ceremonyclient/go-libp2p/p2p/transport/webrtc/hex.go

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2024-06-08 11:32:45 +00:00
package libp2pwebrtc
// The code in this file is adapted from the Go standard library's hex package.
// As found in https://cs.opensource.google/go/go/+/refs/tags/go1.20.2:src/encoding/hex/hex.go
//
// The reason we adapted the original code is to allow us to deal with interspersed requirements
// while at the same time hex encoding/decoding, without having to do so in two passes.
import (
"encoding/hex"
"errors"
)
// encodeInterspersedHex encodes a byte slice into a string of hex characters,
// separating each encoded byte with a colon (':').
//
// Example: { 0x01, 0x02, 0x03 } -> "01:02:03"
func encodeInterspersedHex(src []byte) string {
if len(src) == 0 {
return ""
}
s := hex.EncodeToString(src)
n := len(s)
// Determine number of colons
colons := n / 2
if n%2 == 0 {
colons--
}
buffer := make([]byte, n+colons)
for i, j := 0, 0; i < n; i, j = i+2, j+3 {
copy(buffer[j:j+2], s[i:i+2])
if j+3 < len(buffer) {
buffer[j+2] = ':'
}
}
return string(buffer)
}
var errUnexpectedIntersperseHexChar = errors.New("unexpected character in interspersed hex string")
// decodeInterspersedHexFromASCIIString decodes an ASCII string of hex characters into a byte slice,
// where the hex characters are expected to be separated by a colon (':').
//
// NOTE that this function returns an error in case the input string contains non-ASCII characters.
//
// Example: "01:02:03" -> { 0x01, 0x02, 0x03 }
func decodeInterspersedHexFromASCIIString(s string) ([]byte, error) {
n := len(s)
buffer := make([]byte, n/3*2+n%3)
j := 0
for i := 0; i < n; i++ {
if i%3 == 2 {
if s[i] != ':' {
return nil, errUnexpectedIntersperseHexChar
}
} else {
if s[i] == ':' {
return nil, errUnexpectedIntersperseHexChar
}
buffer[j] = s[i]
j++
}
}
dst := make([]byte, hex.DecodedLen(len(buffer)))
if _, err := hex.Decode(dst, buffer); err != nil {
return nil, err
}
return dst, nil
}