From ac04f8141807d44160d169c498ec757eaa93d316 Mon Sep 17 00:00:00 2001
From: Raashish Aggarwal <94279692+raashish1601@users.noreply.github.com>
Date: Mon, 11 May 2026 22:24:37 +0530
Subject: [PATCH] fix: allow lenient chunk-size whitespace

---
 lib/dispatcher/client-h1.js |  1 +
 test/parser-issues.js       | 59 +++++++++++++++++++++++++++++++++++--
 2 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/lib/dispatcher/client-h1.js b/lib/dispatcher/client-h1.js
index f1c52fb5f11..8e65560964c 100644
--- a/lib/dispatcher/client-h1.js
+++ b/lib/dispatcher/client-h1.js
@@ -211,6 +211,7 @@ class Parser {
   constructor (client, socket, { exports }) {
     this.llhttp = exports
     this.ptr = this.llhttp.llhttp_alloc(constants.TYPE.RESPONSE)
+    this.llhttp.llhttp_set_lenient_spaces_after_chunk_size(this.ptr, 1)
     this.client = client
     /**
      * @type {import('net').Socket}
diff --git a/test/parser-issues.js b/test/parser-issues.js
index 4e398cdba01..27d00fa7fe8 100644
--- a/test/parser-issues.js
+++ b/test/parser-issues.js
@@ -14,6 +14,17 @@ const truncatedChunkedResponse = Buffer.from(
   'hel\r\n'
 )
 
+const chunkedResponseWithTrailingSpaceAfterChunkSize = Buffer.from(
+  'HTTP/1.1 200 OK\r\n' +
+  'Transfer-Encoding: chunked\r\n' +
+  'Connection: close\r\n' +
+  '\r\n' +
+  '7\r\n' +
+  'hello, \r\n' +
+  '0  \r\n' +
+  '\r\n'
+)
+
 function createTrackedServer (onConnection) {
   const sockets = new Set()
   const server = net.createServer(socket => {
@@ -255,17 +266,18 @@ test('refreshes wasm input view after reallocating parser buffer', async (t) =>
 })
 
 test('truncated chunked responses terminated by EOF error the response body', async (t) => {
+  const ctx = t
   t = tspl(t, { plan: 3 })
 
   const server = net.createServer((socket) => {
     socket.end(truncatedChunkedResponse)
   })
-  after(() => server.close())
+  ctx.after(() => server.close())
 
   await new Promise(resolve => server.listen(0, resolve))
 
   const client = new Client(`http://localhost:${server.address().port}`)
-  after(() => client.destroy())
+  ctx.after(() => client.destroy())
 
   client.request({
     method: 'GET',
@@ -286,13 +298,54 @@ test('truncated chunked responses terminated by EOF error the response body', as
   await t.completed
 })
 
+test('accepts chunked response with spaces after chunk size', async (t) => {
+  const ctx = t
+  t = tspl(t, { plan: 2 })
+
+  const server = net.createServer((socket) => {
+    socket.end(chunkedResponseWithTrailingSpaceAfterChunkSize)
+  })
+  ctx.after(() => server.close())
+
+  await new Promise(resolve => server.listen(0, resolve))
+
+  const client = new Client(`http://localhost:${server.address().port}`)
+  ctx.after(() => client.destroy())
+
+  client.request({
+    method: 'GET',
+    path: '/'
+  }, (err, data) => {
+    t.ifError(err)
+    if (err) {
+      return
+    }
+
+    const chunks = []
+
+    data.body
+      .on('data', chunk => {
+        chunks.push(chunk)
+      })
+      .on('error', err => {
+        t.ifError(err)
+      })
+      .on('end', () => {
+        t.strictEqual(Buffer.concat(chunks).toString(), 'hello, ')
+      })
+  })
+
+  await t.completed
+})
+
 test('fetch rejects truncated chunked responses terminated by EOF', async (t) => {
+  const ctx = t
   t = tspl(t, { plan: 3 })
 
   const server = net.createServer((socket) => {
     socket.end(truncatedChunkedResponse)
   })
-  after(() => server.close())
+  ctx.after(() => server.close())
 
   await new Promise(resolve => server.listen(0, resolve))