mime: cannot round-trip Word{En,De}coder #14608
Description
WordEncoder sometimes passes text straight through, sometimes it does not. From the example_test.go:
fmt.Println(mime.QEncoding.Encode("utf-8", "¡Hola, señor!"))
fmt.Println(mime.QEncoding.Encode("utf-8", "Hello!"))prints
// Output:
// =?utf-8?q?=C2=A1Hola,_se=C3=B1or!?=
// Hello!
The problem is that, given an arbitrary output of a WordEncoder, how should a user tell whether or not to pass it to a WordDecoder to recover the original? A WD returns an error if the input isn't actually escaped:
func main() {
testCases := []string{
"=?utf-8?q?=C2=A1Hola,_se=C3=B1or!?=",
"Hello!",
}
for _, tc := range testCases {
d := new(mime.WordDecoder)
fmt.Println(d.Decode(tc))
}
}prints
¡Hola, señor! <nil>
mime: invalid RFC 2047 encoded-word
RFC 2047 actually says that Generally, an "encoded-word" is a sequence of printable ASCII characters that begins with "=?", ends with "?=", and has two "?"s in between and, as a workaround, users of the mime package can check that before calling Decode.
Still, this should probably be provided by the library, instead of users of that library. I can think of two possible solutions:
- Add a WordDecoder.CanDecode(string) bool method. The caller should call that before calling Decode.
- Export the existing errInvalidWord as ErrInvalidWord (or as a better name). The caller should check err == mime.ErrInvalidWord after calling Decode.
@bradfitz, WDYT?