feat(etag): allow for custom hashing methods to be used to etag

src/middleware/etag/digest.ts

@@ -9,7 +9,8 @@ const mergeBuffers = (buffer1: ArrayBuffer | undefined, buffer2: Uint8Array): Ui
 }
 
 export const generateDigest = async (
-  stream: ReadableStream<Uint8Array> | null
+  stream: ReadableStream<Uint8Array> | null,
+  generator: (body: Uint8Array) => ArrayBuffer | Promise<ArrayBuffer>
 ): Promise<string | null> => {
   if (!stream || !crypto || !crypto.subtle) {
     return null
@@ -24,12 +25,7 @@ export const generateDigest = async (
       break
     }
 
-    result = await crypto.subtle.digest(
-      {
-        name: 'SHA-1',
-      },
-      mergeBuffers(result, value)
-    )
+    result = await generator(mergeBuffers(result, value))
   }
 
   if (!result) {

src/middleware/etag/index.test.ts

@@ -20,6 +20,39 @@ describe('Etag Middleware', () => {
     expect(res.headers.get('ETag')).toBe('"4515561204e8269cb4468d5b39288d8f2482dcfe"')
   })
 
+  it('Should return etag header with another algorithm', async () => {
+    const app = new Hono()
+    app.use(
+      '/etag/*',
+      etag({
+        generateDigest: (body) =>
+          crypto.subtle.digest(
+            {
+              name: 'SHA-256',
+            },
+            body
+          ),
+      })
+    )
+    app.get('/etag/abc', (c) => {
+      return c.text('Hono is cool')
+    })
+    app.get('/etag/def', (c) => {
+      return c.json({ message: 'Hono is cool' })
+    })
+    let res = await app.request('http://localhost/etag/abc')
+    expect(res.headers.get('ETag')).not.toBeFalsy()
+    expect(res.headers.get('ETag')).toBe(
+      '"ee7e84f92c4f54fec768123ac23003a6eb8437db95bcfbfc35db477af1ccb49e"'
+    )
+
+    res = await app.request('http://localhost/etag/def')
+    expect(res.headers.get('ETag')).not.toBeFalsy()
+    expect(res.headers.get('ETag')).toBe(
+      '"6ae7438c67f07b60b2ab069dbce206b00d3528c690840a77e0222d37398a8547"'
+    )
+  })
+
   it('Should return etag header - binary', async () => {
     const app = new Hono()
     app.use('/etag/*', etag())

src/middleware/etag/index.ts

@@ -9,6 +9,7 @@ import { generateDigest } from './digest'
 type ETagOptions = {
   retainedHeaders?: string[]
   weak?: boolean
+  generateDigest?: (body: Uint8Array) => ArrayBuffer | Promise<ArrayBuffer>
 }
 
 /**
@@ -38,6 +39,9 @@ function etagMatches(etag: string, ifNoneMatch: string | null) {
  * @param {ETagOptions} [options] - The options for the ETag middleware.
  * @param {boolean} [options.weak=false] - Define using or not using a weak validation. If true is set, then `W/` is added to the prefix of the value.
  * @param {string[]} [options.retainedHeaders=RETAINED_304_HEADERS] - The headers that you want to retain in the 304 Response.
+ * @param {function(Uint8Array): ArrayBuffer | Promise<ArrayBuffer>} [options.generateDigest] -
+ * A custom digest generation function. By default, it uses 'SHA-1'
+ * This function is called with the response body as a `Uint8Array` and should return a hash as an `ArrayBuffer` or a Promise of one.
  * @returns {MiddlewareHandler} The middleware handler function.
  *
  * @example
@@ -53,6 +57,15 @@ function etagMatches(etag: string, ifNoneMatch: string | null) {
 export const etag = (options?: ETagOptions): MiddlewareHandler => {
   const retainedHeaders = options?.retainedHeaders ?? RETAINED_304_HEADERS
   const weak = options?.weak ?? false
+  const generator =
+    options?.generateDigest ??
+    ((body: Uint8Array) =>
+      crypto.subtle.digest(
+        {
+          name: 'SHA-1',
+        },
+        body
+      ))
 
   return async function etag(c, next) {
     const ifNoneMatch = c.req.header('If-None-Match') ?? null
@@ -63,15 +76,14 @@ export const etag = (options?: ETagOptions): MiddlewareHandler => {
     let etag = res.headers.get('ETag')
 
     if (!etag) {
-      const hash = await generateDigest(res.clone().body)
+      const hash = await generateDigest(res.clone().body, generator)
       if (hash === null) {
         return
       }
       etag = weak ? `W/"${hash}"` : `"${hash}"`
     }
 
     if (etagMatches(etag, ifNoneMatch)) {
-      await c.res.blob() // Force using body
       c.res = new Response(null, {
         status: 304,
         statusText: 'Not Modified',