Of nextTicks and sockets

socket-destroyed.js

var http = require('http')

var server = http.createServer(function (req, res) {
	res.writeHead(200, {'Content-Type': 'text/plain'})
	res.end('Hello World\n')
}).listen(1337)

var agent = new http.Agent({maxSockets: 1})

agent.on('free', function (socket, host, port) {
	console.log('freeing socket. destroyed? ', socket.destroyed)
})

var requestOptions = { agent: agent, host: 'localhost', port: 1337, path: '/' }

var request1 = http.get(
	requestOptions,
	function (response) {
		// assert request2 is queued in the agent
		console.assert(agent.requests['localhost:1337'].length === 1)
		console.log('got response1')
		request1.socket.on(
			'close',
			function () {
				console.log('request1 socket closed')
			}
		)
		response.pipe(process.stdout)
		response.on(
			'end',
			function () {
				console.log('response1 done')
				/////////////////////////////////
				//
				// THE IMPORTANT PART
				//
				// It is possible for the socket to get destroyed and other work
				// to run before the 'close' event fires because it happens on
				// nextTick. This example is contrived because it destroys the
				// socket manually at just the right time, but at Voxer we have
				// seen cases where the socket is destroyed by non-user code
				// then handed out again by an agent *before* the 'close' event
				// is triggered.
				request1.socket.destroy()


				process.nextTick(
					function () {
						// assert request2 was removed from the queue
						console.assert(!agent.requests['localhost:1337'])
						console.log("waiting for request2.onSocket's nextTick")
						process.nextTick(
							function () {
								// assert that the same socket is assigned to request2
								console.assert(request1.socket === request2.socket)
								console.assert(!request2.socket.destroyed, 'the socket is destroyed')
							}
						)
					}
				)
			}
		)
	}
)

var request2 = http.get(
	requestOptions,
	function (response) {
		console.assert(!request2.socket.destroyed)
		// assert reusing the same socket
		console.assert(request1.socket === request2.socket)
		console.log('got response2')
		request2.socket.on(
			'close',
			function () {
				console.log('request2 socket closed')
			}
		)
		response.pipe(process.stdout)
		response.on('end', function () {
			console.log('response2 done')
		})
	}
)