This is a port of commit e3f3054f8b74caa639a6d9be09702693af9a70e7 from
meek.
In the previous commit, we changed from separate Listen and Serve steps
to always calling ListenAndServe. However, we would really like to
immediately get feedback if any errors happen in the Listen step inside
the call, because it's much better for debugging if those errors get
reported to tor through SMETHOD-ERROR--rather than reporting success to
tor and actually logging an error only in the snowflake log. So we wait
100 ms for an error to occur before deciding that the Listen succeeded.
We don't need to apply this hack to the ACME HTTP-01 listener, because
it's a plaintext listener. Unlike in the TLS case, there isn't any
internal magic that the net library does that we have to rely on. We
just call net.ListenTCP and check for an error.
This is a port of commit cea86c937dc278ba6b2100c238b1d5206bbae2f0 from
meek. Its purpose is to remove the need to copy-paste parts of
net/http.Server.ListenAndServeTLS. Here is a copy of the commit message
from meek:
The net/http package provides ListenAndServe and ListenAndServeTLS
functions, but it doesn't provide a way to set up a listener without
also entering an infinite serve loop. This matters for
ListenAndServeTLS, which sets up a lot of magic behind the scenes for
TLS and HTTP/2 support. Formerly, we had copy-pasted code from
ListenAndServeTLS, but that code has only gotten more complicated in
upstream net/http.
The price we pay for this is that it's no longer possible for a server
bindaddr to ask to listen on port 0 (i.e., a random ephemeral port).
That's because we never get a change to find out what the listening
address is, before entering the serve loop.
What we gain is HTTP/2 support; formerly our copy-pasted code had the
side effect of disabling HTTP/2, because it was copied from an older
version and did things like
config.NextProtos = []string{"http/1.1"}
The new code calls http2.ConfigureServer first, but that's not what's
providing HTTP/2 support. HTTP/2 support happens by default. The reason
we call http2.ConfigureServer is because we need to set
TLSConfig.GetCertificate, and http2.ConfigureServer is a convenient way
to initialize TLSConfig in a way that is guaranteed to work with HTTP/2.
As with commit fcc274ac68 for the broker,
we need to start using the HTTP-01 challenge type in the Snowflake
websocket server transport plugin.
https://bugs.torproject.org/25346
Current versions of tor accept USERADDR with or without a port number,
but future versions may become more strict and require the port number.
https://bugs.torproject.org/23080
This way, we don't lose state of certificates every time the process is
restarted. There's a possibility, otherwise, that if you have to restart
the server rapidly, you might run into Let's Encrypt rate limits and be
unable to create a cert for a while.
https://godoc.org/rsc.io/letsencrypt#hdr-Persistent_Storage
This removes the --tls-cert and --tls-keys options and replaces them
with --acme-hostname and (optional) --acme-email. It uses
https://godoc.org/golang.org/x/crypto/acme/autocert, which is kind of a
successor to https://godoc.org/rsc.io/letsencrypt.
The autocert package only works when the listener runs on port 443. For
that reason, if TOR_PT_SERVER_BINDADDR asks for a port other than 443,
the program will open an *additional* listening port on 443. If there is
an error opening the listener, it is reported through an SMETHOD-ERROR
for the requested address.
The inspiration for this code came from George Tankersley's patch for
meek-server:
https://bugs.torproject.org/18655#comment:8https://github.com/gtank/meek/tree/letsencrypt
