Parse a URL encoded form event in AWS Lambda

parse-url-encoded-form-event.ts

import type { APIGatewayProxyEventV2 } from "aws-lambda"
import busboy from "busboy"

// https://github.com/francismeynard/lambda-multipart-parser/blob/master/index.js
async function parseUrlEncodedFormEvent<T>(
  event: APIGatewayProxyEventV2,
): Promise<T> {
  return new Promise((resolve, reject) => {
    const fields: Record<string, unknown> = {}
    const bb = busboy({ headers: event.headers })
    bb.on("field", (name, value, info) => {
      fields[name] = value
    })
    bb.on("finish", () => {
      resolve(fields as T)
    })
    bb.on("error", reject)

    const encoding = event.isBase64Encoded ? "base64" : "binary"
    bb.write(event.body, encoding)
    bb.end()
  })
}