From f50ef06ab6cf4b32de48bbc0193c6df97878d46f Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Mon, 27 Apr 2026 21:37:50 -0700
Subject: [PATCH] fix(http2): respect peer max concurrent streams

Assisted-by: openai:gpt-5.5
Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
---
 lib/dispatcher/client-h2.js |  8 ++++++
 test/h2c-client.js          | 50 +++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/lib/dispatcher/client-h2.js b/lib/dispatcher/client-h2.js
index 0c9ae1e0cd1..a286ae9ee33 100644
--- a/lib/dispatcher/client-h2.js
+++ b/lib/dispatcher/client-h2.js
@@ -233,6 +233,14 @@ function connectH2 (client, socket) {
      * @returns {boolean}
     */
     busy (request) {
+      if (session[kRemoteSettings] === false && client[kRunning] > 0) {
+        return true
+      }
+
+      if (client[kRunning] >= client[kMaxConcurrentStreams]) {
+        return true
+      }
+
       if (request != null) {
         if (client[kRunning] > 0) {
           // We are already processing requests
diff --git a/test/h2c-client.js b/test/h2c-client.js
index eecd3991006..6c46fb417b5 100644
--- a/test/h2c-client.js
+++ b/test/h2c-client.js
@@ -83,6 +83,56 @@ test('Should support h2c connection with body', async t => {
   planner.equal(Buffer.concat(bodyChunks).toString(), 'Hello, world!')
 })
 
+test('Should queue h2c requests above the remote max concurrent streams setting', async t => {
+  const planner = tspl(t, { plan: 3 })
+  let activeStreams = 0
+  let maxActiveStreams = 0
+  const paths = []
+
+  const server = createServer({
+    settings: {
+      maxConcurrentStreams: 1
+    }
+  })
+
+  server.on('stream', (stream, headers) => {
+    activeStreams++
+    maxActiveStreams = Math.max(maxActiveStreams, activeStreams)
+    paths.push(headers[':path'])
+
+    stream.respond({ ':status': 200 })
+    setTimeout(() => {
+      activeStreams--
+      stream.end('Hello, world!')
+    }, 50)
+  })
+
+  server.listen()
+  await once(server, 'listening')
+  const client = new H2CClient(`http://localhost:${server.address().port}/`, {
+    maxConcurrentStreams: 10,
+    pipelining: 10
+  })
+
+  t.after(() => client.close())
+  t.after(() => server.close())
+
+  const responses = await Promise.all(Array.from({ length: 5 }, async (_, i) => {
+    const response = await client.request({ path: `/${i}`, method: 'GET' })
+    return {
+      statusCode: response.statusCode,
+      body: await response.body.text()
+    }
+  }))
+
+  planner.strictEqual(maxActiveStreams, 1)
+  planner.deepStrictEqual(paths, ['/0', '/1', '/2', '/3', '/4'])
+  planner.deepStrictEqual(responses, Array.from({ length: 5 }, () => ({
+    statusCode: 200,
+    body: 'Hello, world!'
+  })))
+})
+
 test('Should reject request if not h2c supported', async t => {
   const planner = tspl(t, { plan: 1 })