80 lines
1.8 KiB
Go
80 lines
1.8 KiB
Go
package litestream
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import (
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"encoding/binary"
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"encoding/hex"
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"io"
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"strings"
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)
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// Magic number specified at the beginning of WAL files.
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const (
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MagicLittleEndian = 0x377f0682
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MagicBigEndian = 0x377f0683
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)
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const (
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WriteVersionOffset = 18
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ReadVersionOffset = 19
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)
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// ReadVersion returns the SQLite write & read version.
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// Returns 1 for legacy & 2 for WAL.
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func ReadVersion(b []byte) (writeVersion, readVersion uint8, err error) {
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if len(b) < ReadVersionOffset {
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return 0, 0, io.ErrUnexpectedEOF
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}
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return b[WriteVersionOffset], b[ReadVersionOffset], nil
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}
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// Checksum computes a running checksum over a byte slice.
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func Checksum(bo binary.ByteOrder, s uint64, b []byte) (_ uint64, err error) {
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// Ensure byte slice length is divisible by 8.
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if len(b)%8 != 0 {
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return 0, ErrChecksumMisaligned
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}
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// Iterate over 8-byte units and compute checksum.
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s0, s1 := uint32(s>>32), uint32(s&0xFFFFFFFF)
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for i := 0; i < len(b); i += 8 {
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s0 += bo.Uint32(b[i:]) + s1
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s1 += bo.Uint32(b[i+4:]) + s0
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}
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return uint64(s0)<<32 | uint64(s1), nil
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}
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// HexDump returns hexdump output but with duplicate lines removed.
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func HexDump(b []byte) string {
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const prefixN = len("00000000")
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var output []string
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var prev string
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var ellipsis bool
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lines := strings.Split(strings.TrimSpace(hex.Dump(b)), "\n")
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for i, line := range lines {
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// Add line to output if it is not repeating or the last line.
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if i == 0 || i == len(lines)-1 || trimPrefixN(line, prefixN) != trimPrefixN(prev, prefixN) {
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output = append(output, line)
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prev, ellipsis = line, false
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continue
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}
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// Add an ellipsis for the first duplicate line.
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if !ellipsis {
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output = append(output, "...")
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ellipsis = true
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continue
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}
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}
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return strings.Join(output, "\n")
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}
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func trimPrefixN(s string, n int) string {
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if len(s) < n {
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return ""
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}
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return s[n:]
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}
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