From 5a86c7a637da1467c9890d31aaccdf4c428dd87d Mon Sep 17 00:00:00 2001
From: Sadeep Madurange <sadeep@asciimx.com>
Date: Wed, 12 Aug 2026 23:29:03 +0800
Subject: Lock-file semaphore for CGI script.

---
 lex.cgi | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

(limited to 'lex.cgi')

diff --git a/lex.cgi b/lex.cgi
index 9c11b28..797fa1c 100755
--- a/lex.cgi
+++ b/lex.cgi
@@ -2,13 +2,14 @@
 
 use strict;
 use warnings;
+use Email::MIME;
+use Fcntl qw(:flock);
 use File::Spec;
 use File::Find;
 use File::Path qw(make_path);
-use Time::HiRes qw(time);
-use Email::MIME;
 use OpenBSD::Pledge;
 use OpenBSD::Unveil;
+use Time::HiRes qw(time);
 
 my $start_time = time();
 
@@ -43,8 +44,9 @@ unveil("/dev/null", "rw") or die "unveil /dev/null failed: $!";
 unveil($base_dir, "rwc") or die "unveil $base_dir failed: $!";
 unveil() or die "unveil lock failed: $!";
 
-pledge('stdio rpath wpath cpath') or die "pledge failed: $!";
+pledge('stdio rpath wpath cpath flock') or die "pledge failed: $!";
 
+my $dop = 5;
 my $log_file = "$base_dir/debug.log";
 my $max_log_bytes = 1024 * 1024; # 1 MB cap
 
@@ -107,6 +109,40 @@ sub verify_pgp_signature {
 	return $verified ? 1 : 0;
 }
 
+sub acquire_lock {
+	my ($max_slots) = @_;
+	my $lock_dir = "$base_dir/locks";
+
+	unless (-d $lock_dir) {
+		make_path($lock_dir) or do {
+			log_msg("ERROR: Failed to create lock dir $lock_dir: $!");
+			return undef;
+		};
+	}
+
+	for my $i (1 .. $max_slots) {
+		my $slot_file = "$lock_dir/slot_$i.lock";
+		my $fh;
+		
+		unless (open($fh, '>>', $slot_file)) {
+			next;
+		}
+
+		if (flock($fh, LOCK_EX | LOCK_NB)) {
+			return $fh;
+		}
+		close($fh);
+	}
+
+	return undef; # All slots full
+}
+
+my $lock_fh = acquire_lock($dop);
+unless ($lock_fh) {
+	log_msg("WARN: Concurrency limit ($dop) reached. Dropping request.");
+	respond_ok();
+}
+
 my $content_type   = $ENV{'CONTENT_TYPE'} // '';
 my $content_length = $ENV{'CONTENT_LENGTH'} // 0;
 
-- 
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