Send-only bus (#59)

* Fixed PostgreSQL transport example

* Added bootstrap for a send-only bus

* Added checks for the send-only bus initialization

It can only be initialized once and it must not have any registered
handlers.

* Test that no handlers were added for send-only bus

Author: Zehelein

packages/bus-core/src/application-bootstrap/application-bootstrap.spec.ts

@@ -1,12 +1,11 @@
 import { ApplicationBootstrap } from './application-bootstrap'
 import { Mock, IMock, Times, It } from 'typemoq'
 import { Bus } from '../service-bus'
-import { HandlerRegistry } from '../handler'
+import { HandlerRegistry, HandlerResolver } from '../handler'
 import { Logger } from '@node-ts/logger-core'
 import { Container } from 'inversify'
 import { TestCommandHandler, TestCommand } from '../test'
 import { Transport } from '../transport'
-import { Message } from '@node-ts/bus-messages'
 
 describe('ApplicationBootstrap', () => {
   let sut: ApplicationBootstrap
@@ -50,6 +49,39 @@ describe('ApplicationBootstrap', () => {
     })
   })
 
+  describe('when initializing send only', () => {
+    let container: IMock<Container>
+    describe('that starts successfully', () => {
+      beforeEach(async () => {
+        container = Mock.ofType<Container>()
+        await sut.initializeSendOnly()
+      })
+      it('should bind no handlers to the IoC container', () => {
+        handlerRegistry.verify(
+          h => h.bindHandlersToContainer(container.object),
+          Times.never()
+        )
+      })
+      it('should not start the bus', () => {
+        bus.verify(
+          async b => b.start(),
+          Times.never()
+        )
+      })
+      it('should throw an exception when initializing twice', async () => {
+        await expect(sut.initializeSendOnly()).rejects.toThrowError()
+      })
+    })
+    describe('when handlers have been registered', () => {
+      it('should throw an error', async () => {
+        handlerRegistry
+          .setup(h => h.messageSubscriptions)
+          .returns(() => [{} as HandlerResolver])
+        await expect(sut.initializeSendOnly()).rejects.toThrowError()
+      })
+    })
+  })
+
   describe('when registering handlers', () => {
     beforeEach(() => {
       sut.registerHandler(TestCommandHandler)

packages/bus-core/src/application-bootstrap/application-bootstrap.ts

@@ -27,14 +27,25 @@ export class ApplicationBootstrap {
     }
     this.logger.info('Initializing bus application...')
     this.handlerRegistry.bindHandlersToContainer(container)
-    if (this.transport.initialize) {
-      await this.transport.initialize(this.handlerRegistry)
-    }
+    await this.initializeTransport()
     await this.bus.start()
     this.isInitialized = true
     this.logger.info('Bus application initialized')
   }
 
+  async initializeSendOnly (): Promise<void> {
+    if (this.isInitialized) {
+      throw new Error('Application already initialized')
+    }
+    if (this.handlerRegistry.messageSubscriptions.length > 0) {
+      throw new Error('A send-only bus cannot have registered handlers')
+    }
+    this.logger.info('Initializing send only bus application...')
+    await this.initializeTransport()
+    this.isInitialized = true
+    this.logger.info('Send only bus application initialized')
+  }
+
   async dispose (): Promise<void> {
     if (!this.isInitialized) {
       throw new Error('Application has not been initialized')
@@ -72,4 +83,10 @@ export class ApplicationBootstrap {
       prototype.$topicIdentifier
     )
   }
+
+  private async initializeTransport (): Promise<void> {
+    if (this.transport.initialize) {
+      await this.transport.initialize(this.handlerRegistry)
+    }
+  }
 }