add vendoring

vendor/github.com/jhillyerd/enmime/internal/coding/headerext.go

@@ -0,0 +1,135 @@
+package coding
+
+import (
+	"fmt"
+	"io"
+	"mime"
+	"strings"
+)
+
+// NewExtMimeDecoder creates new MIME word decoder which allows decoding of additional charsets.
+func NewExtMimeDecoder() *mime.WordDecoder {
+	return &mime.WordDecoder{
+		CharsetReader: NewCharsetReader,
+	}
+}
+
+// DecodeExtHeader decodes a single line (per RFC 2047, aka Message Header Extensions) using Golang's
+// mime.WordDecoder.
+func DecodeExtHeader(input string) string {
+	if !strings.Contains(input, "=?") {
+		// Don't scan if there is nothing to do here
+		return input
+	}
+
+	header, err := NewExtMimeDecoder().DecodeHeader(input)
+	if err != nil {
+		return input
+	}
+
+	return header
+}
+
+// RFC2047Decode returns a decoded string if the input uses RFC2047 encoding, otherwise it will
+// return the input.
+//
+// RFC2047 Example: `=?UTF-8?B?bmFtZT0iw7DCn8KUwoo=?=`
+func RFC2047Decode(s string) string {
+	// Convert CR/LF to spaces.
+	s = strings.Map(func(r rune) rune {
+		if r == '\n' || r == '\r' {
+			return ' '
+		}
+		return r
+	}, s)
+
+	var err error
+	decoded := false
+	for {
+		s, err = rfc2047Recurse(s)
+		switch err {
+		case nil:
+			decoded = true
+			continue
+
+		default:
+			if decoded {
+				keyValuePair := strings.SplitAfter(s, "=")
+				if len(keyValuePair) < 2 {
+					return s
+				}
+
+				// Add quotes as needed.
+				if !strings.HasPrefix(keyValuePair[1], "\"") {
+					keyValuePair[1] = fmt.Sprintf("\"%s", keyValuePair[1])
+				}
+				if !strings.HasSuffix(keyValuePair[1], "\"") {
+					keyValuePair[1] = fmt.Sprintf("%s\"", keyValuePair[1])
+				}
+
+				return strings.Join(keyValuePair, "")
+			}
+
+			return s
+		}
+	}
+}
+
+// rfc2047Recurse is called for if the value contains content encoded in RFC2047 format and decodes
+// it.
+func rfc2047Recurse(s string) (string, error) {
+	us := strings.ToUpper(s)
+	if !strings.Contains(us, "?Q?") && !strings.Contains(us, "?B?") {
+		return s, io.EOF
+	}
+
+	var val string
+	if val = DecodeExtHeader(s); val == s {
+		if val = DecodeExtHeader(fixRFC2047String(val)); val == s {
+			return val, io.EOF
+		}
+	}
+
+	return val, nil
+}
+
+// fixRFC2047String removes the following characters from charset and encoding segments of an
+// RFC2047 string: '\n', '\r' and ' '
+func fixRFC2047String(s string) string {
+	inString := false
+	isWithinTerminatingEqualSigns := false
+	questionMarkCount := 0
+	sb := &strings.Builder{}
+	for _, v := range s {
+		switch v {
+		case '=':
+			if questionMarkCount == 3 {
+				inString = false
+			} else {
+				isWithinTerminatingEqualSigns = true
+			}
+			sb.WriteRune(v)
+
+		case '?':
+			if isWithinTerminatingEqualSigns {
+				inString = true
+			} else {
+				questionMarkCount++
+			}
+			isWithinTerminatingEqualSigns = false
+			sb.WriteRune(v)
+
+		case '\n', '\r', ' ':
+			if !inString {
+				sb.WriteRune(v)
+			}
+			isWithinTerminatingEqualSigns = false
+
+		default:
+			isWithinTerminatingEqualSigns = false
+			sb.WriteRune(v)
+		}
+	}
+
+	return sb.String()
+}