Add log_filter: pluggable per-unit output filter subprocess

Each unit can specify log_filter: <path> pointing to any executable
that reads stdin and writes filtered output to stdout. The daemon
spawns it once at startup (and on SIGHUP), pipes raw log data through
it before ring-buffering and broadcasting to attached clients.

filter.c handles spawn (fork/exec with pipes), per-chunk apply
(write + poll with 250ms timeout, pass-through on silence/timeout),
and stop (SIGTERM + fd cleanup). Filters are stopped and restarted
cleanly on SIGHUP alongside log_tail.

Bundled filters in filters/:
  source.py    — TF2, GMod: strips server_cvar/stuck/path_goal spam,
                 strips the L MM/DD/YYYY - HH:MM:SS: prefix
  minecraft.py — vanilla/Paper/Spigot: strips keepAlive, autosave,
                 internal class logs, strips [HH:MM:SS] [thread] prefix
  terraria.py  — vanilla/tModLoader: strips blank lines and mod
                 loading noise during startup

Any executable reading stdin/writing stdout works as a custom filter.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

3 files changed, 113 insertions, 0 deletions

diff --git a/filters/minecraft.py b/filters/minecraft.py
new file mode 100644
index 0000000..d4112d6
--- /dev/null
+++ b/filters/minecraft.py
@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+"""
+Minecraft log filter for Umbrella (vanilla, Paper, Spigot, Fabric, etc.)
+
+Strips low-value noise:
+  - keepAlive packet spam (Paper/Spigot debug logs)
+  - Internal class/library log lines
+  - Advancement grant/revoke noise
+  - Saving chunks / autosave lines
+  - UUID cache loading lines
+
+Strips the "[HH:MM:SS] [Thread/LEVEL]: " prefix from standard Minecraft
+log format, since the daemon already timestamps output.
+
+Install: /usr/lib/umbrella/filters/minecraft.py
+Unit YAML: log_filter: /usr/lib/umbrella/filters/minecraft.py
+"""
+
+import sys
+import re
+
+# Standard Minecraft log prefix: [HH:MM:SS] [Server thread/INFO]:
+PREFIX = re.compile(r'^\[\d{2}:\d{2}:\d{2}\] \[[^\]]+\]: ')
+
+SKIP = re.compile(
+    r'keepAlive'                     # packet keepAlive debug
+    r'|Saving chunks for level'      # periodic autosave
+    r'|Saving and pausing game'
+    r'|com\.mojang\.'                # internal Mojang class logs
+    r'|RCON Client /'                # RCON connection noise
+    r'|RCON Listener'
+    r'|Preparing spawn area'
+    r'|Loading libraries'
+    r'|Loaded \d+ recipes'
+    r'|Loaded \d+ advancements'
+    r'|\[uuid-cache\]'
+    r'|^\s*$'
+)
+
+for line in sys.stdin:
+    if SKIP.search(line):
+        continue
+    line = PREFIX.sub('', line)
+    sys.stdout.write(line)
+    sys.stdout.flush()
diff --git a/filters/source.py b/filters/source.py
new file mode 100644
index 0000000..a42e185
--- /dev/null
+++ b/filters/source.py
@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+"""
+Source engine log filter for Umbrella (TF2, GMod, CS2, etc.)
+
+Strips noisy lines that flood the output without useful information:
+  - server_cvar changes (spammy on startup and plugin reloads)
+  - Bot navigation stuck/path_goal spam
+  - Empty lines
+
+Strips the "L MM/DD/YYYY - HH:MM:SS: " timestamp prefix so output
+is shorter in the CLI. The umbrella daemon log already has its own
+timestamps if you need them.
+
+Install: /usr/lib/umbrella/filters/source.py
+Unit YAML: log_filter: /usr/lib/umbrella/filters/source.py
+"""
+
+import sys
+import re
+
+PREFIX   = re.compile(r'^L \d{2}/\d{2}/\d{4} - \d{2}:\d{2}:\d{2}: ')
+
+SKIP = re.compile(
+    r'server_cvar:'           # cvar change spam
+    r'|" stuck \(position'   # bot navigation noise
+    r'|^\s*path_goal \('     # bot path_goal continuation lines
+    r'|^\s*$'                # blank lines
+)
+
+for line in sys.stdin:
+    if SKIP.search(line):
+        continue
+    line = PREFIX.sub('', line)
+    sys.stdout.write(line)
+    sys.stdout.flush()
diff --git a/filters/terraria.py b/filters/terraria.py
new file mode 100644
index 0000000..93b5d91
--- /dev/null
+++ b/filters/terraria.py
@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+"""
+Terraria log filter for Umbrella (vanilla, tModLoader)
+
+Vanilla and tModLoader produce fairly clean output, so this filter
+mostly just strips blank lines and tModLoader's internal loading/debug
+noise during startup.
+
+Vanilla format:  plain text, e.g. ": <Player> has joined."
+tModLoader format varies; startup emits many mod loading lines.
+
+Install: /usr/lib/umbrella/filters/terraria.py
+Unit YAML: log_filter: /usr/lib/umbrella/filters/terraria.py
+"""
+
+import sys
+import re
+
+SKIP = re.compile(
+    r'^\s*$'                         # blank lines
+    r'|^: $'                         # bare colon lines (vanilla idle)
+    r'|\[tML\].*Loading mod'         # tModLoader mod loading spam
+    r'|\[tML\].*Unloading mod'
+    r'|\[tML\].*Reloading mods'
+    r'|Received mods from'           # mod sync noise in multiplayer
+    r'|Joining world\.\.\.'
+)
+
+for line in sys.stdin:
+    if SKIP.search(line):
+        continue
+    sys.stdout.write(line)
+    sys.stdout.flush()