etag

Kind: Function

Source: src/middleware/etag/index.ts

Part of: Middleware

ETag Middleware for Hono.

etag creates an ETag header from a response body after downstream handlers run. When the request includes a matching If-None-Match header, it replaces the response with a Not Modified response.

Signature

ts
function etag(options: ETagOptions): MiddlewareHandler

Parameters

Returns: MiddlewareHandler

Diagram

mermaid
graph LR
  Request --> ETagMiddleware
  ETagMiddleware --> Handler
  Handler --> Response
  Response --> ETagMiddleware
  ETagMiddleware -->|Sets ETag header| Client
  ETagMiddleware -->|Matching If-None-Match| NotModifiedResponse

Usage

ts
import { Hono } from 'hono'
import { etag } from 'hono/etag'

const app = new Hono()

app.use(etag())

app.get('/profile', (c) => {
  return c.json({ name: 'Ada' })
})

export default app

AI Coding Instructions

• Register etag() before routes whose responses should include an ETag header.
• Allow downstream handlers to create the response before adding logic that depends on response content.
• Preserve an ETag header set explicitly by a route or another middleware.
• Test conditional requests with an If-None-Match header that matches the response ETag.