From e12c250705f727543e342d791146f4ef1f1d4bb3 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Wed, 15 Apr 2026 12:19:18 +0100
Subject: [PATCH] s3: fix empty delimiter parameter rejected by Archiware P5
 server

Some S3-compatible servers (e.g. Archiware P5) reject requests with an
empty `?delimiter=` query parameter. For recursive listings, pass `nil`
instead of a pointer to an empty string so the parameter is omitted
entirely from the request.

Fixes #9342
---
 backend/s3/s3.go | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/backend/s3/s3.go b/backend/s3/s3.go
index 5bfc118a9..2543c01f9 100644
--- a/backend/s3/s3.go
+++ b/backend/s3/s3.go
@@ -2343,9 +2343,11 @@ func (f *Fs) list(ctx context.Context, opt listOpt, fn listFn) error {
 			opt.directory += "/"
 		}
 	}
-	delimiter := ""
+	// Use nil delimiter for recursive listings to omit the parameter
+	// entirely. Some S3-compatible servers reject an empty delimiter.
+	var delimiter *string
 	if !opt.recurse {
-		delimiter = "/"
+		delimiter = aws.String("/")
 	}
 	// URL encode the listings so we can use control characters in object names
 	// See: https://github.com/aws/aws-sdk-go/issues/1914
@@ -2365,7 +2367,7 @@ func (f *Fs) list(ctx context.Context, opt listOpt, fn listFn) error {
 	urlEncodeListings := f.opt.ListURLEncode.Value
 	req := s3.ListObjectsV2Input{
 		Bucket:    &opt.bucket,
-		Delimiter: &delimiter,
+		Delimiter: delimiter,
 		Prefix:    &opt.directory,
 		MaxKeys:   &f.opt.ListChunk,
 	}