Subject: Re: [PATCH] connect, protocol: log negotiated protocol version

From: Josh Steadmon <[email-masked]>
Date: Wed, 4 Aug 2021 14:37:53 -0700

On 2021.08.03 17:12, Taylor Blau wrote:
> On Tue, Aug 03, 2021 at 01:13:02PM -0700, Josh Steadmon wrote:
> > [...] Therefore, log the negotiated wire protocol version via trace2,
> > for both clients and servers.
> 
> Seems useful, thanks.
> 
> > Do people have a preference for logging this as an integer (and
> > therefore having "unknown protocol version" show up as "-1", or should I
> > add a protocol_version_to_string function so that we can format it
> > properly? For now I've erred on the side of having a smaller diff.
> 
> I probably have a slight preference for converting the protocol_version
> to a string and passing that along to trace2_data_string() instead. That
> would let you more cleanly log "<unknown>", without needing to expose
> implementation details like which enum has what value.

V2 will include a format_protocol_version().

> > diff --git a/connect.c b/connect.c
> > index 70b13389ba..6e23e3ff2d 100644
> > --- a/connect.c
> > +++ b/connect.c
> > @@ -164,6 +164,7 @@ enum protocol_version discover_version(struct packet_reader *reader)
> >  		BUG("unknown protocol version");
> >  	}
> >
> > +	trace2_data_intmax("transfer", NULL, "negotiated-version", version);
> 
> Small nit-pick, this could come between the two switch statements, not
> at the end of the function (since we know what we are going to return
> before we switch on version.

Fixed in V2.

> (I was a little surprised to see that these functions now have the
> side-effect of writing to trace2, since I would have instead expected
> to see new lines added at the callers. But this makes it more
> convenient, and I do not feel strongly about it)
> 
> In any case, connect.c:discover_version() is handling the client side,
> but...
> 
> > diff --git a/protocol.c b/protocol.c
> > index 052d7edbb9..3791d8499e 100644
> > --- a/protocol.c
> > +++ b/protocol.c
> > @@ -89,5 +89,6 @@ enum protocol_version determine_protocol_version_client(const char *server_respo
> >  			die("protocol error: server explicitly said version 0");
> >  	}
> >
> > +	trace2_data_intmax("transfer", NULL, "negotiated-version", version);
> >  	return version;
> >  }
> > --
> 
> This function is used by discover_version to parse the server's
> response. If you are trying to log what protocol was agreed on from the
> server's perspective, I think you are looking instead for
> determine_protocol_version_server().
> 
> If you aren't (and are only interested in the client's point-of-view),
> then I am pretty sure that this latter hunk is redundant.

Thanks for catching this dumb mistake. Fixed in V2, and added tests to
make sure the trace message shows up on both client- & server-side.

> Thanks,
> Taylor