serve: introduce the server-option capability

Introduce the "server-option" capability to protocol version 2.  This
enables future clients the ability to send server specific options in
command requests when using protocol version 2.

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

Documentation/technical/protocol-v2.txt

@@ -393,3 +393,13 @@ header.
 		1 - pack data
 		2 - progress messages
 		3 - fatal error message just before stream aborts
+
+ server-option
+~~~~~~~~~~~~~~~
+
+If advertised, indicates that any number of server specific options can be
+included in a request.  This is done by sending each option as a
+"server-option=<option>" capability line in the capability-list section of
+a request.
+
+The provided options must not contain a NUL or LF character.

serve.c

@@ -56,6 +56,7 @@ static struct protocol_capability capabilities[] = {
 	{ "agent", agent_advertise, NULL },
 	{ "ls-refs", always_advertise, ls_refs },
 	{ "fetch", upload_pack_advertise, upload_pack_v2 },
+	{ "server-option", always_advertise, NULL },
 };
 
 static void advertise_capabilities(void)

t/t5701-git-serve.sh

@@ -10,6 +10,7 @@ test_expect_success 'test capability advertisement' '
 	agent=git/$(git version | cut -d" " -f3)
 	ls-refs
 	fetch=shallow
+	server-option
 	0000
 	EOF
 
@@ -173,4 +174,24 @@ test_expect_success 'symrefs parameter' '
 	test_cmp actual expect
 '
 
+test_expect_success 'sending server-options' '
+	test-pkt-line pack >in <<-EOF &&
+	command=ls-refs
+	server-option=hello
+	server-option=world
+	0001
+	ref-prefix HEAD
+	0000
+	EOF
+
+	cat >expect <<-EOF &&
+	$(git rev-parse HEAD) HEAD
+	0000
+	EOF
+
+	git serve --stateless-rpc <in >out &&
+	test-pkt-line unpack <out >actual &&
+	test_cmp actual expect
+'
+
 test_done