Initialize module and dependencies

vendor/github.com/emersion/go-message/charset.go

@@ -0,0 +1,66 @@
+package message
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"mime"
+	"strings"
+)
+
+type UnknownCharsetError struct {
+	e error
+}
+
+func (u UnknownCharsetError) Unwrap() error { return u.e }
+
+func (u UnknownCharsetError) Error() string {
+	return "unknown charset: " + u.e.Error()
+}
+
+// IsUnknownCharset returns a boolean indicating whether the error is known to
+// report that the charset advertised by the entity is unknown.
+func IsUnknownCharset(err error) bool {
+	return errors.As(err, new(UnknownCharsetError))
+}
+
+// CharsetReader, if non-nil, defines a function to generate charset-conversion
+// readers, converting from the provided charset into UTF-8. Charsets are always
+// lower-case. utf-8 and us-ascii charsets are handled by default. One of the
+// the CharsetReader's result values must be non-nil.
+//
+// Importing github.com/emersion/go-message/charset will set CharsetReader to
+// a function that handles most common charsets. Alternatively, CharsetReader
+// can be set to e.g. golang.org/x/net/html/charset.NewReaderLabel.
+var CharsetReader func(charset string, input io.Reader) (io.Reader, error)
+
+// charsetReader calls CharsetReader if non-nil.
+func charsetReader(charset string, input io.Reader) (io.Reader, error) {
+	charset = strings.ToLower(charset)
+	if charset == "utf-8" || charset == "us-ascii" {
+		return input, nil
+	}
+	if CharsetReader != nil {
+		r, err := CharsetReader(charset, input)
+		if err != nil {
+			return r, UnknownCharsetError{err}
+		}
+		return r, nil
+	}
+	return input, UnknownCharsetError{fmt.Errorf("message: unhandled charset %q", charset)}
+}
+
+// decodeHeader decodes an internationalized header field. If it fails, it
+// returns the input string and the error.
+func decodeHeader(s string) (string, error) {
+	wordDecoder := mime.WordDecoder{CharsetReader: charsetReader}
+	dec, err := wordDecoder.DecodeHeader(s)
+	if err != nil {
+		return s, err
+	}
+	return dec, nil
+}
+
+func encodeHeader(s string) string {
+	return mime.QEncoding.Encode("utf-8", s)
+}