From 8085c49b03cb7e6722fdbe89dcd366bb5bbb10b5 Mon Sep 17 00:00:00 2001
From: Timofey Koolin <rekby@yandex-team.com>
Date: Thu, 18 Apr 2024 13:55:30 +0300
Subject: [PATCH] Fixed data race in logger ydb/log/WithNames

---
 CHANGELOG.md        |  2 ++
 log/context.go      | 12 +++++++++---
 log/context_test.go | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03957b2fc..608699669 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+* Fixed data race in logger ydb/log/WithNames 
+
 ## v3.65.1
 * Updated dependency `ydb-go-genproto`
 * Added processing of `Ydb.StatusIds_EXTERNAL_ERROR` in `retry.Retry`
diff --git a/log/context.go b/log/context.go
index 81231df01..b724e5ec3 100644
--- a/log/context.go
+++ b/log/context.go
@@ -1,6 +1,8 @@
 package log
 
-import "context"
+import (
+	"context"
+)
 
 type (
 	ctxLevelKey struct{}
@@ -18,7 +20,11 @@ func LevelFromContext(ctx context.Context) Level {
 }
 
 func WithNames(ctx context.Context, names ...string) context.Context {
-	return context.WithValue(ctx, ctxNamesKey{}, append(NamesFromContext(ctx), names...))
+	// trim capacity for force allocate new memory while append and prevent data race
+	oldNames := NamesFromContext(ctx)
+	oldNames = oldNames[:len(oldNames):len(oldNames)]
+
+	return context.WithValue(ctx, ctxNamesKey{}, append(oldNames, names...))
 }
 
 func NamesFromContext(ctx context.Context) []string {
@@ -27,7 +33,7 @@ func NamesFromContext(ctx context.Context) []string {
 		return []string{}
 	}
 
-	return v
+	return v[:len(v):len(v)] // prevent re
 }
 
 func with(ctx context.Context, lvl Level, names ...string) context.Context {
diff --git a/log/context_test.go b/log/context_test.go
index 3d8c05067..a3bfb6250 100644
--- a/log/context_test.go
+++ b/log/context_test.go
@@ -2,9 +2,13 @@ package log
 
 import (
 	"context"
+	"strconv"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
+
+	"github.com/ydb-platform/ydb-go-sdk/v3/internal/xtest"
 )
 
 func TestLevelFromContext(t *testing.T) {
@@ -54,3 +58,34 @@ func TestNamesFromContext(t *testing.T) {
 		})
 	}
 }
+
+func TestWithNamesRaceRegression(t *testing.T) {
+	count := 100
+	xtest.TestManyTimes(t, func(t testing.TB) {
+		ctx := WithNames(context.Background(), "test")
+		ctx = WithNames(ctx, "test")
+		ctx = WithNames(ctx, "test")
+		res := make([]context.Context, count)
+
+		start := make(chan bool)
+		finished := make(chan bool)
+		for i := 0; i < count; i++ {
+			go func(index int) {
+				res[index] = WithNames(ctx, strconv.Itoa(index))
+				finished <- true
+			}(i)
+		}
+
+		time.Sleep(time.Microsecond)
+		close(start)
+
+		for i := 0; i < count; i++ {
+			<-finished
+		}
+
+		for i := 0; i < count; i++ {
+			expected := []string{"test", "test", "test", strconv.Itoa(i)}
+			require.Equal(t, expected, NamesFromContext(res[i]))
+		}
+	})
+}