From 3f542c196a9893af3ef0e79bc6319d198c7b9c8e Mon Sep 17 00:00:00 2001
From: savearray2 <46784573+savearray2@users.noreply.github.com>
Date: Wed, 27 Jan 2021 19:22:04 +0900
Subject: [PATCH] Adds Support for Generating Weak ETags (#31) (#32)

* Adds Support for Generating Weak ETags (#31)

* Adds Support for Generating Weak ETags (#31)

Refactors the buildHashFn function to use external variable for ETag prefix.

Co-authored-by: savearray2 <savearray2>
---
 README.md       |  2 ++
 index.d.ts      |  1 +
 index.js        |  9 +++++----
 test/generic.js | 11 +++++++++++
 4 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index e61adb9..063c909 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,8 @@ app.listen(3000)
 * `algorithm`: all hashing algorithm that Node.js support, and
   `'fnv1a'`. Default: `'fnv1a'`.
 
+* `weak`: generates weak ETags by default. Default: `false`.
+
 ## Acknowledgements
 
 The fnv1a logic was forked from https://github.com/sindresorhus/fnv1a
diff --git a/index.d.ts b/index.d.ts
index b3d1305..6264af2 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -3,6 +3,7 @@ import { Server, IncomingMessage, ServerResponse } from 'http';
 
 export interface FastifyEtagOptions {
   algorithm?: 'fnv1a' | string;
+  weak?: false | boolean;
 }
 
 declare const fastifyEtag: FastifyPlugin<FastifyEtagOptions>
diff --git a/index.js b/index.js
index 558b9bf..bf2070a 100644
--- a/index.js
+++ b/index.js
@@ -4,17 +4,18 @@ const fp = require('fastify-plugin')
 const { createHash } = require('crypto')
 const fnv1a = require('./fnv1a')
 
-function buildHashFn (algorithm = 'fnv1a') {
+function buildHashFn (algorithm = 'fnv1a', weak = false) {
+  const prefix = weak ? 'W/"' : '"'
   if (algorithm === 'fnv1a') {
-    return (payload) => '"' + fnv1a(payload).toString(36) + '"'
+    return (payload) => prefix + fnv1a(payload).toString(36) + '"'
   }
 
-  return (payload) => '"' + createHash(algorithm)
+  return (payload) => prefix + createHash(algorithm)
     .update(payload).digest().toString('base64') + '"'
 }
 
 module.exports = fp(async function etag (app, opts) {
-  const hash = buildHashFn(opts.algorithm)
+  const hash = buildHashFn(opts.algorithm, opts.weak)
 
   app.addHook('onSend', function (req, reply, payload, done) {
     let etag = reply.getHeader('etag')
diff --git a/test/generic.js b/test/generic.js
index 4025770..61d3f81 100644
--- a/test/generic.js
+++ b/test/generic.js
@@ -89,4 +89,15 @@ module.exports = function ({ test }, etagOpts, hashFn) {
       etag: '"foobar"'
     })
   })
+
+  test('returns a weak etag for each request when weak is in opts', async (t) => {
+    const res = await build({ weak: true }).inject({
+      url: '/'
+    })
+
+    t.same(JSON.parse(res.body), { hello: 'world' })
+    t.match(res.headers, {
+      etag: 'W/' + hash
+    })
+  })
 }