fetch: send server options when using protocol v2

Teach fetch to optionally accept server options by specifying them on
the cmdline via '-o' or '--server-option'.  These server options are
sent to the remote end when performing a fetch communicating using
protocol version 2.

If communicating using a protocol other than v2 the provided options are
ignored and not sent to the remote end.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/fetch-options.txt

@@ -188,6 +188,14 @@ endif::git-pull[]
 	is specified. This flag forces progress status even if the
 	standard error stream is not directed to a terminal.
 
+-o <option>::
+--server-option=<option>::
+	Transmit the given string to the server when communicating using
+	protocol version 2.  The given string must not contain a NUL or LF
+	character.
+	When multiple `--server-option=<option>` are given, they are all
+	sent to the other side in the order listed on the command line.
+
 -4::
 --ipv4::
 	Use IPv4 addresses only, ignoring IPv6 addresses.

builtin/fetch.c

@@ -62,6 +62,7 @@ static int shown_url = 0;
 static int refmap_alloc, refmap_nr;
 static const char **refmap_array;
 static struct list_objects_filter_options filter_options;
+static struct string_list server_options = STRING_LIST_INIT_DUP;
 
 static int git_fetch_config(const char *k, const char *v, void *cb)
 {
@@ -170,6 +171,7 @@ static struct option builtin_fetch_options[] = {
 		 N_("accept refs that update .git/shallow")),
 	{ OPTION_CALLBACK, 0, "refmap", NULL, N_("refmap"),
 	  N_("specify fetch refmap"), PARSE_OPT_NONEG, parse_refmap_arg },
+	OPT_STRING_LIST('o', "server-option", &server_options, N_("server-specific"), N_("option to transmit")),
 	OPT_SET_INT('4', "ipv4", &family, N_("use IPv4 addresses only"),
 			TRANSPORT_FAMILY_IPV4),
 	OPT_SET_INT('6', "ipv6", &family, N_("use IPv6 addresses only"),
@@ -1417,6 +1419,9 @@ static int fetch_one(struct remote *remote, int argc, const char **argv, int pru
 		}
 	}
 
+	if (server_options.nr)
+		gtransport->server_options = &server_options;
+
 	sigchain_push_common(unlock_pack_on_signal);
 	atexit(unlock_pack);
 	refspec = parse_fetch_refspec(ref_nr, refs);

fetch-pack.c

@@ -1174,6 +1174,13 @@ static int send_fetch_request(int fd_out, const struct fetch_pack_args *args,
 		packet_buf_write(&req_buf, "command=fetch");
 	if (server_supports_v2("agent", 0))
 		packet_buf_write(&req_buf, "agent=%s", git_user_agent_sanitized());
+	if (args->server_options && args->server_options->nr &&
+	    server_supports_v2("server-option", 1)) {
+		int i;
+		for (i = 0; i < args->server_options->nr; i++)
+			packet_write_fmt(fd_out, "server-option=%s",
+					 args->server_options->items[i].string);
+	}
 
 	packet_buf_delim(&req_buf);
 	if (args->use_thin_pack)

fetch-pack.h

@@ -15,6 +15,7 @@ struct fetch_pack_args {
 	const char *deepen_since;
 	const struct string_list *deepen_not;
 	struct list_objects_filter_options filter_options;
+	const struct string_list *server_options;
 	unsigned deepen_relative:1;
 	unsigned quiet:1;
 	unsigned keep_pack:1;

t/t5702-protocol-v2.sh

@@ -217,6 +217,22 @@ test_expect_success 'ref advertisment is filtered during fetch using protocol v2
 	! grep "refs/tags/three" log
 '
 
+test_expect_success 'server-options are sent when fetching' '
+	test_when_finished "rm -f log" &&
+
+	test_commit -C file_parent four &&
+
+	GIT_TRACE_PACKET="$(pwd)/log" git -C file_child -c protocol.version=2 \
+		fetch -o hello -o world origin master &&
+
+	git -C file_child log -1 --format=%s origin/master >actual &&
+	git -C file_parent log -1 --format=%s >expect &&
+	test_cmp expect actual &&
+
+	grep "server-option=hello" log &&
+	grep "server-option=world" log
+'
+
 # Test protocol v2 with 'http://' transport
 #
 . "$TEST_DIRECTORY"/lib-httpd.sh

transport.c

@@ -266,6 +266,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 	args.no_dependents = data->options.no_dependents;
 	args.filter_options = data->options.filter_options;
 	args.stateless_rpc = transport->stateless_rpc;
+	args.server_options = transport->server_options;
 
 	if (!data->got_remote_heads)
 		refs_tmp = get_refs_via_connect(transport, 0, NULL);