consensus: attempt to repair the WAL file on data corruption (#4682)

Closes: #4578

Co-authored-by: Anton Kaliaev <anton.kalyaev@gmail.com>

libs/os/os.go

@@ -2,6 +2,7 @@ package os
 
 import (
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"os/signal"
@@ -80,3 +81,27 @@ func MustWriteFile(filePath string, contents []byte, mode os.FileMode) {
 		Exit(fmt.Sprintf("MustWriteFile failed: %v", err))
 	}
 }
+
+// CopyFile copies a file. It truncates the destination file if it exists.
+func CopyFile(src, dst string) error {
+	info, err := os.Stat(src)
+	if err != nil {
+		return err
+	}
+
+	srcfile, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer srcfile.Close()
+
+	// create new file, truncate if exists and apply same permissions as the original one
+	dstfile, err := os.OpenFile(dst, os.O_RDWR|os.O_CREATE|os.O_TRUNC, info.Mode().Perm())
+	if err != nil {
+		return err
+	}
+	defer dstfile.Close()
+
+	_, err = io.Copy(dstfile, srcfile)
+	return err
+}

libs/os/os_test.go

@@ -0,0 +1,37 @@
+package os
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestCopyFile(t *testing.T) {
+	tmpfile, err := ioutil.TempFile("", "example")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(tmpfile.Name())
+	content := []byte("hello world")
+	if _, err := tmpfile.Write(content); err != nil {
+		t.Fatal(err)
+	}
+
+	copyfile := fmt.Sprintf("%s.copy", tmpfile.Name())
+	if err := CopyFile(tmpfile.Name(), copyfile); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(copyfile); os.IsNotExist(err) {
+		t.Fatal("copy should exist")
+	}
+	data, err := ioutil.ReadFile(copyfile)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(data, content) {
+		t.Fatalf("copy file content differs: expected %v, got %v", content, data)
+	}
+	os.Remove(copyfile)
+}