Add SetAttributes as an alternate option.

This would replace the SetStat public function from the last commit.

Instead, this makes it practical to construct a Setstat request.

From some quick testing, this appears to do the job correctly, and it
feels like a lot less of hack.

It still doesn't feel entirely right, but it's closer.

request-attrs.go

@@ -44,6 +44,37 @@ func newFileAttrFlags(flags uint32) FileAttrFlags {
 	}
 }
 
+func (r *Request) SetAttributes(flags FileAttrFlags, attrs FileStat) error {
+	r.Method = "Setstat"
+
+	buf := []byte{}
+
+	r.Flags = 0
+
+	if flags.Size {
+		r.Flags |= sshFileXferAttrSize
+		buf = marshalUint64(buf, attrs.Size)
+	}
+	if flags.UidGid {
+		r.Flags |= sshFileXferAttrUIDGID
+		buf = marshalUint32(buf, attrs.UID)
+		buf = marshalUint32(buf, attrs.GID)
+	}
+	if flags.Permissions {
+		r.Flags |= sshFileXferAttrPermissions
+		buf = marshalUint32(buf, attrs.Mode)
+	}
+
+	if flags.Acmodtime {
+		r.Flags |= sshFileXferAttrACmodTime
+		buf = marshalUint32(buf, attrs.Atime)
+		buf = marshalUint32(buf, attrs.Mtime)
+	}
+
+	r.Attrs = buf
+	return nil
+}
+
 // AttrFlags returns a FileAttrFlags boolean struct based on the
 // bitmap/uint32 file attribute flags from the SFTP packaet.
 func (r *Request) AttrFlags() FileAttrFlags {