receive-pack: add new proc-receive hook

Git calls an internal `execute_commands` function to handle commands
sent from client to `git-receive-pack`.  Regardless of what references
the user pushes, git creates or updates the corresponding references if
the user has write-permission.  A contributor who has no
write-permission, cannot push to the repository directly.  So, the
contributor has to write commits to an alternate location, and sends
pull request by emails or by other ways.  We call this workflow as a
distributed workflow.

It would be more convenient to work in a centralized workflow like what
Gerrit provided for some cases.  For example, a read-only user who
cannot push to a branch directly can run the following `git push`
command to push commits to a pseudo reference (has a prefix "refs/for/",
not "refs/heads/") to create a code review.

    git push origin \
        HEAD:refs/for/<branch-name>/<session>

The `<branch-name>` in the above example can be as simple as "master",
or a more complicated branch name like "foo/bar".  The `<session>` in
the above example command can be the local branch name of the client
side, such as "my/topic".

We cannot implement a centralized workflow elegantly by using
"pre-receive" + "post-receive", because Git will call the internal
function "execute_commands" to create references (even the special
pseudo reference) between these two hooks.  Even though we can delete
the temporarily created pseudo reference via the "post-receive" hook,
having a temporary reference is not safe for concurrent pushes.

So, add a filter and a new handler to support this kind of workflow.
The filter will check the prefix of the reference name, and if the
command has a special reference name, the filter will turn a specific
field (`run_proc_receive`) on for the command.  Commands with this filed
turned on will be executed by a new handler (a hook named
"proc-receive") instead of the internal `execute_commands` function.
We can use this "proc-receive" command to create pull requests or send
emails for code review.

Suggested by Junio, this "proc-receive" hook reads the commands,
push-options (optional), and send result using a protocol in pkt-line
format.  In the following example, the letter "S" stands for
"receive-pack" and letter "H" stands for the hook.

    # Version and features negotiation.
    S: PKT-LINE(version=1\0push-options atomic...)
    S: flush-pkt
    H: PKT-LINE(version=1\0push-options...)
    H: flush-pkt

    # Send commands from server to the hook.
    S: PKT-LINE(<old-oid> <new-oid> <ref>)
    S: ... ...
    S: flush-pkt
    # Send push-options only if the 'push-options' feature is enabled.
    S: PKT-LINE(push-option)
    S: ... ...
    S: flush-pkt

    # Receive result from the hook.
    # OK, run this command successfully.
    H: PKT-LINE(ok <ref>)
    # NO, I reject it.
    H: PKT-LINE(ng <ref> <reason>)
    # Fall through, let 'receive-pack' to execute it.
    H: PKT-LINE(ok <ref>)
    H: PKT-LINE(option fall-through)
    # OK, but has an alternate reference.  The alternate reference name
    # and other status can be given in options
    H: PKT-LINE(ok <ref>)
    H: PKT-LINE(option refname <refname>)
    H: PKT-LINE(option old-oid <old-oid>)
    H: PKT-LINE(option new-oid <new-oid>)
    H: PKT-LINE(option forced-update)
    H: ... ...
    H: flush-pkt

After receiving a command, the hook will execute the command, and may
create/update different reference.  For example, a command for a pseudo
reference "refs/for/master/topic" may create/update different reference
such as "refs/pull/123/head".  The alternate reference name and other
status are given in option lines.

The list of commands returned from "proc-receive" will replace the
relevant commands that are sent from user to "receive-pack", and
"receive-pack" will continue to run the "execute_commands" function and
other routines.  Finally, the result of the execution of these commands
will be reported to end user.

The reporting function from "receive-pack" to "send-pack" will be
extended in latter commit just like what the "proc-receive" hook reports
to "receive-pack".

Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 293 insertions, 3 deletions

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index a00f91c1a0..2b63b92545 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -308,11 +308,15 @@ static void write_head_info(void)
 	packet_flush(1);
 }
 
+#define RUN_PROC_RECEIVE_SCHEDULED	1
+#define RUN_PROC_RECEIVE_RETURNED	2
 struct command {
 	struct command *next;
 	const char *error_string;
+	struct ref_push_report *report;
 	unsigned int skip_update:1,
-		     did_not_exist:1;
+		     did_not_exist:1,
+		     run_proc_receive:2;
 	int index;
 	struct object_id old_oid;
 	struct object_id new_oid;
@@ -838,6 +842,268 @@ static int run_update_hook(struct command *cmd)
 	return finish_command(&proc);
 }
 
+static struct command *find_command_by_refname(struct command *list,
+					       const char *refname)
+{
+	for (; list; list = list->next)
+		if (!strcmp(list->ref_name, refname))
+			return list;
+	return NULL;
+}
+
+static int read_proc_receive_report(struct packet_reader *reader,
+				    struct command *commands,
+				    struct strbuf *errmsg)
+{
+	struct command *cmd;
+	struct command *hint = NULL;
+	struct ref_push_report *report = NULL;
+	int new_report = 0;
+	int code = 0;
+	int once = 0;
+
+	for (;;) {
+		struct object_id old_oid, new_oid;
+		const char *head;
+		const char *refname;
+		char *p;
+
+		if (packet_reader_read(reader) != PACKET_READ_NORMAL)
+			break;
+
+		head = reader->line;
+		p = strchr(head, ' ');
+		if (!p) {
+			strbuf_addf(errmsg, "proc-receive reported incomplete status line: '%s'\n", head);
+			code = -1;
+			continue;
+		}
+		*p++ = '\0';
+		if (!strcmp(head, "option")) {
+			const char *key, *val;
+
+			if (!hint || !(report || new_report)) {
+				if (!once++)
+					strbuf_addstr(errmsg, "proc-receive reported 'option' without a matching 'ok/ng' directive\n");
+				code = -1;
+				continue;
+			}
+			if (new_report) {
+				if (!hint->report) {
+					hint->report = xcalloc(1, sizeof(struct ref_push_report));
+					report = hint->report;
+				} else {
+					report = hint->report;
+					while (report->next)
+						report = report->next;
+					report->next = xcalloc(1, sizeof(struct ref_push_report));
+					report = report->next;
+				}
+				new_report = 0;
+			}
+			key = p;
+			p = strchr(key, ' ');
+			if (p)
+				*p++ = '\0';
+			val = p;
+			if (!strcmp(key, "refname"))
+				report->ref_name = xstrdup_or_null(val);
+			else if (!strcmp(key, "old-oid") && val &&
+				 !parse_oid_hex(val, &old_oid, &val))
+				report->old_oid = oiddup(&old_oid);
+			else if (!strcmp(key, "new-oid") && val &&
+				 !parse_oid_hex(val, &new_oid, &val))
+				report->new_oid = oiddup(&new_oid);
+			else if (!strcmp(key, "forced-update"))
+				report->forced_update = 1;
+			else if (!strcmp(key, "fall-through"))
+				/* Fall through, let 'receive-pack' to execute it. */
+				hint->run_proc_receive = 0;
+			continue;
+		}
+
+		report = NULL;
+		new_report = 0;
+		refname = p;
+		p = strchr(refname, ' ');
+		if (p)
+			*p++ = '\0';
+		if (strcmp(head, "ok") && strcmp(head, "ng")) {
+			strbuf_addf(errmsg, "proc-receive reported bad status '%s' on ref '%s'\n",
+				    head, refname);
+			code = -1;
+			continue;
+		}
+
+		/* first try searching at our hint, falling back to all refs */
+		if (hint)
+			hint = find_command_by_refname(hint, refname);
+		if (!hint)
+			hint = find_command_by_refname(commands, refname);
+		if (!hint) {
+			strbuf_addf(errmsg, "proc-receive reported status on unknown ref: %s\n",
+				    refname);
+			code = -1;
+			continue;
+		}
+		if (!hint->run_proc_receive) {
+			strbuf_addf(errmsg, "proc-receive reported status on unexpected ref: %s\n",
+				    refname);
+			code = -1;
+			continue;
+		}
+		hint->run_proc_receive |= RUN_PROC_RECEIVE_RETURNED;
+		if (!strcmp(head, "ng")) {
+			if (p)
+				hint->error_string = xstrdup(p);
+			else
+				hint->error_string = "failed";
+			code = -1;
+			continue;
+		}
+		new_report = 1;
+	}
+
+	for (cmd = commands; cmd; cmd = cmd->next)
+		if (cmd->run_proc_receive && !cmd->error_string &&
+		    !(cmd->run_proc_receive & RUN_PROC_RECEIVE_RETURNED)) {
+		    cmd->error_string = "proc-receive failed to report status";
+		    code = -1;
+		}
+	return code;
+}
+
+static int run_proc_receive_hook(struct command *commands,
+				 const struct string_list *push_options)
+{
+	struct child_process proc = CHILD_PROCESS_INIT;
+	struct async muxer;
+	struct command *cmd;
+	const char *argv[2];
+	struct packet_reader reader;
+	struct strbuf cap = STRBUF_INIT;
+	struct strbuf errmsg = STRBUF_INIT;
+	int hook_use_push_options = 0;
+	int version = 0;
+	int code;
+
+	argv[0] = find_hook("proc-receive");
+	if (!argv[0]) {
+		rp_error("cannot find hook 'proc-receive'");
+		return -1;
+	}
+	argv[1] = NULL;
+
+	proc.argv = argv;
+	proc.in = -1;
+	proc.out = -1;
+	proc.trace2_hook_name = "proc-receive";
+
+	if (use_sideband) {
+		memset(&muxer, 0, sizeof(muxer));
+		muxer.proc = copy_to_sideband;
+		muxer.in = -1;
+		code = start_async(&muxer);
+		if (code)
+			return code;
+		proc.err = muxer.in;
+	} else {
+		proc.err = 0;
+	}
+
+	code = start_command(&proc);
+	if (code) {
+		if (use_sideband)
+			finish_async(&muxer);
+		return code;
+	}
+
+	sigchain_push(SIGPIPE, SIG_IGN);
+
+	/* Version negotiaton */
+	packet_reader_init(&reader, proc.out, NULL, 0,
+			   PACKET_READ_CHOMP_NEWLINE |
+			   PACKET_READ_GENTLE_ON_EOF);
+	if (use_atomic)
+		strbuf_addstr(&cap, " atomic");
+	if (use_push_options)
+		strbuf_addstr(&cap, " push-options");
+	if (cap.len) {
+		packet_write_fmt(proc.in, "version=1%c%s\n", '\0', cap.buf + 1);
+		strbuf_release(&cap);
+	} else {
+		packet_write_fmt(proc.in, "version=1\n");
+	}
+	packet_flush(proc.in);
+
+	for (;;) {
+		int linelen;
+
+		if (packet_reader_read(&reader) != PACKET_READ_NORMAL)
+			break;
+
+		if (reader.pktlen > 8 && starts_with(reader.line, "version=")) {
+			version = atoi(reader.line + 8);
+			linelen = strlen(reader.line);
+			if (linelen < reader.pktlen) {
+				const char *feature_list = reader.line + linelen + 1;
+				if (parse_feature_request(feature_list, "push-options"))
+					hook_use_push_options = 1;
+			}
+		}
+	}
+
+	if (version != 1) {
+		strbuf_addf(&errmsg, "proc-receive version '%d' is not supported",
+			    version);
+		code = -1;
+		goto cleanup;
+	}
+
+	/* Send commands */
+	for (cmd = commands; cmd; cmd = cmd->next) {
+		if (!cmd->run_proc_receive || cmd->skip_update || cmd->error_string)
+			continue;
+		packet_write_fmt(proc.in, "%s %s %s",
+				 oid_to_hex(&cmd->old_oid),
+				 oid_to_hex(&cmd->new_oid),
+				 cmd->ref_name);
+	}
+	packet_flush(proc.in);
+
+	/* Send push options */
+	if (hook_use_push_options) {
+		struct string_list_item *item;
+
+		for_each_string_list_item(item, push_options)
+			packet_write_fmt(proc.in, "%s", item->string);
+		packet_flush(proc.in);
+	}
+
+	/* Read result from proc-receive */
+	code = read_proc_receive_report(&reader, commands, &errmsg);
+
+cleanup:
+	close(proc.in);
+	close(proc.out);
+	if (use_sideband)
+		finish_async(&muxer);
+	if (finish_command(&proc))
+		code = -1;
+	if (errmsg.len >0) {
+		char *p = errmsg.buf;
+
+		p += errmsg.len - 1;
+		if (*p == '\n')
+			*p = '\0';
+		rp_error("%s", errmsg.buf);
+		strbuf_release(&errmsg);
+	}
+	sigchain_pop(SIGPIPE);
+
+	return code;
+}
+
 static char *refuse_unconfigured_deny_msg =
 	N_("By default, updating the current branch in a non-bare repository\n"
 	   "is denied, because it will make the index and work tree inconsistent\n"
@@ -1413,7 +1679,7 @@ static void execute_commands_non_atomic(struct command *commands,
 	struct strbuf err = STRBUF_INIT;
 
 	for (cmd = commands; cmd; cmd = cmd->next) {
-		if (!should_process_cmd(cmd))
+		if (!should_process_cmd(cmd) || cmd->run_proc_receive)
 			continue;
 
 		transaction = ref_transaction_begin(&err);
@@ -1453,7 +1719,7 @@ static void execute_commands_atomic(struct command *commands,
 	}
 
 	for (cmd = commands; cmd; cmd = cmd->next) {
-		if (!should_process_cmd(cmd))
+		if (!should_process_cmd(cmd) || cmd->run_proc_receive)
 			continue;
 
 		cmd->error_string = update(cmd, si);
@@ -1489,6 +1755,7 @@ static void execute_commands(struct command *commands,
 	struct iterate_data data;
 	struct async muxer;
 	int err_fd = 0;
+	int run_proc_receive = 0;
 
 	if (unpacker_error) {
 		for (cmd = commands; cmd; cmd = cmd->next)
@@ -1518,6 +1785,21 @@ static void execute_commands(struct command *commands,
 
 	reject_updates_to_hidden(commands);
 
+	/*
+	 * Try to find commands that have special prefix in their reference names,
+	 * and mark them to run an external "proc-receive" hook later.
+	 */
+	for (cmd = commands; cmd; cmd = cmd->next) {
+		if (!should_process_cmd(cmd))
+			continue;
+
+		/* TODO: replace the fixed prefix by looking up git config variables. */
+		if (!strncmp(cmd->ref_name, "refs/for/", 9)) {
+			cmd->run_proc_receive = RUN_PROC_RECEIVE_SCHEDULED;
+			run_proc_receive = 1;
+		}
+	}
+
 	if (run_receive_hook(commands, "pre-receive", 0, push_options)) {
 		for (cmd = commands; cmd; cmd = cmd->next) {
 			if (!cmd->error_string)
@@ -1544,6 +1826,14 @@ static void execute_commands(struct command *commands,
 	free(head_name_to_free);
 	head_name = head_name_to_free = resolve_refdup("HEAD", 0, NULL, NULL);
 
+	if (run_proc_receive &&
+	    run_proc_receive_hook(commands, push_options))
+		for (cmd = commands; cmd; cmd = cmd->next)
+			if (!cmd->error_string &&
+			    !(cmd->run_proc_receive & RUN_PROC_RECEIVE_RETURNED) &&
+			    (cmd->run_proc_receive || use_atomic))
+				cmd->error_string = "fail to run proc-receive hook";
+
 	if (use_atomic)
 		execute_commands_atomic(commands, si);
 	else