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>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/umbrella.h b/src/umbrella.h
index 2e9d440..ff1873f 100644
--- a/src/umbrella.h
+++ b/src/umbrella.h
@@ -91,12 +91,19 @@ typedef struct {
     Action actions[MAX_ACTIONS];
     int action_count;
 
+    char log_filter[MAX_PATH];  /* path to filter executable, or empty */
+
     /* Runtime state (populated by process/rcon layer, not yaml) */
     ProcessState state;
     pid_t pid;                  /* only for CONSOLE_STDIN */
     int stdin_fd;               /* only for CONSOLE_STDIN */
     int stdout_fd;              /* only for CONSOLE_STDIN */
     RingBuffer *output;
+
+    /* Log filter subprocess (populated at runtime if log_filter is set) */
+    pid_t filter_pid;
+    int   filter_in_fd;         /* write end: daemon → filter stdin  */
+    int   filter_out_fd;        /* read end:  filter stdout → daemon */
 } Unit;
 
 /* ── Client: a connected socket client ───────────────────────────────────── */