[PATCH v4 8/8] fetch-pack: implement ref-in-want

[Brandon Williams <bmwill@google.com>]

Implement ref-in-want on the client side so that when a server supports
the "ref-in-want" feature, a client will send "want-ref" lines for each
reference the client wants to fetch.  This feature allows clients to
tolerate inconsistencies that exist when a remote repository's refs
change during the course of negotiation.

This allows a client to request to request a particular ref without
specifying the OID of the ref.  This means that instead of hitting an
error when a ref no longer points at the OID it did at the beginning of
negotiation, negotiation can continue and the value of that ref will be
sent at the termination of negotiation, just before a packfile is sent.

More information on the ref-in-want feature can be found in
Documentation/technical/protocol-v2.txt.

Signed-off-by: Brandon Williams <bmwill@google.com>
---
 fetch-pack.c                       | 35 +++++++++++++++++++++++++++---
 remote.c                           |  1 +
 remote.h                           |  1 +
 t/t5703-upload-pack-ref-in-want.sh |  4 ++--
 4 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/fetch-pack.c b/fetch-pack.c
index 73890b894..3a18f5bcd 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -1102,9 +1102,10 @@ static void add_shallow_requests(struct strbuf *req_buf,
 
 static void add_wants(const struct ref *wants, struct strbuf *req_buf)
 {
+	int use_ref_in_want = server_supports_feature("fetch", "ref-in-want", 0);
+
 	for ( ; wants ; wants = wants->next) {
 		const struct object_id *remote = &wants->old_oid;
-		const char *remote_hex;
 		struct object *o;
 
 		/*
@@ -1122,8 +1123,10 @@ static void add_wants(const struct ref *wants, struct strbuf *req_buf)
 			continue;
 		}
 
-		remote_hex = oid_to_hex(remote);
-		packet_buf_write(req_buf, "want %s\n", remote_hex);
+		if (!use_ref_in_want || wants->exact_oid)
+			packet_buf_write(req_buf, "want %s\n", oid_to_hex(remote));
+		else
+			packet_buf_write(req_buf, "want-ref %s\n", wants->name);
 	}
 }
 
@@ -1334,6 +1337,29 @@ static void receive_shallow_info(struct fetch_pack_args *args,
 	args->deepen = 1;
 }
 
+static void receive_wanted_refs(struct packet_reader *reader, struct ref *refs)
+{
+	process_section_header(reader, "wanted-refs", 0);
+	while (packet_reader_read(reader) == PACKET_READ_NORMAL) {
+		struct object_id oid;
+		const char *end;
+		struct ref *r = NULL;
+
+		if (parse_oid_hex(reader->line, &oid, &end) || *end++ != ' ')
+			die("expected wanted-ref, got '%s'", reader->line);
+
+		for (r = refs; r; r = r->next) {
+			if (!strcmp(end, r->name)) {
+				oidcpy(&r->old_oid, &oid);
+				break;
+			}
+		}
+	}
+
+	if (reader->status != PACKET_READ_DELIM)
+		die("error processing wanted refs: %d", reader->status);
+}
+
 enum fetch_state {
 	FETCH_CHECK_LOCAL = 0,
 	FETCH_SEND_REQUEST,
@@ -1408,6 +1434,9 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 			if (process_section_header(&reader, "shallow-info", 1))
 				receive_shallow_info(args, &reader);
 
+			if (process_section_header(&reader, "wanted-refs", 1))
+				receive_wanted_refs(&reader, ref);
+
 			/* get the pack */
 			process_section_header(&reader, "packfile", 0);
 			if (get_pack(args, fd, pack_lockfile))
diff --git a/remote.c b/remote.c
index abe80c139..2c2376fff 100644
--- a/remote.c
+++ b/remote.c
@@ -1735,6 +1735,7 @@ int get_fetch_map(const struct ref *remote_refs,
 		if (refspec->exact_sha1) {
 			ref_map = alloc_ref(name);
 			get_oid_hex(name, &ref_map->old_oid);
+			ref_map->exact_oid = 1;
 		} else {
 			ref_map = get_remote_ref(remote_refs, name);
 		}
diff --git a/remote.h b/remote.h
index 45ecc6cef..976292152 100644
--- a/remote.h
+++ b/remote.h
@@ -73,6 +73,7 @@ struct ref {
 		force:1,
 		forced_update:1,
 		expect_old_sha1:1,
+		exact_oid:1,
 		deletion:1;
 
 	enum {
diff --git a/t/t5703-upload-pack-ref-in-want.sh b/t/t5703-upload-pack-ref-in-want.sh
index 979ab6d03..b94a51380 100755
--- a/t/t5703-upload-pack-ref-in-want.sh
+++ b/t/t5703-upload-pack-ref-in-want.sh
@@ -204,7 +204,7 @@ test_expect_success 'server is initially ahead - no ref in want' '
 	grep "ERR upload-pack: not our ref" err
 '
 
-test_expect_failure 'server is initially ahead - ref in want' '
+test_expect_success 'server is initially ahead - ref in want' '
 	git -C "$REPO" config uploadpack.allowRefInWant true &&
 	rm -rf local &&
 	cp -r "$LOCAL_PRISTINE" local &&
@@ -228,7 +228,7 @@ test_expect_success 'server is initially behind - no ref in want' '
 	test_cmp expected actual
 '
 
-test_expect_failure 'server is initially behind - ref in want' '
+test_expect_success 'server is initially behind - ref in want' '
 	git -C "$REPO" config uploadpack.allowRefInWant true &&
 	rm -rf local &&
 	cp -r "$LOCAL_PRISTINE" local &&
-- 
2.18.0.rc2.346.g013aa6912e-goog