Re: [PATCH] transport: don't flush when disconnecting stateless-rpc helper

[Derrick Stolee <stolee@gmail.com>]

On 1/8/2020 2:10 AM, Jeff King wrote:
> On Wed, Jan 08, 2020 at 03:34:51AM +0000, brian m. carlson wrote:
> 
>> A colleague (Jon Simons) today pointed out an interesting behavior of
>> git ls-remote with protocol v2: it makes a second POST request and sends
>> only a flush packet.  This can be demonstrated with the following:
>>
>>   GIT_CURL_VERBOSE=1 git -c protocol.version=2 ls-remote origin
>>
>> The Content-Length header on the second request will be exactly 4 bytes.

Good find!
 
> But when we've initiated a v2 stateless-connect session over a transport
> helper, there's no point in sending this flush packet. Each operation
> we've performed is self-contained, and the other side is fine with us
> hanging up between operations.

Makes sense to me.

> But much worse, by sending the flush packet we may cause the helper to
> issue an entirely new request _just_ to send the flush packet. So we can
> incur an extra network request just to say "by the way, we have nothing
> more to send".
> 
> Let's drop this extra flush packet. As the test shows, this reduces the
> number of POSTs required for a v2 ls-remote over http from 2 to 1.

> +test_expect_success 'ls-remote with v2 http sends only one POST' '
> +	test_when_finished "rm -f log" &&
> +
> +	git ls-remote "$HTTPD_DOCUMENT_ROOT_PATH/http_parent" >expect &&
> +	GIT_TRACE_CURL="$(pwd)/log" git -c protocol.version=2 \
> +		ls-remote "$HTTPD_URL/smart/http_parent" >actual &&
> +	test_cmp expect actual &&
> +
> +	grep "Send header: POST" log >posts &&
> +	test_line_count = 1 posts
> +'
> +

Nice test!

> diff --git a/transport.c b/transport.c
> index 83379a037d..1fdc7dac1a 100644
> --- a/transport.c
> +++ b/transport.c
> @@ -737,7 +737,7 @@ static int disconnect_git(struct transport *transport)
>  {
>  	struct git_transport_data *data = transport->data;
>  	if (data->conn) {
> -		if (data->got_remote_heads)
> +		if (data->got_remote_heads && !transport->stateless_rpc)
>  			packet_flush(data->fd[1]);
>  		close(data->fd[0]);
>  		close(data->fd[1]);

Looks good to me. Thanks!

-Stolee