From 79703f8ad20a3563a175efc3e6b9368476287204 Mon Sep 17 00:00:00 2001
From: Sai Asish Y <say.apm35@gmail.com>
Date: Wed, 13 May 2026 14:17:11 -0700
Subject: [PATCH] fix: preserve trailing slash in joinURL when path is "/"
 (#134)

---
 src/_utils.ts       | 4 ++--
 test/_utils.test.ts | 8 ++++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/_utils.ts b/src/_utils.ts
index 5c4ea97..85898ae 100644
--- a/src/_utils.ts
+++ b/src/_utils.ts
@@ -184,8 +184,8 @@ export function joinURL(base: string | undefined, path: string | undefined): str
   if (!base || base === "/") {
     return path || "/";
   }
-  if (!path || path === "/") {
-    return base || "/";
+  if (!path) {
+    return base;
   }
   // eslint-disable-next-line unicorn/prefer-at
   const baseHasTrailing = base[base.length - 1] === "/";
diff --git a/test/_utils.test.ts b/test/_utils.test.ts
index 9e1026f..d110446 100644
--- a/test/_utils.test.ts
+++ b/test/_utils.test.ts
@@ -609,6 +609,14 @@ describe("lib/http-proxy/common.js", () => {
     it("should concat when base has trailing slash and path has no leading slash", () => {
       expect(common.joinURL("/base/", "path")).to.eql("/base/path");
     });
+
+    it("should preserve trailing slash when path is exactly /", () => {
+      expect(common.joinURL("/maildev", "/")).to.eql("/maildev/");
+    });
+
+    it("should keep a single trailing slash when both base ends and path is /", () => {
+      expect(common.joinURL("/maildev/", "/")).to.eql("/maildev/");
+    });
   });
 
   describe("#rewriteCookieProperty", () => {