Re: [PATCH] send-email: handle adjacent RFC 2047-encoded words properly

[Jeff King <peff@peff.net>]

On Mon, Nov 24, 2014 at 02:50:04AM +0300, Роман Донченко wrote:

> The RFC says that they are to be concatenated after decoding (i.e. the
> intervening whitespace is ignored).
> 
> I change the sender's name to an all-Cyrillic string in the tests so that
> its encoded form goes over the 76 characters in a line limit, forcing
> format-patch to split it into multiple encoded words.
> 
> Since I have to modify the regular expression for an encoded word anyway,
> I take the opportunity to bring it closer to the spec, most notably
> disallowing embedded spaces and making it case-insensitive (thus allowing
> the encoding to be specified as both "q" and "Q").

The overall goal makes sense to me. Thanks for working on this. I have a
few questions/comments, though.

>  sub unquote_rfc2047 {
>  	local ($_) = @_;
> +
> +	my $et = qr/[!->@-~]+/; # encoded-text from RFC 2047
> +	my $sep = qr/[ \t]+/;
> +	my $encoded_word = qr/=\?($et)\?q\?($et)\?=/i;

The first $et in $encoded_word is actually the charset, which is defined
by RFC 2047 as:

     charset = token    ; see section 3

     token = 1*<Any CHAR except SPACE, CTLs, and especials>

     especials = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "
	               <"> / "/" / "[" / "]" / "?" / "." / "="

Your regex is a little more liberal. I doubt that it is a big deal in
practice (actually, in practice, I suspect [a-zA-Z0-9-] would be fine).
But if we are tightening things up in general, it may make sense to do
so here (and I notice that is_rfc2047_quoted does a more thorough $token
definition, and it probably makes sense for the two functions to be
consistent).

For your definition of encoded-text, RFC 2047 says:

     encoded-text = 1*<Any printable ASCII character other than "?"
                          or SPACE>

It looks like you pulled the definition of $et from is_rfc2047_quoted,
but I am not clear on where that original came from (it is from a3a8262,
but that commit message does not explain the regex).

Also, I note that we handle 'q'-style encodings here, but not 'b'. I
wonder if it is worth adding that in while we are in the area (it is not
a big deal if you always send-email git-generated patches, as we never
generate it).

> +	s{$encoded_word(?:$sep$encoded_word)+}{

If I am reading this right, it requires at least two $encoded_words.
Should this "+" be a "*"?

> +		my @words = split $sep, $&;
> +		foreach (@words) {
> +			m/$encoded_word/;
> +			$encoding = $1;
> +			$_ = $2;
> +			s/_/ /g;
> +			s/=([0-9A-F]{2})/chr(hex($1))/eg;

In the spirit of your earlier change, should this final regex be
case-insensitive? RFC 2047 says only "Upper case should be used for
hexadecimal digits "A" through "F." but that does not seem like a "MUST"
to me.

-Peff