hash.go

// Code extracted from vendor/github.com/ethereum/go-ethereum/common/types.go

package types

import (
	"encoding/hex"
	"fmt"
	"reflect"
)

const (
	// HashLength is the expected length of the hash
	HashLength = 32
)

// Hash represents the 32 byte Keccak256 hash of arbitrary data.
type Hash [HashLength]byte

var hashT = reflect.TypeOf(Hash{})

// Encode encodes b as a hex string with 0x prefix.
func encode(b []byte) string {
	enc := make([]byte, len(b)*2+2)
	copy(enc, "0x")
	hex.Encode(enc[2:], b)
	return string(enc)
}

// FromHex returns the bytes represented by the hexadecimal string s.
// s may be prefixed with "0x".
func FromHex(s string) []byte {
	if has0xPrefix(s) {
		s = s[2:]
	}
	if len(s)%2 == 1 {
		s = "0" + s
	}
	return Hex2Bytes(s)
}

// HexToHash sets byte representation of s to hash.
// If b is larger than len(h), b will be cropped from the left.
func HexToHash(s string) Hash { return BytesToHash(FromHex(s)) }

// Hex converts a hash to a hex string.
func (h *Hash) Hex() string { return encode(h[:]) }

// Bytes gets the byte representation of the underlying hash.
func (h Hash) Bytes() []byte { return h[:] }

// String implements the stringer interface and is used also by the logger when
// doing full logging into a file.
func (h Hash) String() string {
	return h.Hex()
}

// SetBytes sets the hash to the value of b.
// If b is larger than len(h), b will be cropped from the left.
func (h *Hash) SetBytes(b []byte) {
	if len(b) > len(h) {
		b = b[len(b)-HashLength:]
	}

	copy(h[HashLength-len(b):], b)
}

// UnmarshalText parses a hash in hex syntax.
func (h *Hash) UnmarshalText(input []byte) error {
	return UnmarshalFixedText("Hash", input, h[:])
}

// UnmarshalJSON parses a hash in hex syntax.
func (h *Hash) UnmarshalJSON(input []byte) error {
	return UnmarshalFixedJSON(hashT, input, h[:])
}

// MarshalText returns the hex representation of h.
func (h Hash) MarshalText() ([]byte, error) {
	return HexBytes(h[:]).MarshalText()
}

// BytesToHash sets b to hash.
// If b is larger than len(h), b will be cropped from the left.
func BytesToHash(b []byte) Hash {
	var h Hash
	h.SetBytes(b)
	return h
}

// UnmarshalFixedJSON decodes the input as a string with 0x prefix. The length of out
// determines the required input length. This function is commonly used to implement the
// UnmarshalJSON method for fixed-size types.
func UnmarshalFixedJSON(typ reflect.Type, input, out []byte) error {
	if !isString(input) {
		return errNonString(typ)
	}
	return wrapTypeError(UnmarshalFixedText(typ.String(), input[1:len(input)-1], out), typ)
}

// UnmarshalFixedText decodes the input as a string with 0x prefix. The length of out
// determines the required input length. This function is commonly used to implement the
// UnmarshalText method for fixed-size types.
func UnmarshalFixedText(typname string, input, out []byte) error {
	raw, err := checkText(input, true)
	if err != nil {
		return err
	}
	if len(raw)/2 != len(out) {
		return fmt.Errorf("hex string has length %d, want %d for %s", len(raw), len(out)*2, typname)
	}
	// Pre-verify syntax before modifying out.
	for _, b := range raw {
		if decodeNibble(b) == badNibble {
			return ErrSyntax
		}
	}
	_, err = hex.Decode(out, raw)
	return err
}