Subject: [PATCH v3 14/17] proc-receive: acquire hook list from hook.h

From: Emily Shaffer <[email-masked]>
Date: Mon, 21 Dec 2020 16:04:32 -0800

The proc-receive hook differs from most other hooks Git invokes because
the hook and the parent Git process engage in bidirectional
communication via stdin/stdout. This bidirectional communication is
unsuitable for multiple hooks, whether they are in series or in
parallel, and is incompatible with run-command.h:run_processes_parallel:

- The proc-receive hook is intended to modify the state of the Git repo.
  From 'git help githooks':
    This [proc-receive] hook is responsible for updating the relevant
    references and reporting the results back to 'receive-pack'.
  This prevents parallelization and implies, at least, specific ordering
  of hook execution.
- The proc-receive hook can reject a push by aborting early with an
  error code. If a former hook ran through the entire push contents
  successfully but a later hook rejects some of the push, the repo may
  be left in a partially-updated (and corrupt) state.
- The callback model of the run_processes_parallel() API is unsuited to
  the current implementation of proc-receive, which loops through
  "send-receive-consider" with the child process. proc-receive today
  relies on stateful communication with the child process, which would be
  unwieldy to implement with callbacks and saved state.
- Additionally, run_processes_parallel() is designed to collate the
  output of many child processes into a single output (stderr or callback),
  and would require significant work to tell the caller which process sent
  the output, and indeed to collect any output before the child process
  has exited.

So, rather than using hook.h:run_hooks() to invoke the proc-receive
hook, receive-pack.c can learn to ask hook.h:hook_list() for the
location of a hook to run. This allows users to configure their
proc-receive in a global config for all repos if they want, or a local
config if they just don't want to use the hookdir. Because running more
than one proc-receive hook doesn't make sense from a repo state
perspective, we can explicitly ban configuring more than one
proc-receive hook at a time.

If a user wants to globally configure one proc-receive hook for most of
their repos, but override that hook in a single repo, they should use
'skip' to manually remove the global hook in their special repo:

~/.gitconfig:
[hook.proc-receive]
  command = /usr/bin/usual-proc-receive

~/special-repo/.git/config:
[hookcmd./usr/bin/usual-proc-receive]
  skip = true
[hook.proc-receive]
  command = /usr/bin/special-proc-receive

Signed-off-by: Emily Shaffer <[email-masked]>
---
 Documentation/githooks.txt                |  4 ++
 builtin/receive-pack.c                    | 33 +++++++++++++++-
 t/t5411/test-0015-too-many-hooks-error.sh | 47 +++++++++++++++++++++++
 3 files changed, 82 insertions(+), 2 deletions(-)
 create mode 100644 t/t5411/test-0015-too-many-hooks-error.sh

diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt
index 2b3a74f249..2c59c537f9 100644
--- a/Documentation/githooks.txt
+++ b/Documentation/githooks.txt
@@ -423,6 +423,10 @@ the input.  The exit status of the 'proc-receive' hook only determines
 the success or failure of the group of commands sent to it, unless
 atomic push is in use.
 
+It is forbidden to specify more than one hook for 'proc-receive'. If a
+globally-configured 'proc-receive' must be overridden, use
+'hookcmd.<global-hook>.skip = true' to ignore it.
+
 [[post-receive]]
 post-receive
 ~~~~~~~~~~~~
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 57f3bb979c..4a6ad27404 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -1145,11 +1145,40 @@ static int run_proc_receive_hook(struct command *commands,
 	int version = 0;
 	int code;
 
-	argv[0] = find_hook("proc-receive");
-	if (!argv[0]) {
+	struct strbuf hookname = STRBUF_INIT;
+	struct hook *proc_receive = NULL;
+	struct list_head *pos, *hooks;
+
+	strbuf_addstr(&hookname, "proc-receive");
+	hooks = hook_list(&hookname);
+
+	list_for_each(pos, hooks) {
+		if (proc_receive) {
+			rp_error("only one 'proc-receive' hook can be specified");
+			return -1;
+		}
+		proc_receive = list_entry(pos, struct hook, list);
+		/* check if the hookdir hook should be ignored */
+		if (proc_receive->from_hookdir) {
+			switch (configured_hookdir_opt()) {
+			case HOOKDIR_INTERACTIVE:
+			case HOOKDIR_NO:
+				proc_receive = NULL;
+				break;
+			default:
+				break;
+			}
+		}
+
+	}
+
+	if (!proc_receive) {
 		rp_error("cannot find hook 'proc-receive'");
 		return -1;
 	}
+
+
+	argv[0] = proc_receive->command.buf;
 	argv[1] = NULL;
 
 	proc.argv = argv;
diff --git a/t/t5411/test-0015-too-many-hooks-error.sh b/t/t5411/test-0015-too-many-hooks-error.sh
new file mode 100644
index 0000000000..2d64534510
--- /dev/null
+++ b/t/t5411/test-0015-too-many-hooks-error.sh
@@ -0,0 +1,47 @@
+test_expect_success "setup too  many proc-receive hooks (ok, $PROTOCOL)" '
+	write_script "proc-receive" <<-EOF &&
+	printf >&2 "# proc-receive hook\n"
+	test-tool proc-receive -v \
+		-r "ok refs/for/main/topic"
+	EOF
+
+	git -C "$upstream" config --add "hook.proc-receive.command" proc-receive &&
+	cp proc-receive "$upstream/hooks/proc-receive"
+'
+
+# Refs of upstream : main(A)
+# Refs of workbench: main(A)  tags/v123
+# git push         :                       next(A)  refs/for/main/topic(A)
+test_expect_success "proc-receive: reject more than one configured hook" '
+	test_must_fail git -C workbench push origin \
+		HEAD:next \
+		HEAD:refs/for/main/topic \
+		>out 2>&1 &&
+	make_user_friendly_and_stable_output <out >actual &&
+	cat >expect <<-EOF &&
+	remote: # pre-receive hook
+	remote: pre-receive< <ZERO-OID> <COMMIT-A> refs/heads/next
+	remote: pre-receive< <ZERO-OID> <COMMIT-A> refs/for/main/topic
+	remote: error: only one "proc-receive" hook can be specified
+	remote: # post-receive hook
+	remote: post-receive< <ZERO-OID> <COMMIT-A> refs/heads/next
+	To <URL/of/upstream.git>
+	 * [new branch] HEAD -> next
+	 ! [remote rejected] HEAD -> refs/for/main/topic (fail to run proc-receive hook)
+	EOF
+	test_cmp expect actual &&
+	git -C "$upstream" show-ref >out &&
+	make_user_friendly_and_stable_output <out >actual &&
+	cat >expect <<-EOF &&
+	<COMMIT-A> refs/heads/main
+	<COMMIT-A> refs/heads/next
+	EOF
+	test_cmp expect actual
+'
+
+# Refs of upstream : main(A)             next(A)
+# Refs of workbench: main(A)  tags/v123
+test_expect_success "cleanup ($PROTOCOL)" '
+	git -C "$upstream" config --unset "hook.proc-receive.command" "proc-receive" &&
+	git -C "$upstream" update-ref -d refs/heads/next
+'
-- 
2.28.0.rc0.142.g3c755180ce-goog