@middy/http-response-serializer/README.md

# Middy http-response-serializer middleware

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  <p><strong>HTTP response serializer middleware for the middy framework, the stylish Node.js middleware engine for AWS Lambda</strong></p>
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The Http Serializer middleware lets you define serialization mechanisms based on the current content negotiation.


## Install

To install this middleware you can use NPM:

```bash
npm install --save @middy/http-response-serializer
```


## Configuration

The middleware is configured by defining some `serializers`.

```
{
  serializers: [
    {
      regex: /^application\/xml$/,
      serializer: ({ body }) => `<message>${body}</message>`,
    },
    {
      regex: /^application\/json$/,
      serializer: ({ body }) => JSON.stringify(body)
    },
    {
      regex: /^text\/plain$/,
      serializer: ({ body }) => body
    }
  ],
  default: 'application/json'
}
```

The `default` (optional) option is used if the request and handler don't specify what type is wanted.


## Serializer Functions

When a matching serializer is found, the `Content-Type` header is set and the serializer function is run.

The function is passed the entire `response` object, and should return either a string or an object.

If a string is returned, the `body` attribute of the response is updated.

If an object is returned, the entire response object is replaced. This is useful if you want to manipulate headers or add additional attributes in the Lambda response.


## Content Type Negotiation

The header is not the only way the middleware decides which serializer to execute.

The content type is determined in the following order:

 * `event.requiredContentType` -- allows the handler to override everything else
 * The `Accept` header via [accept](https://www.npmjs.com/package/accept)
 * `event.preferredContentType` -- allows the handler to override the default, but lets the request ask first
 * `default` middleware configuration

All options allow for multiple types to be specified in your order of preference, and the first matching serializer will be executed.


## Error Handling

This middleware does work with `http-error-handler`. To serialize error responses, ensure the `httpErrorHandler` middleware is configured before `httpResponseSerializer`.


## Dependencies

Thie middleware does not rely on any other middlewares.


## Sample usage

```javascript
import middy from '@middy/core'
import httpResponseSerializer from '@middy/http-response-serializer'

const handler = middy((event, context) => {
  const body = 'Hello World'

  return cb(null, {
    statusCode: 200,
    body
  })
})

handler
  .use(httpResponseSerializer({
    serializers: [
      {
        regex: /^application\/xml$/,
        serializer: ({ body }) => `<message>${body}</message>`,
      },
      {
        regex: /^application\/json$/,
        serializer: ({ body }) => JSON.stringify(body)
      },
      {
        regex: /^text\/plain$/,
        serializer: ({ body }) => body
      }
    ],
    default: 'application/json'
  }))

const event = {
  headers: {
    'Accept': 'application/xml;q=0.9, text/x-dvi; q=0.8, text/x-c'
  }
}

handler(event, {}, (_, response) => {
  t.is(response.body,'<message>Hello World</message>')
})
```


## Middy documentation and examples

For more documentation and examples, refers to the main [Middy monorepo on GitHub](https://github.com/middyjs/middy) or [Middy official website](https://middy.js.org).


## Contributing

Everyone is very welcome to contribute to this repository. Feel free to [raise issues](https://github.com/middyjs/middy/issues) or to [submit Pull Requests](https://github.com/middyjs/middy/pulls).


## License

Licensed under [MIT License](LICENSE). Copyright (c) 2017-2021 Luciano Mammino, will Farrell, and the [Middy team](https://github.com/middyjs/middy/graphs/contributors).

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