Initial commit

vendor/github.com/emersion/go-imap/utf7/encoder.go

@@ -0,0 +1,96 @@
+package utf7
+
+import (
+	"unicode/utf16"
+	"unicode/utf8"
+
+	"golang.org/x/text/encoding"
+	"golang.org/x/text/transform"
+)
+
+var Encoder = &encoding.Encoder{
+	Transformer: &encoder{},
+}
+
+type encoder struct{}
+
+func (e *encoder) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
+	for i := 0; i < len(src); {
+		ch := src[i]
+
+		var b []byte
+		if min <= ch && ch <= max {
+			b = []byte{ch}
+			if ch == '&' {
+				b = append(b, '-')
+			}
+
+			i++
+		} else {
+			start := i
+
+			// Find the next printable ASCII code point
+			i++
+			for i < len(src) && (src[i] < min || src[i] > max) {
+				i++
+			}
+
+			if !atEOF && i == len(src) {
+				err = transform.ErrShortSrc
+				return
+			}
+
+			b = encode(src[start:i])
+		}
+
+		if nDst+len(b) > len(dst) {
+			err = transform.ErrShortDst
+			return
+		}
+
+		nSrc = i
+
+		for _, ch := range b {
+			dst[nDst] = ch
+			nDst++
+		}
+	}
+
+	return
+}
+
+func (e *encoder) Reset() {}
+
+// Converts string s from UTF-8 to UTF-16-BE, encodes the result as base64,
+// removes the padding, and adds UTF-7 shifts.
+func encode(s []byte) []byte {
+	// len(s) is sufficient for UTF-8 to UTF-16 conversion if there are no
+	// control code points (see table below).
+	b := make([]byte, 0, len(s)+4)
+	for len(s) > 0 {
+		r, size := utf8.DecodeRune(s)
+		if r > utf8.MaxRune {
+			r, size = utf8.RuneError, 1 // Bug fix (issue 3785)
+		}
+		s = s[size:]
+		if r1, r2 := utf16.EncodeRune(r); r1 != repl {
+			b = append(b, byte(r1>>8), byte(r1))
+			r = r2
+		}
+		b = append(b, byte(r>>8), byte(r))
+	}
+
+	// Encode as base64
+	n := enc.EncodedLen(len(b)) + 2
+	b64 := make([]byte, n)
+	enc.Encode(b64[1:], b)
+
+	// Strip padding
+	n -= 2 - (len(b)+2)%3
+	b64 = b64[:n]
+
+	// Add UTF-7 shifts
+	b64[0] = '&'
+	b64[n-1] = '-'
+	return b64
+}