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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)
}
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