Example: handling webhooks

import { createServer, type IncomingMessage } from 'node:http'
import {
  WebhookSignatureError,
  isMessageEvent,
  verifyWebhook,
  type WebhookEventBase
} from '@isnap/sdk'

const secret = process.env.ISNAP_WEBHOOK_SECRET
if (!secret) {
  console.error('Set ISNAP_WEBHOOK_SECRET to the signing secret of your webhook subscription.')
  process.exit(1)
}

// The ids of the events already processed. This set is lost on restart and is not
// shared between processes: replace it with storage of your own.
const processed = new Set<string>()

const processEvent = async (event: WebhookEventBase): Promise<void> => {
  // Other families, probes and event types this script does not know: nothing to do.
  if (!isMessageEvent(event)) return

  const { message } = event.data
  switch (event.event_type) {
    case 'message.received':
      console.log(`${message.id} received on ${message.line_id}`)
      break
    case 'message.failed':
      console.log(`${message.id} failed: ${message.error_code ?? 'reported by the device'}`)
      break
  }
}

const handle = async (req: IncomingMessage): Promise<number> => {
  if (req.method !== 'POST' || req.url !== '/webhooks/isnap') return 404

  // Keep the body as received. Verification fails on a body that was parsed and serialized again.
  const chunks: Buffer[] = []
  for await (const chunk of req) chunks.push(chunk as Buffer)
  const rawBody = Buffer.concat(chunks).toString('utf8')

  let event: WebhookEventBase
  try {
    event = verifyWebhook(rawBody, req.headers, secret)
  } catch (err) {
    if (err instanceof WebhookSignatureError) return 400
    throw err
  }

  // A retry or a replay carries the same event_id.
  if (processed.has(event.event_id)) return 200

  await processEvent(event)
  // Record the event_id only after the work succeeded. When processEvent throws,
  // the server responds 500, and the next attempt, if one remains, processes the event.
  processed.add(event.event_id)
  return 200
}

const server = createServer((req, res) => {
  handle(req).then(
    (status) => {
      res.writeHead(status).end()
    },
    () => {
      res.writeHead(500).end()
    }
  )
})

server.listen(3000, () => {
  console.log('Listening on port 3000, path /webhooks/isnap')
})