parse_feature_request: make it easier to see feature values

We already take care to parse key/value capabilities like
"foo=bar", but the code does not provide a good way of
actually finding out what is on the right-hand side of the
"=".

A server using "parse_feature_request" could accomplish this
with some extra parsing. You must skip past the "key"
portion manually, check for "=" versus NUL or space, and
then find the length by searching for the next space (or
NUL).  But clients can't even do that, since the
"server_supports" interface does not even return the
pointer.

Instead, let's have our parser share more information by
providing a pointer to the value and its length. The
"parse_feature_value" function returns a pointer to the
feature's value portion, along with the length of the value.
If the feature is missing, NULL is returned. If it does not
have an "=", then a zero-length value is returned.

Similarly, "server_feature_value" behaves in the same way,
but always checks the static server_feature_list variable.

We can then implement "server_supports" in terms of
"server_feature_value". We cannot implement the original
"parse_feature_request" in terms of our new function,
because it returned a pointer to the beginning of the
feature. However, no callers actually cared about the value
of the returned pointer, so we can simplify it to a boolean
just as we do for "server_supports".

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

1 files changed, 3 insertions, 1 deletions

diff --git a/cache.h b/cache.h
index 06413e1584..b71b0650f4 100644
--- a/cache.h
+++ b/cache.h
@@ -1030,7 +1030,9 @@ struct extra_have_objects {
 };
 extern struct ref **get_remote_heads(int in, struct ref **list, unsigned int flags, struct extra_have_objects *);
 extern int server_supports(const char *feature);
-extern const char *parse_feature_request(const char *features, const char *feature);
+extern int parse_feature_request(const char *features, const char *feature);
+extern const char *server_feature_value(const char *feature, int *len_ret);
+extern const char *parse_feature_value(const char *feature_list, const char *feature, int *len_ret);
 
 extern struct packed_git *parse_pack_index(unsigned char *sha1, const char *idx_path);