From 1fe811c4db349918d81108c9bbe4fde90b1aa21f Mon Sep 17 00:00:00 2001
From: Peter Verraedt <peter@verraedt.be>
Date: Wed, 15 Mar 2023 13:21:45 +0100
Subject: [PATCH] Marshal extended data if file info supports it

If the file information returned by ListAt supports the
FileInfoExtendedData interface, use it to retrieve extended data and
pass it back to the client. In similar fashion, we add the
FileInfoUidGid interface to allow for implementations to return uid and
gid data, even if the os lacks support in syscall.Stat_t.

Signed-off-by: Peter Verraedt <peter@verraedt.be>
---
 attrs.go         | 36 ++++++++++++++++++++++++++++++++++++
 ls_formatting.go |  7 +++++++
 packet.go        |  9 +++++++++
 3 files changed, 52 insertions(+)

diff --git a/attrs.go b/attrs.go
index 2bb2d576..2b788916 100644
--- a/attrs.go
+++ b/attrs.go
@@ -69,6 +69,20 @@ func fileInfoFromStat(stat *FileStat, name string) os.FileInfo {
 	}
 }
 
+// FileInfoUidGid extends os.FileInfo and adds callbacks for Uid and Gid retrieval,
+// as an alternative to *syscall.Stat_t objects on unix systems.
+type FileInfoUidGid interface {
+	os.FileInfo
+	Uid() uint32
+	Gid() uint32
+}
+
+// FileInfoUidGid extends os.FileInfo and adds a callbacks for extended data retrieval.
+type FileInfoExtendedData interface {
+	os.FileInfo
+	Extended() []StatExtended
+}
+
 func fileStatFromInfo(fi os.FileInfo) (uint32, *FileStat) {
 	mtime := fi.ModTime().Unix()
 	atime := mtime
@@ -86,5 +100,27 @@ func fileStatFromInfo(fi os.FileInfo) (uint32, *FileStat) {
 	// os specific file stat decoding
 	fileStatFromInfoOs(fi, &flags, fileStat)
 
+	// The call above will include the sshFileXferAttrUIDGID in case
+	// the os.FileInfo can be casted to *syscall.Stat_t on unix.
+	// If implementations of RequestServers Handlers want to implement
+	// setting uids and gids while running on non-unix systems or
+	// without using *syscall.Stat_t underneath on unix, we offer
+	// an alternative way to support this through the FileInfoUidGid
+	// interface.
+	// If fi implements FileInfoUidGid, retrieve Uid, Gid from it.
+	if fiExt, ok := fi.(FileInfoUidGid); ok {
+		flags |= sshFileXferAttrUIDGID
+		fileStat.UID = fiExt.Uid()
+		fileStat.GID = fiExt.Gid()
+	}
+
+	// if fi implements FileInfoExtendedData, retrieve extended data from it
+	if fiExt, ok := fi.(FileInfoExtendedData); ok {
+		fileStat.Extended = fiExt.Extended()
+		if len(fileStat.Extended) > 0 {
+			flags |= sshFileXferAttrExtended
+		}
+	}
+
 	return flags, fileStat
 }
diff --git a/ls_formatting.go b/ls_formatting.go
index e083e22a..19271ad7 100644
--- a/ls_formatting.go
+++ b/ls_formatting.go
@@ -60,6 +60,13 @@ func runLs(idLookup NameLookupFileLister, dirent os.FileInfo) string {
 		uid = lsFormatID(sys.UID)
 		gid = lsFormatID(sys.GID)
 	default:
+		if fiExt, ok := dirent.(FileInfoUidGid); ok {
+			uid = lsFormatID(fiExt.Uid())
+			gid = lsFormatID(fiExt.Gid())
+
+			break
+		}
+
 		numLinks, uid, gid = lsLinksUIDGID(dirent)
 	}
 
diff --git a/packet.go b/packet.go
index d89ad997..b06d0b95 100644
--- a/packet.go
+++ b/packet.go
@@ -71,6 +71,15 @@ func marshalFileInfo(b []byte, fi os.FileInfo) []byte {
 		b = marshalUint32(b, fileStat.Mtime)
 	}
 
+	if flags&sshFileXferAttrExtended != 0 {
+		b = marshalUint32(b, uint32(len(fileStat.Extended)))
+
+		for _, attr := range fileStat.Extended {
+			b = marshalString(b, attr.ExtType)
+			b = marshalString(b, attr.ExtData)
+		}
+	}
+
 	return b
 }