fetch: teach independent negotiation (no packfile)

Currently, the packfile negotiation step within a Git fetch cannot be
done independent of sending the packfile, even though there is at least
one application wherein this is useful. Therefore, make it possible for
this negotiation step to be done independently. A subsequent commit will
use this for one such application - push negotiation.

This feature is for protocol v2 only. (An implementation for protocol v0
would require a separate implementation in the fetch, transport, and
transport helper code.)

In the protocol, the main hindrance towards independent negotiation is
that the server can unilaterally decide to send the packfile. This is
solved by a "wait-for-done" argument: the server will then wait for the
client to say "done". In practice, the client will never say it; instead
it will cease requests once it is satisfied.

In the client, the main change lies in the transport and transport
helper code. fetch_refs_via_pack() performs everything needed - protocol
version and capability checks, and the negotiation itself.

There are 2 code paths that do not go through fetch_refs_via_pack() that
needed to be individually excluded: the bundle transport (excluded
through requiring smart_options, which the bundle transport doesn't
support) and transport helpers that do not support takeover. If or when
we support independent negotiation for protocol v0, we will need to
modify these 2 code paths to support it. But for now, report failure if
independent negotiation is requested in these cases.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 90 insertions, 1 deletions

diff --git a/t/t5701-git-serve.sh b/t/t5701-git-serve.sh
index 509f379d49..f03bb04803 100755
--- a/t/t5701-git-serve.sh
+++ b/t/t5701-git-serve.sh
@@ -16,7 +16,7 @@ test_expect_success 'test capability advertisement' '
 	version 2
 	agent=git/$(git version | cut -d" " -f3)
 	ls-refs=unborn
-	fetch=shallow
+	fetch=shallow wait-for-done
 	server-option
 	object-format=$(test_oid algo)
 	0000
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 2e1243ca40..66af411057 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -585,6 +585,49 @@ test_expect_success 'deepen-relative' '
 	test_cmp expected actual
 '
 
+setup_negotiate_only () {
+	SERVER="$1"
+	URI="$2"
+
+	rm -rf "$SERVER" client
+
+	git init "$SERVER"
+	test_commit -C "$SERVER" one
+	test_commit -C "$SERVER" two
+
+	git clone "$URI" client
+	test_commit -C client three
+}
+
+test_expect_success 'file:// --negotiate-only' '
+	SERVER="server" &&
+	URI="file://$(pwd)/server" &&
+
+	setup_negotiate_only "$SERVER" "$URI" &&
+
+	git -c protocol.version=2 -C client fetch \
+		--no-tags \
+		--negotiate-only \
+		--negotiation-tip=$(git -C client rev-parse HEAD) \
+		origin >out &&
+	COMMON=$(git -C "$SERVER" rev-parse two) &&
+	grep "$COMMON" out
+'
+
+test_expect_success 'file:// --negotiate-only with protocol v0' '
+	SERVER="server" &&
+	URI="file://$(pwd)/server" &&
+
+	setup_negotiate_only "$SERVER" "$URI" &&
+
+	test_must_fail git -c protocol.version=0 -C client fetch \
+		--no-tags \
+		--negotiate-only \
+		--negotiation-tip=$(git -C client rev-parse HEAD) \
+		origin 2>err &&
+	test_i18ngrep "negotiate-only requires protocol v2" err
+'
+
 # Test protocol v2 with 'http://' transport
 #
 . "$TEST_DIRECTORY"/lib-httpd.sh
@@ -1035,6 +1078,52 @@ test_expect_success 'packfile-uri with transfer.fsckobjects fails when .gitmodul
 	test_i18ngrep "disallowed submodule name" err
 '
 
+test_expect_success 'http:// --negotiate-only' '
+	SERVER="$HTTPD_DOCUMENT_ROOT_PATH/server" &&
+	URI="$HTTPD_URL/smart/server" &&
+
+	setup_negotiate_only "$SERVER" "$URI" &&
+
+	git -c protocol.version=2 -C client fetch \
+		--no-tags \
+		--negotiate-only \
+		--negotiation-tip=$(git -C client rev-parse HEAD) \
+		origin >out &&
+	COMMON=$(git -C "$SERVER" rev-parse two) &&
+	grep "$COMMON" out
+'
+
+test_expect_success 'http:// --negotiate-only without wait-for-done support' '
+	SERVER="server" &&
+	URI="$HTTPD_URL/one_time_perl/server" &&
+
+	setup_negotiate_only "$SERVER" "$URI" &&
+
+	echo "s/ wait-for-done/ xxxx-xxx-xxxx/" \
+		>"$HTTPD_ROOT_PATH/one-time-perl" &&
+
+	test_must_fail git -c protocol.version=2 -C client fetch \
+		--no-tags \
+		--negotiate-only \
+		--negotiation-tip=$(git -C client rev-parse HEAD) \
+		origin 2>err &&
+	test_i18ngrep "server does not support wait-for-done" err
+'
+
+test_expect_success 'http:// --negotiate-only with protocol v0' '
+	SERVER="$HTTPD_DOCUMENT_ROOT_PATH/server" &&
+	URI="$HTTPD_URL/smart/server" &&
+
+	setup_negotiate_only "$SERVER" "$URI" &&
+
+	test_must_fail git -c protocol.version=0 -C client fetch \
+		--no-tags \
+		--negotiate-only \
+		--negotiation-tip=$(git -C client rev-parse HEAD) \
+		origin 2>err &&
+	test_i18ngrep "negotiate-only requires protocol v2" err
+'
+
 # DO NOT add non-httpd-specific tests here, because the last part of this
 # test script is only executed when httpd is available and enabled.