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Add snapshot completeness validation #65

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29 changes: 24 additions & 5 deletions decoder.go
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Original file line number Diff line number Diff line change
Expand Up @@ -28,10 +28,11 @@ type Decoder struct {
pageIndex map[uint32]PageIndexElem
state string

chksum Checksum
hash hash.Hash64
pageN int // pages read
n int64 // bytes read
chksum Checksum
hash hash.Hash64
pageN int // pages read
n int64 // bytes read
lastPgno uint32 // last page number read (for snapshot validation)
}

// NewDecoder returns a new instance of Decoder.
Expand Down Expand Up @@ -102,8 +103,23 @@ func (dec *Decoder) Close() error {
return fmt.Errorf("unmarshal trailer: %w", err)
}

// TODO: Ensure last read page is equal to the commit for snapshot LTX files
// Ensure last read page is equal to the commit for snapshot LTX files
if dec.header.IsSnapshot() && dec.lastPgno != 0 {
// For snapshots, we expect all pages from 1 to commit (excluding lock page)
expectedLastPage := dec.header.Commit
lockPgno := LockPgno(dec.header.PageSize)

// If commit is past the lock page, the last page should be commit
// If commit is the lock page, the last page should be commit-1
// If commit is before the lock page, the last page should be commit
if dec.header.Commit == lockPgno {
expectedLastPage = dec.header.Commit - 1
}

if dec.lastPgno != expectedLastPage {
return fmt.Errorf("snapshot incomplete: expected last page %d, got %d", expectedLastPage, dec.lastPgno)
}
}
// Compare file checksum with checksum in trailer.
if chksum := ChecksumFlag | Checksum(dec.hash.Sum64()); chksum != dec.trailer.FileChecksum {
return ErrChecksumMismatch
Expand Down Expand Up @@ -218,6 +234,9 @@ func (dec *Decoder) DecodePage(hdr *PageHeader, data []byte) error {
dec.writeToHash(data)
dec.pageN++

// Track the last page number read
dec.lastPgno = hdr.Pgno

// Calculate checksum while decoding snapshots if tracking checksums.
if dec.header.IsSnapshot() && !dec.header.NoChecksum() {
if hdr.Pgno != LockPgno(dec.header.PageSize) {
Expand Down
193 changes: 193 additions & 0 deletions decoder_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -384,3 +384,196 @@ func TestDecoder_64KBPageSize(t *testing.T) {
}
})
}

// TestDecoder_SnapshotCompleteness validates that the decoder properly checks
// for snapshot completeness when closing. For snapshot LTX files (MinTXID=1),
// the decoder must verify that all pages from 1 to Commit have been read,
// excluding the lock page which is always zero and never written.
func TestDecoder_SnapshotCompleteness(t *testing.T) {
t.Run("CompleteSnapshot", func(t *testing.T) {
spec := &ltx.FileSpec{
Header: ltx.Header{
Version: ltx.Version,
Flags: ltx.HeaderFlagNoChecksum,
PageSize: 512,
Commit: 3,
MinTXID: 1,
MaxTXID: 1,
Timestamp: 1000,
},
Pages: []ltx.PageSpec{
{Header: ltx.PageHeader{Pgno: 1}, Data: bytes.Repeat([]byte("1"), 512)},
{Header: ltx.PageHeader{Pgno: 2}, Data: bytes.Repeat([]byte("2"), 512)},
{Header: ltx.PageHeader{Pgno: 3}, Data: bytes.Repeat([]byte("3"), 512)},
},
Trailer: ltx.Trailer{},
}

var buf bytes.Buffer
writeFileSpec(t, &buf, spec)
dec := ltx.NewDecoder(&buf)

if err := dec.DecodeHeader(); err != nil {
t.Fatal(err)
}

for i := 0; i < 3; i++ {
var hdr ltx.PageHeader
data := make([]byte, 512)
if err := dec.DecodePage(&hdr, data); err != nil {
t.Fatal(err)
}
}

var hdr ltx.PageHeader
data := make([]byte, 512)
if err := dec.DecodePage(&hdr, data); err != io.EOF {
t.Fatalf("expected EOF, got: %v", err)
}

if err := dec.Close(); err != nil {
t.Fatal(err)
}
})

t.Run("IncompleteSnapshot", func(t *testing.T) {
spec := &ltx.FileSpec{
Header: ltx.Header{
Version: ltx.Version,
Flags: ltx.HeaderFlagNoChecksum,
PageSize: 512,
Commit: 3,
MinTXID: 1,
MaxTXID: 1,
Timestamp: 1000,
},
Pages: []ltx.PageSpec{
{Header: ltx.PageHeader{Pgno: 1}, Data: bytes.Repeat([]byte("1"), 512)},
{Header: ltx.PageHeader{Pgno: 2}, Data: bytes.Repeat([]byte("2"), 512)},
},
Trailer: ltx.Trailer{},
}

var buf bytes.Buffer
writeFileSpec(t, &buf, spec)
dec := ltx.NewDecoder(&buf)

if err := dec.DecodeHeader(); err != nil {
t.Fatal(err)
}

for i := 0; i < 2; i++ {
var hdr ltx.PageHeader
data := make([]byte, 512)
if err := dec.DecodePage(&hdr, data); err != nil {
t.Fatal(err)
}
}

var hdr ltx.PageHeader
data := make([]byte, 512)
if err := dec.DecodePage(&hdr, data); err != io.EOF {
t.Fatalf("expected EOF, got: %v", err)
}

if err := dec.Close(); err == nil || err.Error() != "snapshot incomplete: expected last page 3, got 2" {
t.Fatalf("expected snapshot incomplete error, got: %v", err)
}
})

t.Run("SnapshotWithLockPage", func(t *testing.T) {
if testing.Short() {
t.Skip("skipping in short mode")
}

lockPgno := ltx.LockPgno(4096)

spec := &ltx.FileSpec{
Header: ltx.Header{
Version: ltx.Version,
Flags: ltx.HeaderFlagNoChecksum,
PageSize: 4096,
Commit: lockPgno,
MinTXID: 1,
MaxTXID: 1,
Timestamp: 1000,
},
Pages: []ltx.PageSpec{},
Trailer: ltx.Trailer{},
}

for pgno := uint32(1); pgno < lockPgno; pgno++ {
spec.Pages = append(spec.Pages, ltx.PageSpec{
Header: ltx.PageHeader{Pgno: pgno},
Data: bytes.Repeat([]byte{byte(pgno % 256)}, 4096),
})
}

var buf bytes.Buffer
writeFileSpec(t, &buf, spec)
dec := ltx.NewDecoder(&buf)

if err := dec.DecodeHeader(); err != nil {
t.Fatal(err)
}

for i := 0; i < len(spec.Pages); i++ {
var hdr ltx.PageHeader
data := make([]byte, 4096)
if err := dec.DecodePage(&hdr, data); err != nil {
t.Fatal(err)
}
}

var hdr ltx.PageHeader
data := make([]byte, 4096)
if err := dec.DecodePage(&hdr, data); err != io.EOF {
t.Fatalf("expected EOF, got: %v", err)
}

if err := dec.Close(); err != nil {
t.Fatal(err)
}
})

t.Run("NonSnapshot", func(t *testing.T) {
spec := &ltx.FileSpec{
Header: ltx.Header{
Version: ltx.Version,
Flags: 0,
PageSize: 512,
Commit: 3,
MinTXID: 2,
MaxTXID: 2,
Timestamp: 1000,
PreApplyChecksum: ltx.ChecksumFlag | 1,
},
Pages: []ltx.PageSpec{
{Header: ltx.PageHeader{Pgno: 2}, Data: bytes.Repeat([]byte("2"), 512)},
},
Trailer: ltx.Trailer{PostApplyChecksum: ltx.ChecksumFlag | 2},
}

var buf bytes.Buffer
writeFileSpec(t, &buf, spec)
dec := ltx.NewDecoder(&buf)

if err := dec.DecodeHeader(); err != nil {
t.Fatal(err)
}

var hdr ltx.PageHeader
data := make([]byte, 512)
if err := dec.DecodePage(&hdr, data); err != nil {
t.Fatal(err)
}

if err := dec.DecodePage(&hdr, data); err != io.EOF {
t.Fatalf("expected EOF, got: %v", err)
}

if err := dec.Close(); err != nil {
t.Fatal(err)
}
})
}