[RFC PATCH v2 31/36] transport: add connections for 'features' capability

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

To allow 'git clone' to check the 'features' capability, we need to fill
in some boilerplate methods that help detect if the capability exists
and then to execute the get_recommended_features() method with the
proper context. This involves jumping through some vtables.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 transport-helper.c   | 13 +++++++++++++
 transport-internal.h |  9 +++++++++
 transport.c          | 38 ++++++++++++++++++++++++++++++++++++++
 transport.h          |  5 +++++
 4 files changed, 65 insertions(+)

diff --git a/transport-helper.c b/transport-helper.c
index 398712c76f3..782aa1f43a2 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -1160,6 +1160,18 @@ static int push_refs(struct transport *transport,
 	return -1;
 }
 
+static int get_features(struct transport *transport,
+		      struct string_list *list)
+{
+	get_helper(transport);
+
+	if (process_connect(transport, 0)) {
+		do_take_over(transport);
+		return transport->vtable->get_features(transport, list);
+	}
+
+	return -1;
+}
 
 static int has_attribute(const char *attrs, const char *attr)
 {
@@ -1285,6 +1297,7 @@ static struct transport_vtable vtable = {
 	.get_bundle_uri = get_bundle_uri,
 	.fetch_refs	= fetch_refs,
 	.push_refs	= push_refs,
+	.get_features	= get_features,
 	.connect	= connect_helper,
 	.disconnect	= release_helper
 };
diff --git a/transport-internal.h b/transport-internal.h
index 90ea749e5cf..969cb30f510 100644
--- a/transport-internal.h
+++ b/transport-internal.h
@@ -5,6 +5,7 @@ struct ref;
 struct transport;
 struct strvec;
 struct transport_ls_refs_options;
+struct string_list;
 
 struct transport_vtable {
 	/**
@@ -58,6 +59,14 @@ struct transport_vtable {
 	 * process involved generating new commits.
 	 **/
 	int (*push_refs)(struct transport *transport, struct ref *refs, int flags);
+
+	/**
+	 * get_features() requests a list of recommended features and
+	 * populates the given string_list with those 'key=value' pairs.
+	 */
+	int (*get_features)(struct transport *transport,
+			    struct string_list *list);
+
 	int (*connect)(struct transport *connection, const char *name,
 		       const char *executable, int fd[2]);
 
diff --git a/transport.c b/transport.c
index 7e5e1192f95..42a726dc066 100644
--- a/transport.c
+++ b/transport.c
@@ -205,6 +205,20 @@ struct git_transport_data {
 	struct oid_array shallow;
 };
 
+static int get_features(struct transport *transport,
+		      struct string_list *list)
+{
+	struct git_transport_data *data = transport->data;
+	struct packet_reader reader;
+
+	packet_reader_init(&reader, data->fd[0], NULL, 0,
+			   PACKET_READ_CHOMP_NEWLINE |
+			   PACKET_READ_GENTLE_ON_EOF);
+
+	return get_recommended_features(data->fd[1], &reader, list,
+					transport->stateless_rpc);
+}
+
 static int set_git_option(struct git_transport_options *opts,
 			  const char *name, const char *value)
 {
@@ -948,6 +962,7 @@ static struct transport_vtable taken_over_vtable = {
 	.get_bundle_uri = get_bundle_uri,
 	.fetch_refs	= fetch_refs_via_pack,
 	.push_refs	= git_transport_push,
+	.get_features	= get_features,
 	.disconnect	= disconnect_git
 };
 
@@ -1102,6 +1117,7 @@ static struct transport_vtable builtin_smart_vtable = {
 	.get_bundle_uri = get_bundle_uri,
 	.fetch_refs	= fetch_refs_via_pack,
 	.push_refs	= git_transport_push,
+	.get_features	= get_features,
 	.connect	= connect_git,
 	.disconnect	= disconnect_git
 };
@@ -1606,6 +1622,28 @@ void transport_unlock_pack(struct transport *transport, unsigned int flags)
 		string_list_clear(&transport->pack_lockfiles, 0);
 }
 
+struct string_list *transport_remote_features(struct transport *transport)
+{
+	const struct transport_vtable *vtable = transport->vtable;
+	struct string_list *list = NULL;
+
+	if (!server_supports_v2("features", 0))
+		return NULL;
+
+	if (!vtable->get_features) {
+		warning(_("'features' not supported by this remote"));
+		return NULL;
+	}
+
+	CALLOC_ARRAY(list, 1);
+	string_list_init_dup(list);
+
+	if (vtable->get_features(transport, list))
+		warning(_("failed to get recommended features from remote"));
+
+	return list;
+}
+
 int transport_connect(struct transport *transport, const char *name,
 		      const char *exec, int fd[2])
 {
diff --git a/transport.h b/transport.h
index ed5ebcf1466..7afc02eb683 100644
--- a/transport.h
+++ b/transport.h
@@ -322,6 +322,11 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs);
  */
 void transport_unlock_pack(struct transport *transport, unsigned int flags);
 
+/**
+ * Get recommended config from remote.
+ */
+struct string_list *transport_remote_features(struct transport *transport);
+
 int transport_disconnect(struct transport *transport);
 char *transport_anonymize_url(const char *url);
 void transport_take_over(struct transport *transport,
-- 
2.36.0.rc2.902.g60576bbc845