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

@@ -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
 }

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)
 	}
 

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
 }