pretty: quote rfc822 specials in email addresses

If somebody has a name that includes an rfc822 special, we
will output it literally in the "From:" header. This is
usually OK, but certain characters (like ".") are supposed
to be enclosed in double-quotes in a mail header.

In practice, whether this matters may depend on your MUA.
Some MUAs will happily take in:

   From: Foo B. Bar <author@example.com>

without quotes, and properly quote the "." when they send
the actual mail.  Others may not, or may screw up harder
things like:

  From: Foo "The Baz" Bar <author@example.com>

For example, mutt will strip the quotes, thinking they are
actual syntactic rfc822 quotes.

So let's quote properly, and then (if necessary) we still
apply rfc2047 encoding on top of that, which should make all
MUAs happy.

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

pretty.c

@@ -208,6 +208,58 @@ int has_non_ascii(const char *s)
 	return 0;
 }
 
+static int is_rfc822_special(char ch)
+{
+	switch (ch) {
+	case '(':
+	case ')':
+	case '<':
+	case '>':
+	case '[':
+	case ']':
+	case ':':
+	case ';':
+	case '@':
+	case ',':
+	case '.':
+	case '"':
+	case '\\':
+		return 1;
+	default:
+		return 0;
+	}
+}
+
+static int has_rfc822_specials(const char *s, int len)
+{
+	int i;
+	for (i = 0; i < len; i++)
+		if (is_rfc822_special(s[i]))
+			return 1;
+	return 0;
+}
+
+static void add_rfc822_quoted(struct strbuf *out, const char *s, int len)
+{
+	int i;
+
+	/* just a guess, we may have to also backslash-quote */
+	strbuf_grow(out, len + 2);
+
+	strbuf_addch(out, '"');
+	for (i = 0; i < len; i++) {
+		switch (s[i]) {
+		case '"':
+		case '\\':
+			strbuf_addch(out, '\\');
+			/* fall through */
+		default:
+			strbuf_addch(out, s[i]);
+		}
+	}
+	strbuf_addch(out, '"');
+}
+
 static int is_rfc2047_special(char ch)
 {
 	return (non_ascii(ch) || (ch == '=') || (ch == '?') || (ch == '_'));
@@ -293,7 +345,14 @@ void pp_user_info(const char *what, enum cmit_fmt fmt, struct strbuf *sb,
 			name_tail--;
 		display_name_length = name_tail - line;
 		strbuf_addstr(sb, "From: ");
-		add_rfc2047(sb, line, display_name_length, encoding);
+		if (!has_rfc822_specials(line, display_name_length)) {
+			add_rfc2047(sb, line, display_name_length, encoding);
+		} else {
+			struct strbuf quoted = STRBUF_INIT;
+			add_rfc822_quoted(&quoted, line, display_name_length);
+			add_rfc2047(sb, quoted.buf, quoted.len, encoding);
+			strbuf_release(&quoted);
+		}
 		strbuf_add(sb, name_tail, namelen - display_name_length);
 		strbuf_addch(sb, '\n');
 	} else {

t/t4014-format-patch.sh

@@ -793,4 +793,46 @@ test_expect_success 'format-patch wraps extremely long headers (rfc2047)' '
 	test_cmp expect subject
 '
 
+check_author() {
+	echo content >>file &&
+	git add file &&
+	GIT_AUTHOR_NAME=$1 git commit -m author-check &&
+	git format-patch --stdout -1 >patch &&
+	grep ^From: patch >actual &&
+	test_cmp expect actual
+}
+
+cat >expect <<'EOF'
+From: "Foo B. Bar" <author@example.com>
+EOF
+test_expect_success 'format-patch quotes dot in headers' '
+	check_author "Foo B. Bar"
+'
+
+cat >expect <<'EOF'
+From: "Foo \"The Baz\" Bar" <author@example.com>
+EOF
+test_expect_success 'format-patch quotes double-quote in headers' '
+	check_author "Foo \"The Baz\" Bar"
+'
+
+cat >expect <<'EOF'
+From: =?UTF-8?q?"F=C3=B6o=20B.=20Bar"?= <author@example.com>
+EOF
+test_expect_success 'rfc2047-encoded headers also double-quote 822 specials' '
+	check_author "Föo B. Bar"
+'
+
+cat >expect <<'EOF'
+Subject: header with . in it
+EOF
+test_expect_success 'subject lines do not have 822 atom-quoting' '
+	echo content >>file &&
+	git add file &&
+	git commit -m "header with . in it" &&
+	git format-patch -k -1 --stdout >patch &&
+	grep ^Subject: patch >actual &&
+	test_cmp expect actual
+'
+
 test_done