From f1d631d66e1c3101a8968e0713fac29e67329134 Mon Sep 17 00:00:00 2001
From: Jakob Borg <jakob@kastelo.net>
Date: Sat, 13 Jun 2026 08:31:26 +0200
Subject: [PATCH] fix(protocol): loosen restriction on size of directory
 entries (#10743)

The synthetic directory size must be permitted.

Ref #10737.

---------

Signed-off-by: Jakob Borg <jakob@kastelo.net>
---
 lib/protocol/protocol.go      |  8 +++--
 lib/protocol/protocol_test.go | 55 +++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/lib/protocol/protocol.go b/lib/protocol/protocol.go
index 03ec3e138..9204ef35b 100644
--- a/lib/protocol/protocol.go
+++ b/lib/protocol/protocol.go
@@ -640,8 +640,12 @@ func checkFileInfoConsistency(f FileInfo) error {
 		// Only files should have blocks
 		return errNonFileHasBlocks
 
-	case f.Type != FileInfoTypeFile && f.Size != 0:
-		// Only files should have a size
+	case f.IsDirectory() && f.Size != 0 && f.Size != SyntheticDirectorySize:
+		// Directories should be size zero or the synthetic directory size
+		return errNonFileHasSize
+
+	case f.IsSymlink() && f.Size != 0:
+		// Symlinks should be size zero
 		return errNonFileHasSize
 
 	case !f.Deleted && !f.IsInvalid() && f.Type == FileInfoTypeFile && len(f.Blocks) == 0:
diff --git a/lib/protocol/protocol_test.go b/lib/protocol/protocol_test.go
index dda4ba86a..1bba358b3 100644
--- a/lib/protocol/protocol_test.go
+++ b/lib/protocol/protocol_test.go
@@ -451,6 +451,61 @@ func TestCheckConsistency(t *testing.T) {
 			},
 			ok: false,
 		},
+		{
+			// directory with zero size
+			fi: FileInfo{
+				Name: "foo",
+				Type: FileInfoTypeDirectory,
+			},
+			ok: true,
+		},
+		{
+			// directory with synthetic size
+			fi: FileInfo{
+				Name: "foo",
+				Type: FileInfoTypeDirectory,
+				Size: SyntheticDirectorySize,
+			},
+			ok: true,
+		},
+		{
+			// directory with arbitrary size
+			fi: FileInfo{
+				Name: "foo",
+				Type: FileInfoTypeDirectory,
+				Size: 42,
+			},
+			ok: false,
+		},
+		{
+			// symlink with zero size
+			fi: FileInfo{
+				Name:          "foo",
+				Type:          FileInfoTypeSymlink,
+				SymlinkTarget: []byte("bar"),
+			},
+			ok: true,
+		},
+		{
+			// symlink with synthetic directory size (not permitted)
+			fi: FileInfo{
+				Name:          "foo",
+				Type:          FileInfoTypeSymlink,
+				SymlinkTarget: []byte("bar"),
+				Size:          SyntheticDirectorySize,
+			},
+			ok: false,
+		},
+		{
+			// symlink with arbitrary size
+			fi: FileInfo{
+				Name:          "foo",
+				Type:          FileInfoTypeSymlink,
+				SymlinkTarget: []byte("bar"),
+				Size:          42,
+			},
+			ok: false,
+		},
 	}
 
 	for _, tc := range cases {