strutil.go

package cli

import (
	"unicode/utf16"
	"unicode/utf8"
	"unsafe"
)

const (
	replacementChar = '\uFFFD' // Unicode replacement character

	// 0xd800-0xdc00 encodes the high 10 bits of a pair.
	// 0xdc00-0xe000 encodes the low 10 bits of a pair.
	// the value is those 20 bits plus 0x10000.
	surr1 = 0xd800
	surr2 = 0xdc00
	surr3 = 0xe000
)

// StringToUTF16 returns the UTF-16 encoding of the UTF-8 string s,
// with a terminating NUL added.
func stringToUTF16(s string) []uint16 { return utf16.Encode([]rune(s + "\x00")) }

// UTF16ToString returns the UTF-8 encoding of the UTF-16 sequence s,
// with a terminating NUL removed.
func utf16ToString(s []uint16) string {
	for i, v := range s {
		if v == 0 {
			s = s[0:i]
			break
		}
	}
	return string(utf16.Decode(s))
}

// StringToUTF16Ptr returns pointer to the UTF-16 encoding of
// the UTF-8 string s, with a terminating NUL added.
func stringToUTF16Ptr(s string) *uint16 { return &stringToUTF16(s)[0] }

// utf16toutf8 returns the UTF-8 encoding of the UTF-16 sequence s,
// with a terminating NUL removed.
func utf16ToUTF8(s []uint16) []byte {
	for i, v := range s {
		if v == 0 {
			s = s[0:i]
			break
		}
	}
	buf := make([]byte, 0, len(s)*2) // allow 2 bytes for every rune
	b := make([]byte, 4)
	for i := 0; i < len(s); i++ {
		var rr rune
		switch r := s[i]; {
		case surr1 <= r && r < surr2 && i+1 < len(s) &&
			surr2 <= s[i+1] && s[i+1] < surr3:
			// valid surrogate sequence
			rr = utf16.DecodeRune(rune(r), rune(s[i+1]))
			i++
		case surr1 <= r && r < surr3:
			// invalid surrogate sequence
			rr = replacementChar
		default:
			// normal rune
			rr = rune(r)
		}
		b := b[:cap(b)]
		n := utf8.EncodeRune(b, rr)
		b = b[:n]
		buf = append(buf, b...)
	}
	return buf
}

// extractUTF16Str uses unsafe package to copy UTF16 string
// to a byte slice. Needed for INOUT stored procedure parameter.
func extractUTF16Str(s []uint16) []byte {
	var out []byte
	for i := range s {
		b := extract(unsafe.Pointer(&s[i]), unsafe.Sizeof(s[i]))
		out = append(out, b...)
	}
	return out
}