Create 'datadir' package responsible for paths.

server/config/config.go

@@ -25,6 +25,7 @@ import (
 	"go.etcd.io/etcd/client/pkg/v3/transport"
 	"go.etcd.io/etcd/client/pkg/v3/types"
 	"go.etcd.io/etcd/pkg/v3/netutil"
+	"go.etcd.io/etcd/server/v3/datadir"
 
 	bolt "go.etcd.io/bbolt"
 	"go.uber.org/zap"
@@ -274,13 +275,13 @@ func (c *ServerConfig) advertiseMatchesCluster() error {
 	return fmt.Errorf("failed to resolve %s to match --initial-cluster=%s (%v)", apStr, umap.String(), err)
 }
 
-func (c *ServerConfig) MemberDir() string { return filepath.Join(c.DataDir, "member") }
+func (c *ServerConfig) MemberDir() string { return datadir.ToMemberDir(c.DataDir) }
 
 func (c *ServerConfig) WALDir() string {
 	if c.DedicatedWALDir != "" {
 		return c.DedicatedWALDir
 	}
-	return filepath.Join(c.MemberDir(), "wal")
+	return datadir.ToWalDir(c.DataDir)
 }
 
 func (c *ServerConfig) SnapDir() string { return filepath.Join(c.MemberDir(), "snap") }
@@ -324,4 +325,4 @@ func (c *ServerConfig) BootstrapTimeoutEffective() time.Duration {
 	return time.Second
 }
 
-func (c *ServerConfig) BackendPath() string { return filepath.Join(c.SnapDir(), "db") }
+func (c *ServerConfig) BackendPath() string { return datadir.ToBackendFileName(c.DataDir) }

server/datadir/datadir.go

@@ -0,0 +1,40 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package datadir
+
+import "path/filepath"
+
+const (
+	memberDirSegment   = "member"
+	snapDirSegment     = "snap"
+	walDirSegment      = "wal"
+	backendFileSegment = "db"
+)
+
+func ToBackendFileName(dataDir string) string {
+	return filepath.Join(ToSnapDir(dataDir), backendFileSegment)
+}
+
+func ToSnapDir(dataDir string) string {
+	return filepath.Join(ToMemberDir(dataDir), snapDirSegment)
+}
+
+func ToWalDir(dataDir string) string {
+	return filepath.Join(ToMemberDir(dataDir), walDirSegment)
+}
+
+func ToMemberDir(dataDir string) string {
+	return filepath.Join(dataDir, memberDirSegment)
+}

server/datadir/datadir_test.go

@@ -0,0 +1,33 @@
+package datadir_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.etcd.io/etcd/server/v3/datadir"
+)
+
+func TestToBackendFileName(t *testing.T) {
+	result := datadir.ToBackendFileName("/dir/data-dir")
+	assert.Equal(t, "/dir/data-dir/member/snap/db", result)
+}
+
+func TestToMemberDir(t *testing.T) {
+	result := datadir.ToMemberDir("/dir/data-dir")
+	assert.Equal(t, "/dir/data-dir/member", result)
+}
+
+func TestToSnapDir(t *testing.T) {
+	result := datadir.ToSnapDir("/dir/data-dir")
+	assert.Equal(t, "/dir/data-dir/member/snap", result)
+}
+
+func TestToWalDir(t *testing.T) {
+	result := datadir.ToWalDir("/dir/data-dir")
+	assert.Equal(t, "/dir/data-dir/member/wal", result)
+}
+
+func TestToWalDirSlash(t *testing.T) {
+	result := datadir.ToWalDir("/dir/data-dir/")
+	assert.Equal(t, "/dir/data-dir/member/wal", result)
+}

server/datadir/doc.go

@@ -0,0 +1,17 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package datadir
+
+// datadir contains functions to navigate file-layout of etcd data-directory.