wal decoding: Add optional mode to ignore CRC errors.

Signed-off-by: Piotr Tabor <ptab@google.com>

server/storage/wal/decoder.go

@@ -40,6 +40,11 @@ type decoder struct {
 	// lastValidOff file offset following the last valid decoded record
 	lastValidOff int64
 	crc          hash.Hash32
+
+	// continueOnCrcError - causes the decoder to continue working even in case of crc mismatch.
+	// This is a desired mode for tools performing inspection of the corrupted WAL logs.
+	// See comments on 'decode' method for semantic.
+	continueOnCrcError bool
 }
 
 func newDecoder(r ...fileutil.FileReader) *decoder {
@@ -53,6 +58,11 @@ func newDecoder(r ...fileutil.FileReader) *decoder {
 	}
 }
 
+// decode reads the next record out of the file.
+// In the success path, fills 'rec' and returns nil.
+// When it fails, it returns err and usually resets 'rec' to the defaults.
+// When continueOnCrcError is set, the method may return ErrUnexpectedEOF or ErrCRCMismatch, but preserve the read
+// (potentially corrupted) record content.
 func (d *decoder) decode(rec *walpb.Record) error {
 	rec.Reset()
 	d.mu.Lock()
@@ -108,6 +118,13 @@ func (d *decoder) decodeRecord(rec *walpb.Record) error {
 	if rec.Type != crcType {
 		d.crc.Write(rec.Data)
 		if err := rec.Validate(d.crc.Sum32()); err != nil {
+			if !d.continueOnCrcError {
+				rec.Reset()
+			} else {
+				// If we continue, we want to update lastValidOff, such that following errors are consistent
+				defer func() { d.lastValidOff += frameSizeBytes + recBytes + padBytes }()
+			}
+
 			if d.isTornEntry(data) {
 				return fmt.Errorf("%w: in file '%s' at position: %d", io.ErrUnexpectedEOF, fileBufReader.FileInfo().Name(), d.lastValidOff)
 			}

server/storage/wal/repair.go

@@ -15,6 +15,7 @@
 package wal
 
 import (
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -45,8 +46,8 @@ func Repair(lg *zap.Logger, dirpath string) bool {
 	for {
 		lastOffset := decoder.lastOffset()
 		err := decoder.decode(rec)
-		switch err {
-		case nil:
+		switch {
+		case err == nil:
 			// update crc of the decoder when necessary
 			switch rec.Type {
 			case crcType:
@@ -60,11 +61,11 @@ func Repair(lg *zap.Logger, dirpath string) bool {
 			}
 			continue
 
-		case io.EOF:
+		case errors.Is(err, io.EOF):
 			lg.Info("repaired", zap.String("path", f.Name()), zap.Error(io.EOF))
 			return true
 
-		case io.ErrUnexpectedEOF:
+		case errors.Is(err, io.ErrUnexpectedEOF):
 			brokenName := f.Name() + ".broken"
 			bf, bferr := os.Create(brokenName)
 			if bferr != nil {

server/storage/wal/repair_test.go

@@ -16,6 +16,8 @@ package wal
 
 import (
 	"fmt"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"io"
 	"os"
 	"testing"
@@ -43,86 +45,59 @@ func TestRepairTruncate(t *testing.T) {
 }
 
 func testRepair(t *testing.T, ents [][]raftpb.Entry, corrupt corruptFunc, expectedEnts int) {
+	lg := zaptest.NewLogger(t)
 	p := t.TempDir()
 
 	// create WAL
-	w, err := Create(zaptest.NewLogger(t), p, nil)
+	w, err := Create(lg, p, nil)
 	defer func() {
-		if err = w.Close(); err != nil {
-			t.Fatal(err)
-		}
+		// The Close might fail.
+		_ = w.Close()
 	}()
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
 
 	for _, es := range ents {
-		if err = w.Save(raftpb.HardState{}, es); err != nil {
-			t.Fatal(err)
-		}
+		assert.NoError(t, w.Save(raftpb.HardState{}, es))
 	}
 
 	offset, err := w.tail().Seek(0, io.SeekCurrent)
-	if err != nil {
-		t.Fatal(err)
-	}
-	w.Close()
+	require.NoError(t, err)
+	require.NoError(t, w.Close())
 
-	err = corrupt(p, offset)
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, corrupt(p, offset))
 
 	// verify we broke the wal
 	w, err = Open(zaptest.NewLogger(t), p, walpb.Snapshot{})
-	if err != nil {
-		t.Fatal(err)
-	}
+	require.NoError(t, err)
+
 	_, _, _, err = w.ReadAll()
-	if err != io.ErrUnexpectedEOF {
-		t.Fatalf("err = %v, want error %v", err, io.ErrUnexpectedEOF)
-	}
-	w.Close()
+	require.ErrorIs(t, err, io.ErrUnexpectedEOF)
+	require.NoError(t, w.Close())
 
 	// repair the wal
-	if ok := Repair(zaptest.NewLogger(t), p); !ok {
-		t.Fatalf("'Repair' returned '%v', want 'true'", ok)
-	}
+	require.True(t, Repair(lg, p), "'Repair' returned 'false', want 'true'")
 
 	// read it back
-	w, err = Open(zaptest.NewLogger(t), p, walpb.Snapshot{})
-	if err != nil {
-		t.Fatal(err)
-	}
+	w, err = Open(lg, p, walpb.Snapshot{})
+	require.NoError(t, err)
+
 	_, _, walEnts, err := w.ReadAll()
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(walEnts) != expectedEnts {
-		t.Fatalf("len(ents) = %d, want %d", len(walEnts), expectedEnts)
-	}
+	require.NoError(t, err)
+	assert.Len(t, walEnts, expectedEnts)
 
 	// write some more entries to repaired log
 	for i := 1; i <= 10; i++ {
 		es := []raftpb.Entry{{Index: uint64(expectedEnts + i)}}
-		if err = w.Save(raftpb.HardState{}, es); err != nil {
-			t.Fatal(err)
-		}
+		require.NoError(t, w.Save(raftpb.HardState{}, es))
 	}
-	w.Close()
+	require.NoError(t, w.Close())
 
 	// read back entries following repair, ensure it's all there
-	w, err = Open(zaptest.NewLogger(t), p, walpb.Snapshot{})
-	if err != nil {
-		t.Fatal(err)
-	}
+	w, err = Open(lg, p, walpb.Snapshot{})
+	require.NoError(t, err)
 	_, _, walEnts, err = w.ReadAll()
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(walEnts) != expectedEnts+10 {
-		t.Fatalf("len(ents) = %d, want %d", len(walEnts), expectedEnts+10)
-	}
+	require.NoError(t, err)
+	assert.Len(t, walEnts, expectedEnts+10)
 }
 
 func makeEnts(ents int) (ret [][]raftpb.Entry) {

server/storage/wal/walpb/record.go

@@ -14,7 +14,10 @@
 
 package walpb
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
 var (
 	ErrCRCMismatch = errors.New("walpb: crc mismatch")
@@ -24,8 +27,7 @@ func (rec *Record) Validate(crc uint32) error {
 	if rec.Crc == crc {
 		return nil
 	}
-	rec.Reset()
-	return ErrCRCMismatch
+	return fmt.Errorf("%w: expected: %x computed: %x", ErrCRCMismatch, rec.Crc, crc)
 }
 
 // ValidateSnapshotForWrite ensures the Snapshot the newly written snapshot is valid.