58 lines
1.7 KiB
Go
58 lines
1.7 KiB
Go
package message
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import (
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"fmt"
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"io"
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"mime"
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"strings"
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)
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type unknownCharsetError struct {
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error
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}
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// IsUnknownCharset returns a boolean indicating whether the error is known to
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// report that the charset advertised by the entity is unknown.
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func IsUnknownCharset(err error) bool {
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_, ok := err.(unknownCharsetError)
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return ok
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}
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// CharsetReader, if non-nil, defines a function to generate charset-conversion
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// readers, converting from the provided charset into UTF-8. Charsets are always
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// lower-case. utf-8 and us-ascii charsets are handled by default. One of the
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// the CharsetReader's result values must be non-nil.
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//
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// Importing github.com/emersion/go-message/charset will set CharsetReader to
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// a function that handles most common charsets. Alternatively, CharsetReader
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// can be set to e.g. golang.org/x/net/html/charset.NewReaderLabel.
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var CharsetReader func(charset string, input io.Reader) (io.Reader, error)
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// charsetReader calls CharsetReader if non-nil.
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func charsetReader(charset string, input io.Reader) (io.Reader, error) {
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charset = strings.ToLower(charset)
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// "ascii" is not in the spec but is common
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if charset == "utf-8" || charset == "us-ascii" || charset == "ascii" {
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return input, nil
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}
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if CharsetReader != nil {
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return CharsetReader(charset, input)
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}
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return input, fmt.Errorf("message: unhandled charset %q", charset)
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}
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// decodeHeader decodes an internationalized header field. If it fails, it
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// returns the input string and the error.
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func decodeHeader(s string) (string, error) {
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wordDecoder := mime.WordDecoder{CharsetReader: charsetReader}
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dec, err := wordDecoder.DecodeHeader(s)
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if err != nil {
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return s, err
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}
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return dec, nil
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}
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func encodeHeader(s string) string {
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return mime.QEncoding.Encode("utf-8", s)
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}
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