| 1 | package moves |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "encoding/binary" |
| 6 | "errors" |
| 7 | "fmt" |
| 8 | "io" |
| 9 | "os" |
| 10 | |
| 11 | "github.com/superfly/ltx" |
| 12 | ) |
| 13 | |
| 14 | // sqliteHeaderSize is the SQLite database header, the first 100 bytes of |
| 15 | // page 1. |
| 16 | const sqliteHeaderSize = 100 |
| 17 | |
| 18 | var sqliteMagic = []byte("SQLite format 3\x00") |
| 19 | |
| 20 | // ReadDBHeader reads the page size (header bytes 16-17; the value 1 means |
| 21 | // 65536) and the in-header database size in pages (bytes 28-31) of the |
| 22 | // SQLite database at path. The in-header size is what SQLite keeps current |
| 23 | // in WAL mode and what litestream's restore writes; BuildGeneration checks |
| 24 | // it against the file size before trusting it. |
| 25 | func ReadDBHeader(path string) (pageSize uint32, pageCount uint32, err error) { |
| 26 | f, err := os.Open(path) |
| 27 | if err != nil { |
| 28 | return 0, 0, err |
| 29 | } |
| 30 | defer f.Close() |
| 31 | var hdr [sqliteHeaderSize]byte |
| 32 | if _, err := io.ReadFull(f, hdr[:]); err != nil { |
| 33 | return 0, 0, fmt.Errorf("read sqlite header of %s: %w", path, err) |
| 34 | } |
| 35 | if !bytes.Equal(hdr[:len(sqliteMagic)], sqliteMagic) { |
| 36 | return 0, 0, fmt.Errorf("%s is not a SQLite database", path) |
| 37 | } |
| 38 | pageSize = uint32(binary.BigEndian.Uint16(hdr[16:18])) |
| 39 | if pageSize == 1 { |
| 40 | pageSize = 65536 |
| 41 | } |
| 42 | if !ltx.IsValidPageSize(pageSize) { |
| 43 | return 0, 0, fmt.Errorf("%s has an invalid page size %d", path, pageSize) |
| 44 | } |
| 45 | pageCount = binary.BigEndian.Uint32(hdr[28:32]) |
| 46 | if pageCount == 0 { |
| 47 | return 0, 0, fmt.Errorf("%s has no in-header database size", path) |
| 48 | } |
| 49 | return pageSize, pageCount, nil |
| 50 | } |
| 51 | |
| 52 | // EncodeFull encodes every page of db, pages 1 to pageCount in order, as |
| 53 | // one LTX file [min, max] with the NoChecksum flag, and returns the bytes |
| 54 | // and the trailer's CRC-64 file checksum. SQLite's lock page |
| 55 | // (ltx.LockPgno(pageSize), the page holding PENDING_BYTE) is skipped: the |
| 56 | // encoder refuses it, litestream never ships it, and the decoder writes it |
| 57 | // back as zeros; Commit keeps the full page count. With min 1 the file is |
| 58 | // a snapshot; with min == max == N and walOffset litestream.WALHeaderSize |
| 59 | // it is the anchor litestream's open reads its position from (§5.1 step |
| 60 | // 7). The header timestamp is an input, so the same inputs give the same |
| 61 | // bytes, which is what lets a replayed PUT repeat its object. The bytes |
| 62 | // are read back and verified before they are returned. |
| 63 | func EncodeFull(db io.ReaderAt, pageSize, pageCount uint32, min, max ltx.TXID, timestamp int64, walOffset int64) (data []byte, crc64 uint64, err error) { |
| 64 | if pageCount == 0 { |
| 65 | return nil, 0, errors.New("moves: cannot encode an empty database") |
| 66 | } |
| 67 | var buf bytes.Buffer |
| 68 | enc, err := ltx.NewEncoder(&buf) |
| 69 | if err != nil { |
| 70 | return nil, 0, err |
| 71 | } |
| 72 | if err := enc.EncodeHeader(ltx.Header{ |
| 73 | Version: ltx.Version, |
| 74 | Flags: ltx.HeaderFlagNoChecksum, |
| 75 | PageSize: pageSize, |
| 76 | Commit: pageCount, |
| 77 | MinTXID: min, |
| 78 | MaxTXID: max, |
| 79 | Timestamp: timestamp, |
| 80 | WALOffset: walOffset, |
| 81 | }); err != nil { |
| 82 | return nil, 0, fmt.Errorf("moves: encode header: %w", err) |
| 83 | } |
| 84 | lock := ltx.LockPgno(pageSize) |
| 85 | page := make([]byte, pageSize) |
| 86 | for pgno := uint32(1); pgno <= pageCount; pgno++ { |
| 87 | if pgno == lock { |
| 88 | continue |
| 89 | } |
| 90 | if _, err := db.ReadAt(page, int64(pgno-1)*int64(pageSize)); err != nil { |
| 91 | return nil, 0, fmt.Errorf("moves: read page %d: %w", pgno, err) |
| 92 | } |
| 93 | if err := enc.EncodePage(ltx.PageHeader{Pgno: pgno}, page); err != nil { |
| 94 | return nil, 0, fmt.Errorf("moves: encode page %d: %w", pgno, err) |
| 95 | } |
| 96 | } |
| 97 | if err := enc.Close(); err != nil { |
| 98 | return nil, 0, fmt.Errorf("moves: close encoder: %w", err) |
| 99 | } |
| 100 | data = buf.Bytes() |
| 101 | dec := ltx.NewDecoder(bytes.NewReader(data)) |
| 102 | if err := dec.Verify(); err != nil { |
| 103 | return nil, 0, fmt.Errorf("moves: verify encoded %s: %w", ltx.FormatFilename(min, max), err) |
| 104 | } |
| 105 | if dec.Trailer().FileChecksum != enc.Trailer().FileChecksum { |
| 106 | return nil, 0, fmt.Errorf("moves: encoded %s reads back with another checksum", ltx.FormatFilename(min, max)) |
| 107 | } |
| 108 | return data, uint64(dec.Trailer().FileChecksum), nil |
| 109 | } |
| 110 | |
amadan