Test parseResponseHeaders function and extract to module

This pulls the `parseResponseHeaders` function out of `DS.RestAdapter`
and moves it to its own module.

The main reason for this was to make it easier to unit test in order to
document current behavior before working on fixing the
emberjs#4122

addon/-private/adapters/parse-response-headers.js

@@ -0,0 +1,27 @@
+import EmptyObject from 'ember-data/-private/system/empty-object';
+
+export default function parseResponseHeaders(headersString) {
+  let headers = new EmptyObject();
+
+  if (!headersString) {
+    return headers;
+  }
+
+  let headerPairs = headersString.split('\u000d\u000a');
+
+  for (let i = 0; i < headerPairs.length; i++) {
+    let headerPair = headerPairs[i];
+    // Can't use split() here because it does the wrong thing
+    // if the header value has the string ": " in it.
+    let index = headerPair.indexOf('\u003a\u0020');
+
+    if (index > 0) {
+      let key = headerPair.substring(0, index);
+      let val = headerPair.substring(index + 2);
+
+      headers[key] = val;
+    }
+  }
+
+  return headers;
+}

addon/adapters/rest.js

@@ -10,9 +10,9 @@ import {
   TimeoutError,
   AbortError
 } from 'ember-data/-private/adapters/errors';
-import EmptyObject from "ember-data/-private/system/empty-object";
 import BuildURLMixin from "ember-data/-private/adapters/build-url-mixin";
 import isEnabled from 'ember-data/-private/features';
+import parseResponseHeaders from 'ember-data/-private/adapters/parse-response-headers';
 
 const {
   MapWithDefault,
@@ -1006,26 +1006,6 @@ export default Adapter.extend(BuildURLMixin, {
   }
 });
 
-function parseResponseHeaders(headerStr) {
-  var headers = new EmptyObject();
-  if (!headerStr) { return headers; }
-
-  var headerPairs = headerStr.split('\u000d\u000a');
-  for (var i = 0; i < headerPairs.length; i++) {
-    var headerPair = headerPairs[i];
-    // Can't use split() here because it does the wrong thing
-    // if the header value has the string ": " in it.
-    var index = headerPair.indexOf('\u003a\u0020');
-    if (index > 0) {
-      var key = headerPair.substring(0, index);
-      var val = headerPair.substring(index + 2);
-      headers[key] = val;
-    }
-  }
-
-  return headers;
-}
-
 //From http://stackoverflow.com/questions/280634/endswith-in-javascript
 function endsWith(string, suffix) {
   if (typeof String.prototype.endsWith !== 'function') {

tests/unit/adapters/parse-response-headers-test.js

@@ -0,0 +1,43 @@
+import EmptyObject from 'ember-data/-private/system/empty-object';
+import parseResponseHeaders from 'ember-data/-private/adapters/parse-response-headers';
+import { module, test } from 'qunit';
+
+const CRLF = '\u000d\u000a';
+
+module('unit/adapters/parse-response-headers');
+
+test('returns an EmptyObject when headersString is undefined', function(assert) {
+  let headers = parseResponseHeaders(undefined);
+
+  assert.deepEqual(headers, new EmptyObject(), 'EmptyObject is returned');
+});
+
+test('header parsing', function(assert) {
+  let headersString = [
+    'Content-Encoding: gzip',
+    'content-type: application/json; charset=utf-8',
+    'date: Fri, 05 Feb 2016 21:47:56 GMT',
+    'Apple-Field: value with leading whitespace',
+    'Bear-Field: value that contains: a colon'
+  ].join(CRLF);
+
+  let headers = parseResponseHeaders(headersString);
+
+  assert.equal(headers['Content-Encoding'], 'gzip', 'parses basic header pair');
+  assert.equal(headers['content-type'], 'application/json; charset=utf-8', 'parses header with complex value');
+  assert.equal(headers['date'], 'Fri, 05 Feb 2016 21:47:56 GMT', 'parses header with date value');
+  assert.equal(headers['Apple-Field'], 'value with leading whitespace', 'strips leading whitespace from field-value');
+  assert.equal(headers['Bear-Field'], 'value that contains: a colon', 'has correct value when value contins a colon');
+});
+
+test('ignores headers that do not contain a colon', function(assert) {
+  let headersString = [
+    'Content-Encoding: gzip',
+    'I am ignored because I do not contain a colon'
+  ].join(CRLF);
+
+  let headers = parseResponseHeaders(headersString);
+
+  assert.deepEqual(headers['Content-Encoding'], 'gzip', 'parses basic header pair');
+  assert.equal(Object.keys(headers).length, 1, 'only has the one valid header');
+});