Skip compression for partial content responses

HISTORY.md

@@ -1,3 +1,8 @@
+unreleased
+==========
+
+  * Skip compression for `206 Partial Content` responses
+
 1.8.1 / 2025-07-17
 ==========
 

README.md

@@ -41,7 +41,9 @@ the middleware, based on the given `options`.
 
 This middleware will never compress responses that include a `Cache-Control`
 header with the [`no-transform` directive](https://tools.ietf.org/html/rfc7234#section-5.2.2.4),
-as compressing will transform the body.
+as compressing will transform the body. It will also never compress
+[`206 Partial Content`](https://www.rfc-editor.org/rfc/rfc9110#section-15.3.7)
+responses, as the `Content-Range` header describes the uncompressed body.
 
 #### Options
 

index.js

@@ -171,6 +171,12 @@ function compression (options) {
         return
       }
 
+      // response is partial content
+      if (res.statusCode === 206) {
+        nocompress('partial content')
+        return
+      }
+
       // vary
       vary(res, 'Accept-Encoding')
 

test/compression.js

@@ -67,6 +67,43 @@ describe('compression()', function () {
       .expect(200, 'hello, world', done)
   })
 
+  it('should skip partial content responses', function (done) {
+    var server = createServer({ threshold: 0 }, function (req, res) {
+      res.statusCode = 206
+      res.setHeader('Content-Type', 'text/plain')
+      res.setHeader('Content-Range', 'bytes 0-4/12')
+      res.setHeader('Content-Length', '5')
+      res.end('hello')
+    })
+
+    request(server)
+      .get('/')
+      .set('Accept-Encoding', 'gzip')
+      .expect(shouldNotHaveHeader('Content-Encoding'))
+      .expect(shouldNotHaveHeader('Vary'))
+      .expect('Content-Range', 'bytes 0-4/12')
+      .expect('Content-Length', '5')
+      .expect(206, 'hello', done)
+  })
+
+  it('should skip partial content responses set via writeHead', function (done) {
+    var server = createServer({ threshold: 0 }, function (req, res) {
+      res.writeHead(206, {
+        'Content-Type': 'text/plain',
+        'Content-Range': 'bytes 0-4/12',
+        'Content-Length': '5'
+      })
+      res.end('hello')
+    })
+
+    request(server)
+      .get('/')
+      .set('Accept-Encoding', 'gzip')
+      .expect(shouldNotHaveHeader('Content-Encoding'))
+      .expect('Content-Range', 'bytes 0-4/12')
+      .expect(206, 'hello', done)
+  })
+
   it('should set Vary', function (done) {
     var server = createServer({ threshold: 0 }, function (req, res) {
       res.setHeader('Content-Type', 'text/plain')