67 lines
1.6 KiB
Go
67 lines
1.6 KiB
Go
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// Package hidden provides the ability to "hide" binary data in a string using
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// a hex encoding with non-printing characters. Hidden data is demarcated with
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// a leading and trailing NUL character.
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package hidden
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import (
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"bytes"
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"fmt"
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"regexp"
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"github.com/getlantern/hex"
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)
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// 16 non-printing characters
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const hextable = "\x01\x02\x03\x04\x05\x06\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17"
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var (
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hexencoding = hex.NewEncoding(hextable)
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re *regexp.Regexp
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)
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func init() {
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var err error
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re, err = regexp.Compile(fmt.Sprintf("\x00[%v]+\x00", hextable))
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if err != nil {
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panic(err)
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}
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}
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// ToString encodes the given data as a hidden string, including leadnig and
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// trailing NULs.
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func ToString(data []byte) string {
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buf := bytes.NewBuffer(make([]byte, 0, 2+hex.EncodedLen(len(data))))
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// Leading NUL
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buf.WriteByte(0)
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buf.WriteString(hexencoding.EncodeToString(data))
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// Trailing NUL
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buf.WriteByte(0)
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return buf.String()
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}
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// FromString extracts the hidden data from a string, which is expected to
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// contain leading and trailing NULs.
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func FromString(str string) ([]byte, error) {
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return hexencoding.DecodeString(str[1 : len(str)-1])
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}
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// Extract extracts all hidden data from an arbitrary string.
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func Extract(str string) ([][]byte, error) {
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m := re.FindAllString(str, -1)
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result := make([][]byte, 0, len(m))
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for _, s := range m {
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b, err := FromString(s)
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if err != nil {
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return nil, err
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}
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result = append(result, b)
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}
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return result, nil
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}
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// Clean removes any hidden data from an arbitrary string.
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func Clean(str string) string {
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return re.ReplaceAllString(str, "")
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}
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