Mode parameter for listeners only supports decimal

[matrixbot]

This issue has been migrated from #16302.

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Description

When setting a mode in the listener config when listening on a unix domain socket, the mode needs to be specified in decimal. That isn't very obvious from the documentation: https://matrix-org.github.io/synapse/latest/usage/configuration/config_documentation.html#listeners

The documentation says it defaults to 666, however it actually defaults to 0o666 or rather 438. This leads the reader to believe they can specify a different mode like 660, however they would need to specify 432. Specifying octal does not work with the yaml parser synapse uses (0o660 is parsed as a string).

It would be good if the documentation mentioned that or required the mode to be passed as a string.

Steps to reproduce

• setup a listener on a unix domain socket with a non-default mode. It will have the wrong values when checking the permissions of the created socket, if the value is passed as a decimal number, but is actually octal.

Homeserver

neko.dev

Synapse Version

1.92.0_rc1

Installation Method

Other (please mention below)

Database

postgres, one db

Workers

Multiple workers

Platform

Gentoo

Configuration

No response

Relevant log output

s-w--w-r-T 1 synapse synapse 0 Sep 11 16:56 /run/synapse/event_creator.replication.sock

when mode 660 is specified.

### Anything else that would be useful to know?

_No response_