Link device QR code fails with 412 M_CONCURRENT_WRITE #18155
Comments
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@sandhose would you please check te log above, I don't see any problems with etag. |
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I've tested MAS with completely new Synapse instance without workers with the same result. |
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Seems login via QR doesn't work now even on beta.element.io, it worked fine few days back. It fails after timeout on the 6-letter confirmation code screen on Element X. |
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This feels like there is a caching proxy in front of Synapse, or something that compresses on the fly. Do you happen to have Cloudflare in front of Synapse? Or nginx with |
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@sandhose you are right, turning off gzip for Synapse on my nginx proxy did the trick, PUT forwards |
It's
You can build it locally with That patch should make it unnecessary to exclude certain endpoint from compression |
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I built docker image and deployed it to my test Synapse container (with gzip enabled), however it still returns 412 :( |
I tried that, and it looks like this can happen when the local session doesn't have access to the cross-signing key or isn't connected to the key backup
Can you check in your request logs in EW? Right after you display the QR code, you should see:
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Here's a script I have to make sure a rendezvous implementation works correctly: # /// script
# requires-python = ">=3.12"
# dependencies = ["requests"]
# ///
import logging
from http.client import HTTPConnection
import requests
HTTPConnection.debuglevel = 1
logging.basicConfig()
logging.getLogger().setLevel(logging.DEBUG)
requests_log = logging.getLogger("urllib3")
requests_log.setLevel(logging.DEBUG)
requests_log.propagate = True
base = "https://example.com" # CHANGE ME
response = requests.post(
f"{base}/_matrix/client/unstable/org.matrix.msc4108/rendezvous",
data="INIITIAL" * 128,
headers={"Content-Type": "text/plain"},
)
assert response.status_code == 201, response.status_code
session = response.json()["url"]
assert "ETag" in response.headers
etag = response.headers["ETag"]
response = requests.get(session, headers={"If-None-Match": etag})
assert response.status_code == 304, response.status_code
response = requests.get(session)
assert response.status_code == 200, response.status_code
assert response.text == "INIITIAL" * 128
assert response.headers["ETag"] == etag
response = requests.put(
session, data="UPDATED\n" * 128, headers={"If-Match": etag, "Content-Type": "text/plain"}
)
assert response.status_code == 202, response.status_code
assert "ETag" in response.headers
assert response.headers["ETag"] != etagIf you have Change the 'base' with where Synapse is exposed |
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With etag values visible... That was exactly my suspicions. |
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This is super useful: I think this is because nginx will switch to |
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Unfortunatelly... |
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I missed that before, looks like nginx still Do you have |
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Unfortunately |
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The workaround to force uncompressed response from Synapse's side would be header like: Anyway, why is uncompressed response required? Etags are the same, the only difference is the weak validator. |
Whilst this is true for nginx, it isn't the case for other implementations like Caddy, which output a strong ETag with
That's on the client side, right? I guess it would require a change on the MSC for that, I don't really like this workaround :( I don't really know how we could fix this on the Synapse side, other than asking people to check their reverse proxy config and disable compression |
Then nginx should be fixed. Will try to investigate...
Yes, it's client side, not Synapse as I wrote.
Disabling gzip for those enpoints works for me, I can live with that. However it would be good to document it, because it will be a problem for others when MAS is used widely. Thank you for helping me to investigate the issue. |
Description
I have set up MAS (with Authentik OIDC) on my Matrix instance, enabled MSC3861 and MSC4108 on Synapse according docs, everything looks good, login via Authentik works fine, however...
I want to add another Android device via QR code, when I scan QR code with Element X from Element Web following Element Web GET requests to
https://matrix.domain/_matrix/client/v3/devices/ZD6NzBC8RQ38jWLUIXBmQFPXB81etmMpbdD423%2F00BAfails with 404{"errcode":"M_NOT_FOUND","error":"Not found"}Not sure if this is expected.
After the 2-digit code from Element X is entered on Element Web folowing PUT request to
https://matrix.domain/_synapse/client/rendezvous/01JKWWGPR4N9YXYG6RCCY38H0Wfails with{"errcode":"M_UNKNOWN","error":"ETag does not match","org.matrix.msc4108.errcode":"M_CONCURRENT_WRITE"}MAS request is confirmed and page closed, Element X stucks on that 2-digit code screen and fails after timeout same as Element Web.
What could be wrong there?
Are docs regarding worker settings up to date?
https://element-hq.github.io/synapse/develop/workers.html?highlight=workers#worker-configuration
Currently the
/_synapse/client/rendezvous/{id}and/_matrix/client/v3/devices/{id}endpoints are handled by master worker instead of client worker.Thanks.
EDIT: rolling back MAS, still unstable and broken...
Error: [{"message":"Database inconsistency on table compat_sessions column device_id row 01HQ3FB21QVAPX9E710P93212F","locations":[{"line":7,"column":7}],"path":["viewer","appSessions"]}]while listing user account sessions
Steps to reproduce
above
Homeserver
Synapse
Synapse Version
1.124.0
Installation Method
Docker (matrixdotorg/synapse)
Database
Postgres 16
Workers
Multiple workers
Platform
Fedora 41
Configuration
No response
Relevant log output
Anything else that would be useful to know?
No response
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