feat: add a basic decorator

Implement a `@txIdFromHeader()` decorator that can annotate a
controller operation to receive the value of `X-Trasaction-Id` Header.

Author: virkt25

package.json

@@ -21,7 +21,7 @@
     "tslint:fix": "npm run lint -- --fix",
     "prepublish": "npm run build",
     "pretest": "npm run clean && npm run build",
-    "test": "mocha",
+    "test": "/bin/bash -c '[[ $(node -v) =~ [[:digit:]]+ ]] && [[ ${BASH_REMATCH[0]} -gt 6 ]]' && mocha dist/test || mocha dist6/test",
     "posttest": "npm run lint",
     "test:dev": "mocha && npm run lint"
   },

src/decorators/README.md

@@ -0,0 +1,28 @@
+# Decorators
+
+## Overview
+
+Decorators provide annotations for class methods and arguments. Decorators use the form `@decorator` where `decorator` is the name of the function that will be called at runtime. 
+
+## Basic Usage
+
+### txIdFromHeader
+
+This simple decorator allows you to annotate a `Controller` method argument. The decorator will annotate the method argument with the value of the header `X-Transaction-Id` from the request. 
+
+**Example**
+```
+class MyController {
+  @get('/')
+  getHandler(@txIdFromHeader() txId: string) {
+    return `Your transaction id is: ${txId}`;
+  }
+}
+```
+
+## Related Resources
+
+You can check out the following resource to learn more about decorators and how they are used in LoopBack Next.
+
+- [TypeScript Handbook: Decorators](https://www.typescriptlang.org/docs/handbook/decorators.html)
+- [Decorators in LoopBack](http://loopback.io/doc/en/lb4/Decorators.html)

src/decorators/txIdFromHeader.decorator.ts

@@ -0,0 +1,14 @@
+// Copyright IBM Corp. 2017. All Rights Reserved.
+// Node module: loopback-next-extension-starter
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+import {param} from '@loopback/rest';
+
+/**
+ * Decorator to inject the current transaction-id from a request's
+ * 'X-Transaction-Id' header into the decorated function.
+ */
+export function txIdFromHeader() {
+  return param.header.string('X-Transaction-Id');
+}

src/index.ts

@@ -2,3 +2,5 @@
 // Node module: loopback-next-extension-starter
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
+
+export * from './decorators/txIdFromHeader.decorator';

test/acceptance/decorators/txIdFromHeader.acceptance.ts

@@ -0,0 +1,57 @@
+// Copyright IBM Corp. 2017. All Rights Reserved.
+// Node module: loopback-next-hello-extension
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+import {Application} from '@loopback/core';
+import {get, RestComponent, RestServer} from '@loopback/rest';
+import {txIdFromHeader} from '../../..';
+import {Client, createClientForHandler} from '@loopback/testlab';
+
+describe('@txIdFromHeader() (acceptance)', () => {
+  let app: Application;
+  let server: RestServer;
+
+  beforeEach(createApp);
+  beforeEach(createController);
+  beforeEach(getServerFromApp);
+
+  it('works with header set', async () => {
+    const client: Client = createClientForHandler(server.handleHttp);
+
+    await client
+      .get('/')
+      .set('X-Transaction-Id', 'testid123')
+      .expect(200, 'Your id is testid123');
+  });
+
+  it('works without header', async () => {
+    const client: Client = createClientForHandler(server.handleHttp);
+
+    await client.get('/').expect(200, 'Your id is undefined');
+  });
+
+  async function createApp() {
+    app = new Application({
+      components: [RestComponent],
+      rest: {
+        port: 3000,
+      },
+    });
+  }
+
+  function createController() {
+    class MyController {
+      @get('/')
+      test(@txIdFromHeader() txId: string) {
+        return `Your id is ${txId}`;
+      }
+    }
+
+    app.controller(MyController);
+  }
+
+  async function getServerFromApp() {
+    server = await app.getServer(RestServer);
+  }
+});

test/mocha.opts

@@ -1,3 +1,2 @@
 --recursive
 --reporter dot
-dist/test

test/smoke.test.ts

@@ -0,0 +1,27 @@
+// Copyright IBM Corp. 2017. All Rights Reserved.
+// Node module: loopback-next-hello-extension
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+import {expect} from '@loopback/testlab';
+import {get, getControllerSpec} from '@loopback/rest';
+import {txIdFromHeader} from '../../..';
+
+describe('@txHeaderFromId() (unit)', () => {
+  it('defines a parameter for X-Transaction-Id', () => {
+    class MyController {
+      @get('/')
+      hello(@txIdFromHeader() txId: string) {}
+    }
+
+    const actualSpec = getControllerSpec(MyController);
+
+    expect(actualSpec.paths['/']['get'].parameters).to.eql([
+      {
+        name: 'X-Transaction-Id',
+        type: 'string',
+        in: 'header',
+      },
+    ]);
+  });
+});