This commit extends the forward HTLC intercept response with fields that
can be used in conjunction with a `ResumeModified` action to modify the
intercepted HTLC p2p message.
The grpc stream.Recv() will decode an ForwardHtlcInterceptResponse
without an IncomingCircuit, which will leave that pointer nil,
causing a nil pointer dereferece when components of in.IncomingCircuitKey
are used in the resolveFromClient() function.
This commit checks for the nil pointer and returns an error before
the rest of the parsing.
Add a new subpackage to `lnd/channeldb` to hold some of the types that
are used in the package itself and in other packages that should not
depend on `channeldb`.
In this commit we move the tracking of the outstanding intercepted htlcs
to InterceptableSwitch. This is a preparation for making the htlc
interceptor required.
Required interception involves tracking outstanding htlcs across
multiple grpc client sessions. The per-session routerrpc
forwardInterceptor object is therefore no longer the best place for
that.
This commit ensures htlcs currently held by the interceptor
Are not sent again. This prevents potential races in the user code that
may lead to loosing funds.
In this commit we add the ability to intercept forwarded htlc packets
straight from the RPC layer. The RPC layer handles a bidrectional stream
that comminucates to the client the intercepted packets and handles its
response by coordinating with the interceptable switch.
