Merge branch 'jt/cdn-offload'

The "fetch/clone" protocol has been updated to allow the server to
instruct the clients to grab pre-packaged packfile(s) in addition
to the packed object data coming over the wire.

* jt/cdn-offload:
  upload-pack: fix a sparse '0 as NULL pointer' warning
  upload-pack: send part of packfile response as uri
  fetch-pack: support more than one pack lockfile
  upload-pack: refactor reading of pack-objects out
  Documentation: add Packfile URIs design doc
  Documentation: order protocol v2 sections
  http-fetch: support fetching packfiles by URL
  http-fetch: refactor into function
  http: refactor finish_http_pack_request()
  http: use --stdin when indexing dumb HTTP pack

19 files changed, 750 insertions, 167 deletions

diff --git a/Documentation/git-http-fetch.txt b/Documentation/git-http-fetch.txt
index 666b042679..4deb4893f5 100644
--- a/Documentation/git-http-fetch.txt
+++ b/Documentation/git-http-fetch.txt
@@ -9,7 +9,7 @@ git-http-fetch - Download from a remote Git repository via HTTP
 SYNOPSIS
 --------
 [verse]
-'git http-fetch' [-c] [-t] [-a] [-d] [-v] [-w filename] [--recover] [--stdin] <commit> <url>
+'git http-fetch' [-c] [-t] [-a] [-d] [-v] [-w filename] [--recover] [--stdin | --packfile=<hash> | <commit>] <url>
 
 DESCRIPTION
 -----------
@@ -40,6 +40,13 @@ commit-id::
 
 		<commit-id>['\t'<filename-as-in--w>]
 
+--packfile=<hash>::
+	Instead of a commit id on the command line (which is not expected in
+	this case), 'git http-fetch' fetches the packfile directly at the given
+	URL and uses index-pack to generate corresponding .idx and .keep files.
+	The hash is used to determine the name of the temporary file and is
+	arbitrary. The output of index-pack is printed to stdout.
+
 --recover::
 	Verify that everything reachable from target is fetched.  Used after
 	an earlier fetch is interrupted.
diff --git a/Documentation/technical/packfile-uri.txt b/Documentation/technical/packfile-uri.txt
new file mode 100644
index 0000000000..318713abc3
--- /dev/null
+++ b/Documentation/technical/packfile-uri.txt
@@ -0,0 +1,78 @@
+Packfile URIs
+=============
+
+This feature allows servers to serve part of their packfile response as URIs.
+This allows server designs that improve scalability in bandwidth and CPU usage
+(for example, by serving some data through a CDN), and (in the future) provides
+some measure of resumability to clients.
+
+This feature is available only in protocol version 2.
+
+Protocol
+--------
+
+The server advertises the `packfile-uris` capability.
+
+If the client then communicates which protocols (HTTPS, etc.) it supports with
+a `packfile-uris` argument, the server MAY send a `packfile-uris` section
+directly before the `packfile` section (right after `wanted-refs` if it is
+sent) containing URIs of any of the given protocols. The URIs point to
+packfiles that use only features that the client has declared that it supports
+(e.g. ofs-delta and thin-pack). See protocol-v2.txt for the documentation of
+this section.
+
+Clients should then download and index all the given URIs (in addition to
+downloading and indexing the packfile given in the `packfile` section of the
+response) before performing the connectivity check.
+
+Server design
+-------------
+
+The server can be trivially made compatible with the proposed protocol by
+having it advertise `packfile-uris`, tolerating the client sending
+`packfile-uris`, and never sending any `packfile-uris` section. But we should
+include some sort of non-trivial implementation in the Minimum Viable Product,
+at least so that we can test the client.
+
+This is the implementation: a feature, marked experimental, that allows the
+server to be configured by one or more `uploadpack.blobPackfileUri=<sha1>
+<uri>` entries. Whenever the list of objects to be sent is assembled, all such
+blobs are excluded, replaced with URIs. The client will download those URIs,
+expecting them to each point to packfiles containing single blobs.
+
+Client design
+-------------
+
+The client has a config variable `fetch.uriprotocols` that determines which
+protocols the end user is willing to use. By default, this is empty.
+
+When the client downloads the given URIs, it should store them with "keep"
+files, just like it does with the packfile in the `packfile` section. These
+additional "keep" files can only be removed after the refs have been updated -
+just like the "keep" file for the packfile in the `packfile` section.
+
+The division of work (initial fetch + additional URIs) introduces convenient
+points for resumption of an interrupted clone - such resumption can be done
+after the Minimum Viable Product (see "Future work").
+
+Future work
+-----------
+
+The protocol design allows some evolution of the server and client without any
+need for protocol changes, so only a small-scoped design is included here to
+form the MVP. For example, the following can be done:
+
+ * On the server, more sophisticated means of excluding objects (e.g. by
+   specifying a commit to represent that commit and all objects that it
+   references).
+ * On the client, resumption of clone. If a clone is interrupted, information
+   could be recorded in the repository's config and a "clone-resume" command
+   can resume the clone in progress. (Resumption of subsequent fetches is more
+   difficult because that must deal with the user wanting to use the repository
+   even after the fetch was interrupted.)
+
+There are some possible features that will require a change in protocol:
+
+ * Additional HTTP headers (e.g. authentication)
+ * Byte range support
+ * Different file formats referenced by URIs (e.g. raw object)
diff --git a/Documentation/technical/protocol-v2.txt b/Documentation/technical/protocol-v2.txt
index 3996d70891..5852f499a6 100644
--- a/Documentation/technical/protocol-v2.txt
+++ b/Documentation/technical/protocol-v2.txt
@@ -325,13 +325,26 @@ included in the client's request:
 	indicating its sideband (1, 2, or 3), and the server may send "0005\2"
 	(a PKT-LINE of sideband 2 with no payload) as a keepalive packet.
 
+If the 'packfile-uris' feature is advertised, the following argument
+can be included in the client's request as well as the potential
+addition of the 'packfile-uris' section in the server's response as
+explained below.
+
+    packfile-uris <comma-separated list of protocols>
+	Indicates to the server that the client is willing to receive
+	URIs of any of the given protocols in place of objects in the
+	sent packfile. Before performing the connectivity check, the
+	client should download from all given URIs. Currently, the
+	protocols supported are "http" and "https".
+
 The response of `fetch` is broken into a number of sections separated by
 delimiter packets (0001), with each section beginning with its section
-header.
+header. Most sections are sent only when the packfile is sent.
 
-    output = *section
-    section = (acknowledgments | shallow-info | wanted-refs | packfile)
-	      (flush-pkt | delim-pkt)
+    output = acknowledgements flush-pkt |
+	     [acknowledgments delim-pkt] [shallow-info delim-pkt]
+	     [wanted-refs delim-pkt] [packfile-uris delim-pkt]
+	     packfile flush-pkt
 
     acknowledgments = PKT-LINE("acknowledgments" LF)
 		      (nak | *ack)
@@ -349,13 +362,17 @@ header.
 		  *PKT-LINE(wanted-ref LF)
     wanted-ref = obj-id SP refname
 
+    packfile-uris = PKT-LINE("packfile-uris" LF) *packfile-uri
+    packfile-uri = PKT-LINE(40*(HEXDIGIT) SP *%x20-ff LF)
+
     packfile = PKT-LINE("packfile" LF)
 	       *PKT-LINE(%x01-03 *%x00-ff)
 
     acknowledgments section
-	* If the client determines that it is finished with negotiations
-	  by sending a "done" line, the acknowledgments sections MUST be
-	  omitted from the server's response.
+	* If the client determines that it is finished with negotiations by
+	  sending a "done" line (thus requiring the server to send a packfile),
+	  the acknowledgments sections MUST be omitted from the server's
+	  response.
 
 	* Always begins with the section header "acknowledgments"
 
@@ -406,9 +423,6 @@ header.
 	  which the client has not indicated was shallow as a part of
 	  its request.
 
-	* This section is only included if a packfile section is also
-	  included in the response.
-
     wanted-refs section
 	* This section is only included if the client has requested a
 	  ref using a 'want-ref' line and if a packfile section is also
@@ -422,6 +436,20 @@ header.
 	* The server MUST NOT send any refs which were not requested
 	  using 'want-ref' lines.
 
+    packfile-uris section
+	* This section is only included if the client sent
+	  'packfile-uris' and the server has at least one such URI to
+	  send.
+
+	* Always begins with the section header "packfile-uris".
+
+	* For each URI the server sends, it sends a hash of the pack's
+	  contents (as output by git index-pack) followed by the URI.
+
+	* The hashes are 40 hex characters long. When Git upgrades to a new
+	  hash algorithm, this might need to be updated. (It should match
+	  whatever index-pack outputs after "pack\t" or "keep\t".
+
     packfile section
 	* This section is only included if the client has sent 'want'
 	  lines in its request and either requested that no more
diff --git a/builtin/fetch-pack.c b/builtin/fetch-pack.c
index 94b0c89b82..bbb5c96167 100644
--- a/builtin/fetch-pack.c
+++ b/builtin/fetch-pack.c
@@ -48,8 +48,8 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	struct ref **sought = NULL;
 	int nr_sought = 0, alloc_sought = 0;
 	int fd[2];
-	char *pack_lockfile = NULL;
-	char **pack_lockfile_ptr = NULL;
+	struct string_list pack_lockfiles = STRING_LIST_INIT_DUP;
+	struct string_list *pack_lockfiles_ptr = NULL;
 	struct child_process *conn;
 	struct fetch_pack_args args;
 	struct oid_array shallow = OID_ARRAY_INIT;
@@ -134,7 +134,7 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 		}
 		if (!strcmp("--lock-pack", arg)) {
 			args.lock_pack = 1;
-			pack_lockfile_ptr = &pack_lockfile;
+			pack_lockfiles_ptr = &pack_lockfiles;
 			continue;
 		}
 		if (!strcmp("--check-self-contained-and-connected", arg)) {
@@ -235,10 +235,15 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	}
 
 	ref = fetch_pack(&args, fd, ref, sought, nr_sought,
-			 &shallow, pack_lockfile_ptr, version);
-	if (pack_lockfile) {
-		printf("lock %s\n", pack_lockfile);
+			 &shallow, pack_lockfiles_ptr, version);
+	if (pack_lockfiles.nr) {
+		int i;
+
+		printf("lock %s\n", pack_lockfiles.items[0].string);
 		fflush(stdout);
+		for (i = 1; i < pack_lockfiles.nr; i++)
+			warning(_("Lockfile created but not reported: %s"),
+				pack_lockfiles.items[i].string);
 	}
 	if (args.check_self_contained_and_connected &&
 	    args.self_contained_and_connected) {
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index c5b433a23f..7016b28485 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -117,6 +117,8 @@ static unsigned long window_memory_limit = 0;
 
 static struct list_objects_filter_options filter_options;
 
+static struct string_list uri_protocols = STRING_LIST_INIT_NODUP;
+
 enum missing_action {
 	MA_ERROR = 0,      /* fail if any missing objects are encountered */
 	MA_ALLOW_ANY,      /* silently allow ALL missing objects */
@@ -125,6 +127,15 @@ enum missing_action {
 static enum missing_action arg_missing_action;
 static show_object_fn fn_show_object;
 
+struct configured_exclusion {
+	struct oidmap_entry e;
+	char *pack_hash_hex;
+	char *uri;
+};
+static struct oidmap configured_exclusions;
+
+static struct oidset excluded_by_config;
+
 /*
  * stats
  */
@@ -969,6 +980,25 @@ static void write_reused_pack(struct hashfile *f)
 	unuse_pack(&w_curs);
 }
 
+static void write_excluded_by_configs(void)
+{
+	struct oidset_iter iter;
+	const struct object_id *oid;
+
+	oidset_iter_init(&excluded_by_config, &iter);
+	while ((oid = oidset_iter_next(&iter))) {
+		struct configured_exclusion *ex =
+			oidmap_get(&configured_exclusions, oid);
+
+		if (!ex)
+			BUG("configured exclusion wasn't configured");
+		write_in_full(1, ex->pack_hash_hex, strlen(ex->pack_hash_hex));
+		write_in_full(1, " ", 1);
+		write_in_full(1, ex->uri, strlen(ex->uri));
+		write_in_full(1, "\n", 1);
+	}
+}
+
 static const char no_split_warning[] = N_(
 "disabling bitmap writing, packs are split due to pack.packSizeLimit"
 );
@@ -1266,6 +1296,25 @@ static int want_object_in_pack(const struct object_id *oid,
 		}
 	}
 
+	if (uri_protocols.nr) {
+		struct configured_exclusion *ex =
+			oidmap_get(&configured_exclusions, oid);
+		int i;
+		const char *p;
+
+		if (ex) {
+			for (i = 0; i < uri_protocols.nr; i++) {
+				if (skip_prefix(ex->uri,
+						uri_protocols.items[i].string,
+						&p) &&
+				    *p == ':') {
+					oidset_insert(&excluded_by_config, oid);
+					return 0;
+				}
+			}
+		}
+	}
+
 	return 1;
 }
 
@@ -2864,6 +2913,29 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 			    pack_idx_opts.version);
 		return 0;
 	}
+	if (!strcmp(k, "uploadpack.blobpackfileuri")) {
+		struct configured_exclusion *ex = xmalloc(sizeof(*ex));
+		const char *oid_end, *pack_end;
+		/*
+		 * Stores the pack hash. This is not a true object ID, but is
+		 * of the same form.
+		 */
+		struct object_id pack_hash;
+
+		if (parse_oid_hex(v, &ex->e.oid, &oid_end) ||
+		    *oid_end != ' ' ||
+		    parse_oid_hex(oid_end + 1, &pack_hash, &pack_end) ||
+		    *pack_end != ' ')
+			die(_("value of uploadpack.blobpackfileuri must be "
+			      "of the form '<object-hash> <pack-hash> <uri>' (got '%s')"), v);
+		if (oidmap_get(&configured_exclusions, &ex->e.oid))
+			die(_("object already configured in another "
+			      "uploadpack.blobpackfileuri (got '%s')"), v);
+		ex->pack_hash_hex = xcalloc(1, pack_end - oid_end);
+		memcpy(ex->pack_hash_hex, oid_end + 1, pack_end - oid_end - 1);
+		ex->uri = xstrdup(pack_end + 1);
+		oidmap_put(&configured_exclusions, ex);
+	}
 	return git_default_config(k, v, cb);
 }
 
@@ -3462,6 +3534,9 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 			 N_("do not pack objects in promisor packfiles")),
 		OPT_BOOL(0, "delta-islands", &use_delta_islands,
 			 N_("respect islands during delta compression")),
+		OPT_STRING_LIST(0, "uri-protocol", &uri_protocols,
+				N_("protocol"),
+				N_("exclude any configured uploadpack.blobpackfileuri with this protocol")),
 		OPT_END(),
 	};
 
@@ -3650,6 +3725,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 	}
 
 	trace2_region_enter("pack-objects", "write-pack-file", the_repository);
+	write_excluded_by_configs();
 	write_pack_file();
 	trace2_region_leave("pack-objects", "write-pack-file", the_repository);
 
diff --git a/connected.c b/connected.c
index 3135b71e19..937b4bae38 100644
--- a/connected.c
+++ b/connected.c
@@ -43,10 +43,12 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
 
 	if (transport && transport->smart_options &&
 	    transport->smart_options->self_contained_and_connected &&
-	    transport->pack_lockfile &&
-	    strip_suffix(transport->pack_lockfile, ".keep", &base_len)) {
+	    transport->pack_lockfiles.nr == 1 &&
+	    strip_suffix(transport->pack_lockfiles.items[0].string,
+			 ".keep", &base_len)) {
 		struct strbuf idx_file = STRBUF_INIT;
-		strbuf_add(&idx_file, transport->pack_lockfile, base_len);
+		strbuf_add(&idx_file, transport->pack_lockfiles.items[0].string,
+			   base_len);
 		strbuf_addstr(&idx_file, ".idx");
 		new_pack = add_packed_git(idx_file.buf, idx_file.len, 1);
 		strbuf_release(&idx_file);
diff --git a/fetch-pack.c b/fetch-pack.c
index d8bbf45ee2..acd55ba6e8 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -38,6 +38,7 @@ static int server_supports_filtering;
 static struct shallow_lock shallow_lock;
 static const char *alternate_shallow_file;
 static struct strbuf fsck_msg_types = STRBUF_INIT;
+static struct string_list uri_protocols = STRING_LIST_INIT_DUP;
 
 /* Remember to update object flag allocation in object.h */
 #define COMPLETE	(1U << 0)
@@ -794,7 +795,8 @@ static void write_promisor_file(const char *keep_name,
 }
 
 static int get_pack(struct fetch_pack_args *args,
-		    int xd[2], char **pack_lockfile,
+		    int xd[2], struct string_list *pack_lockfiles,
+		    int only_packfile,
 		    struct ref **sought, int nr_sought)
 {
 	struct async demux;
@@ -838,7 +840,7 @@ static int get_pack(struct fetch_pack_args *args,
 	}
 
 	if (do_keep || args->from_promisor) {
-		if (pack_lockfile)
+		if (pack_lockfiles)
 			cmd.out = -1;
 		cmd_name = "index-pack";
 		argv_array_push(&cmd.args, cmd_name);
@@ -855,15 +857,22 @@ static int get_pack(struct fetch_pack_args *args,
 					"--keep=fetch-pack %"PRIuMAX " on %s",
 					(uintmax_t)getpid(), hostname);
 		}
-		if (args->check_self_contained_and_connected)
+		if (only_packfile && args->check_self_contained_and_connected)
 			argv_array_push(&cmd.args, "--check-self-contained-and-connected");
+		else
+			/*
+			 * We cannot perform any connectivity checks because
+			 * not all packs have been downloaded; let the caller
+			 * have this responsibility.
+			 */
+			args->check_self_contained_and_connected = 0;
 		/*
 		 * If we're obtaining the filename of a lockfile, we'll use
 		 * that filename to write a .promisor file with more
 		 * information below. If not, we need index-pack to do it for
 		 * us.
 		 */
-		if (!(do_keep && pack_lockfile) && args->from_promisor)
+		if (!(do_keep && pack_lockfiles) && args->from_promisor)
 			argv_array_push(&cmd.args, "--promisor");
 	}
 	else {
@@ -899,8 +908,9 @@ static int get_pack(struct fetch_pack_args *args,
 	cmd.git_cmd = 1;
 	if (start_command(&cmd))
 		die(_("fetch-pack: unable to fork off %s"), cmd_name);
-	if (do_keep && pack_lockfile) {
-		*pack_lockfile = index_pack_lockfile(cmd.out);
+	if (do_keep && pack_lockfiles) {
+		string_list_append_nodup(pack_lockfiles,
+					 index_pack_lockfile(cmd.out));
 		close(cmd.out);
 	}
 
@@ -922,8 +932,8 @@ static int get_pack(struct fetch_pack_args *args,
 	 * Now that index-pack has succeeded, write the promisor file using the
 	 * obtained .keep filename if necessary
 	 */
-	if (do_keep && pack_lockfile && args->from_promisor)
-		write_promisor_file(*pack_lockfile, sought, nr_sought);
+	if (do_keep && pack_lockfiles && pack_lockfiles->nr && args->from_promisor)
+		write_promisor_file(pack_lockfiles->items[0].string, sought, nr_sought);
 
 	return 0;
 }
@@ -940,7 +950,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 				 const struct ref *orig_ref,
 				 struct ref **sought, int nr_sought,
 				 struct shallow_info *si,
-				 char **pack_lockfile)
+				 struct string_list *pack_lockfiles)
 {
 	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
@@ -1067,7 +1077,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 		alternate_shallow_file = setup_temporary_shallow(si->shallow);
 	else
 		alternate_shallow_file = NULL;
-	if (get_pack(args, fd, pack_lockfile, sought, nr_sought))
+	if (get_pack(args, fd, pack_lockfiles, 1, sought, nr_sought))
 		die(_("git fetch-pack: fetch failed."));
 
  all_done:
@@ -1221,6 +1231,26 @@ static int send_fetch_request(struct fetch_negotiator *negotiator, int fd_out,
 		warning("filtering not recognized by server, ignoring");
 	}
 
+	if (server_supports_feature("fetch", "packfile-uris", 0)) {
+		int i;
+		struct strbuf to_send = STRBUF_INIT;
+
+		for (i = 0; i < uri_protocols.nr; i++) {
+			const char *s = uri_protocols.items[i].string;
+
+			if (!strcmp(s, "https") || !strcmp(s, "http")) {
+				if (to_send.len)
+					strbuf_addch(&to_send, ',');
+				strbuf_addstr(&to_send, s);
+			}
+		}
+		if (to_send.len) {
+			packet_buf_write(&req_buf, "packfile-uris %s",
+					 to_send.buf);
+			strbuf_release(&to_send);
+		}
+	}
+
 	/* add wants */
 	add_wants(args->no_dependents, wants, &req_buf);
 
@@ -1443,6 +1473,21 @@ static void receive_wanted_refs(struct packet_reader *reader,
 		die(_("error processing wanted refs: %d"), reader->status);
 }
 
+static void receive_packfile_uris(struct packet_reader *reader,
+				  struct string_list *uris)
+{
+	process_section_header(reader, "packfile-uris", 0);
+	while (packet_reader_read(reader) == PACKET_READ_NORMAL) {
+		if (reader->pktlen < the_hash_algo->hexsz ||
+		    reader->line[the_hash_algo->hexsz] != ' ')
+			die("expected '<hash> <uri>', got: %s\n", reader->line);
+
+		string_list_append(uris, reader->line);
+	}
+	if (reader->status != PACKET_READ_DELIM)
+		die("expected DELIM");
+}
+
 enum fetch_state {
 	FETCH_CHECK_LOCAL = 0,
 	FETCH_SEND_REQUEST,
@@ -1464,7 +1509,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				    struct ref **sought, int nr_sought,
 				    struct oid_array *shallows,
 				    struct shallow_info *si,
-				    char **pack_lockfile)
+				    struct string_list *pack_lockfiles)
 {
 	struct repository *r = the_repository;
 	struct ref *ref = copy_ref_list(orig_ref);
@@ -1476,6 +1521,8 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	struct fetch_negotiator negotiator_alloc;
 	struct fetch_negotiator *negotiator;
 	int seen_ack = 0;
+	struct string_list packfile_uris = STRING_LIST_INIT_DUP;
+	int i;
 
 	if (args->no_dependents) {
 		negotiator = NULL;
@@ -1569,9 +1616,12 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 			if (process_section_header(&reader, "wanted-refs", 1))
 				receive_wanted_refs(&reader, sought, nr_sought);
 
-			/* get the pack */
+			/* get the pack(s) */
+			if (process_section_header(&reader, "packfile-uris", 1))
+				receive_packfile_uris(&reader, &packfile_uris);
 			process_section_header(&reader, "packfile", 0);
-			if (get_pack(args, fd, pack_lockfile, sought, nr_sought))
+			if (get_pack(args, fd, pack_lockfiles,
+				     !packfile_uris.nr, sought, nr_sought))
 				die(_("git fetch-pack: fetch failed."));
 			do_check_stateless_delimiter(args, &reader);
 
@@ -1582,8 +1632,55 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 		}
 	}
 
+	for (i = 0; i < packfile_uris.nr; i++) {
+		struct child_process cmd = CHILD_PROCESS_INIT;
+		char packname[GIT_MAX_HEXSZ + 1];
+		const char *uri = packfile_uris.items[i].string +
+			the_hash_algo->hexsz + 1;
+
+		argv_array_push(&cmd.args, "http-fetch");
+		argv_array_pushf(&cmd.args, "--packfile=%.*s",
+				 (int) the_hash_algo->hexsz,
+				 packfile_uris.items[i].string);
+		argv_array_push(&cmd.args, uri);
+		cmd.git_cmd = 1;
+		cmd.no_stdin = 1;
+		cmd.out = -1;
+		if (start_command(&cmd))
+			die("fetch-pack: unable to spawn http-fetch");
+
+		if (read_in_full(cmd.out, packname, 5) < 0 ||
+		    memcmp(packname, "keep\t", 5))
+			die("fetch-pack: expected keep then TAB at start of http-fetch output");
+
+		if (read_in_full(cmd.out, packname,
+				 the_hash_algo->hexsz + 1) < 0 ||
+		    packname[the_hash_algo->hexsz] != '\n')
+			die("fetch-pack: expected hash then LF at end of http-fetch output");
+
+		packname[the_hash_algo->hexsz] = '\0';
+
+		close(cmd.out);
+
+		if (finish_command(&cmd))
+			die("fetch-pack: unable to finish http-fetch");
+
+		if (memcmp(packfile_uris.items[i].string, packname,
+			   the_hash_algo->hexsz))
+			die("fetch-pack: pack downloaded from %s does not match expected hash %.*s",
+			    uri, (int) the_hash_algo->hexsz,
+			    packfile_uris.items[i].string);
+
+		string_list_append_nodup(pack_lockfiles,
+					 xstrfmt("%s/pack/pack-%s.keep",
+						 get_object_directory(),
+						 packname));
+	}
+	string_list_clear(&packfile_uris, 0);
+
 	if (negotiator)
 		negotiator->release(negotiator);
+
 	oidset_clear(&common);
 	return ref;
 }
@@ -1620,6 +1717,14 @@ static void fetch_pack_config(void)
 	git_config_get_bool("repack.usedeltabaseoffset", &prefer_ofs_delta);
 	git_config_get_bool("fetch.fsckobjects", &fetch_fsck_objects);
 	git_config_get_bool("transfer.fsckobjects", &transfer_fsck_objects);
+	if (!uri_protocols.nr) {
+		char *str;
+
+		if (!git_config_get_string("fetch.uriprotocols", &str) && str) {
+			string_list_split(&uri_protocols, str, ',', -1);
+			free(str);
+		}
+	}
 
 	git_config(fetch_pack_config_cb, NULL);
 }
@@ -1772,7 +1877,7 @@ struct ref *fetch_pack(struct fetch_pack_args *args,
 		       const struct ref *ref,
 		       struct ref **sought, int nr_sought,
 		       struct oid_array *shallow,
-		       char **pack_lockfile,
+		       struct string_list *pack_lockfiles,
 		       enum protocol_version version)
 {
 	struct ref *ref_cpy;
@@ -1807,11 +1912,11 @@ struct ref *fetch_pack(struct fetch_pack_args *args,
 		memset(&si, 0, sizeof(si));
 		ref_cpy = do_fetch_pack_v2(args, fd, ref, sought, nr_sought,
 					   &shallows_scratch, &si,
-					   pack_lockfile);
+					   pack_lockfiles);
 	} else {
 		prepare_shallow_info(&si, shallow);
 		ref_cpy = do_fetch_pack(args, fd, ref, sought, nr_sought,
-					&si, pack_lockfile);
+					&si, pack_lockfiles);
 	}
 	reprepare_packed_git(the_repository);
 
diff --git a/fetch-pack.h b/fetch-pack.h
index 67f684229a..85d1e39fe7 100644
--- a/fetch-pack.h
+++ b/fetch-pack.h
@@ -83,7 +83,7 @@ struct ref *fetch_pack(struct fetch_pack_args *args,
 		       struct ref **sought,
 		       int nr_sought,
 		       struct oid_array *shallow,
-		       char **pack_lockfile,
+		       struct string_list *pack_lockfiles,
 		       enum protocol_version version);
 
 /*
diff --git a/http-fetch.c b/http-fetch.c
index a32ac118d9..1df376e745 100644
--- a/http-fetch.c
+++ b/http-fetch.c
@@ -5,22 +5,90 @@
 #include "walker.h"
 
 static const char http_fetch_usage[] = "git http-fetch "
-"[-c] [-t] [-a] [-v] [--recover] [-w ref] [--stdin] commit-id url";
+"[-c] [-t] [-a] [-v] [--recover] [-w ref] [--stdin | --packfile=hash | commit-id] url";
 
-int cmd_main(int argc, const char **argv)
+static int fetch_using_walker(const char *raw_url, int get_verbosely,
+			      int get_recover, int commits, char **commit_id,
+			      const char **write_ref, int commits_on_stdin)
 {
+	char *url = NULL;
 	struct walker *walker;
+	int rc;
+
+	str_end_url_with_slash(raw_url, &url);
+
+	http_init(NULL, url, 0);
+
+	walker = get_http_walker(url);
+	walker->get_verbosely = get_verbosely;
+	walker->get_recover = get_recover;
+	walker->get_progress = 0;
+
+	rc = walker_fetch(walker, commits, commit_id, write_ref, url);
+
+	if (commits_on_stdin)
+		walker_targets_free(commits, commit_id, write_ref);
+
+	if (walker->corrupt_object_found) {
+		fprintf(stderr,
+"Some loose object were found to be corrupt, but they might be just\n"
+"a false '404 Not Found' error message sent with incorrect HTTP\n"
+"status code.  Suggest running 'git fsck'.\n");
+	}
+
+	walker_free(walker);
+	http_cleanup();
+	free(url);
+
+	return rc;
+}
+
+static void fetch_single_packfile(struct object_id *packfile_hash,
+				  const char *url) {
+	struct http_pack_request *preq;
+	struct slot_results results;
+	int ret;
+
+	http_init(NULL, url, 0);
+
+	preq = new_direct_http_pack_request(packfile_hash->hash, xstrdup(url));
+	if (preq == NULL)
+		die("couldn't create http pack request");
+	preq->slot->results = &results;
+	preq->generate_keep = 1;
+
+	if (start_active_slot(preq->slot)) {
+		run_active_slot(preq->slot);
+		if (results.curl_result != CURLE_OK) {
+			die("Unable to get pack file %s\n%s", preq->url,
+			    curl_errorstr);
+		}
+	} else {
+		die("Unable to start request");
+	}
+
+	if ((ret = finish_http_pack_request(preq)))
+		die("finish_http_pack_request gave result %d", ret);
+
+	release_http_pack_request(preq);
+	http_cleanup();
+}
+
+int cmd_main(int argc, const char **argv)
+{
 	int commits_on_stdin = 0;
 	int commits;
 	const char **write_ref = NULL;
 	char **commit_id;
-	char *url = NULL;
 	int arg = 1;
-	int rc = 0;
 	int get_verbosely = 0;
 	int get_recover = 0;
+	int packfile = 0;
+	struct object_id packfile_hash;
 
 	while (arg < argc && argv[arg][0] == '-') {
+		const char *p;
+
 		if (argv[arg][1] == 't') {
 		} else if (argv[arg][1] == 'c') {
 		} else if (argv[arg][1] == 'a') {
@@ -35,46 +103,34 @@ int cmd_main(int argc, const char **argv)
 			get_recover = 1;
 		} else if (!strcmp(argv[arg], "--stdin")) {
 			commits_on_stdin = 1;
+		} else if (skip_prefix(argv[arg], "--packfile=", &p)) {
+			const char *end;
+
+			packfile = 1;
+			if (parse_oid_hex(p, &packfile_hash, &end) || *end)
+				die(_("argument to --packfile must be a valid hash (got '%s')"), p);
 		}
 		arg++;
 	}
-	if (argc != arg + 2 - commits_on_stdin)
+	if (argc != arg + 2 - (commits_on_stdin || packfile))
 		usage(http_fetch_usage);
-	if (commits_on_stdin) {
-		commits = walker_targets_stdin(&commit_id, &write_ref);
-	} else {
-		commit_id = (char **) &argv[arg++];
-		commits = 1;
-	}
-
-	if (argv[arg])
-		str_end_url_with_slash(argv[arg], &url);
 
 	setup_git_directory();
 
 	git_config(git_default_config, NULL);
 
-	http_init(NULL, url, 0);
-	walker = get_http_walker(url);
-	walker->get_verbosely = get_verbosely;
-	walker->get_recover = get_recover;
-
-	rc = walker_fetch(walker, commits, commit_id, write_ref, url);
-
-	if (commits_on_stdin)
-		walker_targets_free(commits, commit_id, write_ref);
-
-	if (walker->corrupt_object_found) {
-		fprintf(stderr,
-"Some loose object were found to be corrupt, but they might be just\n"
-"a false '404 Not Found' error message sent with incorrect HTTP\n"
-"status code.  Suggest running 'git fsck'.\n");
+	if (packfile) {
+		fetch_single_packfile(&packfile_hash, argv[arg]);
+		return 0;
 	}
 
-	walker_free(walker);
-	http_cleanup();
-
-	free(url);
-
-	return rc;
+	if (commits_on_stdin) {
+		commits = walker_targets_stdin(&commit_id, &write_ref);
+	} else {
+		commit_id = (char **) &argv[arg++];
+		commits = 1;
+	}
+	return fetch_using_walker(argv[arg], get_verbosely, get_recover,
+				  commits, commit_id, write_ref,
+				  commits_on_stdin);
 }
diff --git a/http-push.c b/http-push.c
index 822f326599..ac7868ffee 100644
--- a/http-push.c
+++ b/http-push.c
@@ -117,6 +117,7 @@ enum transfer_state {
 
 struct transfer_request {
 	struct object *obj;
+	struct packed_git *target;
 	char *url;
 	char *dest;
 	struct remote_lock *lock;
@@ -314,17 +315,18 @@ static void start_fetch_packed(struct transfer_request *request)
 		release_request(request);
 		return;
 	}
+	close_pack_index(target);
+	request->target = target;
 
 	fprintf(stderr,	"Fetching pack %s\n",
 		hash_to_hex(target->hash));
 	fprintf(stderr, " which contains %s\n", oid_to_hex(&request->obj->oid));
 
-	preq = new_http_pack_request(target, repo->url);
+	preq = new_http_pack_request(target->hash, repo->url);
 	if (preq == NULL) {
 		repo->can_update_info_refs = 0;
 		return;
 	}
-	preq->lst = &repo->packs;
 
 	/* Make sure there isn't another open request for this pack */
 	while (check_request) {
@@ -597,6 +599,8 @@ static void finish_request(struct transfer_request *request)
 		}
 		if (fail)
 			repo->can_update_info_refs = 0;
+		else
+			http_install_packfile(request->target, &repo->packs);
 		release_request(request);
 	}
 }
diff --git a/http-walker.c b/http-walker.c
index fe15e325fa..4fb1235cd4 100644
--- a/http-walker.c
+++ b/http-walker.c
@@ -439,6 +439,7 @@ static int http_fetch_pack(struct walker *walker, struct alt_base *repo, unsigne
 	target = find_sha1_pack(sha1, repo->packs);
 	if (!target)
 		return -1;
+	close_pack_index(target);
 
 	if (walker->get_verbosely) {
 		fprintf(stderr, "Getting pack %s\n",
@@ -447,10 +448,9 @@ static int http_fetch_pack(struct walker *walker, struct alt_base *repo, unsigne
 			hash_to_hex(sha1));
 	}
 
-	preq = new_http_pack_request(target, repo->base);
+	preq = new_http_pack_request(target->hash, repo->base);
 	if (preq == NULL)
 		goto abort;
-	preq->lst = &repo->packs;
 	preq->slot->results = &results;
 
 	if (start_active_slot(preq->slot)) {
@@ -469,6 +469,7 @@ static int http_fetch_pack(struct walker *walker, struct alt_base *repo, unsigne
 	release_http_pack_request(preq);
 	if (ret)
 		return ret;
+	http_install_packfile(target, &repo->packs);
 
 	return 0;
 
diff --git a/http.c b/http.c
index 0eb1931a15..3b12843a5b 100644
--- a/http.c
+++ b/http.c
@@ -2261,70 +2261,74 @@ void release_http_pack_request(struct http_pack_request *preq)
 
 int finish_http_pack_request(struct http_pack_request *preq)
 {
-	struct packed_git **lst;
-	struct packed_git *p = preq->target;
-	char *tmp_idx;
-	size_t len;
 	struct child_process ip = CHILD_PROCESS_INIT;
-
-	close_pack_index(p);
+	int tmpfile_fd;
+	int ret = 0;
 
 	fclose(preq->packfile);
 	preq->packfile = NULL;
 
-	lst = preq->lst;
-	while (*lst != p)
-		lst = &((*lst)->next);
-	*lst = (*lst)->next;
-
-	if (!strip_suffix(preq->tmpfile.buf, ".pack.temp", &len))
-		BUG("pack tmpfile does not end in .pack.temp?");
-	tmp_idx = xstrfmt("%.*s.idx.temp", (int)len, preq->tmpfile.buf);
+	tmpfile_fd = xopen(preq->tmpfile.buf, O_RDONLY);
 
 	argv_array_push(&ip.args, "index-pack");
-	argv_array_pushl(&ip.args, "-o", tmp_idx, NULL);
-	argv_array_push(&ip.args, preq->tmpfile.buf);
+	argv_array_push(&ip.args, "--stdin");
 	ip.git_cmd = 1;
-	ip.no_stdin = 1;
-	ip.no_stdout = 1;
+	ip.in = tmpfile_fd;
+	if (preq->generate_keep) {
+		argv_array_pushf(&ip.args, "--keep=git %"PRIuMAX,
+				 (uintmax_t)getpid());
+		ip.out = 0;
+	} else {
+		ip.no_stdout = 1;
+	}
 
 	if (run_command(&ip)) {
-		unlink(preq->tmpfile.buf);
-		unlink(tmp_idx);
-		free(tmp_idx);
-		return -1;
+		ret = -1;
+		goto cleanup;
 	}
 
-	unlink(sha1_pack_index_name(p->hash));
+cleanup:
+	close(tmpfile_fd);
+	unlink(preq->tmpfile.buf);
+	return ret;
+}
 
-	if (finalize_object_file(preq->tmpfile.buf, sha1_pack_name(p->hash))
-	 || finalize_object_file(tmp_idx, sha1_pack_index_name(p->hash))) {
-		free(tmp_idx);
-		return -1;
-	}
+void http_install_packfile(struct packed_git *p,
+			   struct packed_git **list_to_remove_from)
+{
+	struct packed_git **lst = list_to_remove_from;
+
+	while (*lst != p)
+		lst = &((*lst)->next);
+	*lst = (*lst)->next;
 
 	install_packed_git(the_repository, p);
-	free(tmp_idx);
-	return 0;
 }
 
 struct http_pack_request *new_http_pack_request(
-	struct packed_git *target, const char *base_url)
+	const unsigned char *packed_git_hash, const char *base_url) {
+
+	struct strbuf buf = STRBUF_INIT;
+
+	end_url_with_slash(&buf, base_url);
+	strbuf_addf(&buf, "objects/pack/pack-%s.pack",
+		hash_to_hex(packed_git_hash));
+	return new_direct_http_pack_request(packed_git_hash,
+					    strbuf_detach(&buf, NULL));
+}
+
+struct http_pack_request *new_direct_http_pack_request(
+	const unsigned char *packed_git_hash, char *url)
 {
 	off_t prev_posn = 0;
-	struct strbuf buf = STRBUF_INIT;
 	struct http_pack_request *preq;
 
 	preq = xcalloc(1, sizeof(*preq));
 	strbuf_init(&preq->tmpfile, 0);
-	preq->target = target;
 
-	end_url_with_slash(&buf, base_url);
-	strbuf_addf(&buf, "objects/pack/pack-%s.pack",
-		hash_to_hex(target->hash));
-	preq->url = strbuf_detach(&buf, NULL);
+	preq->url = url;
 
-	strbuf_addf(&preq->tmpfile, "%s.temp", sha1_pack_name(target->hash));
+	strbuf_addf(&preq->tmpfile, "%s.temp", sha1_pack_name(packed_git_hash));
 	preq->packfile = fopen(preq->tmpfile.buf, "a");
 	if (!preq->packfile) {
 		error("Unable to open local file %s for pack",
@@ -2348,7 +2352,7 @@ struct http_pack_request *new_http_pack_request(
 		if (http_is_verbose)
 			fprintf(stderr,
 				"Resuming fetch of pack %s at byte %"PRIuMAX"\n",
-				hash_to_hex(target->hash),
+				hash_to_hex(packed_git_hash),
 				(uintmax_t)prev_posn);
 		http_opt_request_remainder(preq->slot->curl, prev_posn);
 	}
diff --git a/http.h b/http.h
index faf8cbb0d1..5de792ef3f 100644
--- a/http.h
+++ b/http.h
@@ -216,18 +216,36 @@ int http_get_info_packs(const char *base_url,
 
 struct http_pack_request {
 	char *url;
-	struct packed_git *target;
-	struct packed_git **lst;
+
+	/*
+	 * If this is true, finish_http_pack_request() will pass "--keep" to
+	 * index-pack, resulting in the creation of a keep file, and will not
+	 * suppress its stdout (that is, the "keep\t<hash>\n" line will be
+	 * printed to stdout).
+	 */
+	unsigned generate_keep : 1;
+
 	FILE *packfile;
 	struct strbuf tmpfile;
 	struct active_request_slot *slot;
 };
 
 struct http_pack_request *new_http_pack_request(
-	struct packed_git *target, const char *base_url);
+	const unsigned char *packed_git_hash, const char *base_url);
+struct http_pack_request *new_direct_http_pack_request(
+	const unsigned char *packed_git_hash, char *url);
 int finish_http_pack_request(struct http_pack_request *preq);
 void release_http_pack_request(struct http_pack_request *preq);
 
+/*
+ * Remove p from the given list, and invoke install_packed_git() on it.
+ *
+ * This is a convenience function for users that have obtained a list of packs
+ * from http_get_info_packs() and have chosen a specific pack to fetch.
+ */
+void http_install_packfile(struct packed_git *p,
+			   struct packed_git **list_to_remove_from);
+
 /* Helpers for fetching object */
 struct http_object_request {
 	char *url;
diff --git a/t/t5550-http-fetch-dumb.sh b/t/t5550-http-fetch-dumb.sh
index 50485300eb..ca2e8af022 100755
--- a/t/t5550-http-fetch-dumb.sh
+++ b/t/t5550-http-fetch-dumb.sh
@@ -199,6 +199,28 @@ test_expect_success 'fetch packed objects' '
 	git clone $HTTPD_URL/dumb/repo_pack.git
 '
 
+test_expect_success 'http-fetch --packfile' '
+	# Arbitrary hash. Use rev-parse so that we get one of the correct
+	# length.
+	ARBITRARY=$(git -C "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git rev-parse HEAD) &&
+
+	git init packfileclient &&
+	p=$(cd "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git && ls objects/pack/pack-*.pack) &&
+	git -C packfileclient http-fetch --packfile=$ARBITRARY "$HTTPD_URL"/dumb/repo_pack.git/$p >out &&
+
+	grep "^keep.[0-9a-f]\{16,\}$" out &&
+	cut -c6- out >packhash &&
+
+	# Ensure that the expected files are generated
+	test -e "packfileclient/.git/objects/pack/pack-$(cat packhash).pack" &&
+	test -e "packfileclient/.git/objects/pack/pack-$(cat packhash).idx" &&
+	test -e "packfileclient/.git/objects/pack/pack-$(cat packhash).keep" &&
+
+	# Ensure that it has the HEAD of repo_pack, at least
+	HASH=$(git -C "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git rev-parse HEAD) &&
+	git -C packfileclient cat-file -e "$HASH"
+'
+
 test_expect_success 'fetch notices corrupt pack' '
 	cp -R "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git "$HTTPD_DOCUMENT_ROOT_PATH"/repo_bad1.git &&
 	(cd "$HTTPD_DOCUMENT_ROOT_PATH"/repo_bad1.git &&
@@ -214,6 +236,14 @@ test_expect_success 'fetch notices corrupt pack' '
 	)
 '
 
+test_expect_success 'http-fetch --packfile with corrupt pack' '
+	rm -rf packfileclient &&
+	git init packfileclient &&
+	p=$(cd "$HTTPD_DOCUMENT_ROOT_PATH"/repo_bad1.git && ls objects/pack/pack-*.pack) &&
+	test_must_fail git -C packfileclient http-fetch --packfile \
+		"$HTTPD_URL"/dumb/repo_bad1.git/$p
+'
+
 test_expect_success 'fetch notices corrupt idx' '
 	cp -R "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git "$HTTPD_DOCUMENT_ROOT_PATH"/repo_bad2.git &&
 	(cd "$HTTPD_DOCUMENT_ROOT_PATH"/repo_bad2.git &&
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 8da65e60de..7ab0217fb3 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -795,6 +795,94 @@ test_expect_success 'when server does not send "ready", expect FLUSH' '
 	test_i18ngrep "expected no other sections to be sent after no .ready." err
 '
 
+configure_exclusion () {
+	git -C "$1" hash-object "$2" >objh &&
+	git -C "$1" pack-objects "$HTTPD_DOCUMENT_ROOT_PATH/mypack" <objh >packh &&
+	git -C "$1" config --add \
+		"uploadpack.blobpackfileuri" \
+		"$(cat objh) $(cat packh) $HTTPD_URL/dumb/mypack-$(cat packh).pack" &&
+	cat objh
+}
+
+test_expect_success 'part of packfile response provided as URI' '
+	P="$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
+	rm -rf "$P" http_child log &&
+
+	git init "$P" &&
+	git -C "$P" config "uploadpack.allowsidebandall" "true" &&
+
+	echo my-blob >"$P/my-blob" &&
+	git -C "$P" add my-blob &&
+	echo other-blob >"$P/other-blob" &&
+	git -C "$P" add other-blob &&
+	git -C "$P" commit -m x &&
+
+	configure_exclusion "$P" my-blob >h &&
+	configure_exclusion "$P" other-blob >h2 &&
+
+	GIT_TRACE=1 GIT_TRACE_PACKET="$(pwd)/log" GIT_TEST_SIDEBAND_ALL=1 \
+	git -c protocol.version=2 \
+		-c fetch.uriprotocols=http,https \
+		clone "$HTTPD_URL/smart/http_parent" http_child &&
+
+	# Ensure that my-blob and other-blob are in separate packfiles.
+	for idx in http_child/.git/objects/pack/*.idx
+	do
+		git verify-pack --verbose $idx >out &&
+		{
+			grep "^[0-9a-f]\{16,\} " out || :
+		} >out.objectlist &&
+		if test_line_count = 1 out.objectlist
+		then
+			if grep $(cat h) out
+			then
+				>hfound
+			fi &&
+			if grep $(cat h2) out
+			then
+				>h2found
+			fi
+		fi
+	done &&
+	test -f hfound &&
+	test -f h2found &&
+
+	# Ensure that there are exactly 6 files (3 .pack and 3 .idx).
+	ls http_child/.git/objects/pack/* >filelist &&
+	test_line_count = 6 filelist
+'
+
+test_expect_success 'fetching with valid packfile URI but invalid hash fails' '
+	P="$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
+	rm -rf "$P" http_child log &&
+
+	git init "$P" &&
+	git -C "$P" config "uploadpack.allowsidebandall" "true" &&
+
+	echo my-blob >"$P/my-blob" &&
+	git -C "$P" add my-blob &&
+	echo other-blob >"$P/other-blob" &&
+	git -C "$P" add other-blob &&
+	git -C "$P" commit -m x &&
+
+	configure_exclusion "$P" my-blob >h &&
+	# Configure a URL for other-blob. Just reuse the hash of the object as
+	# the hash of the packfile, since the hash does not matter for this
+	# test as long as it is not the hash of the pack, and it is of the
+	# expected length.
+	git -C "$P" hash-object other-blob >objh &&
+	git -C "$P" pack-objects "$HTTPD_DOCUMENT_ROOT_PATH/mypack" <objh >packh &&
+	git -C "$P" config --add \
+		"uploadpack.blobpackfileuri" \
+		"$(cat objh) $(cat objh) $HTTPD_URL/dumb/mypack-$(cat packh).pack" &&
+
+	test_must_fail env GIT_TEST_SIDEBAND_ALL=1 \
+		git -c protocol.version=2 \
+		-c fetch.uriprotocols=http,https \
+		clone "$HTTPD_URL/smart/http_parent" http_child 2>err &&
+	test_i18ngrep "pack downloaded from.*does not match expected hash" 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.
 
diff --git a/transport-helper.c b/transport-helper.c
index a46afcb69d..93a6f50793 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -410,10 +410,11 @@ static int fetch_with_fetch(struct transport *transport,
 			exit(128);
 
 		if (skip_prefix(buf.buf, "lock ", &name)) {
-			if (transport->pack_lockfile)
+			if (transport->pack_lockfiles.nr)
 				warning(_("%s also locked %s"), data->name, name);
 			else
-				transport->pack_lockfile = xstrdup(name);
+				string_list_append(&transport->pack_lockfiles,
+						   name);
 		}
 		else if (data->check_connectivity &&
 			 data->transport_options.check_self_contained_and_connected &&
diff --git a/transport.c b/transport.c
index 7d50c502ad..6ee6771f55 100644
--- a/transport.c
+++ b/transport.c
@@ -378,7 +378,7 @@ static int fetch_refs_via_pack(struct transport *transport,
 	refs = fetch_pack(&args, data->fd,
 			  refs_tmp ? refs_tmp : transport->remote_refs,
 			  to_fetch, nr_heads, &data->shallow,
-			  &transport->pack_lockfile, data->version);
+			  &transport->pack_lockfiles, data->version);
 
 	close(data->fd[0]);
 	close(data->fd[1]);
@@ -921,6 +921,7 @@ struct transport *transport_get(struct remote *remote, const char *url)
 	struct transport *ret = xcalloc(1, sizeof(*ret));
 
 	ret->progress = isatty(2);
+	string_list_init(&ret->pack_lockfiles, 1);
 
 	if (!remote)
 		BUG("No remote provided to transport_get()");
@@ -1316,10 +1317,11 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs)
 
 void transport_unlock_pack(struct transport *transport)
 {
-	if (transport->pack_lockfile) {
-		unlink_or_warn(transport->pack_lockfile);
-		FREE_AND_NULL(transport->pack_lockfile);
-	}
+	int i;
+
+	for (i = 0; i < transport->pack_lockfiles.nr; i++)
+		unlink_or_warn(transport->pack_lockfiles.items[i].string);
+	string_list_clear(&transport->pack_lockfiles, 0);
 }
 
 int transport_connect(struct transport *transport, const char *name,
diff --git a/transport.h b/transport.h
index 4298c855be..05efa72db1 100644
--- a/transport.h
+++ b/transport.h
@@ -5,8 +5,7 @@
 #include "run-command.h"
 #include "remote.h"
 #include "list-objects-filter-options.h"
-
-struct string_list;
+#include "string-list.h"
 
 struct git_transport_options {
 	unsigned thin : 1;
@@ -98,7 +97,8 @@ struct transport {
 	 */
 	const struct string_list *server_options;
 
-	char *pack_lockfile;
+	struct string_list pack_lockfiles;
+
 	signed verbose : 3;
 	/**
 	 * Transports should not set this directly, and should use this
diff --git a/upload-pack.c b/upload-pack.c
index f899fdf46a..39d0cf00be 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -84,6 +84,7 @@ struct upload_pack_data {
 	/* 0 for no sideband, otherwise DEFAULT_PACKET_MAX or LARGE_PACKET_MAX */
 	int use_sideband;
 
+	struct string_list uri_protocols;
 	enum allow_uor allow_uor;
 
 	struct list_objects_filter_options filter_options;
@@ -117,6 +118,7 @@ static void upload_pack_data_init(struct upload_pack_data *data)
 	struct oid_array haves = OID_ARRAY_INIT;
 	struct object_array shallows = OBJECT_ARRAY_INIT;
 	struct string_list deepen_not = STRING_LIST_INIT_DUP;
+	struct string_list uri_protocols = STRING_LIST_INIT_DUP;
 	struct object_array extra_edge_obj = OBJECT_ARRAY_INIT;
 
 	memset(data, 0, sizeof(*data));
@@ -127,6 +129,7 @@ static void upload_pack_data_init(struct upload_pack_data *data)
 	data->haves = haves;
 	data->shallows = shallows;
 	data->deepen_not = deepen_not;
+	data->uri_protocols = uri_protocols;
 	data->extra_edge_obj = extra_edge_obj;
 	packet_writer_init(&data->writer, 1);
 
@@ -179,13 +182,86 @@ static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 	return 0;
 }
 
-static void create_pack_file(struct upload_pack_data *pack_data)
+struct output_state {
+	char buffer[8193];
+	int used;
+	unsigned packfile_uris_started : 1;
+	unsigned packfile_started : 1;
+};
+
+static int relay_pack_data(int pack_objects_out, struct output_state *os,
+			   int use_sideband, int write_packfile_line)
+{
+	/*
+	 * We keep the last byte to ourselves
+	 * in case we detect broken rev-list, so that we
+	 * can leave the stream corrupted.  This is
+	 * unfortunate -- unpack-objects would happily
+	 * accept a valid packdata with trailing garbage,
+	 * so appending garbage after we pass all the
+	 * pack data is not good enough to signal
+	 * breakage to downstream.
+	 */
+	ssize_t readsz;
+
+	readsz = xread(pack_objects_out, os->buffer + os->used,
+		       sizeof(os->buffer) - os->used);
+	if (readsz < 0) {
+		return readsz;
+	}
+	os->used += readsz;
+
+	while (!os->packfile_started) {
+		char *p;
+		if (os->used >= 4 && !memcmp(os->buffer, "PACK", 4)) {
+			os->packfile_started = 1;
+			if (write_packfile_line) {
+				if (os->packfile_uris_started)
+					packet_delim(1);
+				packet_write_fmt(1, "\1packfile\n");
+			}
+			break;
+		}
+		if ((p = memchr(os->buffer, '\n', os->used))) {
+			if (!os->packfile_uris_started) {
+				os->packfile_uris_started = 1;
+				if (!write_packfile_line)
+					BUG("packfile_uris requires sideband-all");
+				packet_write_fmt(1, "\1packfile-uris\n");
+			}
+			*p = '\0';
+			packet_write_fmt(1, "\1%s\n", os->buffer);
+
+			os->used -= p - os->buffer + 1;
+			memmove(os->buffer, p + 1, os->used);
+		} else {
+			/*
+			 * Incomplete line.
+			 */
+			return readsz;
+		}
+	}
+
+	if (os->used > 1) {
+		send_client_data(1, os->buffer, os->used - 1, use_sideband);
+		os->buffer[0] = os->buffer[os->used - 1];
+		os->used = 1;
+	} else {
+		send_client_data(1, os->buffer, os->used, use_sideband);
+		os->used = 0;
+	}
+
+	return readsz;
+}
+
+static void create_pack_file(struct upload_pack_data *pack_data,
+			     const struct string_list *uri_protocols)
 {
 	struct child_process pack_objects = CHILD_PROCESS_INIT;
-	char data[8193], progress[128];
+	struct output_state output_state = { { 0 } };
+	char progress[128];
 	char abort_msg[] = "aborting due to possible repository "
 		"corruption on the remote side.";
-	int buffered = -1;
 	ssize_t sz;
 	int i;
 	FILE *pipe_fd;
@@ -229,6 +305,11 @@ static void create_pack_file(struct upload_pack_data *pack_data)
 					 spec);
 		}
 	}
+	if (uri_protocols) {
+		for (i = 0; i < uri_protocols->nr; i++)
+			argv_array_pushf(&pack_objects.args, "--uri-protocol=%s",
+					 uri_protocols->items[i].string);
+	}
 
 	pack_objects.in = -1;
 	pack_objects.out = -1;
@@ -318,40 +399,17 @@ static void create_pack_file(struct upload_pack_data *pack_data)
 			continue;
 		}
 		if (0 <= pu && (pfd[pu].revents & (POLLIN|POLLHUP))) {
-			/* Data ready; we keep the last byte to ourselves
-			 * in case we detect broken rev-list, so that we
-			 * can leave the stream corrupted.  This is
-			 * unfortunate -- unpack-objects would happily
-			 * accept a valid packdata with trailing garbage,
-			 * so appending garbage after we pass all the
-			 * pack data is not good enough to signal
-			 * breakage to downstream.
-			 */
-			char *cp = data;
-			ssize_t outsz = 0;
-			if (0 <= buffered) {
-				*cp++ = buffered;
-				outsz++;
-			}
-			sz = xread(pack_objects.out, cp,
-				  sizeof(data) - outsz);
-			if (0 < sz)
-				;
-			else if (sz == 0) {
+			int result = relay_pack_data(pack_objects.out,
+						     &output_state,
+						     pack_data->use_sideband,
+						     !!uri_protocols);
+
+			if (result == 0) {
 				close(pack_objects.out);
 				pack_objects.out = -1;
-			}
-			else
+			} else if (result < 0) {
 				goto fail;
-			sz += outsz;
-			if (1 < sz) {
-				buffered = data[sz-1] & 0xFF;
-				sz--;
 			}
-			else
-				buffered = -1;
-			send_client_data(1, data, sz,
-					 pack_data->use_sideband);
 		}
 
 		/*
@@ -376,9 +434,8 @@ static void create_pack_file(struct upload_pack_data *pack_data)
 	}
 
 	/* flush the data */
-	if (0 <= buffered) {
-		data[0] = buffered;
-		send_client_data(1, data, 1,
+	if (output_state.used > 0) {
+		send_client_data(1, output_state.buffer, output_state.used,
 				 pack_data->use_sideband);
 		fprintf(stderr, "flushed.\n");
 	}
@@ -1188,7 +1245,7 @@ void upload_pack(struct upload_pack_options *options)
 		receive_needs(&data, &reader);
 		if (data.want_obj.nr) {
 			get_common_commits(&data, &reader);
-			create_pack_file(&data);
+			create_pack_file(&data, NULL);
 		}
 	}
 
@@ -1341,10 +1398,18 @@ static void process_args(struct packet_reader *request,
 			continue;
 		}
 
+		if (skip_prefix(arg, "packfile-uris ", &p)) {
+			string_list_split(&data->uri_protocols, p, ',', -1);
+			continue;
+		}
+
 		/* ignore unknown lines maybe? */
 		die("unexpected line: '%s'", arg);
 	}
 
+	if (data->uri_protocols.nr && !data->writer.use_sideband)
+		string_list_clear(&data->uri_protocols, 0);
+
 	if (request->status != PACKET_READ_FLUSH)
 		die(_("expected flush after fetch arguments"));
 }
@@ -1502,8 +1567,12 @@ int upload_pack_v2(struct repository *r, struct argv_array *keys,
 			send_wanted_ref_info(&data);
 			send_shallow_info(&data);
 
-			packet_writer_write(&data.writer, "packfile\n");
-			create_pack_file(&data);
+			if (data.uri_protocols.nr) {
+				create_pack_file(&data, &data.uri_protocols);
+			} else {
+				packet_writer_write(&data.writer, "packfile\n");
+				create_pack_file(&data, NULL);
+			}
 			state = FETCH_DONE;
 			break;
 		case FETCH_DONE:
@@ -1522,6 +1591,7 @@ int upload_pack_advertise(struct repository *r,
 		int allow_filter_value;
 		int allow_ref_in_want;
 		int allow_sideband_all_value;
+		char *str = NULL;
 
 		strbuf_addstr(value, "shallow");
 
@@ -1543,6 +1613,14 @@ int upload_pack_advertise(struct repository *r,
 					   &allow_sideband_all_value) &&
 		     allow_sideband_all_value))
 			strbuf_addstr(value, " sideband-all");
+
+		if (!repo_config_get_string(the_repository,
+					    "uploadpack.blobpackfileuri",
+					    &str) &&
+		    str) {
+			strbuf_addstr(value, " packfile-uris");
+			free(str);
+		}
 	}
 
 	return 1;