From 50f1e9e009e44dff10373efd5fef26ac9f148cd3 Mon Sep 17 00:00:00 2001
From: mi <123757457+soyelmismo@users.noreply.github.com>
Date: Fri, 22 May 2026 05:59:21 -0500
Subject: [PATCH] fix: cache compiled RegExp in RTK compression hot path
 (#2553)

Integrated into release/v3.8.2
---
 .../compression/engines/rtk/filterLoader.ts   | 29 +++++++++----
 .../compression/engines/rtk/lineFilter.ts     | 41 ++++++++++++-------
 2 files changed, 46 insertions(+), 24 deletions(-)

diff --git a/open-sse/services/compression/engines/rtk/filterLoader.ts b/open-sse/services/compression/engines/rtk/filterLoader.ts
index 8c776a9b85..d8879a78cd 100644
--- a/open-sse/services/compression/engines/rtk/filterLoader.ts
+++ b/open-sse/services/compression/engines/rtk/filterLoader.ts
@@ -10,6 +10,24 @@ let cache: RtkFilterDefinition[] | null = null;
 let cacheKey: string | null = null;
 let diagnostics: RtkFilterLoadDiagnostic[] = [];
 
+// RegExp cache for matchPatterns — same pattern strings are tested against
+// many different lines across requests; avoid compiling them every time.
+const regexCache = new Map<string, RegExp>();
+
+function cachedMatchPattern(pattern: string, value: string): boolean {
+  const key = `${pattern}::im`;
+  let re = regexCache.get(key);
+  if (!re) {
+    try {
+      re = new RegExp(pattern, "im");
+      regexCache.set(key, re);
+    } catch {
+      return false;
+    }
+  }
+  return re.test(value);
+}
+
 export interface RtkFilterLoadDiagnostic {
   source: "project" | "global" | "builtin";
   path?: string;
@@ -196,23 +214,16 @@ export function matchRtkFilter(
 ): RtkFilterDefinition | null {
   const detection = detectCommandType(text, command);
   const detectedCommand = detection.command ?? command ?? "";
-  const matchesPattern = (pattern: string, value: string): boolean => {
-    try {
-      return new RegExp(pattern, "im").test(value);
-    } catch {
-      return false;
-    }
-  };
   const filters = loadRtkFilters(options);
   return (
     filters.find((filter) => filter.commandTypes.includes(detection.type)) ??
     filters.find(
       (filter) =>
         detectedCommand &&
-        filter.commandPatterns.some((pattern) => matchesPattern(pattern, detectedCommand))
+        filter.commandPatterns.some((pattern) => cachedMatchPattern(pattern, detectedCommand))
     ) ??
     filters.find((filter) =>
-      filter.matchPatterns.some((pattern) => matchesPattern(pattern, text))
+      filter.matchPatterns.some((pattern) => cachedMatchPattern(pattern, text))
     ) ??
     filters.find((filter) => filter.commandTypes.includes("generic-output")) ??
     null
diff --git a/open-sse/services/compression/engines/rtk/lineFilter.ts b/open-sse/services/compression/engines/rtk/lineFilter.ts
index 589b618086..5be2b1a93f 100644
--- a/open-sse/services/compression/engines/rtk/lineFilter.ts
+++ b/open-sse/services/compression/engines/rtk/lineFilter.ts
@@ -8,30 +8,41 @@ export interface LineFilterResult {
   appliedRules: string[];
 }
 
+// ──────────────── RegExp cache ────────────────
+//
+// Patterns are static (loaded from filter JSON files on boot) but were being
+// compiled via `new RegExp(...)` on every call to applyLineFilter().  For a
+// busy proxy this means thousands of redundant RegExp instantiations per
+// second.  Cache them here once.
+
+const regexCache = new Map<string, RegExp>();
+
+function cachedRegExp(pattern: string, flags: string): RegExp | null {
+  const key = `${pattern}::${flags}`;
+  const cached = regexCache.get(key);
+  if (cached) return cached;
+  try {
+    const re = new RegExp(pattern, flags);
+    regexCache.set(key, re);
+    return re;
+  } catch {
+    return null;
+  }
+}
+
 function compilePatterns(patterns: string[]): RegExp[] {
   return patterns.flatMap((pattern) => {
-    try {
-      return [new RegExp(pattern, "i")];
-    } catch {
-      return [];
-    }
+    const re = cachedRegExp(pattern, "i");
+    return re ? [re] : [];
   });
 }
 
 function compileGlobalPattern(pattern: string): RegExp | null {
-  try {
-    return new RegExp(pattern, "g");
-  } catch {
-    return null;
-  }
+  return cachedRegExp(pattern, "g");
 }
 
 function compileBlobPattern(pattern: string): RegExp | null {
-  try {
-    return new RegExp(pattern, "im");
-  } catch {
-    return null;
-  }
+  return cachedRegExp(pattern, "im");
 }
 
 function stripAnsi(text: string): string {