[PATCH 2/4] receive-pack: implement advertising and receiving push options

[Stefan Beller <sbeller@google.com>]

The pre/post receive hook may be interested in more information from the
user. This information can be transmitted when both client and server
support the "push-options" capability, which when used is a phase directly
after update commands ended by a flush pkt.

Similar to the atomic option, the server capability can be disabled via
the `receive.advertisePushOptions` config variable. While documenting
this, fix a nit in the `receive.advertiseAtomic` wording.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/config.txt                          |  9 +++-
 Documentation/technical/pack-protocol.txt         | 10 ++--
 Documentation/technical/protocol-capabilities.txt |  9 ++++
 builtin/receive-pack.c                            | 59 +++++++++++++++++++++++
 4 files changed, 81 insertions(+), 6 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e208af1..25b5db1 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2410,8 +2410,13 @@ rebase.instructionFormat
 
 receive.advertiseAtomic::
 	By default, git-receive-pack will advertise the atomic push
-	capability to its clients. If you don't want to this capability
-	to be advertised, set this variable to false.
+	capability to its clients. If you don't want to advertise this
+	capability, set this variable to false.
+
+receive.advertisePushOptions::
+	By default, git-receive-pack will advertise the push options
+	capability to its clients. If you don't want to advertise this
+	capability, set this variable to false.
 
 receive.autogc::
 	By default, git-receive-pack will run "git-gc --auto" after
diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index 8b36343..7a2ed30 100644
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -454,7 +454,8 @@ The reference discovery phase is done nearly the same way as it is in the
 fetching protocol. Each reference obj-id and name on the server is sent
 in packet-line format to the client, followed by a flush-pkt.  The only
 real difference is that the capability listing is different - the only
-possible values are 'report-status', 'delete-refs' and 'ofs-delta'.
+possible values are 'report-status', 'delete-refs', 'ofs-delta' and
+'push-options'.
 
 Reference Update Request and Packfile Transfer
 ----------------------------------------------
@@ -465,9 +466,10 @@ that it wants to update, it sends a line listing the obj-id currently on
 the server, the obj-id the client would like to update it to and the name
 of the reference.
 
-This list is followed by a flush-pkt and then the packfile that should
-contain all the objects that the server will need to complete the new
-references.
+This list is followed by a flush-pkt. Then the push options are transmitted
+one per packet followed by another flush-pkt. After that the packfile that
+should contain all the objects that the server will need to complete the new
+references will be sent.
 
 ----
   update-request    =  *shallow ( command-list | push-cert ) [packfile]
diff --git a/Documentation/technical/protocol-capabilities.txt b/Documentation/technical/protocol-capabilities.txt
index eaab6b4..4c28d3a 100644
--- a/Documentation/technical/protocol-capabilities.txt
+++ b/Documentation/technical/protocol-capabilities.txt
@@ -253,6 +253,15 @@ atomic pushes. If the pushing client requests this capability, the server
 will update the refs in one atomic transaction. Either all refs are
 updated or none.
 
+push-options
+------------
+
+If the server sends the 'push-options' capability it is able to accept
+push options after the update commands have been sent, but before the
+packfile is streamed. If the pushing client requests this capability,
+the server will pass the options to the pre- and post- receive hooks
+that process this push request.
+
 allow-tip-sha1-in-want
 ----------------------
 
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 236417e..917ac18 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -44,10 +44,12 @@ static struct strbuf fsck_msg_types = STRBUF_INIT;
 static int receive_unpack_limit = -1;
 static int transfer_unpack_limit = -1;
 static int advertise_atomic_push = 1;
+static int advertise_push_options;
 static int unpack_limit = 100;
 static int report_status;
 static int use_sideband;
 static int use_atomic;
+static int use_push_options;
 static int quiet;
 static int prefer_ofs_delta = 1;
 static int auto_update_server_info;
@@ -193,6 +195,11 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (strcmp(var, "receive.advertisepushoptions") == 0) {
+		advertise_push_options = git_config_bool(var, value);
+		return 0;
+	}
+
 	return git_default_config(var, value, cb);
 }
 
@@ -211,6 +218,8 @@ static void show_ref(const char *path, const unsigned char *sha1)
 			strbuf_addstr(&cap, " ofs-delta");
 		if (push_cert_nonce)
 			strbuf_addf(&cap, " push-cert=%s", push_cert_nonce);
+		if (advertise_push_options)
+			strbuf_addstr(&cap, " push-options");
 		strbuf_addf(&cap, " agent=%s", git_user_agent_sanitized());
 		packet_write(1, "%s %s%c%s\n",
 			     sha1_to_hex(sha1), path, 0, cap.buf);
@@ -1455,6 +1464,9 @@ static struct command *read_head_info(struct sha1_array *shallow)
 			if (advertise_atomic_push
 			    && parse_feature_request(feature_list, "atomic"))
 				use_atomic = 1;
+			if (advertise_push_options
+			    && parse_feature_request(feature_list, "push-options"))
+				use_push_options = 1;
 		}
 
 		if (!strcmp(line, "push-cert")) {
@@ -1487,6 +1499,50 @@ static struct command *read_head_info(struct sha1_array *shallow)
 	return commands;
 }
 
+static struct string_list *read_push_options(void)
+{
+	struct string_list *ret = xmalloc(sizeof(*ret));
+	string_list_init(ret, 1);
+
+	while (1) {
+		char *line, *lf;
+		int len;
+
+		line = packet_read_line(0, &len);
+
+		if (!line)
+			break;
+
+		/*
+		* NEEDSWORK: expose the limitations to be configurable;
+		* Once the limit can be lifted, include a way for payloads
+		* larger than one pkt, e.g use last byte to indicate if
+		* the push option continues in the next packet or implement
+		* larger packets.
+		*/
+		if (len > LARGE_PACKET_MAX - 1) {
+			/*
+			 * NEEDSWORK: The error message in die(..) is not
+			 * transmitted in call cases, so ideally all die(..)
+			 * calls are prefixed with rp_error and then we can
+			 * combine rp_error && die into one helper function.
+			 */
+			rp_error("protocol error: server configuration allows push "
+				 "options of size up to %d bytes",
+				 LARGE_PACKET_MAX - 1);
+			die("protocol error: push options too large");
+		}
+
+		lf = strchr(line, '\n');
+		if (lf)
+			*lf = '\0';
+
+		string_list_append(ret, line);
+	}
+
+	return ret;
+}
+
 static const char *parse_pack_header(struct pack_header *hdr)
 {
 	switch (read_pack_header(0, hdr)) {
@@ -1774,6 +1830,9 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 		const char *unpack_status = NULL;
 		struct string_list *push_options = NULL;
 
+		if (use_push_options)
+			push_options = read_push_options();
+
 		prepare_shallow_info(&si, &shallow);
 		if (!si.nr_ours && !si.nr_theirs)
 			shallow_update = 0;
-- 
2.9.0.247.gf748855.dirty