From a38b2b4c9b7b07cb0f4adc2288a8e8ceaf93ea53 Mon Sep 17 00:00:00 2001
From: tiancaiamao <tiancaiamao@gmail.com>
Date: Sat, 29 Jun 2024 01:06:32 +0800
Subject: [PATCH] executor: fix query panic on
 INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY with some slow query files

---
 pkg/executor/slow_query.go      |  9 ++-------
 pkg/executor/slow_query_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/pkg/executor/slow_query.go b/pkg/executor/slow_query.go
index 2dd5ecb1b0dbf..f7bb535f70102 100644
--- a/pkg/executor/slow_query.go
+++ b/pkg/executor/slow_query.go
@@ -1094,13 +1094,8 @@ func readLastLines(ctx context.Context, file *os.File, endCursor int64) ([]strin
 		lines = append(chars, lines...) // nozero
 
 		// find first '\n' or '\r'
-		for i := 0; i < len(chars); i++ {
-			// reach the line end
-			// the first newline may be in the line end at the first round
-			if i >= len(lines)-1 {
-				break
-			}
-			if (chars[i] == 10 || chars[i] == 13) && chars[i+1] != 10 && chars[i+1] != 13 {
+		for i := 0; i < len(chars)-1; i++ {
+			if (chars[i] == '\n' || chars[i] == '\r') && chars[i+1] != '\n' && chars[i+1] != '\r' {
 				firstNonNewlinePos = i + 1
 				break
 			}
diff --git a/pkg/executor/slow_query_test.go b/pkg/executor/slow_query_test.go
index 8d6a1d19f17ec..7347068a7fdb7 100644
--- a/pkg/executor/slow_query_test.go
+++ b/pkg/executor/slow_query_test.go
@@ -734,3 +734,27 @@ func removeFiles(fileNames []string) {
 		os.Remove(fileName)
 	}
 }
+
+func TestIssue54324(t *testing.T) {
+	f, err := os.CreateTemp("", "test-tidb-slow-query-issue54324")
+	require.NoError(t, err)
+	defer os.Remove(f.Name()) // clean up
+
+	w := bufio.NewWriter(f)
+	for i := 0; i < 8191; i++ {
+		w.WriteByte('x')
+	}
+	w.WriteByte('\n')
+	for i := 0; i < 4096; i++ {
+		w.WriteByte('a')
+	}
+	require.NoError(t, w.Flush())
+
+	stat, err := f.Stat()
+	require.NoError(t, err)
+	endCursor := stat.Size()
+	lines, readBytes, err := readLastLines(context.Background(), f, endCursor)
+	require.NoError(t, err)
+	require.Len(t, lines, 2)
+	require.Equal(t, readBytes, 8192+4096)
+}