fix: throw in (set|get)ters when constant == null

Author: hertzg

lib/index.js

@@ -217,7 +217,10 @@ module.exports.getKeepAliveProbes = function getKeepAliveProbes(socket) {
 /**
  * Sets the TCP_USER_TIMEOUT value for specified socket.
  *
- * Note: The msec will be rounded towards the closest integer
+ * Notes:
+ * * This method is only supported on `linux`, will throw on `darwin` and `freebsd`.
+ * * The msec will be rounded towards the closest integer.
+ *
  *
  * @since v1.4.0
  * @param {Net.Socket} socket to set the value for
@@ -229,19 +232,21 @@ module.exports.getKeepAliveProbes = function getKeepAliveProbes(socket) {
  * NetKeepAlive.setUserTimeout(s, 30000)
  *
  * @throws {AssertionError} setUserTimeout requires two arguments
+ * @throws {AssertionError} setUserTimeout called on unsupported platform
  * @throws {AssertionError} setUserTimeout expects an instance of socket as its first argument
  * @throws {AssertionError} setUserTimeout requires msec to be a Number
  * @throws {ErrnoException|Error} Unexpected error
  */
-module.exports.setUserTimeout = function setUserTimeout(
-  socket,
-  msecs
-) {
+module.exports.setUserTimeout = function setUserTimeout(socket, msecs) {
   Assert.strictEqual(
     arguments.length,
     2,
     'setUserTimeout requires two arguments'
   )
+  Assert(
+    Constants.TCP_USER_TIMEOUT != null,
+    'setUserTimeout called on unsupported platform'
+  )
   Assert(
     _isSocket(socket),
     'setUserTimeout expects an instance of socket as its first argument'
@@ -269,6 +274,8 @@ module.exports.setUserTimeout = function setUserTimeout(
 /**
  * Returns the TCP_USER_TIMEOUT value for specified socket.
  *
+ * Note: This method is only supported on `linux`, will throw on `darwin` and `freebsd`.
+ *
  * @since v1.4.0
  * @param {Net.Socket} socket to check the value for
  *
@@ -278,6 +285,7 @@ module.exports.setUserTimeout = function setUserTimeout(
  * NetKeepAlive.getUserTimeout(s) // returns 30000 based on setter example
  *
  * @throws {AssertionError} getUserTimeout requires one arguments
+ * @throws {AssertionError} getUserTimeout called on unsupported platform
  * @throws {AssertionError} getUserTimeout expects an instance of socket as its first argument
  * @throws {ErrnoException|Error} Unexpected error
  */
@@ -287,6 +295,10 @@ module.exports.getUserTimeout = function getUserTimeout(socket) {
     1,
     'getUserTimeout requires one arguments'
   )
+  Assert(
+    Constants.TCP_USER_TIMEOUT != null,
+    'getUserTimeout called on unsupported platform'
+  )
   Assert(
     _isSocket(socket),
     'getUserTimeout expects an instance of socket as its first argument'