A host-supplied rule for dropping log events.

GamendWeb.LogFilters knows about the noise every Gamend server produces — peer TLS alerts, dead sockets — because they come from the endpoint core owns. Noise from a host's own code is the host's to describe, and a host should not have to patch core to silence it.

# config/config.exs
config :gamend_web, :log_filters, [GamendHost.LogFilters]

defmodule GamendHost.LogFilters do
  @behaviour GamendWeb.LogFilter

  @impl true
  def drop?(%{msg: {:string, message}}),
    do: to_string(message) =~ "some known, harmless noise"

  def drop?(_event), do: false
end

Writing one

The argument is a raw :logger event, not a formatted string — a map with :level, :msg and :meta. :msg is one of {:string, chardata}, {format, args} or {:report, map_or_keyword}, so match on the shape you expect and fall through to false for everything else.

Two rules, both because this runs inside the logging pipeline:

• Never log from drop?/1. Emitting a log event while handling one recurses.
• Be total. A raise is caught and treated as "do not drop", so a broken filter loses its own noise rather than the whole log. It cannot be reported, per the previous rule.

It also runs on every event on every process, so keep it to pattern matching and comparisons — no ETS lookups, no message passing, no regexes over large binaries.