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common/bitutil: fix decompression corner cases; fuzz, test & bench

This commit is contained in:
Péter Szilágyi 2017-05-06 18:35:59 +03:00
parent fd5d51c9ae
commit cf19586cfb
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GPG Key ID: E9AE538CEDF8293D
3 changed files with 302 additions and 43 deletions
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137
common/bitutil/compress.go
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@ -16,78 +16,129 @@
package bitutil
/*
The compression algorithm implemented by CompressBytes and DecompressBytes is
optimized for "sparse" input data which contains a lot of zero bytes. Decompression
requires knowledge of the decompressed data length. Compression works as follows:
import "errors"
if data only contains zeroes,
CompressBytes(data) == nil
otherwise if len(data) <= 1,
CompressBytes(data) == data
otherwise:
CompressBytes(data) == append(CompressBytes(nonZeroBits(data)), nonZeroBytes(data)...)
where
nonZeroBits(data) is a bit vector with len(data) bits (MSB first):
nonZeroBits(data)[i/8] && (1 << (7-i%8)) != 0 if data[i] != 0
len(nonZeroBits(data)) == (len(data)+7)/8
nonZeroBytes(data) contains the non-zero bytes of data in the same order
*/
var (
// ErrMissingData is returned from decompression if the byte referenced by
// the bitset header overflows the input data.
ErrMissingData = errors.New("missing bytes on input")
// CompressBytes compresses the input byte slice
// ErrUnreferencedData is returned from decompression if not all bytes were used
// up from the input data after decompressing it.
ErrUnreferencedData = errors.New("extra bytes on input")
// ErrExceededTarget is returned from decompression if the bitset header has
// more bits defined than the number of target buffer space available.
ErrExceededTarget = errors.New("target data size exceeded")
// ErrZeroContent is returned from decompression if a data byte referenced in
// the bitset header is actually a zero byte.
ErrZeroContent = errors.New("zero byte in input content")
)
// The compression algorithm implemented by CompressBytes and DecompressBytes is
// optimized for sparse input data which contains a lot of zero bytes. Decompression
// requires knowledge of the decompressed data length.
//
// Compression works as follows:
//
// if data only contains zeroes,
// CompressBytes(data) == nil
// otherwise if len(data) <= 1,
// CompressBytes(data) == data
// otherwise:
// CompressBytes(data) == append(CompressBytes(nonZeroBitset(data)), nonZeroBytes(data)...)
// where
// nonZeroBitset(data) is a bit vector with len(data) bits (MSB first):
// nonZeroBitset(data)[i/8] && (1 << (7-i%8)) != 0 if data[i] != 0
// len(nonZeroBitset(data)) == (len(data)+7)/8
// nonZeroBytes(data) contains the non-zero bytes of data in the same order
// CompressBytes compresses the input byte slice according to the sparse bitset
// representation algorithm.
func CompressBytes(data []byte) []byte {
// Empty slices get compressed to nil
if len(data) == 0 {
return nil
}
// One byte slices compress to nil or retain the single byte
if len(data) == 1 {
if data[0] == 0 {
return nil
} else {
}
return data
}
}
bitsLen := (len(data) + 7) / 8
nonZeroBits := make([]byte, bitsLen)
// Calculate the bitset of set bytes, and gather the non-zero bytes
nonZeroBitset := make([]byte, (len(data)+7)/8)
nonZeroBytes := make([]byte, 0, len(data))
for i, b := range data {
if b != 0 {
nonZeroBytes = append(nonZeroBytes, b)
nonZeroBits[i/8] |= 1 << byte(7-i%8)
nonZeroBitset[i/8] |= 1 << byte(7-i%8)
}
}
if len(nonZeroBytes) == 0 {
return nil
}
return append(CompressBytes(nonZeroBits), nonZeroBytes...)
return append(CompressBytes(nonZeroBitset), nonZeroBytes...)
}
// DecompressBytes decompresses data with a known target size.
// In addition to the decompressed output, the function returns the length of
// compressed input data corresponding to the output. The input slice may be longer.
// If the input slice is too short, (nil, -1) is returned.
func DecompressBytes(data []byte, targetLen int) ([]byte, int) {
decomp := make([]byte, targetLen)
// DecompressBytes decompresses data with a known target size. In addition to the
// decompressed output, the function returns the length of compressed input data
// corresponding to the output as the input slice may be longer.
func DecompressBytes(data []byte, target int) ([]byte, error) {
out, size, err := decompressBytes(data, target)
if err != nil {
return nil, err
}
if size != len(data) {
return nil, ErrUnreferencedData
}
return out, nil
}
// decompressBytes decompresses data with a known target size. In addition to the
// decompressed output, the function returns the length of compressed input data
// corresponding to the output as the input slice may be longer.
func decompressBytes(data []byte, target int) ([]byte, int, error) {
// Sanity check 0 targets to avoid infinite recursion
if target == 0 {
return nil, 0, nil
}
// Handle the zero and single byte corner cases
decomp := make([]byte, target)
if len(data) == 0 {
return decomp, 0
return decomp, 0, nil
}
if targetLen == 1 {
return data[0:1], 1
if target == 1 {
decomp[0] = data[0] // copy to avoid referencing the input slice
if data[0] != 0 {
return decomp, 1, nil
}
bitsLen := (targetLen + 7) / 8
nonZeroBits, ptr := DecompressBytes(data, bitsLen)
if ptr < 0 {
return nil, -1
return decomp, 0, nil
}
for i, _ := range decomp {
if nonZeroBits[i/8]&(1<<byte(7-i%8)) != 0 {
if ptr == len(data) {
return nil, -1
// Decompress the bitset of set bytes and distribute the non zero bytes
nonZeroBitset, ptr, err := decompressBytes(data, (target+7)/8)
if err != nil {
return nil, ptr, err
}
for i := 0; i < 8*len(nonZeroBitset); i++ {
if nonZeroBitset[i/8]&(1<<byte(7-i%8)) != 0 {
// Make sure we have enough data to push into the correct slot
if ptr >= len(data) {
return nil, 0, ErrMissingData
}
if i >= len(decomp) {
return nil, 0, ErrExceededTarget
}
// Make sure the data is valid and push into the slot
if data[ptr] == 0 {
return nil, 0, ErrZeroContent
}
decomp[i] = data[ptr]
ptr++
}
}
return decomp, ptr
return decomp, ptr, nil
}

56
common/bitutil/compress_fuzz.go Normal file
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@ -0,0 +1,56 @@
// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
// +build gofuzz
package bitutil
import "bytes"
// Fuzz implements a go-fuzz fuzzer method to test various compression method
// invocations.
func Fuzz(data []byte) int {
if len(data) == 0 {
return -1
}
if data[0]%2 == 0 {
return fuzzCompress(data[1:])
}
return fuzzDecompress(data[1:])
}
// fuzzCompress implements a go-fuzz fuzzer method to test the bit compression and
// decompression algorithm.
func fuzzCompress(data []byte) int {
proc, _ := DecompressBytes(CompressBytes(data), len(data))
if !bytes.Equal(data, proc) {
panic("content mismatch")
}
return 0
}
// fuzzDecompress implements a go-fuzz fuzzer method to test the bit decompression
// and recompression algorithm.
func fuzzDecompress(data []byte) int {
blob, err := DecompressBytes(data, 1024)
if err != nil {
return 0
}
if comp := CompressBytes(blob); !bytes.Equal(comp, data) {
panic("content mismatch")
}
return 0
}

152
common/bitutil/compress_test.go Normal file
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@ -0,0 +1,152 @@
// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package bitutil
import (
"bytes"
"math/rand"
"testing"
"github.com/ethereum/go-ethereum/common/hexutil"
)
// Tests that data compression and decompression works correctly.
func TestCompressCycle(t *testing.T) {
tests := []string{
// Tests generated by go-fuzz to maximize code coverage
"0x000000000000000000",
"0xef0400",
"0xdf7070533534333636313639343638373532313536346c1bc33339343837313070706336343035336336346c65fefb3930393233383838ac2f65fefb",
"0x7b64000000",
"0x000034000000000000",
"0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f0000000000000000000",
"0x4912385c0e7b64000000",
"0x000034000000000000000000000000000000",
"0x00",
"0x000003e834ff7f0000",
"0x0000",
"0x0000000000000000000000000000000000000000000000000000000000ff00",
"0x895f0c6a020f850c6a020f85f88df88d",
"0xdf7070533534333636313639343638373432313536346c1bc3315aac2f65fefb",
"0x0000000000",
"0xdf70706336346c65fefb",
"0x00006d643634000000",
"0xdf7070533534333636313639343638373532313536346c1bc333393438373130707063363430353639343638373532313536346c1bc333393438336336346c65fe",
}
for i, tt := range tests {
data := hexutil.MustDecode(tt)
proc, err := DecompressBytes(CompressBytes(data), len(data))
if err != nil {
t.Errorf("test %d: failed to decompress compressed data: %v", i, err)
continue
}
if !bytes.Equal(data, proc) {
t.Errorf("test %d: compress/decompress mismatch: have %x, want %x", i, proc, data)
}
}
}
// Tests that data decompression works
func TestDecompress(t *testing.T) {
tests := []struct {
size int
input string
fail error
}{
{size: 0, input: "0x"},
// Crashers generated by go-fuzz
{size: 0, input: "0x0020", fail: ErrUnreferencedData},
{size: 0, input: "0x30", fail: ErrUnreferencedData},
{size: 1, input: "0x00", fail: ErrUnreferencedData},
{size: 2, input: "0x07", fail: ErrMissingData},
{size: 1024, input: "0x8000", fail: ErrZeroContent},
// Tests generated by go-fuzz to maximize code coverage
{size: 29490, input: "0x343137343733323134333839373334323073333930783e3078333930783e70706336346c65303e", fail: ErrMissingData},
{size: 59395, input: "0x00", fail: ErrUnreferencedData},
{size: 52574, input: "0x70706336346c65c0de", fail: ErrExceededTarget},
{size: 42264, input: "0x07", fail: ErrMissingData},
{size: 52, input: "0xa5045bad48f4", fail: ErrExceededTarget},
{size: 52574, input: "0xc0de", fail: ErrMissingData},
{size: 52574, input: "0x"},
{size: 29490, input: "0x34313734373332313433383937333432307333393078073034333839373334323073333930783e3078333937333432307333393078073061333930783e70706336346c65303e", fail: ErrMissingData},
{size: 29491, input: "0x3973333930783e30783e", fail: ErrMissingData},
{size: 1024, input: "0x808080608080"},
{size: 1024, input: "0x808470705e3632383337363033313434303137393130306c6580ef46806380635a80"},
{size: 1024, input: "0x8080808070"},
{size: 1024, input: "0x808070705e36346c6580ef46806380635a80"},
{size: 1024, input: "0x80808046802680"},
{size: 1024, input: "0x4040404035"},
{size: 1024, input: "0x4040bf3ba2b3f684402d353234373438373934409fe5b1e7ada94ebfd7d0505e27be4035"},
{size: 1024, input: "0x404040bf3ba2b3f6844035"},
{size: 1024, input: "0x40402d35323437343837393440bfd7d0505e27be4035"},
}
for i, tt := range tests {
data := hexutil.MustDecode(tt.input)
orig, err := DecompressBytes(data, tt.size)
if err != tt.fail {
t.Errorf("test %d: failure mismatch: have %v, want %v", i, err, tt.fail)
}
if err != nil {
continue
}
if comp := CompressBytes(orig); !bytes.Equal(comp, data) {
t.Errorf("test %d: decompress/compress mismatch: have %x, want %x", i, comp, data)
}
}
}
// Crude benchmark for compressing random slices of bytes.
func BenchmarkCompress1KBVerySparse(b *testing.B) { benchmarkCompress(b, 1024, 0.0001) }
func BenchmarkCompress2KBVerySparse(b *testing.B) { benchmarkCompress(b, 2048, 0.0001) }
func BenchmarkCompress4KBVerySparse(b *testing.B) { benchmarkCompress(b, 4096, 0.0001) }
func BenchmarkCompress1KBSparse(b *testing.B) { benchmarkCompress(b, 1024, 0.001) }
func BenchmarkCompress2KBSparse(b *testing.B) { benchmarkCompress(b, 2048, 0.001) }
func BenchmarkCompress4KBSparse(b *testing.B) { benchmarkCompress(b, 4096, 0.001) }
func BenchmarkCompress1KBDense(b *testing.B) { benchmarkCompress(b, 1024, 0.1) }
func BenchmarkCompress2KBDense(b *testing.B) { benchmarkCompress(b, 2048, 0.1) }
func BenchmarkCompress4KBDense(b *testing.B) { benchmarkCompress(b, 4096, 0.1) }
func BenchmarkCompress1KBSaturated(b *testing.B) { benchmarkCompress(b, 1024, 0.5) }
func BenchmarkCompress2KBSaturated(b *testing.B) { benchmarkCompress(b, 2048, 0.5) }
func BenchmarkCompress4KBSaturated(b *testing.B) { benchmarkCompress(b, 4096, 0.5) }
func benchmarkCompress(b *testing.B, bytes int, fill float64) {
// Generate a random slice of bytes to compress
random := rand.NewSource(0) // reproducible and comparable
data := make([]byte, bytes)
bits := int(float64(bytes) * 8 * fill)
for i := 0; i < bits; i++ {
idx := random.Int63() % int64(len(data))
bit := uint(random.Int63() % 8)
data[idx] |= 1 << bit
}
// Reset the benchmark and measure compression/decompression
b.ResetTimer()
b.ReportAllocs()
for i := 0; i < b.N; i++ {
DecompressBytes(CompressBytes(data), len(data))
}
}