chore(gatsby): add generic to GatsbyFunctionRequest (#35029)

Co-authored-by: gatsbybot <[email protected]>
Co-authored-by: Lennart <[email protected]>

Author: 3 people

docs/docs/reference/functions/getting-started.md

@@ -48,11 +48,15 @@ Functions can be written in JavaScript or Typescript.
 ```ts:title=src/api/typescript.ts
 import { GatsbyFunctionRequest, GatsbyFunctionResponse } from "gatsby"
 
+interface ContactBody {
+  message: string
+}
+
 export default function handler(
-  req: GatsbyFunctionRequest,
+  req: GatsbyFunctionRequest<ContactBody>,
   res: GatsbyFunctionResponse
 ) {
-  res.send(`I am TYPESCRIPT`)
+  res.send({ title: `I am TYPESCRIPT`, message: req.body.message })
 }
 ```
 

packages/gatsby/index.d.ts

@@ -1648,7 +1648,7 @@ export interface GatsbyFunctionResponse<T = any> extends ServerResponse {
 /**
  * Gatsby function route request
  */
-export interface GatsbyFunctionRequest extends IncomingMessage {
+export interface GatsbyFunctionRequest<ReqBody = any> extends IncomingMessage {
   /**
    * Object of values from URL query parameters (after the ? in the URL)
    */
@@ -1658,7 +1658,7 @@ export interface GatsbyFunctionRequest extends IncomingMessage {
    * Object of values from route parameters
    */
   params: Record<string, string>
-  body: any
+  body: ReqBody
   /**
    * Object of `cookies` from header
    */