[PATCH 16/24] protocol v2: add server-side "bundle-uri" skeleton

["Ævar Arnfjörð Bjarmason via GitGitGadget" <gitgitgadget@gmail.com>]

From: =?UTF-8?q?=C3=86var=20Arnfj=C3=B6r=C3=B0=20Bjarmason?=
 <avarab@gmail.com>

Add a skeleton server-side implementation of a new "bundle-uri" command
to protocol v2. This will allow conforming clients to optionally seed
their initial clones or incremental fetches from URLs containing
"*.bundle" files created with "git bundle create".

This change only performs the basic boilerplate of advertising a new
protocol v2 capability. The new 'bundle-uri' capability allows a client
to request a list of bundles. Right now, the server only returns a flush
packet, which corresponds to an empty advertisement.

The critical bit right now is that the new boolean
uploadPack.adverstiseBundleURIs config value signals whether or not this
capability should be advertised at all.

RFC TODO: Write documentation.

RFC TODO: Compare to original implementation.

Co-authored-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
---
 bundle-uri.c         | 36 ++++++++++++++++++++++++++++++++++++
 bundle-uri.h         |  7 +++++++
 serve.c              |  6 ++++++
 t/t5701-git-serve.sh | 40 +++++++++++++++++++++++++++++++++++++++-
 4 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/bundle-uri.c b/bundle-uri.c
index 601e6e87822..79a6b7ed8b8 100644
--- a/bundle-uri.c
+++ b/bundle-uri.c
@@ -557,6 +557,42 @@ cleanup:
 	return result;
 }
 
+/**
+ * API for serve.c.
+ */
+
+static int advertise_bundle_uri = -1;
+
+int bundle_uri_advertise(struct repository *r, struct strbuf *value)
+{
+	if (advertise_bundle_uri != -1)
+		goto cached;
+
+	advertise_bundle_uri = 0;
+	git_config_get_maybe_bool("uploadpack.advertisebundleuris", &advertise_bundle_uri);
+
+cached:
+	return advertise_bundle_uri;
+}
+
+int bundle_uri_command(struct repository *r,
+		       struct packet_reader *request)
+{
+	struct packet_writer writer;
+	packet_writer_init(&writer, 1);
+
+	while (packet_reader_read(request) == PACKET_READ_NORMAL)
+		die(_("bundle-uri: unexpected argument: '%s'"), request->line);
+	if (request->status != PACKET_READ_FLUSH)
+		die(_("bundle-uri: expected flush after arguments"));
+
+	/* TODO: Implement the communication */
+
+	packet_writer_flush(&writer);
+
+	return 0;
+}
+
 /**
  * General API for {transport,connect}.c etc.
  */
diff --git a/bundle-uri.h b/bundle-uri.h
index adce5dc07e2..9f6fc2d75f9 100644
--- a/bundle-uri.h
+++ b/bundle-uri.h
@@ -4,6 +4,7 @@
 #include "hashmap.h"
 #include "strbuf.h"
 
+struct packet_reader;
 struct repository;
 struct strbuf;
 struct string_list;
@@ -97,6 +98,12 @@ int parse_bundle_list_in_config_format(const char *uri,
  */
 int fetch_bundle_uri(struct repository *r, const char *uri);
 
+/**
+ * API for serve.c.
+ */
+int bundle_uri_advertise(struct repository *r, struct strbuf *value);
+int bundle_uri_command(struct repository *r, struct packet_reader *request);
+
 /**
  * General API for {transport,connect}.c etc.
  */
diff --git a/serve.c b/serve.c
index b3fe9b5126a..f3e0203d2c6 100644
--- a/serve.c
+++ b/serve.c
@@ -8,6 +8,7 @@
 #include "protocol-caps.h"
 #include "serve.h"
 #include "upload-pack.h"
+#include "bundle-uri.h"
 
 static int advertise_sid = -1;
 static int client_hash_algo = GIT_HASH_SHA1;
@@ -136,6 +137,11 @@ static struct protocol_capability capabilities[] = {
 		.advertise = always_advertise,
 		.command = cap_object_info,
 	},
+	{
+		.name = "bundle-uri",
+		.advertise = bundle_uri_advertise,
+		.command = bundle_uri_command,
+	},
 };
 
 void protocol_v2_advertise_capabilities(void)
diff --git a/t/t5701-git-serve.sh b/t/t5701-git-serve.sh
index 1896f671cb3..f21e5e9d33d 100755
--- a/t/t5701-git-serve.sh
+++ b/t/t5701-git-serve.sh
@@ -13,7 +13,7 @@ test_expect_success 'test capability advertisement' '
 	wrong_algo sha1:sha256
 	wrong_algo sha256:sha1
 	EOF
-	cat >expect <<-EOF &&
+	cat >expect.base <<-EOF &&
 	version 2
 	agent=git/$(git version | cut -d" " -f3)
 	ls-refs=unborn
@@ -21,8 +21,11 @@ test_expect_success 'test capability advertisement' '
 	server-option
 	object-format=$(test_oid algo)
 	object-info
+	EOF
+	cat >expect.trailer <<-EOF &&
 	0000
 	EOF
+	cat expect.base expect.trailer >expect &&
 
 	GIT_TEST_SIDEBAND_ALL=0 test-tool serve-v2 \
 		--advertise-capabilities >out &&
@@ -342,4 +345,39 @@ test_expect_success 'basics of object-info' '
 	test_cmp expect actual
 '
 
+test_expect_success 'test capability advertisement with uploadpack.advertiseBundleURIs' '
+	test_config uploadpack.advertiseBundleURIs true &&
+
+	cat >expect.extra <<-EOF &&
+	bundle-uri
+	EOF
+	cat expect.base \
+	    expect.extra \
+	    expect.trailer >expect &&
+
+	GIT_TEST_SIDEBAND_ALL=0 test-tool serve-v2 \
+		--advertise-capabilities >out &&
+	test-tool pkt-line unpack <out >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'basics of bundle-uri: dies if not enabled' '
+	test-tool pkt-line pack >in <<-EOF &&
+	command=bundle-uri
+	0000
+	EOF
+
+	cat >err.expect <<-\EOF &&
+	fatal: invalid command '"'"'bundle-uri'"'"'
+	EOF
+
+	cat >expect <<-\EOF &&
+	ERR serve: invalid command '"'"'bundle-uri'"'"'
+	EOF
+
+	test_must_fail test-tool serve-v2 --stateless-rpc <in >out 2>err.actual &&
+	test_cmp err.expect err.actual &&
+	test_must_be_empty out
+'
+
 test_done
-- 
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