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crypto: Add compact bit array for intended usage in the multisig

This is in a separate PR for ease of review.
pull/2322/head
ValarDragon 6 years ago
parent
commit
21448bcf4f
2 changed files with 387 additions and 0 deletions
  1. +218
    -0
      crypto/multisig/compact_bit_array.go
  2. +169
    -0
      crypto/multisig/compact_bit_array_test.go

+ 218
- 0
crypto/multisig/compact_bit_array.go View File

@ -0,0 +1,218 @@
package multisig
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"regexp"
"strings"
)
// CompactBitArray is an implementation of a space efficient bit array.
// This is used to ensure that the encoded data takes up a minimal amount of
// space after amino encoding.
// This is not thread safe, and is not intended for concurrent usage.
type CompactBitArray struct {
ExtraBitsStored byte `json:"extra_bits"` // The number of extra bits in elems.
Elems []byte `json:"bits"`
}
// NewCompactBitArray returns a new compact bit array.
// It returns nil if the number of bits is zero.
func NewCompactBitArray(bits int) *CompactBitArray {
if bits <= 0 {
return nil
}
return &CompactBitArray{
ExtraBitsStored: byte(bits % 8),
Elems: make([]byte, (bits+7)/8),
}
}
// Size returns the number of bits in the bitarray
func (bA *CompactBitArray) Size() int {
if bA == nil {
return 0
} else if bA.ExtraBitsStored == byte(0) {
return len(bA.Elems) * 8
}
return (len(bA.Elems)-1)*8 + int(bA.ExtraBitsStored)
}
// GetIndex returns the bit at index i within the bit array.
// The behavior is undefined if i >= bA.Size()
func (bA *CompactBitArray) GetIndex(i int) bool {
if bA == nil {
return false
}
if i >= bA.Size() {
return false
}
return bA.Elems[i>>3]&(uint8(1)<<uint8(7-(i%8))) > 0
}
// SetIndex sets the bit at index i within the bit array.
// The behavior is undefined if i >= bA.Size()
func (bA *CompactBitArray) SetIndex(i int, v bool) bool {
if bA == nil {
return false
}
if i >= bA.Size() {
return false
}
if v {
bA.Elems[i>>3] |= (uint8(1) << uint8(7-(i%8)))
} else {
bA.Elems[i>>3] &= ^(uint8(1) << uint8(7-(i%8)))
}
return true
}
// Copy returns a copy of the provided bit array.
func (bA *CompactBitArray) Copy() *CompactBitArray {
if bA == nil {
return nil
}
c := make([]byte, len(bA.Elems))
copy(c, bA.Elems)
return &CompactBitArray{
ExtraBitsStored: bA.ExtraBitsStored,
Elems: c,
}
}
// String returns a string representation of CompactBitArray: BA{<bit-string>},
// where <bit-string> is a sequence of 'x' (1) and '_' (0).
// The <bit-string> includes spaces and newlines to help people.
// For a simple sequence of 'x' and '_' characters with no spaces or newlines,
// see the MarshalJSON() method.
// Example: "BA{_x_}" or "nil-BitArray" for nil.
func (bA *CompactBitArray) String() string {
return bA.StringIndented("")
}
// StringIndented returns the same thing as String(), but applies the indent
// at every 10th bit, and twice at every 50th bit.
func (bA *CompactBitArray) StringIndented(indent string) string {
if bA == nil {
return "nil-BitArray"
}
lines := []string{}
bits := ""
size := bA.Size()
for i := 0; i < size; i++ {
if bA.GetIndex(i) {
bits += "x"
} else {
bits += "_"
}
if i%100 == 99 {
lines = append(lines, bits)
bits = ""
}
if i%10 == 9 {
bits += indent
}
if i%50 == 49 {
bits += indent
}
}
if len(bits) > 0 {
lines = append(lines, bits)
}
return fmt.Sprintf("BA{%v:%v}", size, strings.Join(lines, indent))
}
// MarshalJSON implements json.Marshaler interface by marshaling bit array
// using a custom format: a string of '-' or 'x' where 'x' denotes the 1 bit.
func (bA *CompactBitArray) MarshalJSON() ([]byte, error) {
if bA == nil {
return []byte("null"), nil
}
bits := `"`
size := bA.Size()
for i := 0; i < size; i++ {
if bA.GetIndex(i) {
bits += `x`
} else {
bits += `_`
}
}
bits += `"`
return []byte(bits), nil
}
var bitArrayJSONRegexp = regexp.MustCompile(`\A"([_x]*)"\z`)
// UnmarshalJSON implements json.Unmarshaler interface by unmarshaling a custom
// JSON description.
func (bA *CompactBitArray) UnmarshalJSON(bz []byte) error {
b := string(bz)
if b == "null" {
// This is required e.g. for encoding/json when decoding
// into a pointer with pre-allocated BitArray.
bA.ExtraBitsStored = 0
bA.Elems = nil
return nil
}
// Validate 'b'.
match := bitArrayJSONRegexp.FindStringSubmatch(b)
if match == nil {
return fmt.Errorf("BitArray in JSON should be a string of format %q but got %s", bitArrayJSONRegexp.String(), b)
}
bits := match[1]
// Construct new CompactBitArray and copy over.
numBits := len(bits)
bA2 := NewCompactBitArray(numBits)
for i := 0; i < numBits; i++ {
if bits[i] == 'x' {
bA2.SetIndex(i, true)
}
}
*bA = *bA2
return nil
}
// CompactMarshal is a space efficient encoding for CompactBitArray.
// It is not amino compatible.
func (bA *CompactBitArray) CompactMarshal() []byte {
size := bA.Size()
if size <= 0 {
return []byte("null")
}
bz := make([]byte, 0, size/8)
// length prefix number of bits, not number of bytes. This difference
// takes 3-4 bits in encoding, as opposed to instead encoding the number of
// bytes (saving 3-4 bits) and including the offset as a full byte.
bz = appendUvarint(bz, uint64(size))
bz = append(bz, bA.Elems...)
return bz
}
// CompactUnmarshal is a space efficient decoding for CompactBitArray.
// It is not amino compatible.
func CompactUnmarshal(bz []byte) (*CompactBitArray, error) {
if len(bz) < 2 {
return nil, errors.New("compact bit array: invalid compact unmarshal size")
} else if bytes.Equal(bz, []byte("null")) {
return NewCompactBitArray(0), nil
}
size, n := binary.Uvarint(bz)
bz = bz[n:]
if len(bz) != int(size+7)/8 {
return nil, errors.New("compact bit array: invalid compact unmarshal size")
}
bA := &CompactBitArray{byte(int(size % 8)), bz}
return bA, nil
}
func appendUvarint(b []byte, x uint64) []byte {
var a [binary.MaxVarintLen64]byte
n := binary.PutUvarint(a[:], x)
return append(b, a[:n]...)
}

+ 169
- 0
crypto/multisig/compact_bit_array_test.go View File

@ -0,0 +1,169 @@
package multisig
import (
"encoding/json"
"math/rand"
"testing"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
cmn "github.com/tendermint/tendermint/libs/common"
)
func randCompactBitArray(bits int) (*CompactBitArray, []byte) {
numBytes := (bits + 7) / 8
src := cmn.RandBytes((bits + 7) / 8)
bA := NewCompactBitArray(bits)
for i := 0; i < numBytes-1; i++ {
for j := uint8(0); j < 8; j++ {
bA.SetIndex(i*8+int(j), src[i]&(uint8(1)<<(8-j)) > 0)
}
}
// Set remaining bits
for i := uint8(0); i < 8-uint8(bA.ExtraBitsStored); i++ {
bA.SetIndex(numBytes*8+int(i), src[numBytes-1]&(uint8(1)<<(8-i)) > 0)
}
return bA, src
}
func TestNewBitArrayNeverCrashesOnNegatives(t *testing.T) {
bitList := []int{-127, -128, -1 << 31}
for _, bits := range bitList {
_ = NewCompactBitArray(bits)
}
}
func TestJSONMarshalUnmarshal(t *testing.T) {
bA1 := NewCompactBitArray(0)
bA2 := NewCompactBitArray(1)
bA3 := NewCompactBitArray(1)
bA3.SetIndex(0, true)
bA4 := NewCompactBitArray(5)
bA4.SetIndex(0, true)
bA4.SetIndex(1, true)
bA5 := NewCompactBitArray(9)
bA5.SetIndex(0, true)
bA5.SetIndex(1, true)
bA5.SetIndex(8, true)
bA6 := NewCompactBitArray(16)
bA6.SetIndex(0, true)
bA6.SetIndex(1, true)
bA6.SetIndex(8, false)
bA6.SetIndex(15, true)
testCases := []struct {
bA *CompactBitArray
marshalledBA string
}{
{nil, `null`},
{bA1, `null`},
{bA2, `"_"`},
{bA3, `"x"`},
{bA4, `"xx___"`},
{bA5, `"xx______x"`},
{bA6, `"xx_____________x"`},
}
for _, tc := range testCases {
t.Run(tc.bA.String(), func(t *testing.T) {
bz, err := json.Marshal(tc.bA)
require.NoError(t, err)
assert.Equal(t, tc.marshalledBA, string(bz))
var unmarshalledBA *CompactBitArray
err = json.Unmarshal(bz, &unmarshalledBA)
require.NoError(t, err)
if tc.bA == nil {
require.Nil(t, unmarshalledBA)
} else {
require.NotNil(t, unmarshalledBA)
assert.EqualValues(t, tc.bA.Elems, unmarshalledBA.Elems)
if assert.EqualValues(t, tc.bA.String(), unmarshalledBA.String()) {
assert.EqualValues(t, tc.bA.Elems, unmarshalledBA.Elems)
}
}
})
}
}
func TestCompactMarshalUnmarshal(t *testing.T) {
bA1 := NewCompactBitArray(0)
bA2 := NewCompactBitArray(1)
bA3 := NewCompactBitArray(1)
bA3.SetIndex(0, true)
bA4 := NewCompactBitArray(5)
bA4.SetIndex(0, true)
bA4.SetIndex(1, true)
bA5 := NewCompactBitArray(9)
bA5.SetIndex(0, true)
bA5.SetIndex(1, true)
bA5.SetIndex(8, true)
bA6 := NewCompactBitArray(16)
bA6.SetIndex(0, true)
bA6.SetIndex(1, true)
bA6.SetIndex(8, false)
bA6.SetIndex(15, true)
testCases := []struct {
bA *CompactBitArray
marshalledBA []byte
}{
{nil, []byte("null")},
{bA1, []byte("null")},
{bA2, []byte{byte(1), byte(0)}},
{bA3, []byte{byte(1), byte(128)}},
{bA4, []byte{byte(5), byte(192)}},
{bA5, []byte{byte(9), byte(192), byte(128)}},
{bA6, []byte{byte(16), byte(192), byte(1)}},
}
for _, tc := range testCases {
t.Run(tc.bA.String(), func(t *testing.T) {
bz := tc.bA.CompactMarshal()
assert.Equal(t, tc.marshalledBA, bz)
unmarshalledBA, err := CompactUnmarshal(bz)
require.NoError(t, err)
if tc.bA == nil {
require.Nil(t, unmarshalledBA)
} else {
require.NotNil(t, unmarshalledBA)
assert.EqualValues(t, tc.bA.Elems, unmarshalledBA.Elems)
if assert.EqualValues(t, tc.bA.String(), unmarshalledBA.String()) {
assert.EqualValues(t, tc.bA.Elems, unmarshalledBA.Elems)
}
}
})
}
}
func TestCompactBitArrayGetSetIndex(t *testing.T) {
r := rand.New(rand.NewSource(100))
numTests := 10
numBitsPerArr := 100
for i := 0; i < numTests; i++ {
bits := r.Intn(1000)
bA, _ := randCompactBitArray(bits)
for j := 0; j < numBitsPerArr; j++ {
copy := bA.Copy()
index := r.Intn(bits)
val := (r.Int63() % 2) == 0
bA.SetIndex(index, val)
require.Equal(t, val, bA.GetIndex(index), "bA.SetIndex(%d, %v) failed on bit array: %s", index, val, copy)
}
}
}

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