[tor-dev] RFC: Using `utls` in meek_lite.

[David Fifield]

On Thu, Jan 24, 2019 at 07:33:39AM +0000, Yawning Angel wrote:
> On 1/24/19 6:47 AM, David Fifield wrote:
> > 	// This also assumes that req.URL.Host will remain constant for the
> > 	// lifetime of the roundTripper, which is a valid assumption for meeklite.
> > 
> > Am I wrong, or is the actual restriction less strict? You can reuse the
> > roundTripper for different hosts--the ServerName is taken from the addr
> > argument to dialTLS--but only if those different hosts negotiate the
> > same ALPN, because the choice of http.Transport or http2.Transport is
> > made only once and persists for the lifetime of the roundTripper.
>
> The lock protecting `roundTripper.initConn` is only held in `dialTLS`,
> and the `roundTripper.transport` is not protected by a lock at all.
> 
> If the target host changes and there is simultaneous access (two threads
> call into `roundTripper.RoundTrip` right after initialization
> simultaneously), there is no guarantee that the connection used to
> create the inner `http.RoundTripper` instance will be passed to the
> correct thread.

I see, you're right. It has to do with the reuse of the initConn.