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// Package percent escapes strings using percent-encoding
package percent
import (
"strings"
)
const upperhex = "0123456789ABCDEF"
func unhex(c byte) byte {
switch {
case '0' <= c && c <= '9':
return c - '0'
case 'a' <= c && c <= 'f':
return c - 'a' + 10
case 'A' <= c && c <= 'F':
return c - 'A' + 10
}
return 0
}
func ishex(c byte) bool {
switch {
case '0' <= c && c <= '9':
return true
case 'a' <= c && c <= 'f':
return true
case 'A' <= c && c <= 'F':
return true
}
return false
}
// Encode escapes the string using percent-encoding, converting the runes found in charsToEncode with hex-encoded %AB sequences
func Encode(s string, charsToEncode string) string {
var t strings.Builder
for _, c := range s {
if strings.IndexRune(charsToEncode, c) != -1 || c == '%' {
for _, b := range []byte(string(c)) {
t.WriteByte('%')
t.WriteByte(upperhex[b>>4])
t.WriteByte(upperhex[b&15])
}
} else {
t.WriteRune(c)
}
}
return t.String()
}
// Decode does the inverse transformation of Encode, converting each 3-byte encoded substring of the form "%AB" into the hex-decoded byte 0xAB
func Decode(s string) string {
var t []byte
for i := 0; i < len(s); i++ {
// check next 2 chars are valid
if s[i] == '%' && i+2 < len(s) && ishex(s[i+1]) && ishex(s[i+2]) {
t = append(t, (unhex(s[i+1])<<4 | unhex(s[i+2])))
i += 2
} else {
t = append(t, s[i])
}
}
return string(t)
}
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