# BusConfiguration

Creates a configuration in order to initialize a new [BusInstance](/reference/businstance.md).

## Methods

### withHandler(classHandler)

Registers a class handler that receives a message and performs a unit of work. When **Bus** is initialized it will configure the transport to subscribe to the type of message handled by the handler and upon receipt will forward the message through to the `handle()` function.

#### **Arguments**

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>classHandler</code></td><td>A class responsible for handling messages that implements <strong>Handler</strong></td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { TestHandler } from './test-handler'

Bus.configure().withHandler(TestHandler)
```

See also [events](/guide/messages/events.md), [commands](/guide/messages/commands.md).

### withHandler(functionHandler)

Registers a function handler that receives a message and performs a unit of work. When **Bus** is initialized it will configure the transport to subscribe to the type of message handled by the function handler and upon receipt will forward the message to the function.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>functionHandler</code></td><td>A functional handler mapping initialized using <code>handlerFor</code></td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus, handlerFor } from '@node-ts/bus-core'
import { TestEvent } from './test-event'

Bus.configure().withHandler(handlerFor(TestEvent, event => {}))
```

See also [events](/guide/messages/events.md), [commands](/guide/messages/commands.md).

### withCustomHandler(messageHandler,  customResolver)

Registers a custom handler that receives messages from external systems, or messages that don't implement the **Message** interface from **@node-ts/bus-messages**.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>messageHandler</code></td><td>A handler that receives the custom message</td><td>None</td></tr><tr><td><code>customResolver</code></td><td>A discriminator that determines if an incoming message should be mapped to this handler</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { S3Event } from 'aws-sdk'

Bus.configure()
  .withCustomHandler(
    async (event: S3Event) => console.log('Received S3 event', { event }),
    {
      resolveWith: event => event.Records
        && event.Records.length
    }
  )   
```

See also [System messages](/guide/messages/system-messages.md).

### withWorkflow(workflow)

Registers a workflow definition so that all of the messages it depends on will be subscribed to and forwarded to the handlers inside the workflow.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>workflow</code></td><td>Workflow definition to register</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { TestWorkflow } from './test-workflow'

Bus.configure().withWorkflow(TestWorkflow) 
```

See also [Workflows](/guide/workflows.md).

### withTransport(transport)

Configures **Bus** to use a different transport than the default **MemoryQueue.**

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>transport</code></td><td>A configured transport to use</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { SqsTransport, SqsTransportConfiguration } from '@node-ts/bus-sqs'

const sqsConfiguration: SqsTransportConfiguration = {
  // ...
}
const sqsTransport = new SqsTransport(sqsConfiguration)
Bus.configure().withTransport(sqsTransport) 
```

See also [Transports](/guide/transports.md).

### withLogger(loggerFactory)

Configures **Bus** to use a different logging provider than the default consoler logger.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>loggerFactory</code></td><td>A factory that creates a new logger</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { CustomLogger } from './custom-logger'

Bus.configure().withLogger((target: string) => new CustomLogger(target))
```

See also [Loggers](/guide/loggers.md).

### withSerializer(serializer)

Configures **Bus** to use a different serialization provider. The provider is responsible for transforming messages to/from a serialized representation, as well as ensuring all object properties are a strong type.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>serializer</code></td><td>Serializer to use</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { ClassSerializer } from '@node-ts/bus-class-serializer'

Bus.configure().withSerializer(new ClassSerializer())
```

See also [Serializer](/guide/serializers.md).

### withPersistence(persistence)

Configures **Bus** to use a different persistence provider than the default InMemoryPersistence provider. This is used to persist workflow data and is unused if not using workflows.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>persistence</code></td><td>Persistence provider to use</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { PostgresPersistence, PostgresConfiguration } from '@node-ts/bus-postgres'

const postgresConfiguration: PostgresConfiguration = {
  connection: {
    connectionString: 'postgres://postgres:password@localhost:5432/postgres'
  },
  schemaName: 'workflows'
}
const postgresPersistence = new PostgresPersistence(postgresConfiguration)
Bus.configure().withPersistence(postgresPersistence)
```

See also [Persistence](/guide/persistence.md).

### withConcurrency(concurrency)

Sets the message handling concurrency beyond the default value of 1, which will increase the number of messages handled in parallel.concurrency

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>concurrency</code></td><td>The number of messages that can be handled in parallel</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'

Bus.configure().withConcurrency(5)
```

### withContainer(containerAdapter)

```typescript
withContainer({
      get <T>(type: ClassConstructor<T>) {
        return container.get<T>(type)
      }
    })
```

Use a local dependency injection/IoC container to resolve handlers and workflows.

Configures **Bus** to use a different persistence provider than the default InMemoryPersistence provider. This is used to persist workflow data and is unused if not using workflows.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>containerAdapter</code></td><td>An adapter that allows <strong>Bus</strong> to resolve class instances from the underlying IoC container</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus } from '@node-ts/bus-core'
import { Container } from 'inversify'

const container = new Container()
Bus.configure().withContainer({
      get <T>(type: ClassConstructor<T>) {
        return container.get<T>(type)
      }
})   
```

See also [Dependency injection.](/guide/dependency-injection.md)

### withMessageReadMiddleware(middleware)

```typescript
  withMessageReadMiddleware<TransportMessageType = unknown> (
    messageReadMiddleware: Middleware<TransportMessage<TransportMessageType>>
  )
```

Run custom middleware before/after the point a message is read from the transport and then dispatched to handlers and workflow handlers.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>middleware</code></td><td>A middleware function that will be executed after a message is read from the transport and before it is dispatched to handlers.</td><td>None</td></tr></tbody></table>

#### Example

```typescript
import { Bus, Middleware, Next, TransportMessage } from '@node-ts/bus-core'

const messageTimingMiddleware = async (
  context: TransportMessage<unknown>,
  next: Next
) => {
  const start = Date.now()
  await next()
  const end = Date.now()
  const durationMs = end - start
  console.log(
    'Message handled',
    { messageName: context.domainMessage.$name, durationMs }
  )
}
const bus = await Bus.configure()
  .withMessageReadMiddleware(messageTimingMiddleware)
```

See also [Middleware](/guide/middleware.md).

### withRetryStrategy(retryStrategy)

```typescript
  withRetryStrategy({
    calculateRetryDelay (currentAttempt: number): number
  })
```

Configure the bus to use a different retry strategy instead of the default.

#### Arguments

<table><thead><tr><th width="220.36412604232706">Argument</th><th width="342.81368434354914">Description</th><th width="150">Default</th></tr></thead><tbody><tr><td><code>retryStrategy</code></td><td>An implementation of <code>RetryStrategy</code> that calculates the delay between retrying failed messages.</td><td><code>DefaultRetryStrategy</code></td></tr></tbody></table>

#### Example

```typescript
const bus = await Bus.configure()
  .withRetryStrategy({
    calculateRetryDelay (currentAttempt: number) { return Math.pow(2, currentAttempt) }
  }) 
  .initialize()
```

See also [Retry Strategies](/guide/retry-strategies.md).

### initialize(\[options])

Initialize a configured **BusInstance**. This should be called after all options have been provided for the configuration.


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