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Middleware and Helpers

Gatsby Functions provides an Express-like architecture that simplifies building Node.js APIs. We include a number of middlewares to parse common request data as well as response helpers.

Data formats

We parse commonly used data types. You can parse more by adding custom middleware. Data available by default on the req object:

  • Cookies at req.cookies
  • URL Queries (e.g. api/foo?query=foo) at req.query
  • Form parameters and data at req.body
  • JSON POST bodies at req.body
  • Files uploaded from forms at req.files

Response helpers

  • res.send(body) — returns the response. The body can be a string, object, or buffer
  • res.json(body) — returns a JSON response. The body can be any value that can be serialized with JSON.stringify()
  • res.status(statusCode) — set the HTTP status for the response. Defaults to 200.
  • res.redirect([statusCode], url) — Returns a redirect to a URL. Optionally set the statusCode which defaults to 302.

Custom middleware

Custom Connect/Express middleware are supported.

An example of how to add CORS support to a Function:

Custom body parsing

Support for overriding default config added in gatsby@4.14.0

By default, Gatsby is using following configuration defaults to parse request body and make it available as req.body field in appropriate format:

Those settings work in most cases, but sometimes you might need to adjust them to cover your use case. Gatsby allows exporting an object named config from your function handler module. This object allows you to control the body-parser middleware used by Gatsby Functions. Gatsby currently supports the limit, type, and extended options for the bodyParser configuration, which are documented by body-parser. The limit property will allow configuration of payload size up to 32mb.


Accessing body as a Buffer

You can modify what Content-type particular body-parser middleware can act on. Following configuration will force every request to use raw parser and result in function handler receiving req.body as a Buffer. A setup like this is useful if you are looking to verify signature of webhooks (e.g. https://stripe.com/docs/webhooks/signatures).

Increasing or decreasing the payload limit

By default, the limit is 100kb. If the request body is larger than that it will result in automatic 413 Request Entity Too Large response without executing function handler at all.

If your use case require a higher limit, you can bump it up in config.

TypeScript (config object type)

You can import GatsbyFunctionConfig from gatsby to type your config export:

How config is applied

When using the config and changing the type on one of the body parser middlewares, it’s important to realize that all body parser middlewares are still being applied with this specific order:

  1. raw
  2. text
  3. urlencoded
  4. json

Here’s a concrete example:

If you want json to be used for all possible requests for a given function, it won’t be enough to just set type: "*/*" for the json middleware. You also need to change the type for middlewares that are higher in priority, so they don’t accidentally match and handle request before the json middleware can process it:

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