Added options.closeTransport.

The internal socket will be closed when the `unicast.Socket` is being closed.
You can change this behavior with this option.

lib/socket.js

@@ -12,6 +12,7 @@ const pRemoteAddress = Symbol('remoteAddress')
 const pRemotePort = Symbol('remotePort')
 const pWritableClosed = Symbol('writableClosed')
 const pReadableClosed = Symbol('readableClosed')
+const pCloseTransport = Symbol('closeTransport')
 
 /**
  * This class implements stream-based dgram socket.
@@ -52,6 +53,8 @@ module.exports = class Socket extends Duplex {
     this.once('finish', () => {
       this[pWritableClosed] = true
     })
+
+    this[pCloseTransport] = isBoolean(options.closeTransport) ? options.closeTransport : true
   }
 
   get remoteAddress() {
@@ -134,7 +137,7 @@ module.exports = class Socket extends Duplex {
   }
 
   close() {
-    if (!this[pSocketClosed]) {
+    if (!this[pSocketClosed] && this[pCloseTransport]) {
       this[pSocket].close()
       this[pSocketClosed] = true
     }
@@ -179,3 +182,12 @@ function handleMessage(message, rinfo) {
     this[pReadQueue].push(message)
   }
 }
+
+/**
+ * Check if argument is boolean.
+ * @param {any} flag
+ * @returns {boolean}
+ */
+function isBoolean(flag) {
+  return typeof flag === 'boolean'
+}

readme.md

@@ -56,6 +56,10 @@ The string representation of the local IP address. If `port` is not specified or
 
 The string representation of the local IP address. If `address` is not specified or is `0.0.0.0`, the operating system will attempt to listen on all addresses.
 
+* `options.closeTransport: boolean [default = true]`
+
+The internal socket will be closed when the `unicast.Socket` is being closed. You can change this behavior with this option.
+
 * `class Socket`
 
 This class is an abstraction of an unicast UDP socket. A `Socket` is also a [duplex stream](https://nodejs.org/api/stream.html#stream_class_stream_duplex), so it can be both readable and writable, and it is also a [EventEmitter](https://nodejs.org/api/events.html#events_class_eventemitter).

test/socket.js

@@ -199,6 +199,58 @@ test('should close when dgram socket is closed', () => {
   expect(mock.close).not.toBeCalled()
 })
 
+test('should not close the socket then `closeTransport = false`', () => {
+  const mock = Object.assign(new Emitter(), {
+    send: jest.fn(),
+    close: jest.fn()
+  })
+
+  const socket = new Socket({
+    socket: mock,
+    remotePort: 1111,
+    remoteAddress: '127.0.0.1',
+    closeTransport: false
+  })
+
+  socket.push = jest.fn(() => true)
+  socket.end = jest.fn()
+
+  socket._read()
+  socket.close()
+
+  expect(socket.push).toHaveBeenCalledTimes(1)
+  expect(socket.push).toHaveBeenCalledWith(null)
+
+  expect(socket.end).toHaveBeenCalledTimes(1)
+  expect(mock.close).toHaveBeenCalledTimes(0)
+})
+
+test('should close the socket then `closeTransport = true`', () => {
+  const mock = Object.assign(new Emitter(), {
+    send: jest.fn(),
+    close: jest.fn()
+  })
+
+  const socket = new Socket({
+    socket: mock,
+    remotePort: 1111,
+    remoteAddress: '127.0.0.1',
+    closeTransport: true
+  })
+
+  socket.push = jest.fn(() => true)
+  socket.end = jest.fn()
+
+  socket._read()
+  socket.close()
+
+  expect(socket.push).toHaveBeenCalledTimes(1)
+  expect(socket.push).toHaveBeenCalledWith(null)
+
+  expect(socket.end).toHaveBeenCalledTimes(1)
+  expect(mock.close).toHaveBeenCalledTimes(1)
+})
+
 test('should free queue when socket is closed', () => {
   const mock = Object.assign(new Emitter(), {
     send: jest.fn(),