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, 12 insertions, 1 deletions

diff --git a/src/main.c b/src/main.c
index 901ce74..af86375 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4,6 +4,7 @@
 #include "client.h"
 #include "log.h"
 #include "log_tail.h"
+#include "filter.h"
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -60,9 +61,12 @@ static void handle_signal(void) {
     case SIGHUP:
         log_info("SIGHUP received — reloading units");
         log_tail_cleanup();
+        filter_stop_all();
         /* Reload unit descriptors. Existing runtime state is preserved. */
         g.unit_count = 0;
         unit_load_all();
+        for (int i = 0; i < g.unit_count; i++)
+            filter_start(&g.units[i]);
         log_tail_init();
         break;
     }
@@ -96,7 +100,10 @@ static void handle_process_output(int fd) {
     }
 
     buf[n] = '\0';
-    ring_push(u->output, buf, n);
+    int nf = (int)n;
+    filter_apply(u, buf, sizeof(buf), &nf);
+    if (nf <= 0) return;
+    ring_push(u->output, buf, nf);
     client_broadcast_output(u->name, buf, 0);
 }
 
@@ -214,6 +221,9 @@ int main(int argc, char *argv[]) {
         return 1;
     }
 
+    for (int i = 0; i < g.unit_count; i++)
+        filter_start(&g.units[i]);
+
     log_tail_init();
 
     /* Set up listening socket */
@@ -235,6 +245,7 @@ int main(int argc, char *argv[]) {
 
     log_info("Shutting down");
     log_tail_cleanup();
+    filter_stop_all();
     daemon_cleanup();
     log_close();
     return 0;