http-response-serializer
The Http Serializer middleware lets you define serialization mechanisms based on the current content negotiation.
Install
To install this middleware you can use NPM:
- npm
- Yarn
npm install --save @middy/http-response-serializer
yarn add @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 with a body
attribute 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 event.preferredContentType
-- allows the handler to override the default, but lets the request ask firstdefault
middleware configuration
All options allow for multiple types to be specified in your order of preference, and the first matching serializer will be executed.
When planning to use Accept
, an external input, it is recommended to validate that it is an expected value.
Sample usage
import middy from '@middy/core'
import httpResponseSerializer from '@middy/http-response-serializer'
const handler = middy((event, context) => {
const body = 'Hello World'
return {
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
}
],
defaultContentType: '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>')
})