This commmit changes the command-line and Bridge line arguments to take
a comma-separated list of front domains. The change is backwards
compatible with old Bridge and ClientTransportPlugin lines. At
rendezvous time, a front domain will be randomly chosen from the list.
This continues to asserts the known version while decoding. The client
will only ever generate the latest version while encoding and if the
response needs to change, the impetus will be a new feature, set in the
deserialized request, which can be used as a distinguisher.
A follow-up wants to pass in a new property from the ClientConfig but it
would be an API breaking change to NewBrokerChannel.
However, it's unclear why NewBrokerChannel is exported at all. No other
package in the repo depends on it and the known users of the library
probably wouldn't be construct them.
While this patch was being reviewed, a new constructor was added,
NewBrokerChannelWithUTLSSettings, with effectively the same issue.
Both of those exported ones are deleted here.
Makes BrokerChannel abstract over a rendezvousMethod. BrokerChannel
itself is responsible for keepLocalAddresses and the NAT type state, as
well as encoding and decoding client poll messages. rendezvousMethod is
only responsible for delivery of encoded messages.
Formerly, BrokerChannel represented the broker URL and possible domain
fronting as
bc.url *url.URL
bc.Host string
That is, bc.url is the URL of the server which we contact directly, and
bc.Host is the Host header to use in the request. With no domain
fronting, bc.url points directly at the broker itself, and bc.Host is
blank. With domain fronting, we do the following reshuffling:
if front != "" {
bc.Host = bc.url.Host
bc.url.Host = front
}
That is, we alter bc.url to reflect that the server to which we send
requests directly is the CDN, not the broker, and store the broker's own
URL in the HTTP Host header.
The above representation was always confusing to me, because in my
mental model, we are always conceptually communicating with the broker;
but we may optionally be using a CDN proxy in the middle. The new
representation is
bc.url *url.URL
bc.front string
bc.url is the URL of the broker itself, and never changes. bc.front is
the optional CDN front domain, and likewise never changes after
initialization. When domain fronting is in use, we do the swap in the
http.Request struct, not in BrokerChannel itself:
if bc.front != "" {
request.Host = request.URL.Host
request.URL.Host = bc.front
}
Compare to the representation in meek-client:
https://gitweb.torproject.org/pluggable-transports/meek.git/tree/meek-client/meek-client.go?h=v0.35.0#n94
var options struct {
URL string
Front string
}
https://gitweb.torproject.org/pluggable-transports/meek.git/tree/meek-client/meek-client.go?h=v0.35.0#n308
if ok { // if front is set
info.Host = info.URL.Host
info.URL.Host = front
}
Send the client poll request and response in a json-encoded format in
the HTTP request body rather than sending the data in HTTP headers. This
will pave the way for using domain-fronting alternatives for the
Snowflake rendezvous.
This update required two main changes to how we use the library. First,
we had to make sure we created the datachannel on the offering peer side
before creating the offer. Second, we had to make sure we wait for the
gathering of all candidates to complete since trickle-ice is enabled by
default. See the release notes for more details:
https://github.com/pion/webrtc/wiki/Release-WebRTC@v3.0.0.
The client and proxy use the net/http default transport to make round
trip connecitons to the broker. These by default don't time out and can
wait indefinitely for the broker to respond if the broker hangs and
doesn't terminate the connection.
Snowflake clients will now attempt NAT discovery using the provided STUN
servers and report their NAT type to the Snowflake broker for matching.
The three possibilities for NAT types are:
- unknown (the client was unable to determine their NAT type),
- restricted (the client has a restrictive NAT and can only be paired
with unrestricted NATs)
- unrestricted (the client can be paired with any other NAT).
Do it as a side effect of NewWebRTCPeer.
Remove WebRTCPeer tests as they currently require invasively modifying
internal fields at different stages of construction.
The other interfaces in client/lib/interfaces.go exist for the purpose
of running tests, but not Snowflake. Existing code would not have worked
with other types anyway, because it does unchecked .(*WebRTCPeer)
conversions.
