Merge branch 'bc/clone-empty-repo-via-protocol-v0'

The server side of "git clone" now advertises the necessary hints
to clients to help them to clone from an empty repository and learn
object hash algorithm and the (unborn) branch pointed at by HEAD,
even over the older v0/v1 protocol.

* bc/clone-empty-repo-via-protocol-v0:
  upload-pack: advertise capabilities when cloning empty repos

Author: gitster

t/t5551-http-fetch-smart.sh

@@ -611,6 +611,33 @@ test_expect_success 'client falls back from v2 to v0 to match server' '
 	grep symref=HEAD:refs/heads/ trace
 '
 
+test_expect_success 'create empty http-accessible SHA-256 repository' '
+	mkdir "$HTTPD_DOCUMENT_ROOT_PATH/sha256.git" &&
+	(cd "$HTTPD_DOCUMENT_ROOT_PATH/sha256.git" &&
+	 git --bare init --object-format=sha256
+	)
+'
+
+test_expect_success 'clone empty SHA-256 repository with protocol v2' '
+	rm -fr sha256 &&
+	echo sha256 >expected &&
+	git -c protocol.version=2 clone "$HTTPD_URL/smart/sha256.git" &&
+	git -C sha256 rev-parse --show-object-format >actual &&
+	test_cmp actual expected &&
+	git ls-remote "$HTTPD_URL/smart/sha256.git" >actual &&
+	test_must_be_empty actual
+'
+
+test_expect_success 'clone empty SHA-256 repository with protocol v0' '
+	rm -fr sha256 &&
+	echo sha256 >expected &&
+	GIT_TRACE=1 GIT_TRACE_PACKET=1 git -c protocol.version=0 clone "$HTTPD_URL/smart/sha256.git" &&
+	git -C sha256 rev-parse --show-object-format >actual &&
+	test_cmp actual expected &&
+	git ls-remote "$HTTPD_URL/smart/sha256.git" >actual &&
+	test_must_be_empty actual
+'
+
 test_expect_success 'passing hostname resolution information works' '
 	BOGUS_HOST=gitbogusexamplehost.invalid &&
 	BOGUS_HTTPD_URL=$HTTPD_PROTO://$BOGUS_HOST:$LIB_HTTPD_PORT &&

t/t5700-protocol-v1.sh

@@ -244,15 +244,28 @@ test_expect_success 'push with ssh:// using protocol v1' '
 	grep "push< version 1" log
 '
 
+test_expect_success 'clone propagates object-format from empty repo' '
+	test_when_finished "rm -fr src256 dst256" &&
+
+	echo sha256 >expect &&
+	git init --object-format=sha256 src256 &&
+	git clone --no-local src256 dst256 &&
+	git -C dst256 rev-parse --show-object-format >actual &&
+
+	test_cmp expect actual
+'
+
 # Test protocol v1 with 'http://' transport
 #
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd
 
-test_expect_success 'create repo to be served by http:// transport' '
+test_expect_success 'create repos to be served by http:// transport' '
 	git init "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
 	git -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" config http.receivepack true &&
-	test_commit -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" one
+	test_commit -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" one &&
+	git init --object-format=sha256 "$HTTPD_DOCUMENT_ROOT_PATH/sha256" &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/sha256" config http.receivepack true
 '
 
 test_expect_success 'clone with http:// using protocol v1' '
@@ -269,6 +282,20 @@ test_expect_success 'clone with http:// using protocol v1' '
 	grep "git< version 1" log
 '
 
+test_expect_success 'clone with http:// using protocol v1 with empty SHA-256 repo' '
+	GIT_TRACE_PACKET=1 GIT_TRACE_CURL=1 git -c protocol.version=1 \
+		clone "$HTTPD_URL/smart/sha256" sha256 2>log &&
+
+	echo sha256 >expect &&
+	git -C sha256 rev-parse --show-object-format >actual &&
+	test_cmp expect actual &&
+
+	# Client requested to use protocol v1
+	grep "Git-Protocol: version=1" log &&
+	# Server responded using protocol v1
+	grep "git< version 1" log
+'
+
 test_expect_success 'fetch with http:// using protocol v1' '
 	test_commit -C "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" two &&
 

upload-pack.c

@@ -120,6 +120,7 @@ struct upload_pack_data {
 	unsigned allow_ref_in_want : 1;				/* v2 only */
 	unsigned allow_sideband_all : 1;			/* v2 only */
 	unsigned advertise_sid : 1;
+	unsigned sent_capabilities : 1;
 };
 
 static void upload_pack_data_init(struct upload_pack_data *data)
@@ -1206,18 +1207,17 @@ static void format_session_id(struct strbuf *buf, struct upload_pack_data *d) {
 		strbuf_addf(buf, " session-id=%s", trace2_session_id());
 }
 
-static int send_ref(const char *refname, const struct object_id *oid,
-		    int flag UNUSED, void *cb_data)
+static void write_v0_ref(struct upload_pack_data *data,
+			const char *refname, const char *refname_nons,
+			const struct object_id *oid)
 {
 	static const char *capabilities = "multi_ack thin-pack side-band"
 		" side-band-64k ofs-delta shallow deepen-since deepen-not"
 		" deepen-relative no-progress include-tag multi_ack_detailed";
-	const char *refname_nons = strip_namespace(refname);
 	struct object_id peeled;
-	struct upload_pack_data *data = cb_data;
 
 	if (mark_our_ref(refname_nons, refname, oid, &data->hidden_refs))
-		return 0;
+		return;
 
 	if (capabilities) {
 		struct strbuf symref_info = STRBUF_INIT;
@@ -1240,12 +1240,20 @@ static int send_ref(const char *refname, const struct object_id *oid,
 			     git_user_agent_sanitized());
 		strbuf_release(&symref_info);
 		strbuf_release(&session_id);
+		data->sent_capabilities = 1;
 	} else {
 		packet_fwrite_fmt(stdout, "%s %s\n", oid_to_hex(oid), refname_nons);
 	}
 	capabilities = NULL;
 	if (!peel_iterated_oid(oid, &peeled))
 		packet_fwrite_fmt(stdout, "%s %s^{}\n", oid_to_hex(&peeled), refname_nons);
+	return;
+}
+
+static int send_ref(const char *refname, const struct object_id *oid,
+		    int flag UNUSED, void *cb_data)
+{
+	write_v0_ref(cb_data, refname, strip_namespace(refname), oid);
 	return 0;
 }
 
@@ -1379,6 +1387,10 @@ void upload_pack(const int advertise_refs, const int stateless_rpc,
 			data.no_done = 1;
 		head_ref_namespaced(send_ref, &data);
 		for_each_namespaced_ref(send_ref, &data);
+		if (!data.sent_capabilities) {
+			const char *refname = "capabilities^{}";
+			write_v0_ref(&data, refname, refname, null_oid());
+		}
 		/*
 		 * fflush stdout before calling advertise_shallow_grafts because send_ref
 		 * uses stdio.