connect: also update offset for features without values

parse_feature_value() takes an offset, and uses it to seek past the
point in features_list that we've already seen. However if the feature
being searched for does not specify a value, the offset is not
updated. Therefore if we call parse_feature_value() in a loop on a
value-less feature, we'll keep on parsing the same feature over and over
again. This usually isn't an issue: there's no point in using
next_server_feature_value() to search for repeated instances of the same
capability unless that capability typically specifies a value - but a
broken server could send a response that omits the value for a feature
even when we are expecting a value.

Therefore we add an offset update calculation for the no-value case,
which helps ensure that loops using next_server_feature_value() will
always terminate.

next_server_feature_value(), and the offset calculation, were first
added in 2.28 in 2c6a403d96 (connect: add function to parse multiple
v1 capability values, 2020-05-25).

Thanks to Peff for authoring the test.

Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Andrzej Hunt <andrzej@ahunt.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/connect.c b/connect.c
index 70b13389ba..71e8757e24 100644
--- a/connect.c
+++ b/connect.c
@@ -555,6 +555,8 @@ const char *parse_feature_value(const char *feature_list, const char *feature, i
 			if (!*value || isspace(*value)) {
 				if (lenp)
 					*lenp = 0;
+				if (offset)
+					*offset = found + len - feature_list;
 				return value;
 			}
 			/* feature with a value (e.g., "agent=git/1.2.3") */