A plugin for Fastify that automatically generates HTTP ETags according to RFC2616-sec13.

The plugin can optionally send a 304 status code when an ETag matches the if-none-match header.

npm i @fastify/etag

'use strict'

const Fastify = require('fastify')
const Etag = require('@fastify/etag')

const app = Fastify()
app.register(Etag)

app.get('/', async (req, reply) => {
  return { hello: 'world' }
})

app.get('/manual-etag', async (req, reply) => {
  // This will disable automatic ETag generation
  // It will still return a 304 if the ETag matches
  reply.header('etag', '"foobar"')
  return 'world'
})

app.listen(3000)

• algorithm: all hashing algorithms the Node.js crypto module supports, and 'fnv1a'. Default: 'sha1'.

• weak: generates weak ETags by default. Default: false.

By default, the plugin sends a 304 status code when the ETag is equal to the Etag specified by the if-none-match request header.

This is often the desired behaviour, but can be disabled by setting replyWith304: false.

The fnv1a logic was forked from https://github.com/sindresorhus/fnv1a and adapted to support buffers.

Generating an etag will always be slower than not generating an etag. The generation speed also depends on the payload size and type (buffer or string):

• For very small payloads (< 2 kb), use 'fnv1a'
• For buffers above 2 mb, use 'md5'
• In all other scenarios, use 'sha1' (default)
• YMMV, see this issue where other algorithms such as crc32 for small payloads and murmurhash3-wasm for big buffers have performed better than the mentioned recommendations
• Any etag generation results in at least 10% less op/s (up to 50% less op/s for huge payloads)

MIT