102 lines
2.5 KiB
Go
102 lines
2.5 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package hex implements hexadecimal encoding and decoding.
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package hex
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import (
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"os"
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"strconv"
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)
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const hextable = "0123456789abcdef"
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// EncodedLen returns the length of an encoding of n source bytes.
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func EncodedLen(n int) int { return n * 2 }
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// Encode encodes src into EncodedLen(len(src))
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// bytes of dst. As a convenience, it returns the number
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// of bytes written to dst, but this value is always EncodedLen(len(src)).
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// Encode implements hexadecimal encoding.
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func Encode(dst, src []byte) int {
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for i, v := range src {
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dst[i*2] = hextable[v>>4]
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dst[i*2+1] = hextable[v&0x0f]
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}
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return len(src) * 2
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}
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// OddLengthInputError results from decoding an odd length slice.
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type OddLengthInputError struct{}
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func (OddLengthInputError) String() string { return "odd length hex string" }
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// InvalidHexCharError results from finding an invalid character in a hex string.
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type InvalidHexCharError byte
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func (e InvalidHexCharError) String() string {
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return "invalid hex char: " + strconv.Itoa(int(e))
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}
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func DecodedLen(x int) int { return x / 2 }
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// Decode decodes src into DecodedLen(len(src)) bytes, returning the actual
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// number of bytes written to dst.
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//
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// If Decode encounters invalid input, it returns an OddLengthInputError or an
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// InvalidHexCharError.
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func Decode(dst, src []byte) (int, os.Error) {
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if len(src)%2 == 1 {
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return 0, OddLengthInputError{}
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}
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for i := 0; i < len(src)/2; i++ {
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a, ok := fromHexChar(src[i*2])
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if !ok {
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return 0, InvalidHexCharError(src[i*2])
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}
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b, ok := fromHexChar(src[i*2+1])
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if !ok {
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return 0, InvalidHexCharError(src[i*2+1])
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}
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dst[i] = (a << 4) | b
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}
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return len(src) / 2, nil
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}
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// fromHexChar converts a hex character into its value and a success flag.
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func fromHexChar(c byte) (byte, bool) {
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switch {
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case '0' <= c && c <= '9':
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return c - '0', true
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case 'a' <= c && c <= 'f':
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return c - 'a' + 10, true
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case 'A' <= c && c <= 'F':
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return c - 'A' + 10, true
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}
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return 0, false
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}
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// EncodeToString returns the hexadecimal encoding of src.
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func EncodeToString(src []byte) string {
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dst := make([]byte, EncodedLen(len(src)))
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Encode(dst, src)
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return string(dst)
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}
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// DecodeString returns the bytes represented by the hexadecimal string s.
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func DecodeString(s string) ([]byte, os.Error) {
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src := []byte(s)
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dst := make([]byte, DecodedLen(len(src)))
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_, err := Decode(dst, src)
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if err != nil {
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return nil, err
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}
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return dst, nil
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}
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