mox!

imapserver/utf7.go

@@ -0,0 +1,83 @@
+package imapserver
+
+import (
+	"encoding/base64"
+	"errors"
+	"fmt"
+)
+
+const utf7chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,"
+
+var utf7encoding = base64.NewEncoding(utf7chars).WithPadding(base64.NoPadding)
+
+var (
+	errUTF7SuperfluousShift = errors.New("utf7: superfluous unshift+shift")
+	errUTF7Base64           = errors.New("utf7: bad base64")
+	errUTF7OddSized         = errors.New("utf7: odd-sized data")
+	errUTF7UnneededShift    = errors.New("utf7: unneeded shift")
+	errUTF7UnfinishedShift  = errors.New("utf7: unfinished shift")
+)
+
+func utf7decode(s string) (string, error) {
+	var r string
+	var shifted bool
+	var b string
+	lastunshift := -2
+
+	for i, c := range s {
+		if !shifted {
+			if c == '&' {
+				if lastunshift == i-1 {
+					return "", errUTF7SuperfluousShift
+				}
+				shifted = true
+			} else {
+				r += string(c)
+			}
+			continue
+		}
+
+		if c != '-' {
+			b += string(c)
+			continue
+		}
+
+		shifted = false
+		lastunshift = i
+		if b == "" {
+			r += "&"
+			continue
+		}
+		buf, err := utf7encoding.DecodeString(b)
+		if err != nil {
+			return "", fmt.Errorf("%w: %q: %v", errUTF7Base64, b, err)
+		}
+		b = ""
+
+		if len(buf)%2 != 0 {
+			return "", errUTF7OddSized
+		}
+
+		x := make([]rune, len(buf)/2)
+		j := 0
+		for i := 0; i < len(buf); i += 2 {
+			x[j] = rune(buf[i])<<8 | rune(buf[i+1])
+			j++
+		}
+
+		need := false
+		for _, c := range x {
+			if c < 0x20 || c > 0x7e || c == '&' {
+				need = true
+			}
+			r += string(c)
+		}
+		if !need {
+			return "", errUTF7UnneededShift
+		}
+	}
+	if shifted {
+		return "", errUTF7UnfinishedShift
+	}
+	return r, nil
+}