From e6c8ee2f1ce468a448e6141783784b5e6639d54c Mon Sep 17 00:00:00 2001
From: Chris Lu <chris.lu@gmail.com>
Date: Wed, 24 Dec 2025 20:42:53 -0800
Subject: [PATCH] testutil: choose lower ephemeral ports (<55535) to avoid
 overflow in master/raft port math

---
 test/s3/testutil/server.go | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/test/s3/testutil/server.go b/test/s3/testutil/server.go
index 7e196d4a1..17bb8dd88 100644
--- a/test/s3/testutil/server.go
+++ b/test/s3/testutil/server.go
@@ -75,14 +75,21 @@ func StartServer(config ServerConfig) (*TestServer, error) {
 	}
 
 	// choose free ports for master, volume, filer and metrics to avoid collisions
+	// pick a free port but avoid very large ephemeral ports that can overflow
+	// internal port math (keep below 55535)
 	pick := func() int {
-		l, err := net.Listen("tcp", "127.0.0.1:0")
-		if err != nil {
-			return 0
+		for i := 0; i < 10; i++ {
+			l, err := net.Listen("tcp", "127.0.0.1:0")
+			if err != nil {
+				continue
+			}
+			p := l.Addr().(*net.TCPAddr).Port
+			l.Close()
+			if p > 1024 && p < 55535 {
+				return p
+			}
 		}
-		p := l.Addr().(*net.TCPAddr).Port
-		l.Close()
-		return p
+		return 0
 	}
 
 	masterPort := pick()