nodejs#3145
PR-URL: nodejs#10557
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/child_process.js

@@ -446,14 +446,20 @@ function setupChannel(target, channel) {
   channel.onread = function(nread, pool, recvHandle) {
     // TODO(bnoordhuis) Check that nread > 0.
     if (pool) {
-      jsonBuffer += decoder.write(pool);
-
-      var i, start = 0;
+      // Linebreak is used as a message end sign
+      var chunks = decoder.write(pool).split('\n');
+      var numCompleteChunks = chunks.length - 1;
+      // Last line does not have trailing linebreak
+      var incompleteChunk = chunks[numCompleteChunks];
+      if (numCompleteChunks === 0) {
+        jsonBuffer += incompleteChunk;
+        this.buffering = jsonBuffer.length !== 0;
+        return;
+      }
+      chunks[0] = jsonBuffer + chunks[0];
 
-      //Linebreak is used as a message end sign
-      while ((i = jsonBuffer.indexOf('\n', start)) >= 0) {
-        var json = jsonBuffer.slice(start, i);
-        var message = JSON.parse(json);
+      for (var i = 0; i < numCompleteChunks; i++) {
+        var message = JSON.parse(chunks[i]);
 
         // There will be at most one NODE_HANDLE message in every chunk we
         // read because SCM_RIGHTS messages don't get coalesced. Make sure
@@ -462,10 +468,8 @@ function setupChannel(target, channel) {
           handleMessage(target, message, recvHandle);
         else
           handleMessage(target, message, undefined);
-
-        start = i + 1;
       }
-      jsonBuffer = jsonBuffer.slice(start);
+      jsonBuffer = incompleteChunk;
       this.buffering = jsonBuffer.length !== 0;
 
     } else {
@@ -494,9 +498,10 @@ function setupChannel(target, channel) {
       var queue = target._handleQueue;
       target._handleQueue = null;
 
-      queue.forEach(function(args) {
+      for (var i = 0; i < queue.length; i++) {
+        var args = queue[i];
         target._send(args.message, args.handle, args.options, args.callback);
-      });
+      }
 
       // Process a pending disconnect (if any).
       if (!target.connected && target.channel && !target._handleQueue)