This was all done through claude.
## Fix flaky `test_edu_large_messages_not_splitting_one_user` (`TooLong`
under `trial -jN`)
### Problem
The "Build .deb packages" CI step intermittently failed with:
```
twisted.protocols.amp.TooLong
...in
tests.rest.client.test_sendtodevice.SendToDeviceTestCase.test_edu_large_messages_not_splitting_one_user
```
The deb build runs the suite with `twisted.trial -j2`. In that mode,
worker log events are shipped to the manager process over Twisted's AMP
protocol, which encodes each value with a 2-byte length prefix — so any
single log line of **64 KiB or more** raises `TooLong`.
### Root cause
Not a bug in the to-device/EDU logic, and **not** debug logging enabled
by the build (it runs at the default `ERROR` level). It's a **log-level
leak between tests sharing a `-j2` worker**:
- `tests/logging/test_loggers.py::ExplicitlyConfiguredLoggerTestCase`
calls `root_logger.setLevel(logging.DEBUG)` directly and never restores
it (no `setUp`/`tearDown`/`addCleanup`).
- When that test runs before
`test_edu_large_messages_not_splitting_one_user` **in the same worker
process**, the root logger is left at `DEBUG`.
- That test deliberately builds an EDU of exactly `SOFT_MAX_EDU_SIZE -
1` (65 535) bytes. Storing it triggers `synapse/storage/database.py`'s
`[SQL values]` DEBUG log, which dumps the full query params — producing
a **65 708-byte**
line that overflows AMP's cap.
It looks "flaky" purely because of `-j2` scheduling: whether the two
tests land on the same worker, and in what order.
### Fix
Three commits:
1. **Restore the root logger level in
`ExplicitlyConfiguredLoggerTestCase`** — `addCleanup` to put the level
back. Fixes the root cause.
2. **Truncate oversized log lines in the test log handler**
(`ToTwistedHandler.emit`) — caps lines at 1000 chars so no debug line
can break `trial -jN`, regardless of which query is logged (defense in
depth).
3. **Truncate values in `[SQL values]` debug logging** — caps the logged
param repr at 1000 chars (guarded by `isEnabledFor(DEBUG)` to keep the
hot path lazy). Keeps production debug logs sane too.
### Testing
- The reproduction (`trial -j2 tests.logging.test_loggers <the EDU
test>`) went from **~3/8 failing** to **10/10 passing**.
- Confirmed the root level is restored after the logging tests, and that
the `[SQL values]` line is now capped (~50 KB with a `[truncated]`
marker, was 65 708).
- `ruff` + `mypy` clean; `tests.logging.test_loggers` and
`tests.rest.client.test_sendtodevice` pass (14/14).
---------
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Eric Eastwood <erice@element.io>
Spawning from getting `HMAC incorrect` errors that seem unexplainable
except for the `registration_shared_secret` being misconfigured. It's
also possible my HMAC calculation is incorrect but every time I
double-check the result with the [known-good Python
example](https://github.com/element-hq/synapse/blob/553e124f766584456fbdb6d1aa37fdd12ad54dad/docs/admin_api/register_api.md)
(which matches [Synapse's
source](https://github.com/element-hq/synapse/blob/24e849e483820762fa2d231ad702e6aeaa23829c/synapse/rest/admin/users.py#L618-L633)),
it's as expected.
With these logs, we can actually debug whether
`registration_shared_secret` is being configured correctly or not.
It also helps specifically when using `registration_shared_secret_path`
since the default Synapse behavior (of creating the file and secret if
it doesn't exist) can mask deployment race condition where we would
start up Synapse before the `registration_shared_secret_path` file was
put in place:
> **`registration_shared_secret_path`**
>
> [...]
>
> If this file does not exist, Synapse will create a new shared secret
on startup and store it in this file.
>
> *-- [Synapse config
docs](https://github.com/element-hq/synapse/blob/6521406a37a40a490a1a435f3616c02cfcbbac16/docs/usage/configuration/config_documentation.md#registration_shared_secret_path)*
This only applies to the [`POST
/_synapse/admin/v1/register`](https://github.com/element-hq/synapse/blob/553e124f766584456fbdb6d1aa37fdd12ad54dad/docs/admin_api/register_api.md)
endpoint but does log very sensitive information so we've made it so you
have to explicitly enable the logs by configuring
`synapse.rest.admin.users.registration_debug` (does not inherit root log
level) (via our new `ExplicitlyConfiguredLogger`)
`homeserver.yaml`
```yaml
log_config: "/myserver.log.config.yaml"
```
`myserver.log.config.yaml`
```yaml
version: 1
formatters:
precise:
format: '%(asctime)s - %(name)s - %(lineno)d - %(levelname)s - %(request)s - %(message)s'
handlers:
# ... file/buffer handler (see `sample_log_config.yaml`)
# A handler that writes logs to stderr. Unused by default, but can be used
# instead of "buffer" and "file" in the logger handlers.
console:
class: logging.StreamHandler
formatter: precise
loggers:
synapse.storage.SQL:
# beware: increasing this to DEBUG will make synapse log sensitive
# information such as access tokens.
level: INFO
# Has to be explicitly configured as such. Will not inherit from the root level even if it's set to DEBUG
synapse.rest.admin.users.registration_debug:
level: DEBUG
root:
level: INFO
handlers: [console]
disable_existing_loggers: false
```
