Merge branch 'ds/bundle-uri-4'

Bundle URIs part 4.

* ds/bundle-uri-4:
  clone: unbundle the advertised bundles
  bundle-uri: download bundles from an advertised list
  bundle-uri: allow relative URLs in bundle lists
  strbuf: introduce strbuf_strip_file_from_path()
  bundle-uri: serve bundle.* keys from config
  bundle-uri client: add helper for testing server
  transport: rename got_remote_heads
  bundle-uri client: add boolean transfer.bundleURI setting
  clone: request the 'bundle-uri' command when available
  t: create test harness for 'bundle-uri' command
  protocol v2: add server-side "bundle-uri" skeleton

24 files changed, 1041 insertions, 12 deletions

diff --git a/Documentation/config/transfer.txt b/Documentation/config/transfer.txt
index 264812cca4..c3ac767d1e 100644
--- a/Documentation/config/transfer.txt
+++ b/Documentation/config/transfer.txt
@@ -115,3 +115,9 @@ transfer.unpackLimit::
 transfer.advertiseSID::
 	Boolean. When true, client and server processes will advertise their
 	unique session IDs to their remote counterpart. Defaults to false.
+
+transfer.bundleURI::
+	When `true`, local `git clone` commands will request bundle
+	information from the remote server (if advertised) and download
+	bundles before continuing the clone through the Git protocol.
+	Defaults to `false`.
diff --git a/Documentation/gitprotocol-v2.txt b/Documentation/gitprotocol-v2.txt
index 59bf41cefb..10bd2d40ce 100644
--- a/Documentation/gitprotocol-v2.txt
+++ b/Documentation/gitprotocol-v2.txt
@@ -578,6 +578,207 @@ and associated requested information, each separated by a single space.
 
 	obj-info = obj-id SP obj-size
 
+bundle-uri
+~~~~~~~~~~
+
+If the 'bundle-uri' capability is advertised, the server supports the
+`bundle-uri' command.
+
+The capability is currently advertised with no value (i.e. not
+"bundle-uri=somevalue"), a value may be added in the future for
+supporting command-wide extensions. Clients MUST ignore any unknown
+capability values and proceed with the 'bundle-uri` dialog they
+support.
+
+The 'bundle-uri' command is intended to be issued before `fetch` to
+get URIs to bundle files (see linkgit:git-bundle[1]) to "seed" and
+inform the subsequent `fetch` command.
+
+The client CAN issue `bundle-uri` before or after any other valid
+command. To be useful to clients it's expected that it'll be issued
+after an `ls-refs` and before `fetch`, but CAN be issued at any time
+in the dialog.
+
+DISCUSSION of bundle-uri
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The intent of the feature is optimize for server resource consumption
+in the common case by changing the common case of fetching a very
+large PACK during linkgit:git-clone[1] into a smaller incremental
+fetch.
+
+It also allows servers to achieve better caching in combination with
+an `uploadpack.packObjectsHook` (see linkgit:git-config[1]).
+
+By having new clones or fetches be a more predictable and common
+negotiation against the tips of recently produces *.bundle file(s).
+Servers might even pre-generate the results of such negotiations for
+the `uploadpack.packObjectsHook` as new pushes come in.
+
+One way that servers could take advantage of these bundles is that the
+server would anticipate that fresh clones will download a known bundle,
+followed by catching up to the current state of the repository using ref
+tips found in that bundle (or bundles).
+
+PROTOCOL for bundle-uri
+^^^^^^^^^^^^^^^^^^^^^^^
+
+A `bundle-uri` request takes no arguments, and as noted above does not
+currently advertise a capability value. Both may be added in the
+future.
+
+When the client issues a `command=bundle-uri` request, the response is a
+list of key-value pairs provided as packet lines with value
+`<key>=<value>`. Each `<key>` should be interpreted as a config key from
+the `bundle.*` namespace to construct a list of bundles. These keys are
+grouped by a `bundle.<id>.` subsection, where each key corresponding to a
+given `<id>` contributes attributes to the bundle defined by that `<id>`.
+See linkgit:git-config[1] for the specific details of these keys and how
+the Git client will interpret their values.
+
+Clients MUST parse the line according to the above format, lines that do
+not conform to the format SHOULD be discarded. The user MAY be warned in
+such a case.
+
+bundle-uri CLIENT AND SERVER EXPECTATIONS
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+URI CONTENTS::
+The content at the advertised URIs MUST be one of two types.
++
+The advertised URI may contain a bundle file that `git bundle verify`
+would accept. I.e. they MUST contain one or more reference tips for
+use by the client, MUST indicate prerequisites (in any) with standard
+"-" prefixes, and MUST indicate their "object-format", if
+applicable.
++
+The advertised URI may alternatively contain a plaintext file that `git
+config --list` would accept (with the `--file` option). The key-value
+pairs in this list are in the `bundle.*` namespace (see
+linkgit:git-config[1]).
+
+bundle-uri CLIENT ERROR RECOVERY::
+A client MUST above all gracefully degrade on errors, whether that
+error is because of bad missing/data in the bundle URI(s), because
+that client is too dumb to e.g. understand and fully parse out bundle
+headers and their prerequisite relationships, or something else.
++
+Server operators should feel confident in turning on "bundle-uri" and
+not worry if e.g. their CDN goes down that clones or fetches will run
+into hard failures. Even if the server bundle bundle(s) are
+incomplete, or bad in some way the client should still end up with a
+functioning repository, just as if it had chosen not to use this
+protocol extension.
++
+All subsequent discussion on client and server interaction MUST keep
+this in mind.
+
+bundle-uri SERVER TO CLIENT::
+The ordering of the returned bundle uris is not significant. Clients
+MUST parse their headers to discover their contained OIDS and
+prerequisites. A client MUST consider the content of the bundle(s)
+themselves and their header as the ultimate source of truth.
++
+A server MAY even return bundle(s) that don't have any direct
+relationship to the repository being cloned (either through accident,
+or intentional "clever" configuration), and expect a client to sort
+out what data they'd like from the bundle(s), if any.
+
+bundle-uri CLIENT TO SERVER::
+The client SHOULD provide reference tips found in the bundle header(s)
+as 'have' lines in any subsequent `fetch` request. A client MAY also
+ignore the bundle(s) entirely if doing so is deemed worse for some
+reason, e.g. if the bundles can't be downloaded, it doesn't like the
+tips it finds etc.
+
+WHEN ADVERTISED BUNDLE(S) REQUIRE NO FURTHER NEGOTIATION::
+If after issuing `bundle-uri` and `ls-refs`, and getting the header(s)
+of the bundle(s) the client finds that the ref tips it wants can be
+retrieved entirely from advertised bundle(s), the client MAY disconnect
+from the Git server. The results of such a 'clone' or 'fetch' should be
+indistinguishable from the state attained without using bundle-uri.
+
+EARLY CLIENT DISCONNECTIONS AND ERROR RECOVERY::
+A client MAY perform an early disconnect while still downloading the
+bundle(s) (having streamed and parsed their headers). In such a case
+the client MUST gracefully recover from any errors related to
+finishing the download and validation of the bundle(s).
++
+I.e. a client might need to re-connect and issue a 'fetch' command,
+and possibly fall back to not making use of 'bundle-uri' at all.
++
+This "MAY" behavior is specified as such (and not a "SHOULD") on the
+assumption that a server advertising bundle uris is more likely than
+not to be serving up a relatively large repository, and to be pointing
+to URIs that have a good chance of being in working order. A client
+MAY e.g. look at the payload size of the bundles as a heuristic to see
+if an early disconnect is worth it, should falling back on a full
+"fetch" dialog be necessary.
+
+WHEN ADVERTISED BUNDLE(S) REQUIRE FURTHER NEGOTIATION::
+A client SHOULD commence a negotiation of a PACK from the server via
+the "fetch" command using the OID tips found in advertised bundles,
+even if's still in the process of downloading those bundle(s).
++
+This allows for aggressive early disconnects from any interactive
+server dialog. The client blindly trusts that the advertised OID tips
+are relevant, and issues them as 'have' lines, it then requests any
+tips it would like (usually from the "ls-refs" advertisement) via
+'want' lines. The server will then compute a (hopefully small) PACK
+with the expected difference between the tips from the bundle(s) and
+the data requested.
++
+The only connection the client then needs to keep active is to the
+concurrently downloading static bundle(s), when those and the
+incremental PACK are retrieved they should be inflated and
+validated. Any errors at this point should be gracefully recovered
+from, see above.
+
+bundle-uri PROTOCOL FEATURES
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The client constructs a bundle list from the `<key>=<value>` pairs
+provided by the server. These pairs are part of the `bundle.*` namespace
+as documented in linkgit:git-config[1]. In this section, we discuss some
+of these keys and describe the actions the client will do in response to
+this information.
+
+In particular, the `bundle.version` key specifies an integer value. The
+only accepted value at the moment is `1`, but if the client sees an
+unexpected value here then the client MUST ignore the bundle list.
+
+As long as `bundle.version` is understood, all other unknown keys MAY be
+ignored by the client. The server will guarantee compatibility with older
+clients, though newer clients may be better able to use the extra keys to
+minimize downloads.
+
+Any backwards-incompatible addition of pre-URI key-value will be
+guarded by a new `bundle.version` value or values in 'bundle-uri'
+capability advertisement itself, and/or by new future `bundle-uri`
+request arguments.
+
+Some example key-value pairs that are not currently implemented but could
+be implemented in the future include:
+
+ * Add a "hash=<val>" or "size=<bytes>" advertise the expected hash or
+   size of the bundle file.
+
+ * Advertise that one or more bundle files are the same (to e.g. have
+   clients round-robin or otherwise choose one of N possible files).
+
+ * A "oid=<OID>" shortcut and "prerequisite=<OID>" shortcut. For
+   expressing the common case of a bundle with one tip and no
+   prerequisites, or one tip and one prerequisite.
++
+This would allow for optimizing the common case of servers who'd like
+to provide one "big bundle" containing only their "main" branch,
+and/or incremental updates thereof.
++
+A client receiving such a a response MAY assume that they can skip
+retrieving the header from a bundle at the indicated URI, and thus
+save themselves and the server(s) the request(s) needed to inspect the
+headers of that bundle or bundles.
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/builtin/clone.c b/builtin/clone.c
index f518bb2dc1..5453ba5277 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -1271,6 +1271,27 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	if (refs)
 		mapped_refs = wanted_peer_refs(refs, &remote->fetch);
 
+	if (!bundle_uri) {
+		/*
+		* Populate transport->got_remote_bundle_uri and
+		* transport->bundle_uri. We might get nothing.
+		*/
+		transport_get_remote_bundle_uri(transport);
+
+		if (transport->bundles &&
+		    hashmap_get_size(&transport->bundles->bundles)) {
+			/* At this point, we need the_repository to match the cloned repo. */
+			if (repo_init(the_repository, git_dir, work_tree))
+				warning(_("failed to initialize the repo, skipping bundle URI"));
+			else if (fetch_bundle_list(the_repository,
+						   transport->bundles))
+				warning(_("failed to fetch advertised bundles"));
+		} else {
+			clear_bundle_list(transport->bundles);
+			FREE_AND_NULL(transport->bundles);
+		}
+	}
+
 	if (mapped_refs) {
 		int hash_algo = hash_algo_by_ptr(transport_get_hash_algo(transport));
 
diff --git a/bundle-uri.c b/bundle-uri.c
index 79a914f961..36268dda17 100644
--- a/bundle-uri.c
+++ b/bundle-uri.c
@@ -7,6 +7,7 @@
 #include "hashmap.h"
 #include "pkt-line.h"
 #include "config.h"
+#include "remote.h"
 
 static int compare_bundles(const void *hashmap_cmp_fn_data,
 			   const struct hashmap_entry *he1,
@@ -49,6 +50,7 @@ void clear_bundle_list(struct bundle_list *list)
 
 	for_all_bundles_in_list(list, clear_remote_bundle_info, NULL);
 	hashmap_clear_and_free(&list->bundles, struct remote_bundle_info, ent);
+	free(list->baseURI);
 }
 
 int for_all_bundles_in_list(struct bundle_list *list,
@@ -163,7 +165,7 @@ static int bundle_list_update(const char *key, const char *value,
 	if (!strcmp(subkey, "uri")) {
 		if (bundle->uri)
 			return -1;
-		bundle->uri = xstrdup(value);
+		bundle->uri = relative_url(list->baseURI, value, NULL);
 		return 0;
 	}
 
@@ -190,6 +192,18 @@ int bundle_uri_parse_config_format(const char *uri,
 		.error_action = CONFIG_ERROR_ERROR,
 	};
 
+	if (!list->baseURI) {
+		struct strbuf baseURI = STRBUF_INIT;
+		strbuf_addstr(&baseURI, uri);
+
+		/*
+		 * If the URI does not end with a trailing slash, then
+		 * remove the filename portion of the path. This is
+		 * important for relative URIs.
+		 */
+		strbuf_strip_file_from_path(&baseURI);
+		list->baseURI = strbuf_detach(&baseURI, NULL);
+	}
 	result = git_config_from_file_with_options(config_to_bundle_list,
 						   filename, list,
 						   &opts);
@@ -563,6 +577,77 @@ cleanup:
 	return result;
 }
 
+int fetch_bundle_list(struct repository *r, struct bundle_list *list)
+{
+	int result;
+	struct bundle_list global_list;
+
+	init_bundle_list(&global_list);
+
+	/* If a bundle is added to this global list, then it is required. */
+	global_list.mode = BUNDLE_MODE_ALL;
+
+	if ((result = download_bundle_list(r, list, &global_list, 0)))
+		goto cleanup;
+
+	result = unbundle_all_bundles(r, &global_list);
+
+cleanup:
+	for_all_bundles_in_list(&global_list, unlink_bundle, NULL);
+	clear_bundle_list(&global_list);
+	return result;
+}
+
+/**
+ * API for serve.c.
+ */
+
+int bundle_uri_advertise(struct repository *r, struct strbuf *value UNUSED)
+{
+	static int advertise_bundle_uri = -1;
+
+	if (advertise_bundle_uri != -1)
+		goto cached;
+
+	advertise_bundle_uri = 0;
+	repo_config_get_maybe_bool(r, "uploadpack.advertisebundleuris", &advertise_bundle_uri);
+
+cached:
+	return advertise_bundle_uri;
+}
+
+static int config_to_packet_line(const char *key, const char *value, void *data)
+{
+	struct packet_reader *writer = data;
+
+	if (!strncmp(key, "bundle.", 7))
+		packet_write_fmt(writer->fd, "%s=%s", key, value);
+
+	return 0;
+}
+
+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"));
+
+	/*
+	 * Read all "bundle.*" config lines to the client as key=value
+	 * packet lines.
+	 */
+	git_config(config_to_packet_line, &writer);
+
+	packet_writer_flush(&writer);
+
+	return 0;
+}
+
 /**
  * General API for {transport,connect}.c etc.
  */
diff --git a/bundle-uri.h b/bundle-uri.h
index 4dbc269823..d5e89f1671 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 string_list;
 
@@ -60,6 +61,20 @@ struct bundle_list {
 	int version;
 	enum bundle_list_mode mode;
 	struct hashmap bundles;
+
+	/**
+	 * The baseURI of a bundle_list is the URI that provided the list.
+	 *
+	 * In the case of the 'bundle-uri' protocol v2 command, the base
+	 * URI is the URI of the Git remote.
+	 *
+	 * Otherwise, the bundle list was downloaded over HTTP from some
+	 * known URI. 'baseURI' is set to that value.
+	 *
+	 * The baseURI is used as the base for any relative URIs
+	 * advertised by the bundle list at that location.
+	 */
+	char *baseURI;
 };
 
 void init_bundle_list(struct bundle_list *list);
@@ -93,6 +108,26 @@ int bundle_uri_parse_config_format(const char *uri,
 int fetch_bundle_uri(struct repository *r, const char *uri);
 
 /**
+ * Given a bundle list that was already advertised (likely by the
+ * bundle-uri protocol v2 verb) at the given uri, fetch and unbundle the
+ * bundles according to the bundle strategy of that list.
+ *
+ * It is expected that the given 'list' is initialized, including its
+ * 'baseURI' value.
+ *
+ * Returns non-zero if there was an error trying to download the list
+ * or any of its advertised bundles.
+ */
+int fetch_bundle_list(struct repository *r,
+		      struct bundle_list *list);
+
+/**
+ * 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/connect.c b/connect.c
index eef752f14b..63e59641c0 100644
--- a/connect.c
+++ b/connect.c
@@ -15,6 +15,7 @@
 #include "version.h"
 #include "protocol.h"
 #include "alias.h"
+#include "bundle-uri.h"
 
 static char *server_capabilities_v1;
 static struct strvec server_capabilities_v2 = STRVEC_INIT;
@@ -493,6 +494,49 @@ static void send_capabilities(int fd_out, struct packet_reader *reader)
 	}
 }
 
+int get_remote_bundle_uri(int fd_out, struct packet_reader *reader,
+			  struct bundle_list *bundles, int stateless_rpc)
+{
+	int line_nr = 1;
+
+	/* Assert bundle-uri support */
+	ensure_server_supports_v2("bundle-uri");
+
+	/* (Re-)send capabilities */
+	send_capabilities(fd_out, reader);
+
+	/* Send command */
+	packet_write_fmt(fd_out, "command=bundle-uri\n");
+	packet_delim(fd_out);
+
+	packet_flush(fd_out);
+
+	/* Process response from server */
+	while (packet_reader_read(reader) == PACKET_READ_NORMAL) {
+		const char *line = reader->line;
+		line_nr++;
+
+		if (!bundle_uri_parse_line(bundles, line))
+			continue;
+
+		return error(_("error on bundle-uri response line %d: %s"),
+			     line_nr, line);
+	}
+
+	if (reader->status != PACKET_READ_FLUSH)
+		return error(_("expected flush after bundle-uri listing"));
+
+	/*
+	 * Might die(), but obscure enough that that's OK, e.g. in
+	 * serve.c we'll call BUG() on its equivalent (the
+	 * PACKET_READ_RESPONSE_END check).
+	 */
+	check_stateless_delimiter(stateless_rpc, reader,
+				  _("expected response end packet after ref listing"));
+
+	return 0;
+}
+
 struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
 			     struct ref **list, int for_push,
 			     struct transport_ls_refs_options *transport_options,
diff --git a/remote.h b/remote.h
index 1c4621b414..1ebbe42792 100644
--- a/remote.h
+++ b/remote.h
@@ -234,6 +234,11 @@ struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
 			     const struct string_list *server_options,
 			     int stateless_rpc);
 
+/* Used for protocol v2 in order to retrieve refs from a remote */
+struct bundle_list;
+int get_remote_bundle_uri(int fd_out, struct packet_reader *reader,
+			  struct bundle_list *bundles, int stateless_rpc);
+
 int resolve_remote_symref(struct ref *ref, struct ref *list);
 
 /*
diff --git a/serve.c b/serve.c
index 733347f602..cbf4a143cf 100644
--- a/serve.c
+++ b/serve.c
@@ -7,6 +7,7 @@
 #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;
@@ -135,6 +136,11 @@ 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/strbuf.c b/strbuf.c
index 0890b1405c..c383f41a3c 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -1200,3 +1200,9 @@ int strbuf_edit_interactively(struct strbuf *buffer, const char *path,
 	free(path2);
 	return res;
 }
+
+void strbuf_strip_file_from_path(struct strbuf *sb)
+{
+	char *path_sep = find_last_dir_sep(sb->buf);
+	strbuf_setlen(sb, path_sep ? path_sep - sb->buf + 1 : 0);
+}
diff --git a/strbuf.h b/strbuf.h
index 76965a17d4..f6dbb9681e 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -664,6 +664,17 @@ int launch_sequence_editor(const char *path, struct strbuf *buffer,
 int strbuf_edit_interactively(struct strbuf *buffer, const char *path,
 			      const char *const *env);
 
+/*
+ * Remove the filename from the provided path string. If the path
+ * contains a trailing separator, then the path is considered a directory
+ * and nothing is modified.
+ *
+ * Examples:
+ * - "/path/to/file" -> "/path/to/"
+ * - "/path/to/dir/" -> "/path/to/dir/"
+ */
+void strbuf_strip_file_from_path(struct strbuf *sb);
+
 void strbuf_add_lines(struct strbuf *sb,
 		      const char *prefix,
 		      const char *buf,
diff --git a/t/helper/test-bundle-uri.c b/t/helper/test-bundle-uri.c
index 25afd39342..5df5bc3b89 100644
--- a/t/helper/test-bundle-uri.c
+++ b/t/helper/test-bundle-uri.c
@@ -3,6 +3,10 @@
 #include "bundle-uri.h"
 #include "strbuf.h"
 #include "string-list.h"
+#include "transport.h"
+#include "ref-filter.h"
+#include "remote.h"
+#include "refs.h"
 
 enum input_mode {
 	KEY_VALUE_PAIRS,
@@ -36,6 +40,8 @@ static int cmd__bundle_uri_parse(int argc, const char **argv, enum input_mode mo
 
 	init_bundle_list(&list);
 
+	list.baseURI = xstrdup("<uri>");
+
 	switch (mode) {
 	case KEY_VALUE_PAIRS:
 		if (argc != 1)
@@ -68,6 +74,46 @@ usage:
 	usage_with_options(usage, options);
 }
 
+static int cmd_ls_remote(int argc, const char **argv)
+{
+	const char *uploadpack = NULL;
+	struct string_list server_options = STRING_LIST_INIT_DUP;
+	const char *dest;
+	struct remote *remote;
+	struct transport *transport;
+	int status = 0;
+
+	dest = argc > 1 ? argv[1] : NULL;
+
+	remote = remote_get(dest);
+	if (!remote) {
+		if (dest)
+			die(_("bad repository '%s'"), dest);
+		die(_("no remote configured to get bundle URIs from"));
+	}
+	if (!remote->url_nr)
+		die(_("remote '%s' has no configured URL"), dest);
+
+	transport = transport_get(remote, NULL);
+	if (uploadpack)
+		transport_set_option(transport, TRANS_OPT_UPLOADPACK, uploadpack);
+	if (server_options.nr)
+		transport->server_options = &server_options;
+
+	if (transport_get_remote_bundle_uri(transport) < 0) {
+		error(_("could not get the bundle-uri list"));
+		status = 1;
+		goto cleanup;
+	}
+
+	print_bundle_list(stdout, transport->bundles);
+
+cleanup:
+	if (transport_disconnect(transport))
+		return 1;
+	return status;
+}
+
 int cmd__bundle_uri(int argc, const char **argv)
 {
 	const char *usage[] = {
@@ -88,6 +134,8 @@ int cmd__bundle_uri(int argc, const char **argv)
 		return cmd__bundle_uri_parse(argc - 1, argv + 1, KEY_VALUE_PAIRS);
 	if (!strcmp(argv[1], "parse-config"))
 		return cmd__bundle_uri_parse(argc - 1, argv + 1, CONFIG_FILE);
+	if (!strcmp(argv[1], "ls-remote"))
+		return cmd_ls_remote(argc - 1, argv + 1);
 	error("there is no test-tool bundle-uri tool '%s'", argv[1]);
 
 usage:
diff --git a/t/lib-bundle-uri-protocol.sh b/t/lib-bundle-uri-protocol.sh
new file mode 100644
index 0000000000..a4a1af8d02
--- /dev/null
+++ b/t/lib-bundle-uri-protocol.sh
@@ -0,0 +1,216 @@
+# Set up and run tests of the 'bundle-uri' command in protocol v2
+#
+# The test that includes this script should set BUNDLE_URI_PROTOCOL
+# to one of "file", "git", or "http".
+
+BUNDLE_URI_TEST_PARENT=
+BUNDLE_URI_TEST_URI=
+BUNDLE_URI_TEST_BUNDLE_URI=
+case "$BUNDLE_URI_PROTOCOL" in
+file)
+	BUNDLE_URI_PARENT=file_parent
+	BUNDLE_URI_REPO_URI="file://$PWD/file_parent"
+	BUNDLE_URI_BUNDLE_URI="$BUNDLE_URI_REPO_URI/fake.bdl"
+	test_set_prereq BUNDLE_URI_FILE
+	;;
+git)
+	. "$TEST_DIRECTORY"/lib-git-daemon.sh
+	start_git_daemon --export-all --enable=receive-pack
+	BUNDLE_URI_PARENT="$GIT_DAEMON_DOCUMENT_ROOT_PATH/parent"
+	BUNDLE_URI_REPO_URI="$GIT_DAEMON_URL/parent"
+	BUNDLE_URI_BUNDLE_URI="https://example.com/fake.bdl"
+	test_set_prereq BUNDLE_URI_GIT
+	;;
+http)
+	. "$TEST_DIRECTORY"/lib-httpd.sh
+	start_httpd
+	BUNDLE_URI_PARENT="$HTTPD_DOCUMENT_ROOT_PATH/http_parent"
+	BUNDLE_URI_REPO_URI="$HTTPD_URL/smart/http_parent"
+	BUNDLE_URI_BUNDLE_URI="https://example.com/fake.bdl"
+	test_set_prereq BUNDLE_URI_HTTP
+	;;
+*)
+	BUG "Need to pass valid BUNDLE_URI_PROTOCOL (was \"$BUNDLE_URI_PROTOCOL\")"
+	;;
+esac
+
+test_expect_success "setup protocol v2 $BUNDLE_URI_PROTOCOL:// tests" '
+	git init "$BUNDLE_URI_PARENT" &&
+	test_commit -C "$BUNDLE_URI_PARENT" one &&
+	git -C "$BUNDLE_URI_PARENT" config uploadpack.advertiseBundleURIs true
+'
+
+case "$BUNDLE_URI_PROTOCOL" in
+http)
+	test_expect_success "setup config for $BUNDLE_URI_PROTOCOL:// tests" '
+		git -C "$BUNDLE_URI_PARENT" config http.receivepack true
+	'
+	;;
+*)
+	;;
+esac
+BUNDLE_URI_BUNDLE_URI_ESCAPED=$(echo "$BUNDLE_URI_BUNDLE_URI" | test_uri_escape)
+
+test_expect_success "connect with $BUNDLE_URI_PROTOCOL:// using protocol v2: no bundle-uri" '
+	test_when_finished "rm -f log" &&
+	test_when_finished "git -C \"$BUNDLE_URI_PARENT\" config uploadpack.advertiseBundleURIs true" &&
+	git -C "$BUNDLE_URI_PARENT" config uploadpack.advertiseBundleURIs false &&
+
+	GIT_TRACE_PACKET="$PWD/log" \
+	git \
+		-c protocol.version=2 \
+		ls-remote --symref "$BUNDLE_URI_REPO_URI" \
+		>actual 2>err &&
+
+	# Server responded using protocol v2
+	grep "< version 2" log &&
+
+	! grep bundle-uri log
+'
+
+test_expect_success "connect with $BUNDLE_URI_PROTOCOL:// using protocol v2: have bundle-uri" '
+	test_when_finished "rm -f log" &&
+
+	GIT_TRACE_PACKET="$PWD/log" \
+	git \
+		-c protocol.version=2 \
+		ls-remote --symref "$BUNDLE_URI_REPO_URI" \
+		>actual 2>err &&
+
+	# Server responded using protocol v2
+	grep "< version 2" log &&
+
+	# Server advertised bundle-uri capability
+	grep "< bundle-uri" log
+'
+
+test_expect_success "clone with $BUNDLE_URI_PROTOCOL:// using protocol v2: request bundle-uris" '
+	test_when_finished "rm -rf log* cloned*" &&
+
+	GIT_TRACE_PACKET="$PWD/log" \
+	git \
+		-c transfer.bundleURI=false \
+		-c protocol.version=2 \
+		clone "$BUNDLE_URI_REPO_URI" cloned \
+		>actual 2>err &&
+
+	# Server responded using protocol v2
+	grep "< version 2" log &&
+
+	# Server advertised bundle-uri capability
+	grep "< bundle-uri" log &&
+
+	# Client did not issue bundle-uri command
+	! grep "> command=bundle-uri" log &&
+
+	GIT_TRACE_PACKET="$PWD/log" \
+	git \
+		-c transfer.bundleURI=true \
+		-c protocol.version=2 \
+		clone "$BUNDLE_URI_REPO_URI" cloned2 \
+		>actual 2>err &&
+
+	# Server responded using protocol v2
+	grep "< version 2" log &&
+
+	# Server advertised bundle-uri capability
+	grep "< bundle-uri" log &&
+
+	# Client issued bundle-uri command
+	grep "> command=bundle-uri" log &&
+
+	GIT_TRACE_PACKET="$PWD/log3" \
+	git \
+		-c transfer.bundleURI=true \
+		-c protocol.version=2 \
+		clone --bundle-uri="$BUNDLE_URI_BUNDLE_URI" \
+		"$BUNDLE_URI_REPO_URI" cloned3 \
+		>actual 2>err &&
+
+	# Server responded using protocol v2
+	grep "< version 2" log3 &&
+
+	# Server advertised bundle-uri capability
+	grep "< bundle-uri" log3 &&
+
+	# Client did not issue bundle-uri command (--bundle-uri override)
+	! grep "> command=bundle-uri" log3
+'
+
+# The remaining tests will all assume transfer.bundleURI=true
+#
+# This test can be removed when transfer.bundleURI is enabled by default.
+test_expect_success 'enable transfer.bundleURI for remaining tests' '
+	git config --global transfer.bundleURI true
+'
+
+test_expect_success "test bundle-uri with $BUNDLE_URI_PROTOCOL:// using protocol v2" '
+	test_config -C "$BUNDLE_URI_PARENT" \
+		bundle.only.uri "$BUNDLE_URI_BUNDLE_URI_ESCAPED" &&
+
+	# All data about bundle URIs
+	cat >expect <<-EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "only"]
+		uri = $BUNDLE_URI_BUNDLE_URI_ESCAPED
+	EOF
+
+	test-tool bundle-uri \
+		ls-remote \
+		"$BUNDLE_URI_REPO_URI" \
+		>actual &&
+	test_cmp_config_output expect actual
+'
+
+test_expect_success "test bundle-uri with $BUNDLE_URI_PROTOCOL:// using protocol v2 and extra data" '
+	test_config -C "$BUNDLE_URI_PARENT" \
+		bundle.only.uri "$BUNDLE_URI_BUNDLE_URI_ESCAPED" &&
+
+	# Extra data should be ignored
+	test_config -C "$BUNDLE_URI_PARENT" bundle.only.extra bogus &&
+
+	# All data about bundle URIs
+	cat >expect <<-EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "only"]
+		uri = $BUNDLE_URI_BUNDLE_URI_ESCAPED
+	EOF
+
+	test-tool bundle-uri \
+		ls-remote \
+		"$BUNDLE_URI_REPO_URI" \
+		>actual &&
+	test_cmp_config_output expect actual
+'
+
+test_expect_success "test bundle-uri with $BUNDLE_URI_PROTOCOL:// using protocol v2 with list" '
+	test_config -C "$BUNDLE_URI_PARENT" \
+		bundle.bundle1.uri "$BUNDLE_URI_BUNDLE_URI_ESCAPED-1.bdl" &&
+	test_config -C "$BUNDLE_URI_PARENT" \
+		bundle.bundle2.uri "$BUNDLE_URI_BUNDLE_URI_ESCAPED-2.bdl" &&
+	test_config -C "$BUNDLE_URI_PARENT" \
+		bundle.bundle3.uri "$BUNDLE_URI_BUNDLE_URI_ESCAPED-3.bdl" &&
+
+	# All data about bundle URIs
+	cat >expect <<-EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "bundle1"]
+		uri = $BUNDLE_URI_BUNDLE_URI_ESCAPED-1.bdl
+	[bundle "bundle2"]
+		uri = $BUNDLE_URI_BUNDLE_URI_ESCAPED-2.bdl
+	[bundle "bundle3"]
+		uri = $BUNDLE_URI_BUNDLE_URI_ESCAPED-3.bdl
+	EOF
+
+	test-tool bundle-uri \
+		ls-remote \
+		"$BUNDLE_URI_REPO_URI" \
+		>actual &&
+	test_cmp_config_output expect actual
+'
diff --git a/t/t5601-clone.sh b/t/t5601-clone.sh
index b2524a24c2..1928ea1dd7 100755
--- a/t/t5601-clone.sh
+++ b/t/t5601-clone.sh
@@ -772,6 +772,65 @@ test_expect_success 'reject cloning shallow repository using HTTP' '
 	git clone --no-reject-shallow $HTTPD_URL/smart/repo.git repo
 '
 
+test_expect_success 'auto-discover bundle URI from HTTP clone' '
+	test_when_finished rm -rf trace.txt repo2 "$HTTPD_DOCUMENT_ROOT_PATH/repo2.git" &&
+	git -C src bundle create "$HTTPD_DOCUMENT_ROOT_PATH/everything.bundle" --all &&
+	git clone --bare --no-local src "$HTTPD_DOCUMENT_ROOT_PATH/repo2.git" &&
+
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo2.git" config \
+		uploadpack.advertiseBundleURIs true &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo2.git" config \
+		bundle.version 1 &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo2.git" config \
+		bundle.mode all &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo2.git" config \
+		bundle.everything.uri "$HTTPD_URL/everything.bundle" &&
+
+	GIT_TRACE2_EVENT="$(pwd)/trace.txt" \
+		git -c protocol.version=2 \
+		    -c transfer.bundleURI=true clone \
+		$HTTPD_URL/smart/repo2.git repo2 &&
+	cat >pattern <<-EOF &&
+	"event":"child_start".*"argv":\["git-remote-https","$HTTPD_URL/everything.bundle"\]
+	EOF
+	grep -f pattern trace.txt
+'
+
+test_expect_success 'auto-discover multiple bundles from HTTP clone' '
+	test_when_finished rm -rf trace.txt repo3 "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" &&
+
+	test_commit -C src new &&
+	git -C src bundle create "$HTTPD_DOCUMENT_ROOT_PATH/new.bundle" HEAD~1..HEAD &&
+	git clone --bare --no-local src "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" &&
+
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" config \
+		uploadpack.advertiseBundleURIs true &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" config \
+		bundle.version 1 &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" config \
+		bundle.mode all &&
+
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" config \
+		bundle.everything.uri "$HTTPD_URL/everything.bundle" &&
+	git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo3.git" config \
+		bundle.new.uri "$HTTPD_URL/new.bundle" &&
+
+	GIT_TRACE2_EVENT="$(pwd)/trace.txt" \
+		git -c protocol.version=2 \
+		    -c transfer.bundleURI=true clone \
+		$HTTPD_URL/smart/repo3.git repo3 &&
+
+	# We should fetch _both_ bundles
+	cat >pattern <<-EOF &&
+	"event":"child_start".*"argv":\["git-remote-https","$HTTPD_URL/everything.bundle"\]
+	EOF
+	grep -f pattern trace.txt &&
+	cat >pattern <<-EOF &&
+	"event":"child_start".*"argv":\["git-remote-https","$HTTPD_URL/new.bundle"\]
+	EOF
+	grep -f pattern trace.txt
+'
+
 # 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.
 
diff --git a/t/t5701-git-serve.sh b/t/t5701-git-serve.sh
index 1896f671cb..f21e5e9d33 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
diff --git a/t/t5730-protocol-v2-bundle-uri-file.sh b/t/t5730-protocol-v2-bundle-uri-file.sh
new file mode 100755
index 0000000000..37bdb725bc
--- /dev/null
+++ b/t/t5730-protocol-v2-bundle-uri-file.sh
@@ -0,0 +1,17 @@
+#!/bin/sh
+
+test_description="Test bundle-uri with protocol v2 and 'file://' transport"
+
+TEST_NO_CREATE_REPO=1
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+# Test protocol v2 with 'file://' transport
+#
+BUNDLE_URI_PROTOCOL=file
+. "$TEST_DIRECTORY"/lib-bundle-uri-protocol.sh
+
+test_done
diff --git a/t/t5731-protocol-v2-bundle-uri-git.sh b/t/t5731-protocol-v2-bundle-uri-git.sh
new file mode 100755
index 0000000000..8add1b37ab
--- /dev/null
+++ b/t/t5731-protocol-v2-bundle-uri-git.sh
@@ -0,0 +1,17 @@
+#!/bin/sh
+
+test_description="Test bundle-uri with protocol v2 and 'git://' transport"
+
+TEST_NO_CREATE_REPO=1
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+# Test protocol v2 with 'git://' transport
+#
+BUNDLE_URI_PROTOCOL=git
+. "$TEST_DIRECTORY"/lib-bundle-uri-protocol.sh
+
+test_done
diff --git a/t/t5732-protocol-v2-bundle-uri-http.sh b/t/t5732-protocol-v2-bundle-uri-http.sh
new file mode 100755
index 0000000000..129daa0226
--- /dev/null
+++ b/t/t5732-protocol-v2-bundle-uri-http.sh
@@ -0,0 +1,17 @@
+#!/bin/sh
+
+test_description="Test bundle-uri with protocol v2 and 'http://' transport"
+
+TEST_NO_CREATE_REPO=1
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+# Test protocol v2 with 'http://' transport
+#
+BUNDLE_URI_PROTOCOL=http
+. "$TEST_DIRECTORY"/lib-bundle-uri-protocol.sh
+
+test_done
diff --git a/t/t5750-bundle-uri-parse.sh b/t/t5750-bundle-uri-parse.sh
index c2fe3f9c5a..7b4f930e53 100755
--- a/t/t5750-bundle-uri-parse.sh
+++ b/t/t5750-bundle-uri-parse.sh
@@ -30,6 +30,58 @@ test_expect_success 'bundle_uri_parse_line() just URIs' '
 	test_cmp_config_output expect actual
 '
 
+test_expect_success 'bundle_uri_parse_line(): relative URIs' '
+	cat >in <<-\EOF &&
+	bundle.one.uri=bundle.bdl
+	bundle.two.uri=../bundle.bdl
+	bundle.three.uri=sub/dir/bundle.bdl
+	EOF
+
+	cat >expect <<-\EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "one"]
+		uri = <uri>/bundle.bdl
+	[bundle "two"]
+		uri = bundle.bdl
+	[bundle "three"]
+		uri = <uri>/sub/dir/bundle.bdl
+	EOF
+
+	test-tool bundle-uri parse-key-values in >actual 2>err &&
+	test_must_be_empty err &&
+	test_cmp_config_output expect actual
+'
+
+test_expect_success 'bundle_uri_parse_line(): relative URIs and parent paths' '
+	cat >in <<-\EOF &&
+	bundle.one.uri=bundle.bdl
+	bundle.two.uri=../bundle.bdl
+	bundle.three.uri=../../bundle.bdl
+	EOF
+
+	cat >expect <<-\EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "one"]
+		uri = <uri>/bundle.bdl
+	[bundle "two"]
+		uri = bundle.bdl
+	[bundle "three"]
+		uri = <uri>/../bundle.bdl
+	EOF
+
+	# TODO: We would prefer if parsing a bundle list would not cause
+	# a die() and instead would give a warning and allow the rest of
+	# a Git command to continue. This test_must_fail is necessary for
+	# now until the interface for relative_url() allows for reporting
+	# an error instead of die()ing.
+	test_must_fail test-tool bundle-uri parse-key-values in >actual 2>err &&
+	grep "fatal: cannot strip one component off url" err
+'
+
 test_expect_success 'bundle_uri_parse_line() parsing edge cases: empty key or value' '
 	cat >in <<-\EOF &&
 	=bogus-value
@@ -136,6 +188,36 @@ test_expect_success 'parse config format: just URIs' '
 	test_cmp_config_output expect actual
 '
 
+test_expect_success 'parse config format: relative URIs' '
+	cat >in <<-\EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "one"]
+		uri = bundle.bdl
+	[bundle "two"]
+		uri = ../bundle.bdl
+	[bundle "three"]
+		uri = sub/dir/bundle.bdl
+	EOF
+
+	cat >expect <<-\EOF &&
+	[bundle]
+		version = 1
+		mode = all
+	[bundle "one"]
+		uri = <uri>/bundle.bdl
+	[bundle "two"]
+		uri = bundle.bdl
+	[bundle "three"]
+		uri = <uri>/sub/dir/bundle.bdl
+	EOF
+
+	test-tool bundle-uri parse-config in >actual 2>err &&
+	test_must_be_empty err &&
+	test_cmp_config_output expect actual
+'
+
 test_expect_success 'parse config format edge cases: empty key or value' '
 	cat >in1 <<-\EOF &&
 	= bogus-value
diff --git a/t/t9119-git-svn-info.sh b/t/t9119-git-svn-info.sh
index 8201c3e808..088d1c57a8 100755
--- a/t/t9119-git-svn-info.sh
+++ b/t/t9119-git-svn-info.sh
@@ -28,7 +28,7 @@ test_cmp_info () {
 	rm -f tmp.expect tmp.actual
 }
 
-quoted_svnrepo="$(echo $svnrepo | sed 's/ /%20/')"
+quoted_svnrepo="$(echo $svnrepo | test_uri_escape)"
 
 test_expect_success 'setup repository and import' '
 	mkdir info &&
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 796093a7b3..0fd7d4a200 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1751,6 +1751,13 @@ test_path_is_hidden () {
 	return 1
 }
 
+# Poor man's URI escaping. Good enough for the test suite whose trash
+# directory has a space in it. See 93c3fcbe4d4 (git-svn: attempt to
+# mimic SVN 1.7 URL canonicalization, 2012-07-28) for prior art.
+test_uri_escape() {
+	sed 's/ /%20/g'
+}
+
 # Check that the given command was invoked as part of the
 # trace2-format trace on stdin.
 #
diff --git a/transport-helper.c b/transport-helper.c
index e95267a4ab..3ea7c2bb5a 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -1267,9 +1267,22 @@ static struct ref *get_refs_list_using_list(struct transport *transport,
 	return ret;
 }
 
+static int get_bundle_uri(struct transport *transport)
+{
+	get_helper(transport);
+
+	if (process_connect(transport, 0)) {
+		do_take_over(transport);
+		return transport->vtable->get_bundle_uri(transport);
+	}
+
+	return -1;
+}
+
 static struct transport_vtable vtable = {
 	.set_option	= set_helper_option,
 	.get_refs_list	= get_refs_list,
+	.get_bundle_uri = get_bundle_uri,
 	.fetch_refs	= fetch_refs,
 	.push_refs	= push_refs,
 	.connect	= connect_helper,
diff --git a/transport-internal.h b/transport-internal.h
index c4ca0b733a..90ea749e5c 100644
--- a/transport-internal.h
+++ b/transport-internal.h
@@ -27,6 +27,13 @@ struct transport_vtable {
 				     struct transport_ls_refs_options *transport_options);
 
 	/**
+	 * Populates the remote side's bundle-uri under protocol v2,
+	 * if the "bundle-uri" capability was advertised. Returns 0 if
+	 * OK, negative values on error.
+	 */
+	int (*get_bundle_uri)(struct transport *transport);
+
+	/**
 	 * Fetch the objects for the given refs. Note that this gets
 	 * an array, and should ignore the list structure.
 	 *
diff --git a/transport.c b/transport.c
index e7b97194c1..77a61a9d7b 100644
--- a/transport.c
+++ b/transport.c
@@ -22,6 +22,7 @@
 #include "protocol.h"
 #include "object-store.h"
 #include "color.h"
+#include "bundle-uri.h"
 
 static int transport_use_color = -1;
 static char transport_colors[][COLOR_MAXLEN] = {
@@ -197,7 +198,7 @@ struct git_transport_data {
 	struct git_transport_options options;
 	struct child_process *conn;
 	int fd[2];
-	unsigned got_remote_heads : 1;
+	unsigned finished_handshake : 1;
 	enum protocol_version version;
 	struct oid_array extra_have;
 	struct oid_array shallow;
@@ -344,7 +345,7 @@ static struct ref *handshake(struct transport *transport, int for_push,
 	case protocol_unknown_version:
 		BUG("unknown protocol version");
 	}
-	data->got_remote_heads = 1;
+	data->finished_handshake = 1;
 	transport->hash_algo = reader.hash_algo;
 
 	if (reader.line_peeked)
@@ -359,6 +360,39 @@ static struct ref *get_refs_via_connect(struct transport *transport, int for_pus
 	return handshake(transport, for_push, options, 1);
 }
 
+static int get_bundle_uri(struct transport *transport)
+{
+	struct git_transport_data *data = transport->data;
+	struct packet_reader reader;
+	int stateless_rpc = transport->stateless_rpc;
+
+	if (!transport->bundles) {
+		CALLOC_ARRAY(transport->bundles, 1);
+		init_bundle_list(transport->bundles);
+	}
+
+	if (!data->finished_handshake) {
+		struct ref *refs = handshake(transport, 0, NULL, 0);
+
+		if (refs)
+			free_refs(refs);
+	}
+
+	/*
+	 * "Support" protocol v0 and v2 without bundle-uri support by
+	 * silently degrading to a NOOP.
+	 */
+	if (!server_supports_v2("bundle-uri"))
+		return 0;
+
+	packet_reader_init(&reader, data->fd[0], NULL, 0,
+			   PACKET_READ_CHOMP_NEWLINE |
+			   PACKET_READ_GENTLE_ON_EOF);
+
+	return get_remote_bundle_uri(data->fd[1], &reader,
+				     transport->bundles, stateless_rpc);
+}
+
 static int fetch_refs_via_pack(struct transport *transport,
 			       int nr_heads, struct ref **to_fetch)
 {
@@ -394,7 +428,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 	args.negotiation_tips = data->options.negotiation_tips;
 	args.reject_shallow_remote = transport->smart_options->reject_shallow;
 
-	if (!data->got_remote_heads) {
+	if (!data->finished_handshake) {
 		int i;
 		int must_list_refs = 0;
 		for (i = 0; i < nr_heads; i++) {
@@ -434,7 +468,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 			  to_fetch, nr_heads, &data->shallow,
 			  &transport->pack_lockfiles, data->version);
 
-	data->got_remote_heads = 0;
+	data->finished_handshake = 0;
 	data->options.self_contained_and_connected =
 		args.self_contained_and_connected;
 	data->options.connectivity_checked = args.connectivity_checked;
@@ -819,7 +853,7 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 	if (transport_color_config() < 0)
 		return -1;
 
-	if (!data->got_remote_heads)
+	if (!data->finished_handshake)
 		get_refs_via_connect(transport, 1, NULL);
 
 	memset(&args, 0, sizeof(args));
@@ -867,7 +901,7 @@ static int git_transport_push(struct transport *transport, struct ref *remote_re
 	else
 		ret = finish_connect(data->conn);
 	data->conn = NULL;
-	data->got_remote_heads = 0;
+	data->finished_handshake = 0;
 
 	return ret;
 }
@@ -887,7 +921,7 @@ static int disconnect_git(struct transport *transport)
 {
 	struct git_transport_data *data = transport->data;
 	if (data->conn) {
-		if (data->got_remote_heads && !transport->stateless_rpc)
+		if (data->finished_handshake && !transport->stateless_rpc)
 			packet_flush(data->fd[1]);
 		close(data->fd[0]);
 		if (data->fd[1] >= 0)
@@ -902,6 +936,7 @@ static int disconnect_git(struct transport *transport)
 
 static struct transport_vtable taken_over_vtable = {
 	.get_refs_list	= get_refs_via_connect,
+	.get_bundle_uri = get_bundle_uri,
 	.fetch_refs	= fetch_refs_via_pack,
 	.push_refs	= git_transport_push,
 	.disconnect	= disconnect_git
@@ -921,7 +956,7 @@ void transport_take_over(struct transport *transport,
 	data->conn = child;
 	data->fd[0] = data->conn->out;
 	data->fd[1] = data->conn->in;
-	data->got_remote_heads = 0;
+	data->finished_handshake = 0;
 	transport->data = data;
 
 	transport->vtable = &taken_over_vtable;
@@ -1054,6 +1089,7 @@ static struct transport_vtable bundle_vtable = {
 
 static struct transport_vtable builtin_smart_vtable = {
 	.get_refs_list	= get_refs_via_connect,
+	.get_bundle_uri = get_bundle_uri,
 	.fetch_refs	= fetch_refs_via_pack,
 	.push_refs	= git_transport_push,
 	.connect	= connect_git,
@@ -1068,6 +1104,9 @@ struct transport *transport_get(struct remote *remote, const char *url)
 	ret->progress = isatty(2);
 	string_list_init_dup(&ret->pack_lockfiles);
 
+	CALLOC_ARRAY(ret->bundles, 1);
+	init_bundle_list(ret->bundles);
+
 	if (!remote)
 		BUG("No remote provided to transport_get()");
 
@@ -1118,7 +1157,7 @@ struct transport *transport_get(struct remote *remote, const char *url)
 		ret->smart_options = &(data->options);
 
 		data->conn = NULL;
-		data->got_remote_heads = 0;
+		data->finished_handshake = 0;
 	} else {
 		/* Unknown protocol in URL. Pass to external handler. */
 		int len = external_specification_len(url);
@@ -1482,6 +1521,34 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs)
 	return rc;
 }
 
+int transport_get_remote_bundle_uri(struct transport *transport)
+{
+	int value = 0;
+	const struct transport_vtable *vtable = transport->vtable;
+
+	/* Check config only once. */
+	if (transport->got_remote_bundle_uri)
+		return 0;
+	transport->got_remote_bundle_uri = 1;
+
+	/*
+	 * Don't request bundle-uri from the server unless configured to
+	 * do so by the transfer.bundleURI=true config option.
+	 */
+	if (git_config_get_bool("transfer.bundleuri", &value) || !value)
+		return 0;
+
+	if (!transport->bundles->baseURI)
+		transport->bundles->baseURI = xstrdup(transport->url);
+
+	if (!vtable->get_bundle_uri)
+		return error(_("bundle-uri operation not supported by protocol"));
+
+	if (vtable->get_bundle_uri(transport) < 0)
+		return error(_("could not retrieve server-advertised bundle-uri list"));
+	return 0;
+}
+
 void transport_unlock_pack(struct transport *transport, unsigned int flags)
 {
 	int in_signal_handler = !!(flags & TRANSPORT_UNLOCK_PACK_IN_SIGNAL_HANDLER);
@@ -1512,6 +1579,8 @@ int transport_disconnect(struct transport *transport)
 		ret = transport->vtable->disconnect(transport);
 	if (transport->got_remote_refs)
 		free_refs((void *)transport->remote_refs);
+	clear_bundle_list(transport->bundles);
+	free(transport->bundles);
 	free(transport);
 	return ret;
 }
diff --git a/transport.h b/transport.h
index b5bf7b3e70..85150f504f 100644
--- a/transport.h
+++ b/transport.h
@@ -62,6 +62,7 @@ enum transport_family {
 	TRANSPORT_FAMILY_IPV6
 };
 
+struct bundle_list;
 struct transport {
 	const struct transport_vtable *vtable;
 
@@ -76,6 +77,18 @@ struct transport {
 	 */
 	unsigned got_remote_refs : 1;
 
+	/**
+	 * Indicates whether we already called get_bundle_uri_list(); set by
+	 * transport.c::transport_get_remote_bundle_uri().
+	 */
+	unsigned got_remote_bundle_uri : 1;
+
+	/*
+	 * The results of "command=bundle-uri", if both sides support
+	 * the "bundle-uri" capability.
+	 */
+	struct bundle_list *bundles;
+
 	/*
 	 * Transports that call take-over destroys the data specific to
 	 * the transport type while doing so, and cannot be reused.
@@ -281,6 +294,12 @@ void transport_ls_refs_options_release(struct transport_ls_refs_options *opts);
 const struct ref *transport_get_remote_refs(struct transport *transport,
 					    struct transport_ls_refs_options *transport_options);
 
+/**
+ * Retrieve bundle URI(s) from a remote. Populates "struct
+ * transport"'s "bundle_uri" and "got_remote_bundle_uri".
+ */
+int transport_get_remote_bundle_uri(struct transport *transport);
+
 /*
  * Fetch the hash algorithm used by a remote.
  *