[PATCH 21/25] serve: advertise 'features' when config exists

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <derrickstolee@github.com>

The 'features' capability allows a server to recommend some Git features
at a high level. Previous changes implemented the capability so servers
understand it, but it was never advertised.

Now, allow it to be advertised, but only when the capability will
actually _do_ something. That is, advertise if and only if a config
value exists with the prefix "serve.". This avoids unnecessary round
trips for an empty result.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 serve.c              | 18 +++++++++++++++---
 t/t5701-git-serve.sh |  9 +++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/serve.c b/serve.c
index a1c853dda1f..7dcabb68147 100644
--- a/serve.c
+++ b/serve.c
@@ -18,12 +18,24 @@ static int always_advertise(struct repository *r,
 	return 1;
 }
 
-static int never_advertise(struct repository *r,
-			   struct strbuf *value)
+static int key_serve_prefix(const char *key, const char *value, void *data)
 {
+	int *signal = data;
+	if (!strncmp(key, "serve.", 6)) {
+		*signal = 1;
+		return 1;
+	}
 	return 0;
 }
 
+static int has_serve_config(struct repository *r,
+			    struct strbuf *value)
+{
+	int signal = 0;
+	repo_config(r, key_serve_prefix, &signal);
+	return signal;
+}
+
 static int agent_advertise(struct repository *r,
 			   struct strbuf *value)
 {
@@ -144,7 +156,7 @@ static struct protocol_capability capabilities[] = {
 	},
 	{
 		.name = "features",
-		.advertise = never_advertise,
+		.advertise = has_serve_config,
 		.command = cap_features,
 	},
 };
diff --git a/t/t5701-git-serve.sh b/t/t5701-git-serve.sh
index 1896f671cb3..6ef721c3f97 100755
--- a/t/t5701-git-serve.sh
+++ b/t/t5701-git-serve.sh
@@ -30,6 +30,15 @@ test_expect_success 'test capability advertisement' '
 	test_cmp expect actual
 '
 
+test_expect_success 'test capability advertisement' '
+	test_when_finished git config --unset serve.bundleuri &&
+	git config serve.bundleuri "file://$(pwd)" &&
+	GIT_TEST_SIDEBAND_ALL=0 test-tool serve-v2 \
+		--advertise-capabilities >out &&
+	test-tool pkt-line unpack <out >actual &&
+	grep features actual
+'
+
 test_expect_success 'stateless-rpc flag does not list capabilities' '
 	# Empty request
 	test-tool pkt-line pack >in <<-EOF &&
-- 
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