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// Copyright (c) 2022+ Klaus Post. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package s2
import (
"bytes"
"encoding/binary"
"encoding/json"
"fmt"
"io"
"sort"
)
const (
S2IndexHeader = "s2idx\x00"
S2IndexTrailer = "\x00xdi2s"
maxIndexEntries = 1 << 16
// If distance is less than this, we do not add the entry.
minIndexDist = 1 << 20
)
// Index represents an S2/Snappy index.
type Index struct {
TotalUncompressed int64 // Total Uncompressed size if known. Will be -1 if unknown.
TotalCompressed int64 // Total Compressed size if known. Will be -1 if unknown.
info []struct {
compressedOffset int64
uncompressedOffset int64
}
estBlockUncomp int64
}
func (i *Index) reset(maxBlock int) {
i.estBlockUncomp = int64(maxBlock)
i.TotalCompressed = -1
i.TotalUncompressed = -1
if len(i.info) > 0 {
i.info = i.info[:0]
}
}
// allocInfos will allocate an empty slice of infos.
func (i *Index) allocInfos(n int) {
if n > maxIndexEntries {
panic("n > maxIndexEntries")
}
i.info = make([]struct {
compressedOffset int64
uncompressedOffset int64
}, 0, n)
}
// add an uncompressed and compressed pair.
// Entries must be sent in order.
func (i *Index) add(compressedOffset, uncompressedOffset int64) error {
if i == nil {
return nil
}
lastIdx := len(i.info) - 1
if lastIdx >= 0 {
latest := i.info[lastIdx]
if latest.uncompressedOffset == uncompressedOffset {
// Uncompressed didn't change, don't add entry,
// but update start index.
latest.compressedOffset = compressedOffset
i.info[lastIdx] = latest
return nil
}
if latest.uncompressedOffset > uncompressedOffset {
return fmt.Errorf("internal error: Earlier uncompressed received (%d > %d)", latest.uncompressedOffset, uncompressedOffset)
}
if latest.compressedOffset > compressedOffset {
return fmt.Errorf("internal error: Earlier compressed received (%d > %d)", latest.uncompressedOffset, uncompressedOffset)
}
if latest.uncompressedOffset+minIndexDist > uncompressedOffset {
// Only add entry if distance is large enough.
return nil
}
}
i.info = append(i.info, struct {
compressedOffset int64
uncompressedOffset int64
}{compressedOffset: compressedOffset, uncompressedOffset: uncompressedOffset})
return nil
}
// Find the offset at or before the wanted (uncompressed) offset.
// If offset is 0 or positive it is the offset from the beginning of the file.
// If the uncompressed size is known, the offset must be within the file.
// If an offset outside the file is requested io.ErrUnexpectedEOF is returned.
// If the offset is negative, it is interpreted as the distance from the end of the file,
// where -1 represents the last byte.
// If offset from the end of the file is requested, but size is unknown,
// ErrUnsupported will be returned.
func (i *Index) Find(offset int64) (compressedOff, uncompressedOff int64, err error) {
if i.TotalUncompressed < 0 {
return 0, 0, ErrCorrupt
}
if offset < 0 {
offset = i.TotalUncompressed + offset
if offset < 0 {
return 0, 0, io.ErrUnexpectedEOF
}
}
if offset > i.TotalUncompressed {
return 0, 0, io.ErrUnexpectedEOF
}
if len(i.info) > 200 {
n := sort.Search(len(i.info), func(n int) bool {
return i.info[n].uncompressedOffset > offset
})
if n == 0 {
n = 1
}
return i.info[n-1].compressedOffset, i.info[n-1].uncompressedOffset, nil
}
for _, info := range i.info {
if info.uncompressedOffset > offset {
break
}
compressedOff = info.compressedOffset
uncompressedOff = info.uncompressedOffset
}
return compressedOff, uncompressedOff, nil
}
// reduce to stay below maxIndexEntries
func (i *Index) reduce() {
if len(i.info) < maxIndexEntries && i.estBlockUncomp >= minIndexDist {
return
}
// Algorithm, keep 1, remove removeN entries...
removeN := (len(i.info) + 1) / maxIndexEntries
src := i.info
j := 0
// Each block should be at least 1MB, but don't reduce below 1000 entries.
for i.estBlockUncomp*(int64(removeN)+1) < minIndexDist && len(i.info)/(removeN+1) > 1000 {
removeN++
}
for idx := 0; idx < len(src); idx++ {
i.info[j] = src[idx]
j++
idx += removeN
}
i.info = i.info[:j]
// Update maxblock estimate.
i.estBlockUncomp += i.estBlockUncomp * int64(removeN)
}
func (i *Index) appendTo(b []byte, uncompTotal, compTotal int64) []byte {
i.reduce()
var tmp [binary.MaxVarintLen64]byte
initSize := len(b)
// We make the start a skippable header+size.
b = append(b, ChunkTypeIndex, 0, 0, 0)
b = append(b, []byte(S2IndexHeader)...)
// Total Uncompressed size
n := binary.PutVarint(tmp[:], uncompTotal)
b = append(b, tmp[:n]...)
// Total Compressed size
n = binary.PutVarint(tmp[:], compTotal)
b = append(b, tmp[:n]...)
// Put EstBlockUncomp size
n = binary.PutVarint(tmp[:], i.estBlockUncomp)
b = append(b, tmp[:n]...)
// Put length
n = binary.PutVarint(tmp[:], int64(len(i.info)))
b = append(b, tmp[:n]...)
// Check if we should add uncompressed offsets
var hasUncompressed byte
for idx, info := range i.info {
if idx == 0 {
if info.uncompressedOffset != 0 {
hasUncompressed = 1
break
}
continue
}
if info.uncompressedOffset != i.info[idx-1].uncompressedOffset+i.estBlockUncomp {
hasUncompressed = 1
break
}
}
b = append(b, hasUncompressed)
// Add each entry
if hasUncompressed == 1 {
for idx, info := range i.info {
uOff := info.uncompressedOffset
if idx > 0 {
prev := i.info[idx-1]
uOff -= prev.uncompressedOffset + (i.estBlockUncomp)
}
n = binary.PutVarint(tmp[:], uOff)
b = append(b, tmp[:n]...)
}
}
// Initial compressed size estimate.
cPredict := i.estBlockUncomp / 2
for idx, info := range i.info {
cOff := info.compressedOffset
if idx > 0 {
prev := i.info[idx-1]
cOff -= prev.compressedOffset + cPredict
// Update compressed size prediction, with half the error.
cPredict += cOff / 2
}
n = binary.PutVarint(tmp[:], cOff)
b = append(b, tmp[:n]...)
}
// Add Total Size.
// Stored as fixed size for easier reading.
binary.LittleEndian.PutUint32(tmp[:], uint32(len(b)-initSize+4+len(S2IndexTrailer)))
b = append(b, tmp[:4]...)
// Trailer
b = append(b, []byte(S2IndexTrailer)...)
// Update size
chunkLen := len(b) - initSize - skippableFrameHeader
b[initSize+1] = uint8(chunkLen >> 0)
b[initSize+2] = uint8(chunkLen >> 8)
b[initSize+3] = uint8(chunkLen >> 16)
//fmt.Printf("chunklen: 0x%x Uncomp:%d, Comp:%d\n", chunkLen, uncompTotal, compTotal)
return b
}
// Load a binary index.
// A zero value Index can be used or a previous one can be reused.
func (i *Index) Load(b []byte) ([]byte, error) {
if len(b) <= 4+len(S2IndexHeader)+len(S2IndexTrailer) {
return b, io.ErrUnexpectedEOF
}
if b[0] != ChunkTypeIndex {
return b, ErrCorrupt
}
chunkLen := int(b[1]) | int(b[2])<<8 | int(b[3])<<16
b = b[4:]
// Validate we have enough...
if len(b) < chunkLen {
return b, io.ErrUnexpectedEOF
}
if !bytes.Equal(b[:len(S2IndexHeader)], []byte(S2IndexHeader)) {
return b, ErrUnsupported
}
b = b[len(S2IndexHeader):]
// Total Uncompressed
if v, n := binary.Varint(b); n <= 0 || v < 0 {
return b, ErrCorrupt
} else {
i.TotalUncompressed = v
b = b[n:]
}
// Total Compressed
if v, n := binary.Varint(b); n <= 0 {
return b, ErrCorrupt
} else {
i.TotalCompressed = v
b = b[n:]
}
// Read EstBlockUncomp
if v, n := binary.Varint(b); n <= 0 {
return b, ErrCorrupt
} else {
if v < 0 {
return b, ErrCorrupt
}
i.estBlockUncomp = v
b = b[n:]
}
var entries int
if v, n := binary.Varint(b); n <= 0 {
return b, ErrCorrupt
} else {
if v < 0 || v > maxIndexEntries {
return b, ErrCorrupt
}
entries = int(v)
b = b[n:]
}
if cap(i.info) < entries {
i.allocInfos(entries)
}
i.info = i.info[:entries]
if len(b) < 1 {
return b, io.ErrUnexpectedEOF
}
hasUncompressed := b[0]
b = b[1:]
if hasUncompressed&1 != hasUncompressed {
return b, ErrCorrupt
}
// Add each uncompressed entry
for idx := range i.info {
var uOff int64
if hasUncompressed != 0 {
// Load delta
if v, n := binary.Varint(b); n <= 0 {
return b, ErrCorrupt
} else {
uOff = v
b = b[n:]
}
}
if idx > 0 {
prev := i.info[idx-1].uncompressedOffset
uOff += prev + (i.estBlockUncomp)
if uOff <= prev {
return b, ErrCorrupt
}
}
if uOff < 0 {
return b, ErrCorrupt
}
i.info[idx].uncompressedOffset = uOff
}
// Initial compressed size estimate.
cPredict := i.estBlockUncomp / 2
// Add each compressed entry
for idx := range i.info {
var cOff int64
if v, n := binary.Varint(b); n <= 0 {
return b, ErrCorrupt
} else {
cOff = v
b = b[n:]
}
if idx > 0 {
// Update compressed size prediction, with half the error.
cPredictNew := cPredict + cOff/2
prev := i.info[idx-1].compressedOffset
cOff += prev + cPredict
if cOff <= prev {
return b, ErrCorrupt
}
cPredict = cPredictNew
}
if cOff < 0 {
return b, ErrCorrupt
}
i.info[idx].compressedOffset = cOff
}
if len(b) < 4+len(S2IndexTrailer) {
return b, io.ErrUnexpectedEOF
}
// Skip size...
b = b[4:]
// Check trailer...
if !bytes.Equal(b[:len(S2IndexTrailer)], []byte(S2IndexTrailer)) {
return b, ErrCorrupt
}
return b[len(S2IndexTrailer):], nil
}
// LoadStream will load an index from the end of the supplied stream.
// ErrUnsupported will be returned if the signature cannot be found.
// ErrCorrupt will be returned if unexpected values are found.
// io.ErrUnexpectedEOF is returned if there are too few bytes.
// IO errors are returned as-is.
func (i *Index) LoadStream(rs io.ReadSeeker) error {
// Go to end.
_, err := rs.Seek(-10, io.SeekEnd)
if err != nil {
return err
}
var tmp [10]byte
_, err = io.ReadFull(rs, tmp[:])
if err != nil {
return err
}
// Check trailer...
if !bytes.Equal(tmp[4:4+len(S2IndexTrailer)], []byte(S2IndexTrailer)) {
return ErrUnsupported
}
sz := binary.LittleEndian.Uint32(tmp[:4])
if sz > maxChunkSize+skippableFrameHeader {
return ErrCorrupt
}
_, err = rs.Seek(-int64(sz), io.SeekEnd)
if err != nil {
return err
}
// Read index.
buf := make([]byte, sz)
_, err = io.ReadFull(rs, buf)
if err != nil {
return err
}
_, err = i.Load(buf)
return err
}
// IndexStream will return an index for a stream.
// The stream structure will be checked, but
// data within blocks is not verified.
// The returned index can either be appended to the end of the stream
// or stored separately.
func IndexStream(r io.Reader) ([]byte, error) {
var i Index
var buf [maxChunkSize]byte
var readHeader bool
for {
_, err := io.ReadFull(r, buf[:4])
if err != nil {
if err == io.EOF {
return i.appendTo(nil, i.TotalUncompressed, i.TotalCompressed), nil
}
return nil, err
}
// Start of this chunk.
startChunk := i.TotalCompressed
i.TotalCompressed += 4
chunkType := buf[0]
if !readHeader {
if chunkType != chunkTypeStreamIdentifier {
return nil, ErrCorrupt
}
readHeader = true
}
chunkLen := int(buf[1]) | int(buf[2])<<8 | int(buf[3])<<16
if chunkLen < checksumSize {
return nil, ErrCorrupt
}
i.TotalCompressed += int64(chunkLen)
_, err = io.ReadFull(r, buf[:chunkLen])
if err != nil {
return nil, io.ErrUnexpectedEOF
}
// The chunk types are specified at
// https://github.com/google/snappy/blob/master/framing_format.txt
switch chunkType {
case chunkTypeCompressedData:
// Section 4.2. Compressed data (chunk type 0x00).
// Skip checksum.
dLen, err := DecodedLen(buf[checksumSize:])
if err != nil {
return nil, err
}
if dLen > maxBlockSize {
return nil, ErrCorrupt
}
if i.estBlockUncomp == 0 {
// Use first block for estimate...
i.estBlockUncomp = int64(dLen)
}
err = i.add(startChunk, i.TotalUncompressed)
if err != nil {
return nil, err
}
i.TotalUncompressed += int64(dLen)
continue
case chunkTypeUncompressedData:
n2 := chunkLen - checksumSize
if n2 > maxBlockSize {
return nil, ErrCorrupt
}
if i.estBlockUncomp == 0 {
// Use first block for estimate...
i.estBlockUncomp = int64(n2)
}
err = i.add(startChunk, i.TotalUncompressed)
if err != nil {
return nil, err
}
i.TotalUncompressed += int64(n2)
continue
case chunkTypeStreamIdentifier:
// Section 4.1. Stream identifier (chunk type 0xff).
if chunkLen != len(magicBody) {
return nil, ErrCorrupt
}
if string(buf[:len(magicBody)]) != magicBody {
if string(buf[:len(magicBody)]) != magicBodySnappy {
return nil, ErrCorrupt
}
}
continue
}
if chunkType <= 0x7f {
// Section 4.5. Reserved unskippable chunks (chunk types 0x02-0x7f).
return nil, ErrUnsupported
}
if chunkLen > maxChunkSize {
return nil, ErrUnsupported
}
// Section 4.4 Padding (chunk type 0xfe).
// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
}
}
// JSON returns the index as JSON text.
func (i *Index) JSON() []byte {
type offset struct {
CompressedOffset int64 `json:"compressed"`
UncompressedOffset int64 `json:"uncompressed"`
}
x := struct {
TotalUncompressed int64 `json:"total_uncompressed"` // Total Uncompressed size if known. Will be -1 if unknown.
TotalCompressed int64 `json:"total_compressed"` // Total Compressed size if known. Will be -1 if unknown.
Offsets []offset `json:"offsets"`
EstBlockUncomp int64 `json:"est_block_uncompressed"`
}{
TotalUncompressed: i.TotalUncompressed,
TotalCompressed: i.TotalCompressed,
EstBlockUncomp: i.estBlockUncomp,
}
for _, v := range i.info {
x.Offsets = append(x.Offsets, offset{CompressedOffset: v.compressedOffset, UncompressedOffset: v.uncompressedOffset})
}
b, _ := json.MarshalIndent(x, "", " ")
return b
}
// RemoveIndexHeaders will trim all headers and trailers from a given index.
// This is expected to save 20 bytes.
// These can be restored using RestoreIndexHeaders.
// This removes a layer of security, but is the most compact representation.
// Returns nil if headers contains errors.
// The returned slice references the provided slice.
func RemoveIndexHeaders(b []byte) []byte {
const save = 4 + len(S2IndexHeader) + len(S2IndexTrailer) + 4
if len(b) <= save {
return nil
}
if b[0] != ChunkTypeIndex {
return nil
}
chunkLen := int(b[1]) | int(b[2])<<8 | int(b[3])<<16
b = b[4:]
// Validate we have enough...
if len(b) < chunkLen {
return nil
}
b = b[:chunkLen]
if !bytes.Equal(b[:len(S2IndexHeader)], []byte(S2IndexHeader)) {
return nil
}
b = b[len(S2IndexHeader):]
if !bytes.HasSuffix(b, []byte(S2IndexTrailer)) {
return nil
}
b = bytes.TrimSuffix(b, []byte(S2IndexTrailer))
if len(b) < 4 {
return nil
}
return b[:len(b)-4]
}
// RestoreIndexHeaders will index restore headers removed by RemoveIndexHeaders.
// No error checking is performed on the input.
// If a 0 length slice is sent, it is returned without modification.
func RestoreIndexHeaders(in []byte) []byte {
if len(in) == 0 {
return in
}
b := make([]byte, 0, 4+len(S2IndexHeader)+len(in)+len(S2IndexTrailer)+4)
b = append(b, ChunkTypeIndex, 0, 0, 0)
b = append(b, []byte(S2IndexHeader)...)
b = append(b, in...)
var tmp [4]byte
binary.LittleEndian.PutUint32(tmp[:], uint32(len(b)+4+len(S2IndexTrailer)))
b = append(b, tmp[:4]...)
// Trailer
b = append(b, []byte(S2IndexTrailer)...)
chunkLen := len(b) - skippableFrameHeader
b[1] = uint8(chunkLen >> 0)
b[2] = uint8(chunkLen >> 8)
b[3] = uint8(chunkLen >> 16)
return b
}
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