lib-mail: rfc822-parser: Improve domain-literal parsing

Strip away folding whitespace. Treat any extra '[' as an error.

src/lib-mail/rfc822-parser.c

@@ -312,6 +312,7 @@ static int
 rfc822_parse_domain_literal(struct rfc822_parser_context *ctx, string_t *str)
 {
 	const unsigned char *start;
+	size_t len;
 
 	/*
 	   domain-literal  = [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS]
@@ -324,15 +325,38 @@ rfc822_parse_domain_literal(struct rfc822_parser_context *ctx, string_t *str)
 	i_assert(ctx->data < ctx->end);
 	i_assert(*ctx->data == '[');
 
-	for (start = ctx->data; ctx->data < ctx->end; ctx->data++) {
-		if (*ctx->data == '\\') {
+	for (start = ctx->data++; ctx->data < ctx->end; ctx->data++) {
+		switch (*ctx->data) {
+		case '[':
+			/* not allowed */
+			return -1;
+		case ']':
+			str_append_data(str, start, ctx->data - start + 1);
+			ctx->data++;
+			return rfc822_skip_lwsp(ctx);
+		case '\n':
+			/* folding whitespace, remove the (CR)LF */
+			len = ctx->data - start;
+			if (len > 0 && start[len-1] == '\r')
+				len--;
+			str_append_data(str, start, len);
+			start = ctx->data + 1;
+			break;
+		case '\\':
+			/* note: the '\' is preserved in the output */
 			ctx->data++;
 			if (ctx->data >= ctx->end)
+				return -1;
+
+			if (*ctx->data == '\r' || *ctx->data == '\n') {
+				/* quoted-pair doesn't allow CR/LF.
+				   They are part of the obs-qp though, so don't
+				   return them as error. */
+				str_append_data(str, start, ctx->data - start);
+				start = ctx->data;
+				ctx->data--;
 				break;
-		} else if (*ctx->data == ']') {
-			ctx->data++;
-			str_append_data(str, start, ctx->data - start);
-			return rfc822_skip_lwsp(ctx);
+			}
 		}
 	}
 

src/lib-mail/test-rfc822-parser.c

@@ -41,6 +41,39 @@ static void test_rfc822_parse_quoted_string(void)
 	test_end();
 }
 
+static void test_rfc822_parse_domain_literal(void)
+{
+	static const struct {
+		const char *input, *output;
+		int ret;
+	} tests[] = {
+		{ "@[", "", -1 },
+		{ "@[foo", "", -1 },
+		{ "@[foo[]", "", -1 },
+		{ "@[foo[]]", "", -1 },
+		{ "@[]", "[]", 0 },
+		{ "@[foo bar]", "[foo bar]", 0 },
+		{ "@[foo\n bar]", "[foo bar]", 0 },
+		{ "@[foo\n\t\t bar]", "[foo\t\t bar]", 0 },
+		{ "@[foo\\\n bar]", "[foo\\ bar]", 0 },
+	};
+	struct rfc822_parser_context parser;
+	string_t *str = t_str_new(64);
+	unsigned int i = 0;
+
+	test_begin("rfc822 parse domain literal");
+	for (i = 0; i < N_ELEMENTS(tests); i++) {
+		rfc822_parser_init(&parser, (const void *)tests[i].input,
+				   strlen(tests[i].input), NULL);
+		test_assert_idx(rfc822_parse_domain(&parser, str) == tests[i].ret, i);
+		test_assert_idx(tests[i].ret < 0 ||
+				strcmp(tests[i].output, str_c(str)) == 0, i);
+		rfc822_parser_deinit(&parser);
+		str_truncate(str, 0);
+	}
+	test_end();
+}
+
 static void test_rfc822_parse_content_param(void)
 {
 	const char *input =
@@ -76,6 +109,7 @@ int main(void)
 {
 	static void (*const test_functions[])(void) = {
 		test_rfc822_parse_quoted_string,
+		test_rfc822_parse_domain_literal,
 		test_rfc822_parse_content_param,
 		NULL
 	};