Cleanup in determining implicit content-type

fetch.js

@@ -128,16 +128,10 @@
       this._bodyInit = body
       if (typeof body === 'string') {
         this._bodyText = body
-        return 'text/plain;charset=UTF-8'
       } else if (support.blob && Blob.prototype.isPrototypeOf(body)) {
         this._bodyBlob = body
-        if (body.type !== '') {
-          return body.type
-        }
       } else if (support.formData && FormData.prototype.isPrototypeOf(body)) {
         this._bodyFormData = body
-        // Since we don't know what the multipart/form-data boundary string
-        // will be, we can't set a Content-Type here
       } else if (!body) {
         this._bodyText = ''
       } else if (support.arrayBuffer && ArrayBuffer.prototype.isPrototypeOf(body)) {
@@ -146,6 +140,14 @@
       } else {
         throw new Error('unsupported BodyInit type')
       }
+
+      if (!this.headers.get('content-type')) {
+        if (typeof body === 'string') {
+          this.headers.set('content-type', 'text/plain;charset=UTF-8')
+        } else if (this._bodyBlob && this._bodyBlob.type) {
+          this.headers.set('content-type', this._bodyBlob.type)
+        }
+      }
     }
 
     if (support.blob) {
@@ -213,7 +215,6 @@
   function Request(input, options) {
     options = options || {}
     var body = options.body
-    var bodyFromOptions = true
     if (Request.prototype.isPrototypeOf(input)) {
       if (input.bodyUsed) {
         throw new TypeError('Already read')
@@ -228,7 +229,6 @@
       if (!body) {
         body = input._bodyInit
         input.bodyUsed = true
-        bodyFromOptions = false
       }
     } else {
       this.url = input
@@ -245,10 +245,7 @@
     if ((this.method === 'GET' || this.method === 'HEAD') && body) {
       throw new TypeError('Body not allowed for GET or HEAD requests')
     }
-    var contentType = this._initBody(body)
-    if (bodyFromOptions && contentType && !this.headers.get('Content-Type')) {
-      this.headers.set('Content-Type', contentType)
-    }
+    this._initBody(body)
   }
 
   Request.prototype.clone = function() {
@@ -287,16 +284,13 @@
       options = {}
     }
 
-    this.headers = options.headers instanceof Headers ? options.headers : new Headers(options.headers)
-    var contentType = this._initBody(bodyInit)
-    if (contentType && !this.headers.get('Content-Type')) {
-      this.headers.set('Content-Type', contentType)
-    }
     this.type = 'default'
     this.status = options.status
     this.ok = this.status >= 200 && this.status < 300
     this.statusText = options.statusText
+    this.headers = options.headers instanceof Headers ? options.headers : new Headers(options.headers)
     this.url = options.url || ''
+    this._initBody(bodyInit)
   }
 
   Body.call(Response.prototype)

test/test.js

@@ -312,7 +312,7 @@ suite('Request', function() {
       body: 'I work out',
       headers: {
         accept: 'application/json',
-        'Content-Type': 'text/plain'
+        'X-Request-ID': '123'
       }
     })
     var request2 = new Request(request1, {
@@ -320,7 +320,7 @@ suite('Request', function() {
     })
 
     assert.equal(request2.headers.get('accept'), undefined)
-    assert.equal(request2.headers.get('content-type'), undefined)
+    assert.equal(request2.headers.get('x-request-id'), undefined)
     assert.equal(request2.headers.get('x-test'), '42')
   })
 
@@ -356,6 +356,18 @@ suite('Request', function() {
     })
   })
 
+  test('GET should not have implicit Content-Type', function() {
+    var req = new Request('https://fetch.spec.whatwg.org/')
+    assert.equal(req.headers.get('content-type'), undefined)
+  })
+
+  test('POST with blank body should not have implicit Content-Type', function() {
+    var req = new Request('https://fetch.spec.whatwg.org/', {
+      method: 'post'
+    })
+    assert.equal(req.headers.get('content-type'), undefined)
+  })
+
   test('construct with string body sets Content-Type header', function() {
     var req = new Request('https://fetch.spec.whatwg.org/', {
       method: 'post',
@@ -365,25 +377,33 @@ suite('Request', function() {
     assert.equal(req.headers.get('content-type'), 'text/plain;charset=UTF-8')
   })
 
-  ;(Request.prototype.blob ? test : test.skip)('construct with Blob body and type sets Content-Type header', function() {
+  featureDependent(test, support.blob, 'construct with Blob body and type sets Content-Type header', function() {
     var req = new Request('https://fetch.spec.whatwg.org/', {
       method: 'post',
-      body: new Blob(['test'], { type: 'text/plain' }),
+      body: new Blob(['test'], { type: 'image/png' })
     })
 
-    assert.equal(req.headers.get('content-type'), 'text/plain')
+    assert.equal(req.headers.get('content-type'), 'image/png')
   })
 
   test('construct with body and explicit header uses header', function() {
     var req = new Request('https://fetch.spec.whatwg.org/', {
       method: 'post',
-      headers: {
-        'Content-Type': 'text/plain'
-      },
+      headers: { 'Content-Type': 'image/png' },
       body: 'I work out'
     })
 
-    assert.equal(req.headers.get('content-type'), 'text/plain')
+    assert.equal(req.headers.get('content-type'), 'image/png')
+  })
+
+  featureDependent(test, support.blob, 'construct with Blob body and explicit Content-Type header', function() {
+    var req = new Request('https://fetch.spec.whatwg.org/', {
+      method: 'post',
+      headers: { 'Content-Type': 'image/png' },
+      body: new Blob(['test'], { type: 'text/plain' })
+    })
+
+    assert.equal(req.headers.get('content-type'), 'image/png')
   })
 
   test('clone request', function() {
@@ -564,7 +584,7 @@ suite('Response', function() {
     assert.equal(r.headers.get('content-type'), 'text/plain;charset=UTF-8')
   })
 
-  ;(Response.prototype.blob ? test : test.skip)('construct with Blob body and type sets Content-Type header', function() {
+  featureDependent(test, support.blob, 'construct with Blob body and type sets Content-Type header', function() {
     var r = new Response(new Blob(['test'], { type: 'text/plain' }))
     assert.equal(r.headers.get('content-type'), 'text/plain')
   })