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hash.go
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hash.go
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// Copyright (c) 2013-2016 The btcsuite developers
// Copyright (c) 2015 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package chainhash
import (
"encoding/hex"
"fmt"
)
// HashSize of array used to store hashes. See Hash.
const HashSize = 32
// MaxHashStringSize is the maximum length of a Hash hash string.
const MaxHashStringSize = HashSize * 2
// ErrHashStrSize describes an error that indicates the caller specified a hash
// string that has too many characters.
var ErrHashStrSize = fmt.Errorf("max hash string length is %v bytes", MaxHashStringSize)
// Hash is used in several of the messages and common structures. It is a
// generic type so that it can represent any fixed-size hash as specified by the
// HashSize.
type Hash [HashSize]byte
// String returns the Hash as the hexadecimal string of the byte-reversed
// hash.
func (hash Hash) String() string {
for i := 0; i < HashSize/2; i++ {
hash[i], hash[HashSize-1-i] = hash[HashSize-1-i], hash[i]
}
return hex.EncodeToString(hash[:])
}
// CloneBytes returns a copy of the bytes which represent the hash as a byte
// slice.
//
// NOTE: It is generally cheaper to just slice the hash directly thereby reusing
// the same bytes rather than calling this method.
func (hash *Hash) CloneBytes() []byte {
newHash := make([]byte, HashSize)
copy(newHash, hash[:])
return newHash
}
// SetBytes sets the bytes which represent the hash. An error is returned if
// the number of bytes passed in is not HashSize.
func (hash *Hash) SetBytes(newHash []byte) error {
nhlen := len(newHash)
if nhlen != HashSize {
return fmt.Errorf("invalid hash length of %v, want %v", nhlen,
HashSize)
}
copy(hash[:], newHash)
return nil
}
// IsEqual returns true if target is the same as hash.
func (hash *Hash) IsEqual(target *Hash) bool {
if hash == nil && target == nil {
return true
}
if hash == nil || target == nil {
return false
}
return *hash == *target
}
// NewHash returns a new Hash from a byte slice. An error is returned if
// the number of bytes passed in is not HashSize.
func NewHash(newHash []byte) (*Hash, error) {
var sh Hash
err := sh.SetBytes(newHash)
if err != nil {
return nil, err
}
return &sh, err
}
// NewHashFromStr creates a Hash from a hash string. The string should be
// the hexadecimal string of a byte-reversed hash, but any missing characters
// result in zero padding at the end of the Hash.
func NewHashFromStr(hash string) (*Hash, error) {
ret := new(Hash)
err := Decode(ret, hash)
if err != nil {
return nil, err
}
return ret, nil
}
// Decode decodes the byte-reversed hexadecimal string encoding of a Hash to a
// destination.
func Decode(dst *Hash, src string) error {
// Return error if hash string is too long.
if len(src) > MaxHashStringSize {
return ErrHashStrSize
}
// Hex decoder expects the hash to be a multiple of two. When not, pad
// with a leading zero.
var srcBytes []byte
if len(src)%2 == 0 {
srcBytes = []byte(src)
} else {
srcBytes = make([]byte, 1+len(src))
srcBytes[0] = '0'
copy(srcBytes[1:], src)
}
// Hex decode the source bytes to a temporary destination.
var reversedHash Hash
_, err := hex.Decode(reversedHash[HashSize-hex.DecodedLen(len(srcBytes)):], srcBytes)
if err != nil {
return err
}
// Reverse copy from the temporary hash to destination. Because the
// temporary was zeroed, the written result will be correctly padded.
for i, b := range reversedHash[:HashSize/2] {
dst[i], dst[HashSize-1-i] = reversedHash[HashSize-1-i], b
}
return nil
}