Subject: Re: [PATCH v2 2/3] transport-helper: run do_take_over in connect_helper

From: Junio C Hamano <[email-masked]>
Date: Mon, 25 Sep 2023 14:34:35 -0700

Jiang Xin <[email-masked]> writes:

> From: Jiang Xin <[email-masked]>
>
> After successfully connecting to the smart transport by calling
> "process_connect_service()" in "connect_helper()", run "do_take_over()"
> to replace the old vtable with a new one which has methods ready for
> the smart transport connection.

The existing pattern among all callers of process_connect() seems to
be

	if (process_connect(...)) {
		do_take_over();
		... dispatch to the underlying method ...
	}
	... otherwise implement the fallback ...

where the return value from process_connect() is the return value of
the call it makes to process_connect_service().

And the only other caller of process_connect_service() is
connect_helper(), so in that sense, making a call to do_take_over()
when process_connect_service() succeeds in the helper does make
things consistent.  The connect_helper() function being static, the
helper transport is the only transport that gets affected, but how
has it been working without having this do_take_over() step?  An
obvious related question is if it has been working so far, would it
break if we have do_take_over() added here?

In any case, this makes me wonder if we should do the following
patch to help developers who may want to add new callers to
process_connect_service() by adding calls to process_connect().

 transport-helper.c | 22 +++++++++-------------
 1 file changed, 9 insertions(+), 13 deletions(-)

diff --git c/transport-helper.c w/transport-helper.c
index 91381be622..566f7473df 100644
--- c/transport-helper.c
+++ w/transport-helper.c
@@ -646,6 +646,7 @@ static int process_connect(struct transport *transport,
 	struct helper_data *data = transport->data;
 	const char *name;
 	const char *exec;
+	int ret;
 
 	name = for_push ? "git-receive-pack" : "git-upload-pack";
 	if (for_push)
@@ -653,7 +654,10 @@ static int process_connect(struct transport *transport,
 	else
 		exec = data->transport_options.uploadpack;
 
-	return process_connect_service(transport, name, exec);
+	ret = process_connect_service(transport, name, exec);
+	if (ret)
+		do_take_over(transport);
+	return ret;
 }
 
 static int connect_helper(struct transport *transport, const char *name,
@@ -685,10 +689,8 @@ static int fetch_refs(struct transport *transport,
 
 	get_helper(transport);
 
-	if (process_connect(transport, 0)) {
-		do_take_over(transport);
+	if (process_connect(transport, 0))
 		return transport->vtable->fetch_refs(transport, nr_heads, to_fetch);
-	}
 
 	/*
 	 * If we reach here, then the server, the client, and/or the transport
@@ -1145,10 +1147,8 @@ static int push_refs(struct transport *transport,
 {
 	struct helper_data *data = transport->data;
 
-	if (process_connect(transport, 1)) {
-		do_take_over(transport);
+	if (process_connect(transport, 1))
 		return transport->vtable->push_refs(transport, remote_refs, flags);
-	}
 
 	if (!remote_refs) {
 		fprintf(stderr,
@@ -1189,11 +1189,9 @@ static struct ref *get_refs_list(struct transport *transport, int for_push,
 {
 	get_helper(transport);
 
-	if (process_connect(transport, for_push)) {
-		do_take_over(transport);
+	if (process_connect(transport, for_push))
 		return transport->vtable->get_refs_list(transport, for_push,
 							transport_options);
-	}
 
 	return get_refs_list_using_list(transport, for_push);
 }
@@ -1277,10 +1275,8 @@ static int get_bundle_uri(struct transport *transport)
 {
 	get_helper(transport);
 
-	if (process_connect(transport, 0)) {
-		do_take_over(transport);
+	if (process_connect(transport, 0))
 		return transport->vtable->get_bundle_uri(transport);
-	}
 
 	return -1;
 }