fastify-line

A Fastify plugin for seamless integration with the LINE Messaging API. It provides signature verification, raw body parsing, and exposes the official LINE Messaging API client on your Fastify instance.

---

Features

• Signature verification for LINE webhooks
• Raw body parsing for webhook requests
• Exposes the official @line/bot-sdk Messaging API client as fastify.line
• Easy route integration with Fastify

Installation

npm install fastify-line @line/bot-sdk

Note: @line/bot-sdk is a peer dependency and must be installed separately.

Compatibility

Plugin Version	Fastify Version
>=0.x	^5.x

Usage

Register the plugin with your LINE channel credentials:

import Fastify from 'fastify'
import fastifyLine, { type WebhookRequestBody } from 'fastify-line'

const fastify = Fastify()

await fastify.register(fastifyLine, {
  channelSecret: process.env.LINE_CHANNEL_SECRET!,
  channelAccessToken: process.env.LINE_CHANNEL_ACCESS_TOKEN!,
})

fastify.post<{ Body: WebhookRequestBody }>(
  '/webhook',
  {
    config: { lineWebhook: true }, // Enable LINE webhook handling for this route
  },
  async (request, reply) => {
    const { events } = request.body

    for (const event of events) {
      if (event.type === 'message' && event.message.type === 'text') {
        await fastify.line.replyMessage({
          replyToken: event.replyToken,
          messages: [
            {
              type: 'text',
              text: `You said: ${event.message.text}`,
            },
          ],
        })
      }
    }

    reply.send({ ok: true })
  },
)

await fastify.listen({ port: 3000 })

Skip Signature Verification

await fastify.register(fastifyLine, {
  channelSecret: process.env.LINE_CHANNEL_SECRET!,
  channelAccessToken: process.env.LINE_CHANNEL_ACCESS_TOKEN!,
  skipVerify: true, // Skip signature verification
})

Warning: Only use skipVerify: true in development/testing environments. Always verify signatures in production to ensure webhook security. If you skip automatic verification, you can manually verify signatures in your webhook handler using validateSignature from @line/bot-sdk.

Options

Option	Type	Required	Default	Description
channelSecret	string	Yes	-	Your LINE channel secret (for signature verification)
channelAccessToken	string	Yes	-	Your LINE channel access token (for Messaging API client)
skipVerify	boolean	No	false	Skip signature verification

How It Works

• Adds a line property to your Fastify instance: fastify.line (an instance of MessagingApiClient from @line/bot-sdk).
• For routes with config: { lineWebhook: true }:
  • Parses the raw request body.
  • Verifies the X-Line-Signature header using your channel secret.
  • Throws MissingSignatureError or InvalidSignatureError if verification fails.

Error Handling

The plugin throws custom errors for signature issues:

• MissingSignatureError: Thrown if the X-Line-Signature header is missing.
• InvalidSignatureError: Thrown if the signature is invalid.

You can handle these errors using Fastify's error handler:

fastify.setErrorHandler((err, _request, reply) => {
  if (err instanceof MissingSignatureError) {
    reply.status(401).send({
      error: err.message,
      message: 'The X-Line-Signature header is missing.',
    })
  }

  if (err instanceof InvalidSignatureError) {
    reply.status(401).send({
      error: err.message,
      message: 'The X-Line-Signature header is invalid.',
      signature: err.signature,
    })
  }

  // Default error handling
  reply.send(err)
})

Types

This plugin augments Fastify's types:

• fastify.line: The LINE Messaging API client
• config.lineWebhook: Set to true on a route to enable LINE webhook handling

Contributing

Contributions are welcome!

License

MIT