Allow passing a Request instance to Request constructor

fetch.js

@@ -200,20 +200,40 @@
     return (methods.indexOf(upcased) > -1) ? upcased : method
   }
 
-  function Request(url, options) {
+  function Request(input, options) {
     options = options || {}
-    this.url = url
+    var body = options.body
+    if (Request.prototype.isPrototypeOf(input)) {
+      if (input.bodyUsed) {
+        throw new TypeError('Already read')
+      }
+      this.url = input.url
+      this.credentials = input.credentials
+      if (!options.headers) {
+        this.headers = new Headers(input.headers)
+      }
+      this.method = input.method
+      this.mode = input.mode
+      if (!body) {
+        body = input._bodyInit
+        input.bodyUsed = true
+      }
+    } else {
+      this.url = input
+    }
 
-    this.credentials = options.credentials || 'omit'
-    this.headers = new Headers(options.headers)
-    this.method = normalizeMethod(options.method || 'GET')
-    this.mode = options.mode || null
+    this.credentials = options.credentials || this.credentials || 'omit'
+    if (options.headers || !this.headers) {
+      this.headers = new Headers(options.headers)
+    }
+    this.method = normalizeMethod(options.method || this.method || 'GET')
+    this.mode = options.mode || this.mode || null
     this.referrer = null
 
-    if ((this.method === 'GET' || this.method === 'HEAD') && options.body) {
+    if ((this.method === 'GET' || this.method === 'HEAD') && body) {
       throw new TypeError('Body not allowed for GET or HEAD requests')
     }
-    this._initBody(options.body)
+    this._initBody(body)
   }
 
   function decode(body) {
@@ -265,7 +285,6 @@
   self.Response = Response;
 
   self.fetch = function(input, init) {
-    // TODO: Request constructor should accept input, init
     var request
     if (Request.prototype.isPrototypeOf(input) && !init) {
       request = input

test/test.js

@@ -202,6 +202,82 @@ suite('Request', function() {
     assert.equal(request.url, 'https://fetch.spec.whatwg.org/')
   })
 
+  test('construct with Request', function() {
+    var request1 = new Request('https://fetch.spec.whatwg.org/', {
+      method: 'post',
+      body: 'I work out',
+      headers: {
+        accept: 'application/json',
+        'Content-Type': 'text/plain'
+      }
+    })
+    var request2 = new Request(request1)
+
+    return request2.text().then(function(body2) {
+      assert.equal(body2, 'I work out')
+      assert.equal(request2.method, 'POST')
+      assert.equal(request2.url, 'https://fetch.spec.whatwg.org/')
+      assert.equal(request2.headers.get('accept'), 'application/json')
+      assert.equal(request2.headers.get('content-type'), 'text/plain')
+
+      return request1.text().then(function() {
+        assert(false, 'original request body should have been consumed')
+      }, function(error) {
+        assert(error instanceof TypeError, 'expected TypeError for already read body')
+      })
+    })
+  })
+
+  test('construct with Request and override headers', function() {
+    var request1 = new Request('https://fetch.spec.whatwg.org/', {
+      method: 'post',
+      body: 'I work out',
+      headers: {
+        accept: 'application/json',
+        'Content-Type': 'text/plain'
+      }
+    })
+    var request2 = new Request(request1, {
+      headers: { 'x-test': '42' }
+    })
+
+    assert.equal(request2.headers.get('accept'), undefined)
+    assert.equal(request2.headers.get('content-type'), undefined)
+    assert.equal(request2.headers.get('x-test'), '42')
+  })
+
+  test('construct with Request and override body', function() {
+    var request1 = new Request('https://fetch.spec.whatwg.org/', {
+      method: 'post',
+      body: 'I work out',
+      headers: {
+        'Content-Type': 'text/plain'
+      }
+    })
+    var request2 = new Request(request1, {
+      body: '{"wiggles": 5}',
+      headers: { 'Content-Type': 'application/json' }
+    })
+
+    return request2.json().then(function(data) {
+      assert.equal(data.wiggles, 5)
+      assert.equal(request2.headers.get('content-type'), 'application/json')
+    })
+  })
+
+  ;(/Chrome\//.test(navigator.userAgent) ? test.skip : test)('construct with used Request body', function() {
+    var request1 = new Request('https://fetch.spec.whatwg.org/', {
+      method: 'post',
+      body: 'I work out'
+    })
+
+    return request1.text().then(function() {
+      assert.throws(function() {
+        new Request(request1)
+      }, TypeError)
+    })
+  })
+
   // https://fetch.spec.whatwg.org/#concept-bodyinit-extract
   suite('BodyInit extract', function() {
     ;(Request.prototype.blob ? suite : suite.skip)('type Blob', function() {
@@ -431,7 +507,11 @@ suite('Body mixin', function() {
         response.formData()
         return response.formData()
       }).catch(function(error) {
-        assert(error instanceof TypeError, 'Promise rejected after body consumed')
+        if (error instanceof chai.AssertionError) {
+          throw error
+        } else {
+          assert(error instanceof TypeError, 'Promise rejected after body consumed')
+        }
       })
     })