From 7678df06aaee159e95b5f8dff495509b833abd5f Mon Sep 17 00:00:00 2001
From: Pierce Lopez <pierce.lopez@gmail.com>
Date: Sun, 29 Jan 2017 12:03:33 -0500
Subject: [PATCH] nsqd: metadata file back-compat only, no rollback-compat

---
 nsqd/nsqd.go      | 54 ++++++-----------------------------------------
 nsqd/nsqd_test.go | 47 ++---------------------------------------
 2 files changed, 9 insertions(+), 92 deletions(-)

diff --git a/nsqd/nsqd.go b/nsqd/nsqd.go
index 02ea507a7..6be4e8ef9 100644
--- a/nsqd/nsqd.go
+++ b/nsqd/nsqd.go
@@ -1,7 +1,6 @@
 package nsqd
 
 import (
-	"bytes"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/json"
@@ -13,7 +12,6 @@ import (
 	"net"
 	"os"
 	"path"
-	"runtime"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -307,30 +305,21 @@ func (n *NSQD) LoadMetadata() error {
 	defer atomic.StoreInt32(&n.isLoading, 0)
 
 	fn := newMetadataFile(n.getOpts())
-	// old metadata filename with ID, maintained in parallel to enable roll-back
-	fnID := oldMetadataFile(n.getOpts())
 
 	data, err := readOrEmpty(fn)
 	if err != nil {
 		return err
 	}
-	dataID, errID := readOrEmpty(fnID)
-	if errID != nil {
-		return errID
-	}
-
-	if data == nil && dataID == nil {
-		return nil // fresh start
-	}
-	if data != nil && dataID != nil {
-		if bytes.Compare(data, dataID) != 0 {
-			return fmt.Errorf("metadata in %s and %s do not match (delete one)", fn, fnID)
+	if data == nil {
+		// try fallback to old metadata filename (with ID)
+		fnID := oldMetadataFile(n.getOpts())
+		data, err = readOrEmpty(fnID)
+		if err != nil {
+			return err
 		}
 	}
 	if data == nil {
-		// only old metadata file exists, use it
-		fn = fnID
-		data = dataID
+		return nil // fresh start
 	}
 
 	var m meta
@@ -366,8 +355,6 @@ func (n *NSQD) LoadMetadata() error {
 func (n *NSQD) PersistMetadata() error {
 	// persist metadata about what topics/channels we have, across restarts
 	fileName := newMetadataFile(n.getOpts())
-	// old metadata filename with ID, maintained in parallel to enable roll-back
-	fileNameID := oldMetadataFile(n.getOpts())
 
 	n.logf("NSQ: persisting topic/channel metadata to %s", fileName)
 
@@ -418,33 +405,6 @@ func (n *NSQD) PersistMetadata() error {
 	}
 	// technically should fsync DataPath here
 
-	stat, err := os.Lstat(fileNameID)
-	if err == nil && stat.Mode()&os.ModeSymlink != 0 {
-		return nil
-	}
-
-	// if no symlink (yet), race condition:
-	// crash right here may cause next startup to see metadata conflict and abort
-
-	tmpFileNameID := fmt.Sprintf("%s.%d.tmp", fileNameID, rand.Int())
-
-	if runtime.GOOS != "windows" {
-		err = os.Symlink(fileName, tmpFileNameID)
-	} else {
-		// on Windows need Administrator privs to Symlink
-		// instead write copy every time
-		err = writeSyncFile(tmpFileNameID, data)
-	}
-	if err != nil {
-		return err
-	}
-
-	err = os.Rename(tmpFileNameID, fileNameID)
-	if err != nil {
-		return err
-	}
-	// technically should fsync DataPath here
-
 	return nil
 }
 
diff --git a/nsqd/nsqd_test.go b/nsqd/nsqd_test.go
index de7fbba8b..272d4d514 100644
--- a/nsqd/nsqd_test.go
+++ b/nsqd/nsqd_test.go
@@ -196,9 +196,9 @@ func TestMetadataMigrate(t *testing.T) {
 	test.Nil(t, err)
 	nsqd.Exit()
 
-	oldFi, err := os.Lstat(oldFn)
+	newFn := newMetadataFile(opts)
+	_, err = os.Stat(newFn)
 	test.Nil(t, err)
-	test.Equal(t, oldFi.Mode()&os.ModeType, os.ModeSymlink)
 
 	_, _, nsqd = mustStartNSQD(opts)
 	err = nsqd.LoadMetadata()
@@ -214,49 +214,6 @@ func TestMetadataMigrate(t *testing.T) {
 	nsqd.Exit()
 }
 
-func TestMetadataConflict(t *testing.T) {
-	old_meta := `
-	{
-	  "topics": [{
-	    "name": "t1", "paused": false,
-	    "channels": [{"name": "c1", "paused": false}]
-	  }],
-	  "version": "1.0.0-alpha"
-	}`
-	new_meta := `
-	{
-	  "topics": [{
-	    "name": "t2", "paused": false,
-	    "channels": [{"name": "c2", "paused": false}]
-	  }],
-	  "version": "1.0.0-alpha"
-	}`
-
-	tmpDir, err := ioutil.TempDir("", "nsq-test-")
-	if err != nil {
-		panic(err)
-	}
-	defer os.RemoveAll(tmpDir)
-
-	opts := NewOptions()
-	opts.DataPath = tmpDir
-	opts.Logger = test.NewTestLogger(t)
-
-	err = ioutil.WriteFile(oldMetadataFile(opts), []byte(old_meta), 0600)
-	if err != nil {
-		panic(err)
-	}
-	err = ioutil.WriteFile(newMetadataFile(opts), []byte(new_meta), 0600)
-	if err != nil {
-		panic(err)
-	}
-
-	_, _, nsqd := mustStartNSQD(opts)
-	err = nsqd.LoadMetadata()
-	test.NotNil(t, err)
-	nsqd.Exit()
-}
-
 func TestEphemeralTopicsAndChannels(t *testing.T) {
 	// ephemeral topics/channels are lazily removed after the last channel/client is removed
 	opts := NewOptions()