fix: throwing w/ fresh ember-cli-fastboot serve

ember-cli-fastboot requires configuring host whitelist before accessing
host from request. In ember-fetch, the error should be lazily thrown.

fastboot/instance-initializers/setup-fetch.js

@@ -9,8 +9,12 @@ function patchFetchForRelativeURLs(instance) {
   const request = fastboot.get('request');
   // Prember is not sending protocol
   const protocol = request.protocol === 'undefined:' ? 'http:' : request.protocol;
-  // host is cp
-  setupFastboot(protocol, request.get('host'));
+  try {
+    // host is cp
+    setupFastboot(protocol, request.get('host'));
+  } catch (_e) {
+    // Do not throw error until request with a relative url.
+  }
 }
 
 export default {

public/fetch-fastboot.js

@@ -8,6 +8,14 @@ define('fetch', ['exports'], function(exports) {
   );
   var nodeFetch = FastBoot.require('node-fetch');
 
+  function _checkHost(host) {
+    if (host === null) {
+      throw new Error(
+        'You are using using fetch with a relative URL, but host is missing from Fastboot request. Please set the hostWhitelist property in your environment.js. https://github.com/ember-fastboot/ember-cli-fastboot#host'
+      );
+    }
+  }
+
   /**
    * Build the absolute url if it's not, can handle:
    * - protocol-relative URL (//can-be-http-or-https.com/)
@@ -20,19 +28,17 @@ define('fetch', ['exports'], function(exports) {
    */
   function buildAbsoluteUrl(url, protocol, host) {
     if (protocolRelativeRegex.test(url)) {
+      _checkHost(host);
       url = host + url;
     } else if (!httpRegex.test(url)) {
-      if (!host) {
-        throw new Error(
-          'You are using using fetch with a path-relative URL, but host is missing from Fastboot request. Please set the hostWhitelist property in your environment.js.'
-        );
-      }
+      _checkHost(host);
       url = protocol + '//' + host + url;
     }
     return url;
   }
 
-  var FastbootHost, FastbootProtocol;
+  var FastbootHost = null;
+  var FastbootProtocol = null;
 
   class FastBootRequest extends nodeFetch.Request {
     constructor(input, init) {

test/fastboot-fetch-test.js

@@ -0,0 +1,55 @@
+'use strict';
+const request = require('request');
+const get = require('rsvp').denodeify(request);
+const chai = require('chai');
+const expect = chai.expect;
+chai.use(require('chai-fs'));
+
+const AddonTestApp = require('ember-cli-addon-tests').AddonTestApp;
+
+describe('renders in fastboot build', function() {
+  this.timeout(300000);
+
+  let app;
+
+  beforeEach(function() {
+    app = new AddonTestApp();
+
+    return app
+      .create('dummy', { skipNpm: true })
+      .then(app =>
+        app.editPackageJSON(pkg => {
+          pkg.devDependencies['ember-cli-fastboot'] = '*';
+          // [email protected] has ember-fetch as dependency, we want to test
+          pkg.devDependencies['ember-fetch-adapter'] = '0.4.0';
+          // These 2 are in ember-fetch's package.json, symlinking to dummy won't help resolve
+          pkg.devDependencies['abortcontroller-polyfill'] = '*';
+          pkg.devDependencies['node-fetch'] = '*';
+        })
+      )
+      .then(function() {
+        return app.run('npm', 'install');
+      })
+      .then(function() {
+        return app.startServer({
+          command: 'serve'
+        });
+      });
+  });
+
+  afterEach(function() {
+    return app.stopServer();
+  });
+
+  it('fetches in fastboot mode', function() {
+    return get({
+      url: 'http://localhost:49741/',
+      headers: {
+        Accept: 'text/html'
+      }
+    }).then(function(response) {
+      expect(response.body).to.contain('Hello World! fetch');
+      expect(response.body).to.contain('Hello World! fetch (Request)');
+    });
+  });
+});

test/fastboot-test.js

@@ -7,7 +7,7 @@ chai.use(require('chai-fs'));
 
 const AddonTestApp = require('ember-cli-addon-tests').AddonTestApp;
 
-describe('renders in fastboot build', function() {
+describe('renders in fastboot build without calling fetch', function() {
   this.timeout(300000);
 
   let app;
@@ -16,7 +16,7 @@ describe('renders in fastboot build', function() {
     app = new AddonTestApp();
 
     return app
-      .create('dummy', { skipNpm: true })
+      .create('fresh', { skipNpm: true, noFixtures: true })
       .then(app =>
         app.editPackageJSON(pkg => {
           pkg.devDependencies['ember-cli-fastboot'] = '*';
@@ -44,18 +44,17 @@ describe('renders in fastboot build', function() {
   it('builds into dist/ember-fetch/fetch-fastboot.js ignoring sub dependency version conflict', function() {
     expect(app.filePath('dist/index.html')).to.be.a.file();
     expect(app.filePath('dist/ember-fetch/fetch-fastboot.js')).to.be.a.file();
-    expect(app.filePath('dist/assets/dummy-fastboot.js')).to.be.a.file();
+    expect(app.filePath('dist/assets/fresh-fastboot.js')).to.be.a.file();
   });
 
-  it('fetches in fastboot mode', function() {
+  it('fresh serve works', function() {
     return get({
       url: 'http://localhost:49741/',
       headers: {
         Accept: 'text/html'
       }
     }).then(function(response) {
-      expect(response.body).to.contain('Hello World! fetch');
-      expect(response.body).to.contain('Hello World! fetch (Request)');
+      expect(response.body).to.contain('Congratulations, you made it!');
     });
   });
 });