aiohttp Broken in with yarl 1.13.0+ working in 3.10.7+,

The Fix

Fixes the issue where the host header incorrectly included the port number, causing failures in URL building with yarl 1.13.0+.

Based on closed aio-libs/aiohttp issue #9360 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -0,0 +1 @@
@@ -0,0 +1 @@
+Fixed assembling the :class:`~yarl.URL` for web requests when the host contains a non-default port or IPv6 address -- by :user:`bdraco`.
diff --git a/aiohttp/web_request.py b/aiohttp/web_request.py
index d593a75da74..b7b54fbd41d 100644

repro.py

import asyncio
import pytest
import subprocess
from aiohttp import web

async def health_check(request):
    return web.Response(text="HEALTHY")

@web.middleware
async def middleware(request, handler):
    # Access request.url.path to trigger the potential error
    print(f"Accessing path: {request.url.path}")
    response = await handler(request)
    return response

async def run_server():
    app = web.Application(middlewares=[middleware])
    app.router.add_get('/health', health_check)
    runner = web.AppRunner(app)
    await runner.setup()
    site = web.TCPSite(runner, 'localhost', 9090)
    await site.start()
    print("Server started on http://localhost:9090")
    return runner

@pytest.mark.asyncio
async def test_health_check():
    runner = await run_server()
    try:
        # Use asyncio.create_subprocess_exec to run curl command
        proc = await asyncio.create_subprocess_exec(
            'curl', '-s', 'http://localhost:9090/health',
            stdout=asyncio.subprocess.PIPE,
            stderr=asyncio.subprocess.PIPE)

        try:
            stdout, stderr = await asyncio.wait_for(proc.communicate(), timeout=5.0)
        except asyncio.TimeoutError:
            print("Curl request timed out")
            proc.kill()
            await proc.wait()
            return

        if proc.returncode != 0:
            print(f"Curl failed with return code {proc.returncode}")
            print(f"stderr: {stderr.decode()}")
        else:
            response = stdout.decode().strip()
            assert response == "HEALTHY", f"Unexpected response: {response}"
            print("Test passed: Received 'HEALTHY' response")
    finally:
        await runner.cleanup()

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Apply the official fix\nFixes the issue where the host header incorrectly included the port number, causing failures in URL building with yarl 1.13.0+.\nWhen NOT to use: This fix should not be applied if the application relies on the incorrect behavior of including port numbers in the host.\n\n

Why This Fix Works in Production

Trigger: 10.3.39.66 [30/Sep/2024:11:09:51 -0800] "GET /health HTTP/1.1" 500 246 "-" "kube-probe/1.29"
Mechanism: Fixes the issue where the host header incorrectly included the port number, causing failures in URL building with yarl 1.13.0+.

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Shows up under Python 3.11.7 in real deployments (not just unit tests).
Surfaces as: 10.3.39.66 [30/Sep/2024:11:09:51 -0800] "GET /health HTTP/1.1" 500 246 "-" "kube-probe/1.29"

Proof / Evidence

GitHub issue: #9360
Fix PR: https://github.com/aio-libs/aiohttp/pull/9309
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.27

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“This looks like a duplicate of https://github.com/aio-libs/aiohttp/issues/9307 which was fixed via https://github.com/aio-libs/aiohttp/pull/9309”

@bdraco · 2024-09-30 · source

“Appears so, I even looked at this PR and it was hard to see it was fixed! Thank you for pointing this out.”

@doctorpangloss · 2024-09-30 · source

“In case it makes a difference in how you deploy”

@bdraco · 2024-09-30 · source

Failure Signature (Search String)

10.3.39.66 [30/Sep/2024:11:09:51 -0800] "GET /health HTTP/1.1" 500 246 "-" "kube-probe/1.29"

Error Message

Stack trace

error.txt

Error Message
-------------
10.3.39.66 [30/Sep/2024:11:09:51 -0800] "GET /health HTTP/1.1" 500 246 "-" "kube-probe/1.29"
Error handling request
Traceback (most recent call last):
  File "C:\Python311\Lib\site-packages\aiohttp\web_protocol.py", line 477, in _handle_request
    resp = await request_handler(request)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Python311\Lib\site-packages\aiohttp\web_app.py", line 559, in _handle
    return await handler(request)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Python311\Lib\site-packages\aiohttp\web_middlewares.py", line 117, in impl
    return await handler(request)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Python311\Lib\site-packages\comfy\vendor\aiohttp_server_instrumentation.py", line 196, in middleware
    or _excluded_urls.url_disabled(request.url.path)
                                   ^^^^^^^^^^^
  File "aiohttp\\_helpers.pyx", line 30, in aiohttp._helpers.reify.__get__
  File "C:\Python311\Lib\site-packages\aiohttp\web_request.py", line 457, in url
    url = URL.build(scheme=self.scheme, host=self.host)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Python311\Lib\site-packages\yarl\_url.py", line 385, in build
    netloc = cls._make_netloc(
             ^^^^^^^^^^^^^^^^^
  File "C:\Python311\Lib\site-packages\yarl\_url.py", line 1057, in _make_netloc
    ret = cls._encode_host(host)
          ^^^^^^^^^^^^^^^^^^^^^^
  File
... (truncated) ...

Minimal Reproduction

repro.py

import asyncio
import pytest
import subprocess
from aiohttp import web

async def health_check(request):
    return web.Response(text="HEALTHY")

@web.middleware
async def middleware(request, handler):
    # Access request.url.path to trigger the potential error
    print(f"Accessing path: {request.url.path}")
    response = await handler(request)
    return response

async def run_server():
    app = web.Application(middlewares=[middleware])
    app.router.add_get('/health', health_check)
    runner = web.AppRunner(app)
    await runner.setup()
    site = web.TCPSite(runner, 'localhost', 9090)
    await site.start()
    print("Server started on http://localhost:9090")
    return runner

@pytest.mark.asyncio
async def test_health_check():
    runner = await run_server()
    try:
        # Use asyncio.create_subprocess_exec to run curl command
        proc = await asyncio.create_subprocess_exec(
            'curl', '-s', 'http://localhost:9090/health',
            stdout=asyncio.subprocess.PIPE,
            stderr=asyncio.subprocess.PIPE)

        try:
            stdout, stderr = await asyncio.wait_for(proc.communicate(), timeout=5.0)
        except asyncio.TimeoutError:
            print("Curl request timed out")
            proc.kill()
            await proc.wait()
            return

        if proc.returncode != 0:
            print(f"Curl failed with return code {proc.returncode}")
            print(f"stderr: {stderr.decode()}")
        else:
            response = stdout.decode().strip()
            assert response == "HEALTHY", f"Unexpected response: {response}"
            print("Test passed: Received 'HEALTHY' response")
    finally:
        await runner.cleanup()

Environment

Python: 3.11.7

What Broke

Requests to the aiohttp server resulted in 500 errors due to incorrect URL parsing.

Fix Options (Details)

Option A — Apply the official fix

Fixes the issue where the host header incorrectly included the port number, causing failures in URL building with yarl 1.13.0+.

When NOT to use: This fix should not be applied if the application relies on the incorrect behavior of including port numbers in the host.

Fix reference: https://github.com/aio-libs/aiohttp/pull/9309

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be applied if the application relies on the incorrect behavior of including port numbers in the host.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.

Version Compatibility Table

Version	Status
1.13.0	Broken
3.10.6	Broken
3.10.7	Broken

Related Issues

No related fixes found.

Cluster: aiohttp:configuration-error All hubs All clusters

Related clusters: Data consistency Race condition Auth

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

aiohttp Broken in with yarl 1.13.0+ working in 3.10.7+, contains test case: aiohttp parses port (Fix)