emit-io-fastify

Fastify plugin for emit-io-core — per-request child logger, request ID, and automatic hook timings.

Install

npm install emit-io-core emit-io-fastify

fastify-plugin is a direct dependency and installed automatically.

Quick Start

import Fastify from 'fastify'
import { EmitIoStrategy, JSONTransport, LogLevelEnum } from 'emit-io-core'
import { loggerPlugin } from 'emit-io-fastify'

const emit = new EmitIoStrategy({
  transports: [new JSONTransport({ minLevel: LogLevelEnum.INFO })],
})

const app = Fastify({ logger: false })

await app.register(loggerPlugin, { logger: emit })

app.get('/orders', async (req) => {
  req.log_.info('fetching orders')
  // req.log_ is a child logger with { requestId, method, path } already bound
  return { orders: [] }
})

await app.listen({ port: 3000 })

API

loggerPlugin

A fastify-plugin compatible with Fastify 4.x and 5.x.

import { loggerPlugin } from 'emit-io-fastify'
import type { LoggerPluginOptions } from 'emit-io-fastify'

await app.register(loggerPlugin, {
  logger: emit, // required: EmitIoStrategy instance
  requestIdHeader: 'x-request-id', // default: 'x-request-id'
  autoLog: true,                   // default: true — logs request-start and request-complete
})

Request Decorators

After registration, every request has:

| Decorator | Type | Description | |---|---|---| | req.log_ | EmitIoStrategy | Child logger bound with { requestId, method, path } | | req.requestId | string | Request ID from header or generated UUID |

app.get('/users/:id', async (req) => {
  const { id } = req.params as { id: string }
  req.log_.info('get user', { userId: id })
  req.log_.captureError('Users', 'not_found', false, new Error('404'), { id })
  return { user: null }
})

Hook Behaviour

When autoLog: true (default):

• onRequest — logs request-start with { method, path }
• onResponse — logs request-complete with { status, durationMs }
• onError — logs request-failed with { method, path, error }

The x-request-id (or configured header) is echoed back in the response.

TypeScript Augmentation

The plugin augments Fastify's types automatically:

// No import needed — available after app.register(loggerPlugin, ...)
app.get('/', async (req) => {
  req.log_    // EmitIoStrategy
  req.requestId  // string
})

Peer Dependencies

| Package | Version | |---|---| | emit-io-core | ^1.0.0 | | fastify | ^4.0.0 \|\| ^5.0.0 |

License

MIT