net: Track state of setKeepAlive and prevent unnecessary system calls

lib/net.js

@@ -258,6 +258,7 @@ function initSocketHandle(self) {
 const kBytesRead = Symbol('kBytesRead');
 const kBytesWritten = Symbol('kBytesWritten');
 const kSetNoDelay = Symbol('kSetNoDelay');
+const kSetKeepAlive = Symbol('kSetKeepAlive');
 
 function Socket(options) {
   if (!(this instanceof Socket)) return new Socket(options);
@@ -273,6 +274,7 @@ function Socket(options) {
   this._host = null;
   this[kSetNoDelay] = false;
   this[kLastWriteQueueSize] = 0;
+  this[kSetKeepAlive] = null;
   this[kTimeout] = null;
   this[kBuffer] = null;
   this[kBufferCb] = null;
@@ -500,13 +502,26 @@ Socket.prototype.setNoDelay = function(enable) {
 
 
 Socket.prototype.setKeepAlive = function(setting, msecs) {
+  if (setting != null && typeof setting !== 'boolean')
+    throw new ERR_INVALID_ARG_TYPE('enable', 'boolean', setting);
+
+  if (msecs != null && typeof msecs !== 'number')
+    throw new ERR_INVALID_ARG_TYPE('msecs', 'number', msecs);
+
+  if (msecs === 0) {
+    return;
+  }
+
   if (!this._handle) {
     this.once('connect', () => this.setKeepAlive(setting, msecs));
     return this;
   }
 
-  if (this._handle.setKeepAlive)
+  if (this._handle.setKeepAlive &&
+    this[kSetKeepAlive] !== setting) {
     this._handle.setKeepAlive(setting, ~~(msecs / 1000));
+    this[kSetKeepAlive] = setting;
+  }
 
   return this;
 };