fix: decompress right-to-left

src/interceptors/fetch/utils/decompression.ts

@@ -42,21 +42,22 @@ function createDecompressionStream(
     return null
   }
 
-  const transformers: Array<TransformStream> = []
+  const transformers = codings.reduceRight<Array<TransformStream>>(
+    (transformers, coding) => {
+      if (coding === 'gzip' || coding === 'x-gzip') {
+        return transformers.concat(new DecompressionStream('gzip'))
+      } else if (coding === 'deflate') {
+        return transformers.concat(new DecompressionStream('deflate'))
+      } else if (coding === 'br') {
+        return transformers.concat(new BrotliDecompressionStream())
+      } else {
+        transformers.length = 0
+      }
 
-  for (let i = 0; i < codings.length; i++) {
-    const coding = codings[i]
-
-    if (coding === 'gzip' || coding === 'x-gzip') {
-      transformers.push(new DecompressionStream('gzip'))
-    } else if (coding === 'deflate') {
-      transformers.push(new DecompressionStream('deflate'))
-    } else if (coding === 'br') {
-      transformers.push(new BrotliDecompressionStream())
-    } else {
-      transformers.length = 0
-    }
-  }
+      return transformers
+    },
+    []
+  )
 
   return new PipelineStream(transformers)
 }

test/helpers.ts

@@ -319,24 +319,25 @@ export const useCors: RequestHandler = (req, res, next) => {
   return next()
 }
 
-function compose(...fns: Array<Function>) {
-  return fns.reduce((f, g) => {
-    return (...args: Array<unknown>) => f(g(...args))
-  })
-}
+/**
+ * Compress the given data using the specified `Content-Encoding` codings
+ * left-to-right.
+ */
+export function compressResponse(
+  codings: Array<'gzip' | 'x-gzip' | 'deflate' | 'br'>,
+  input: string
+) {
+  let output = Buffer.from(input)
+
+  for (const coding of codings) {
+    if (coding === 'gzip' || coding === 'x-gzip') {
+      output = zlib.gzipSync(output)
+    } else if (coding === 'deflate') {
+      output = zlib.deflateSync(output)
+    } else if (coding === 'br') {
+      output = zlib.brotliCompressSync(output)
+    }
+  }
 
-export function compressResponse(codings: Array<string>) {
-  return compose(
-    ...codings.map((coding) => {
-      if (coding === 'gzip' || coding === 'x-gzip') {
-        return zlib.gzipSync
-      } else if (coding === 'deflate') {
-        return zlib.deflateSync
-      } else if (coding === 'br') {
-        return zlib.brotliCompressSync
-      }
-
-      return (data: string) => data
-    })
-  )
+  return output
 }

test/modules/fetch/compliance/response-content-encoding.browser.test.ts

@@ -12,11 +12,11 @@ const server = new HttpServer((app) => {
   app.use(useCors)
   app.get('/resource', (req, res) => {
     const acceptEncoding = req.header('x-accept-encoding')
-    const codings = parseContentEncoding(acceptEncoding || '')
+    const codings = parseContentEncoding(acceptEncoding || '') as any[]
 
     res
       .set('content-encoding', acceptEncoding)
-      .end(compressResponse(codings)('hello world'))
+      .end(compressResponse(codings, 'hello world'))
   })
 })
 

test/modules/fetch/compliance/response-content-encoding.test.ts

@@ -1,5 +1,4 @@
 // @vitest-environment node
-import zlib from 'node:zlib'
 import { it, expect, beforeAll, afterEach, afterAll } from 'vitest'
 import { HttpServer } from '@open-draft/test-server/http'
 import { compressResponse } from '../../../helpers'
@@ -9,11 +8,11 @@ import { parseContentEncoding } from '../../../../src/interceptors/fetch/utils/d
 const httpServer = new HttpServer((app) => {
   app.get('/compressed', (req, res) => {
     const acceptEncoding = req.header('accept-encoding')
-    const codings = parseContentEncoding(acceptEncoding || '')
+    const codings = parseContentEncoding(acceptEncoding || '') as any[]
 
     res
       .set('content-encoding', acceptEncoding)
-      .end(compressResponse(codings)('hello world'))
+      .end(compressResponse(codings, 'hello world'))
   })
 })
 
@@ -36,7 +35,7 @@ afterAll(async () => {
 it('decompresses a mocked "content-encoding: gzip" response body', async () => {
   interceptor.on('request', ({ controller }) => {
     controller.respondWith(
-      new Response(zlib.gzipSync('hello world'), {
+      new Response(compressResponse(['gzip'], 'hello world'), {
         headers: {
           'content-encoding': 'gzip',
         },
@@ -58,7 +57,7 @@ it('decompresses a bypassed "content-encoding: gzip" response body', async () =>
 it('decompresses a mocked "content-encoding: x-gzip" response body', async () => {
   interceptor.on('request', ({ controller }) => {
     controller.respondWith(
-      new Response(zlib.gzipSync('hello world'), {
+      new Response(compressResponse(['gzip'], 'hello world'), {
         headers: {
           'content-encoding': 'x-gzip',
         },
@@ -80,7 +79,7 @@ it('decompresses a bypassed "content-encoding: x-gzip" response body', async ()
 it('decompresses a mocked "content-encoding: deflate" response body', async () => {
   interceptor.on('request', ({ controller }) => {
     controller.respondWith(
-      new Response(zlib.deflateSync('hello world'), {
+      new Response(compressResponse(['deflate'], 'hello world'), {
         headers: {
           'content-encoding': 'deflate',
         },
@@ -102,7 +101,7 @@ it('decompresses a bypassed "content-encoding: deflate" response body', async ()
 it('decompresses a mocked "content-encoding: br" response body', async () => {
   interceptor.on('request', ({ controller }) => {
     controller.respondWith(
-      new Response(zlib.brotliCompressSync('hello world'), {
+      new Response(compressResponse(['br'], 'hello world'), {
         headers: {
           'content-encoding': 'br',
         },
@@ -121,10 +120,32 @@ it('decompresses a bypassed "content-encoding: br" response body', async () => {
   expect(await response.text()).toBe('hello world')
 })
 
+it('decompresses a mocked "content-encoding: gzip, deflate" response body', async () => {
+  interceptor.on('request', ({ controller }) => {
+    controller.respondWith(
+      new Response(compressResponse(['gzip', 'deflate'], 'hello world'), {
+        headers: {
+          'content-encoding': 'gzip, deflate',
+        },
+      })
+    )
+  })
+
+  const response = await fetch('http://localhost/resource')
+  expect(await response.text()).toBe('hello world')
+})
+
+it('decompresses a bypassed "content-encoding: gzip, deflate" response body', async () => {
+  const response = await fetch(httpServer.http.url('/compressed'), {
+    headers: { 'accept-encoding': 'gzip, deflate' },
+  })
+  expect(await response.text()).toBe('hello world')
+})
+
 it('decompresses a mocked "content-encoding: gzip, br" response body', async () => {
   interceptor.on('request', ({ controller }) => {
     controller.respondWith(
-      new Response(compressResponse(['gzip', 'br'])('hello world'), {
+      new Response(compressResponse(['gzip', 'br'], 'hello world'), {
         headers: {
           'content-encoding': 'gzip, br',
         },
@@ -137,6 +158,8 @@ it('decompresses a mocked "content-encoding: gzip, br" response body', async ()
 })
 
 it('decompresses a bypassed "content-encoding: gzip, br" response body', async () => {
-  const response = await fetch(httpServer.http.url('/compressed'))
+  const response = await fetch(httpServer.http.url('/compressed'), {
+    headers: { 'accept-encoding': 'gzip, br' },
+  })
   expect(await response.text()).toBe('hello world')
 })