From 49366df8a925cd8e886ac5b3c317a0f6b0bd3970 Mon Sep 17 00:00:00 2001
From: Dmitri <dmitri666@gmail.com>
Date: Fri, 17 Jan 2025 12:16:33 +0200
Subject: [PATCH] fix(compress): don't compress server-sent events (#3833)

Using both `compress` middleware and the `streamSSE` helper from `hono/streaming` doesn't work correctly -- the SSE messages are not streamed, instead they get buffered by the compression mechanism.

According to [expressjs/compression](https://github.com/expressjs/compression#server-sent-events), it should possible to compress server-sent events, if the underlying compression mechanism supports manual _flushing_. As far as I can tell though, `CompressionStream` (used by Hono's `compress` middleware) doesn't offer this functionality, so the best we can do is not compress SSE streams at all.
---
 src/middleware/compress/index.test.ts | 14 +++++++++++++-
 src/utils/compress.ts                 |  2 +-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/middleware/compress/index.test.ts b/src/middleware/compress/index.test.ts
index d446b451d..df8fa7748 100644
--- a/src/middleware/compress/index.test.ts
+++ b/src/middleware/compress/index.test.ts
@@ -1,4 +1,4 @@
-import { stream } from '../../helper/streaming'
+import { stream, streamSSE } from '../../helper/streaming'
 import { Hono } from '../../hono'
 import { compress } from '.'
 
@@ -65,6 +65,13 @@ describe('Compress Middleware', () => {
       }
     })
   )
+  app.get('/sse', (c) =>
+    streamSSE(c, async (stream) => {
+      for (let i = 0; i < 1000; i++) {
+        await stream.writeSSE({ data: 'chunk' })
+      }
+    })
+  )
   app.notFound((c) => c.text('Custom NotFound', 404))
 
   const testCompression = async (
@@ -155,6 +162,11 @@ describe('Compress Middleware', () => {
       const res = await testCompression('/already-compressed-stream', 'gzip', 'br')
       expect((await res.arrayBuffer()).byteLength).toBe(60000)
     })
+
+    it('should not compress server-sent events', async () => {
+      const res = await testCompression('/sse', 'gzip', null)
+      expect((await res.arrayBuffer()).byteLength).toBe(13000)
+    })
   })
 
   describe('Edge Cases', () => {
diff --git a/src/utils/compress.ts b/src/utils/compress.ts
index a0a6cd7b5..93a660976 100644
--- a/src/utils/compress.ts
+++ b/src/utils/compress.ts
@@ -7,4 +7,4 @@
  * Match for compressible content type.
  */
 export const COMPRESSIBLE_CONTENT_TYPE_REGEX =
-  /^\s*(?:text\/[^;\s]+|application\/(?:javascript|json|xml|xml-dtd|ecmascript|dart|postscript|rtf|tar|toml|vnd\.dart|vnd\.ms-fontobject|vnd\.ms-opentype|wasm|x-httpd-php|x-javascript|x-ns-proxy-autoconfig|x-sh|x-tar|x-virtualbox-hdd|x-virtualbox-ova|x-virtualbox-ovf|x-virtualbox-vbox|x-virtualbox-vdi|x-virtualbox-vhd|x-virtualbox-vmdk|x-www-form-urlencoded)|font\/(?:otf|ttf)|image\/(?:bmp|vnd\.adobe\.photoshop|vnd\.microsoft\.icon|vnd\.ms-dds|x-icon|x-ms-bmp)|message\/rfc822|model\/gltf-binary|x-shader\/x-fragment|x-shader\/x-vertex|[^;\s]+?\+(?:json|text|xml|yaml))(?:[;\s]|$)/i
+  /^\s*(?:text\/(?!event-stream(?:[;\s]|$))[^;\s]+|application\/(?:javascript|json|xml|xml-dtd|ecmascript|dart|postscript|rtf|tar|toml|vnd\.dart|vnd\.ms-fontobject|vnd\.ms-opentype|wasm|x-httpd-php|x-javascript|x-ns-proxy-autoconfig|x-sh|x-tar|x-virtualbox-hdd|x-virtualbox-ova|x-virtualbox-ovf|x-virtualbox-vbox|x-virtualbox-vdi|x-virtualbox-vhd|x-virtualbox-vmdk|x-www-form-urlencoded)|font\/(?:otf|ttf)|image\/(?:bmp|vnd\.adobe\.photoshop|vnd\.microsoft\.icon|vnd\.ms-dds|x-icon|x-ms-bmp)|message\/rfc822|model\/gltf-binary|x-shader\/x-fragment|x-shader\/x-vertex|[^;\s]+?\+(?:json|text|xml|yaml))(?:[;\s]|$)/i