send-email: rfc2047-quote subject lines with non-ascii characters

We always use 'utf-8' as the encoding, since we currently
have no way of getting the information from the user.

This also refactors the quoting of recipient names, since
both processes can share the rfc2047 quoting code.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -534,6 +534,14 @@ sub expand_aliases {
 		if (!$in_body && /^MIME-Version:/i) {
 			$need_8bit_cte = 0;
 		}
+		if (!$in_body && /^Subject: ?(.*)/i) {
+			my $subject = $1;
+			$_ = "Subject: " .
+				($subject =~ /[^[:ascii:]]/ ?
+				 quote_rfc2047($subject) :
+				 $subject) .
+				"\n";
+		}
 		print C2 $_;
 	}
 	close(C);
@@ -624,6 +632,14 @@ sub unquote_rfc2047 {
 	return wantarray ? ($_, $encoding) : $_;
 }
 
+sub quote_rfc2047 {
+	local $_ = shift;
+	my $encoding = shift || 'utf-8';
+	s/([^-a-zA-Z0-9!*+\/])/sprintf("=%02X", ord($1))/eg;
+	s/(.*)/=\?$encoding\?q\?$1\?=/;
+	return $_;
+}
+
 # use the simplest quoting being able to handle the recipient
 sub sanitize_address
 {
@@ -641,8 +657,7 @@ sub sanitize_address
 
 	# rfc2047 is needed if a non-ascii char is included
 	if ($recipient_name =~ /[^[:ascii:]]/) {
-		$recipient_name =~ s/([^-a-zA-Z0-9!*+\/])/sprintf("=%02X", ord($1))/eg;
-		$recipient_name =~ s/(.*)/=\?utf-8\?q\?$1\?=/;
+		$recipient_name = quote_rfc2047($recipient_name);
 	}
 
 	# double quotes are needed if specials or CTLs are included

t/t9001-send-email.sh

@@ -210,4 +210,19 @@ test_expect_success '--compose respects user mime type' '
 	! grep "^Content-Type: text/plain; charset=utf-8" msgtxt1
 '
 
+test_expect_success '--compose adds MIME for utf8 subject' '
+	clean_fake_sendmail &&
+	echo y | \
+	  GIT_EDITOR=$(pwd)/fake-editor \
+	  GIT_SEND_EMAIL_NOTTY=1 \
+	  git send-email \
+	  --compose --subject utf8-sübjëct \
+	  --from="Example <nobody@example.com>" \
+	  --to=nobody@example.com \
+	  --smtp-server="$(pwd)/fake.sendmail" \
+	  $patches &&
+	grep "^fake edit" msgtxt1 &&
+	grep "^Subject: =?utf-8?q?utf8-s=C3=BCbj=C3=ABct?=" msgtxt1
+'
+
 test_done