fix(client): skip body if method is head

In case of HEAD method `client.parser.[HTTPParser.kOnHeadersComplete]`
should tell the http parser to skip the body by returning 1 or true.
Also `this._lastBody` assignment is skipped.

See https://github.com/creationix/http-parser-js/blob/master/http-parser.js#L362

lib/client.js

@@ -217,10 +217,15 @@ class Client extends EventEmitter {
       // TODO move this[kCallbacks] from being an array. The array allocation
       // is showing up in the flamegraph.
       const cb = this[kCallbacks].shift()
+      const request = this[kRequests].shift()
+      let skipBody
       this._needHeaders--
-      this._lastBody = new Readable({ read: this[kRead].bind(this) })
-      this._lastBody.push = this[kRequests].shift().wrapSimple(this._lastBody, this._lastBody.push)
-
+      if (request.method === 'HEAD') {
+        skipBody = 1
+      } else {
+        this._lastBody = new Readable({ read: this[kRead].bind(this) })
+        this._lastBody.push = request.wrapSimple(this._lastBody, this._lastBody.push)
+      }
       cb(null, {
         statusCode,
         headers: parseHeaders(headers),
@@ -230,6 +235,8 @@ class Client extends EventEmitter {
       if (this.closed && this[kQueue].length() === 0) {
         this.destroy()
       }
+
+      return skipBody
     }
 
     this.parser[HTTPParser.kOnBody] = (chunk, offset, length) => {
@@ -239,7 +246,7 @@ class Client extends EventEmitter {
     this.parser[HTTPParser.kOnMessageComplete] = () => {
       const body = this._lastBody
       this._lastBody = null
-      body.push(null)
+      body && body.push(null)
     }
 
     this[kReadCb] = () => {

test/client.js

@@ -36,6 +36,31 @@ test('basic get', (t) => {
   })
 })
 
+test('basic head', (t) => {
+  t.plan(7)
+
+  const server = createServer((req, res) => {
+    t.strictEqual('/', req.url)
+    t.strictEqual('HEAD', req.method)
+    t.strictEqual('localhost', req.headers.host)
+    res.setHeader('content-type', 'text/plain')
+    res.end('hello')
+  })
+  t.tearDown(server.close.bind(server))
+
+  server.listen(0, () => {
+    const client = new Client(`http://localhost:${server.address().port}`)
+    t.tearDown(client.close.bind(client))
+
+    client.request({ path: '/', method: 'HEAD' }, (err, { statusCode, headers, body }) => {
+      t.error(err)
+      t.strictEqual(statusCode, 200)
+      t.strictEqual(headers['content-type'], 'text/plain')
+      t.strictEqual(body, null)
+    })
+  })
+})
+
 test('get with host header', (t) => {
   t.plan(7)
 
@@ -67,6 +92,31 @@ test('get with host header', (t) => {
   })
 })
 
+test('head with host header', (t) => {
+  t.plan(7)
+
+  const server = createServer((req, res) => {
+    t.strictEqual('/', req.url)
+    t.strictEqual('HEAD', req.method)
+    t.strictEqual('example.com', req.headers.host)
+    res.setHeader('content-type', 'text/plain')
+    res.end('hello from ' + req.headers.host)
+  })
+  t.tearDown(server.close.bind(server))
+
+  server.listen(0, () => {
+    const client = new Client(`http://localhost:${server.address().port}`)
+    t.tearDown(client.close.bind(client))
+
+    client.request({ path: '/', method: 'HEAD', headers: { host: 'example.com' } }, (err, { statusCode, headers, body }) => {
+      t.error(err)
+      t.strictEqual(statusCode, 200)
+      t.strictEqual(headers['content-type'], 'text/plain')
+      t.strictEqual(body, null)
+    })
+  })
+})
+
 function postServer (t, expected) {
   return function (req, res) {
     t.strictEqual(req.url, '/')
@@ -290,6 +340,33 @@ test('10 times GET', (t) => {
   })
 })
 
+test('10 times HEAD', (t) => {
+  const num = 10
+  t.plan(3 * 10)
+
+  const server = createServer((req, res) => {
+    res.end(req.url)
+  })
+  t.tearDown(server.close.bind(server))
+
+  server.listen(0, () => {
+    const client = new Client(`http://localhost:${server.address().port}`)
+    t.tearDown(client.close.bind(client))
+
+    for (var i = 0; i < num; i++) {
+      makeRequest(i)
+    }
+
+    function makeRequest (i) {
+      client.request({ path: '/' + i, method: 'HEAD' }, (err, { statusCode, headers, body }) => {
+        t.error(err)
+        t.strictEqual(statusCode, 200)
+        t.strictEqual(body, null)
+      })
+    }
+  })
+})
+
 test('20 times GET with pipelining 10', (t) => {
   const num = 20
   t.plan(3 * num + 1)
@@ -348,6 +425,58 @@ function makeRequestAndExpectUrl (client, i, t, cb) {
   })
 }
 
+test('20 times HEAD with pipelining 10', (t) => {
+  const num = 20
+  t.plan(3 * num + 1)
+
+  let count = 0
+  let countGreaterThanOne = false
+  const server = createServer((req, res) => {
+    count++
+    setTimeout(function () {
+      countGreaterThanOne = countGreaterThanOne || count > 1
+      res.end(req.url)
+    }, 10)
+  })
+  t.tearDown(server.close.bind(server))
+
+  // needed to check for a warning on the maxListeners on the socket
+  process.on('warning', t.fail)
+  t.tearDown(() => {
+    process.removeListener('warning', t.fail)
+  })
+
+  server.listen(0, () => {
+    const client = new Client(`http://localhost:${server.address().port}`, {
+      pipelining: 10
+    })
+    t.tearDown(client.close.bind(client))
+
+    for (let i = 0; i < num; i++) {
+      makeRequest(i)
+    }
+
+    function makeRequest (i) {
+      makeHeadRequestAndExpectUrl(client, i, t, () => {
+        count--
+
+        if (i === num - 1) {
+          t.ok(countGreaterThanOne, 'seen more than one parallel request')
+        }
+      })
+    }
+  })
+})
+
+function makeHeadRequestAndExpectUrl (client, i, t, cb) {
+  return client.request({ path: '/' + i, method: 'HEAD' }, (err, { statusCode, headers, body }) => {
+    cb()
+    t.error(err)
+    t.strictEqual(statusCode, 200)
+    t.strictEqual(body, null)
+  })
+}
+
 test('A client should enqueue as much as twice its pipelining factor', (t) => {
   const num = 10
   let sent = 0