Turn `git serve` into a test helper

The `git serve` built-in was introduced in ed10cb952d31 (serve:
introduce git-serve, 2018-03-15) as a backend to serve Git protocol v2,
probably originally intended to be spawned by `git upload-pack`.

However, in the version that the protocol v2 patches made it into core
Git, `git upload-pack` calls the `serve()` function directly instead of
spawning `git serve`; The only reason in life for `git serve` to survive
as a built-in command is to provide a way to test the protocol v2
functionality.

Meaning that it does not even have to be a built-in that is installed
with end-user facing Git installations, but it can be a test helper
instead.

Let's make it so.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 33 insertions, 0 deletions

diff --git a/t/helper/test-serve-v2.c b/t/helper/test-serve-v2.c
new file mode 100644
index 0000000..aee35e5
--- /dev/null
+++ b/t/helper/test-serve-v2.c
@@ -0,0 +1,31 @@
+#include "test-tool.h"
+#include "cache.h"
+#include "parse-options.h"
+#include "serve.h"
+
+static char const * const serve_usage[] = {
+	N_("test-tool serve-v2 [<options>]"),
+	NULL
+};
+
+int cmd__serve_v2(int argc, const char **argv)
+{
+	struct serve_options opts = SERVE_OPTIONS_INIT;
+
+	struct option options[] = {
+		OPT_BOOL(0, "stateless-rpc", &opts.stateless_rpc,
+			 N_("quit after a single request/response exchange")),
+		OPT_BOOL(0, "advertise-capabilities", &opts.advertise_capabilities,
+			 N_("exit immediately after advertising capabilities")),
+		OPT_END()
+	};
+	const char *prefix = setup_git_directory();
+
+	/* ignore all unknown cmdline switches for now */
+	argc = parse_options(argc, argv, prefix, options, serve_usage,
+			     PARSE_OPT_KEEP_DASHDASH |
+			     PARSE_OPT_KEEP_UNKNOWN);
+	serve(&opts);
+
+	return 0;
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index 2b21943..4bf3666 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -48,6 +48,7 @@ static struct test_cmd cmds[] = {
 	{ "revision-walking", cmd__revision_walking },
 	{ "run-command", cmd__run_command },
 	{ "scrap-cache-tree", cmd__scrap_cache_tree },
+	{ "serve-v2", cmd__serve_v2 },
 	{ "sha1", cmd__sha1 },
 	{ "sha1-array", cmd__sha1_array },
 	{ "sha256", cmd__sha256 },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index 25abed1..bc72370 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -39,6 +39,7 @@ int cmd__repository(int argc, const char **argv);
 int cmd__revision_walking(int argc, const char **argv);
 int cmd__run_command(int argc, const char **argv);
 int cmd__scrap_cache_tree(int argc, const char **argv);
+int cmd__serve_v2(int argc, const char **argv);
 int cmd__sha1(int argc, const char **argv);
 int cmd__sha1_array(int argc, const char **argv);
 int cmd__sha256(int argc, const char **argv);