From 79c19dc1d3385bf1400966ee4c861cfeadd7265a Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Thu, 15 Oct 2026 15:38:05 +0100
Subject: [PATCH] serve s3: allow copying directory markers

CopyObject with a directory marker such as "dir/" as its source failed
with InvalidArgument, although HeadObject and GetObject found it.

It now copies the marker, making the directory of another marker or an
empty object.

See #10082
---
 cmd/serve/s3/backend.go      | 11 +++++++++--
 cmd/serve/s3/backend_test.go | 19 +++++++++++++++++++
 cmd/serve/s3/serve_s3.md     |  7 ++++---
 3 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/cmd/serve/s3/backend.go b/cmd/serve/s3/backend.go
index 0f1bf608e..55c4fa4b1 100644
--- a/cmd/serve/s3/backend.go
+++ b/cmd/serve/s3/backend.go
@@ -824,15 +824,22 @@ func (b *s3Backend) CopyObject(ctx context.Context, srcBucket, srcKey, dstBucket
 	if err != nil {
 		return result, err
 	}
-	fp, err := bucketObjectPath(srcBucket, srcKey)
+	fp, isMarker, err := bucketDirMarkerPath(srcBucket, srcKey)
+	if !isMarker {
+		fp, err = bucketObjectPath(srcBucket, srcKey)
+	}
 	if err != nil {
 		return result, err
 	}
 	cStat, err := _vfs.Stat(fp)
-	if err != nil || !cStat.IsFile() {
+	if err != nil || cStat.IsDir() != isMarker {
 		return result, gofakes3.KeyNotFound(srcKey)
 	}
 	if srcBucket == dstBucket && srcKey == dstKey {
+		if isMarker {
+			// Directory markers have no metadata to replace
+			return result, nil
+		}
 		return result, b.tenant(ctx).storeMeta(_vfs, fp, meta)
 	}
 
diff --git a/cmd/serve/s3/backend_test.go b/cmd/serve/s3/backend_test.go
index 5dd12fb3e..1642a7275 100644
--- a/cmd/serve/s3/backend_test.go
+++ b/cmd/serve/s3/backend_test.go
@@ -408,6 +408,25 @@ func TestDirMarkers(t *testing.T) {
 		assert.True(t, gofakes3.HasErrorCode(err, gofakes3.ErrNoSuchKey), "%s: %v", key, err)
 	}
 
+	// Copying a marker makes the directory of another marker, or an
+	// empty object
+	_, err = b.CopyObject(ctx, "bucket", "dir/sub/", "bucket", "copy/", map[string]string{})
+	require.NoError(t, err)
+	assert.True(t, isDir("copy"))
+	_, err = b.CopyObject(ctx, "bucket", "dir/sub/", "bucket", "empty.txt", map[string]string{})
+	require.NoError(t, err)
+	obj, err = b.HeadObject(ctx, "bucket", "empty.txt")
+	require.NoError(t, err)
+	assert.Equal(t, int64(0), obj.Size)
+	_, err = b.CopyObject(ctx, "bucket", "dir/", "bucket", "dir/", map[string]string{})
+	require.NoError(t, err)
+
+	// A copy needs the "/" for a directory and none for an object
+	for _, key := range []string{"dir", "empty.txt/", "missing/"} {
+		_, err = b.CopyObject(ctx, "bucket", key, "bucket", "other.txt", map[string]string{})
+		assert.True(t, gofakes3.HasErrorCode(err, gofakes3.ErrNoSuchKey), "%s: %v", key, err)
+	}
+
 	// Deleting a marker removes its directory only if empty
 	require.NoError(t, put("dir/sub/file.txt", "data"))
 	require.NoError(t, b.deleteObject(ctx, "bucket", "dir/sub/"))
diff --git a/cmd/serve/s3/serve_s3.md b/cmd/serve/s3/serve_s3.md
index 3a6fdc0e8..201615351 100644
--- a/cmd/serve/s3/serve_s3.md
+++ b/cmd/serve/s3/serve_s3.md
@@ -493,9 +493,10 @@ A key ending in `/`, such as `dir/`, is a directory marker, standing
 for the directory `dir`. Putting an empty directory marker creates the
 directory (one with data is rejected with `400 Bad Request`), and
 deleting it removes the directory if it is empty. Directory markers
-are found by `HeadObject` and `GetObject` for any directory, but only
-the markers of empty directories are listed as objects, as other
-directories may not have been made by putting a marker.
+are found by `HeadObject`, `GetObject` and `CopyObject` for any
+directory, but only the markers of empty directories are listed as
+objects, as other directories may not have been made by putting a
+marker.
 
 As keys are file paths, a key can't be both an object and a directory
 holding other objects, for example `a/b` and `a/b/c`. Writing an