From 1d028880cfb17a7c8a9e3b1f54cf1e980baca63d Mon Sep 17 00:00:00 2001
From: Simon Ruderich <simon@ruderich.org>
Date: Mon, 10 Jun 2019 23:34:45 +0200
Subject: [PATCH] nsscash: add alignBufferTo() helper

---
 group.go  | 12 ++----------
 misc.go   | 37 +++++++++++++++++++++++++++++++++++++
 passwd.go |  7 +------
 3 files changed, 40 insertions(+), 16 deletions(-)
 create mode 100644 misc.go

diff --git a/group.go b/group.go
index b7f7d1b..4513758 100644
--- a/group.go
+++ b/group.go
@@ -114,10 +114,7 @@ func SerializeGroup(g Group) []byte {
 	offPasswd := uint16(data.Len())
 	data.Write([]byte(g.Passwd))
 	data.WriteByte(0)
-	// Padding to align the following uint16
-	if data.Len()%2 != 0 {
-		data.WriteByte(0)
-	}
+	alignBufferTo(&data, 2) // align the following uint16
 	offMemOff := uint16(data.Len())
 	// Offsets for group members
 	offMem := offMemOff + 2*uint16(len(mems_off))
@@ -154,12 +151,7 @@ func SerializeGroup(g Group) []byte {
 	res.Write(data.Bytes())
 	// We must pad each entry so that all uint64 at the beginning of the
 	// struct are 8 byte aligned
-	l := res.Len()
-	if l%8 != 0 {
-		for i := 0; i < 8-l%8; i++ {
-			res.WriteByte(0)
-		}
-	}
+	alignBufferTo(&res, 8)
 
 	return res.Bytes()
 }
diff --git a/misc.go b/misc.go
new file mode 100644
index 0000000..2e60507
--- /dev/null
+++ b/misc.go
@@ -0,0 +1,37 @@
+// Miscellaneous functions
+
+// Copyright (C) 2019  Simon Ruderich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+)
+
+func alignBufferTo(b *bytes.Buffer, align int) {
+	if align <= 0 {
+		panic(fmt.Sprintf("invalid alignment %v", align))
+	}
+
+	l := b.Len()
+	if l%align == 0 {
+		return
+	}
+	for i := 0; i < align-l%align; i++ {
+		b.WriteByte(0)
+	}
+}
diff --git a/passwd.go b/passwd.go
index 9035190..90fed68 100644
--- a/passwd.go
+++ b/passwd.go
@@ -134,12 +134,7 @@ func SerializePasswd(p Passwd) []byte {
 	res.Write(data.Bytes())
 	// We must pad each entry so that all uint64 at the beginning of the
 	// struct are 8 byte aligned
-	l := res.Len()
-	if l%8 != 0 {
-		for i := 0; i < 8-l%8; i++ {
-			res.WriteByte(0)
-		}
-	}
+	alignBufferTo(&res, 8)
 
 	return res.Bytes()
 }
-- 
2.45.2