From 834625a9f75705b19878a9d6b280952712589b89 Mon Sep 17 00:00:00 2001
From: saxon <saxon.milton@gmail.com>
Date: Tue, 5 Feb 2019 12:55:32 +1030
Subject: [PATCH] stream/mts/meta: using order slice so that encoded order
 reamins consistent with order that we added metadata. And also now using
 binary.BigEndian.PutUint16() to encode len into metdata rather than doing
 ugly byte manipulation

---
 stream/mts/meta/meta.go | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/stream/mts/meta/meta.go b/stream/mts/meta/meta.go
index 7a863d0c..eaa0713e 100644
--- a/stream/mts/meta/meta.go
+++ b/stream/mts/meta/meta.go
@@ -45,8 +45,7 @@ const (
 
 // Indices of bytes for uint16 metadata length.
 const (
-	dataLenIdx1 = 2
-	dataLenIdx2 = 3
+	dataLenIdx = 2
 )
 
 var (
@@ -58,9 +57,10 @@ var (
 // Metadata provides functionality for the storage and encoding of metadata
 // using a map.
 type Metadata struct {
-	mu   sync.RWMutex
-	data map[string]string
-	enc  []byte
+	mu    sync.RWMutex
+	data  map[string]string
+	order []string
+	enc   []byte
 }
 
 // New returns a pointer to a new Metadata.
@@ -80,6 +80,7 @@ func New() *Metadata {
 func (m *Metadata) Add(key, val string) {
 	m.mu.Lock()
 	m.data[key] = val
+	m.order = append(m.order, key)
 	m.mu.Unlock()
 }
 
@@ -111,6 +112,12 @@ func (m *Metadata) Delete(key string) error {
 	defer m.mu.Unlock()
 	if _, ok := m.data[key]; ok {
 		delete(m.data, key)
+		for i, k := range m.order {
+			if k == key {
+				m.order = append(m.order[:i], m.order[i+1:]...)
+				break
+			}
+		}
 		return nil
 	}
 	return errKeyAbsent
@@ -123,12 +130,11 @@ func (m *Metadata) Encode() []byte {
 
 	// Iterate over map and append entries, only adding tab if we're not on the
 	// last entry.
-	var i int
 	var entry string
-	for k, v := range m.data {
-		i++
+	for i, k := range m.order {
+		v := m.data[k]
 		entry += k + "=" + v
-		if i < len(m.data) {
+		if i+1 < len(m.data) {
 			entry += "\t"
 		}
 	}
@@ -136,9 +142,7 @@ func (m *Metadata) Encode() []byte {
 
 	// Calculate and set data length in encoded meta header.
 	dataLen := len(m.enc[headSize:])
-	m.enc[dataLenIdx1] = byte(dataLen >> 8)
-	m.enc[dataLenIdx2] = byte(dataLen)
-
+	binary.BigEndian.PutUint16(m.enc[dataLenIdx:dataLenIdx+2], uint16(dataLen))
 	return m.enc
 }