Implement a basic decorator

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

Author: virkt25

index.ts

@@ -0,0 +1,6 @@
+// Copyright IBM Corp. 2013,2017. 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
+
+export * from './src';

package.json

@@ -13,7 +13,8 @@
     "lint": "tslint -c tslint.full.json --project tsconfig.json --type-check",
     "lint:fix": "npm run lint -- --fix",
     "prepublish": "npm run build",
-    "pretest": "npm run build",
+    "clean": "rm -rf dist dist6",
+    "pretest": "npm run clean && npm run build",
     "test": "mocha",
     "posttest": "npm run lint",
     "vscode-test": "mocha && npm run lint"

src/decorators/README.md

@@ -0,0 +1,46 @@
+# Decorators
+
+## Overview
+
+Decorators provide annotations for class methods and properties. 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 operation. The decorator will annotate the operation with the value of the header `X-Transaction-Id` from the request. 
+
+**Example**
+```
+class MyController {
+  @get('/')
+  @txIdFromHeader()
+  getHandler(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)
+
+## Contributions
+
+- [Guidelines](http://loopback.io/doc/en/contrib/index.html)
+- [Join the team](https://github.com/strongloop/loopback-next/issues/110)
+
+## Tests
+
+Run `npm test` from the root folder.
+
+## Contributors
+
+See [all contributors](https://github.com/strongloop/loopback-next-extension-starter/graphs/contributors).
+
+## License
+
+MIT

src/decorators/txIdFromHeader.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/core';
+
+/**
+ * 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';

test/acceptance/txIdFromHeader.test.ts

@@ -0,0 +1,46 @@
+// Copyright IBM Corp. 2017. All Rights Reserved.
+// Node module: @loopback/core
+// This file is licensed under the MIT License.
+// License text available at https://opensource.org/licenses/MIT
+
+import {Application, get} from '@loopback/core';
+import {txIdFromHeader} from '../..';
+import {Client, createClientForApp} from '@loopback/testlab';
+
+describe('@txIdFromHeader() tests', () => {
+  let app: Application;
+
+  beforeEach(createApp);
+  beforeEach(createController);
+
+  it('works with header set', async () => {
+    const client: Client = createClientForApp(app);
+
+    await client
+      .get('/')
+      .set('X-Transaction-Id', 'testid123')
+      .expect(200, 'Your id is testid123');
+  });
+
+  it('works without header', async () => {
+    const client: Client = createClientForApp(app);
+
+    await client.get('/').expect(200, 'Your id is undefined');
+  });
+
+  function createApp() {
+    app = new Application();
+  }
+
+  function createController() {
+    class MyController {
+      @get('/')
+      @txIdFromHeader()
+      test(txId: string) {
+        return `Your id is ${txId}`;
+      }
+    }
+
+    app.controller(MyController);
+  }
+});

test/unit/txIdFromHeader.test.ts

@@ -0,0 +1,28 @@
+// Copyright IBM Corp. 2017. All Rights Reserved.
+// Node module: @loopback/core
+// 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/core';
+import {txIdFromHeader} from '../..';
+
+describe('@txHeaderFromId', () => {
+  it('defines a parameter for X-Transaction-Id', () => {
+    class MyController {
+      @get('/')
+      @txIdFromHeader()
+      hello(txId: string) {}
+    }
+
+    const actualSpec = getControllerSpec(MyController);
+
+    expect(actualSpec.paths['/']['get'].parameters).to.eql([
+      {
+        name: 'X-Transaction-Id',
+        type: 'string',
+        in: 'header',
+      },
+    ]);
+  });
+});