Subject: Re: [PATCH v2 08/11] fetch-pack: advertise trace2 SID in capabilities

From: Josh Steadmon <[email-masked]>
Date: Thu, 5 Nov 2020 10:58:55 -0800

On 2020.11.04 13:22, Junio C Hamano wrote:
> Josh Steadmon <[email-masked]> writes:
> 
> > When trace2 is enabled, the server sent a trace2-sid capability, and
> > trace2.advertiseSID is true, advertise fetch-pack's own session ID back
> > to the server.
> >
> > Signed-off-by: Josh Steadmon <[email-masked]>
> > ---
> >  fetch-pack.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/fetch-pack.c b/fetch-pack.c
> > index b10c432315..7fbefa7b8e 100644
> > --- a/fetch-pack.c
> > +++ b/fetch-pack.c
> > @@ -35,6 +35,8 @@ static int fetch_fsck_objects = -1;
> >  static int transfer_fsck_objects = -1;
> >  static int agent_supported;
> >  static int server_supports_filtering;
> > +static int server_sent_trace2_sid;
> > +static int advertise_trace2_sid;
> >  static struct shallow_lock shallow_lock;
> >  static const char *alternate_shallow_file;
> >  static struct strbuf fsck_msg_types = STRBUF_INIT;
> > @@ -326,6 +328,8 @@ static int find_common(struct fetch_negotiator *negotiator,
> >  			if (deepen_not_ok)      strbuf_addstr(&c, " deepen-not");
> >  			if (agent_supported)    strbuf_addf(&c, " agent=%s",
> >  							    git_user_agent_sanitized());
> > +			if (advertise_trace2_sid && server_sent_trace2_sid && trace2_is_enabled())
> > +				strbuf_addf(&c, " trace2-sid=%s", trace2_session_id());
> >  			if (args->filter_options.choice)
> >  				strbuf_addstr(&c, " filter");
> >  			packet_buf_write(&req_buf, "want %s%s\n", remote_hex, c.buf);
> > @@ -979,6 +983,9 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
> >  				      agent_len, agent_feature);
> >  	}
> >  
> > +	if (server_supports("trace2-sid"))
> > +		server_sent_trace2_sid = 1;
> > +
> >  	if (server_supports("shallow"))
> >  		print_verbose(args, _("Server supports %s"), "shallow");
> >  	else if (args->depth > 0 || is_repository_shallow(r))
> > @@ -1191,6 +1198,8 @@ static int send_fetch_request(struct fetch_negotiator *negotiator, int fd_out,
> >  		packet_buf_write(&req_buf, "command=fetch");
> >  	if (server_supports_v2("agent", 0))
> >  		packet_buf_write(&req_buf, "agent=%s", git_user_agent_sanitized());
> > +	if (advertise_trace2_sid && server_supports_v2("trace2-sid", 0) && trace2_is_enabled())
> > +		packet_buf_write(&req_buf, "trace2-sid=%s", trace2_session_id());
> >  	if (args->server_options && args->server_options->nr &&
> >  	    server_supports_v2("server-option", 1)) {
> >  		int i;
> > @@ -1711,6 +1720,7 @@ static void fetch_pack_config(void)
> >  	git_config_get_bool("repack.usedeltabaseoffset", &prefer_ofs_delta);
> >  	git_config_get_bool("fetch.fsckobjects", &fetch_fsck_objects);
> >  	git_config_get_bool("transfer.fsckobjects", &transfer_fsck_objects);
> > +	git_config_get_bool("trace2.advertisesid", &advertise_trace2_sid);
> >  	if (!uri_protocols.nr) {
> >  		char *str;
> 
> The same comment as 05/11 and 06/11 applies to this repeated
> appearance of this boolean expression:
> 
> 	advertise_trace2_sid && trace2_is_enabled()
> 
> If we are committed to stick to the "even if we were told to
> advertise, do not alllocate a session ID" design, perhaps it is
> cleaner to clear advertise_trace2_sid at the very beginning,
> immediately after we learn that the tracing is disabled and the
> advertiseSID configuration is read.  That way, everybody needs to
> only care about advertise_trace2_sid variable.
> 
> Incidentally, if we decide to change the semantics to auto allocate
> the session ID if advertiseSID configuration asks us to advertise
> (it is OK if we do not enable the full trace2 suite), we can still
> make the code only check advertise_trace2_sid variable, without
> adding repeated check of trace2_is_enabled() everywhere at all.

Good point. Once we settle on whether or not to advertise when tracing
is enabled, I'll update these conditionals in V3.