feature-bit channels
This allows opening zero-conf chan-type, scid-alias chan-type, and
scid-alias feature-bit channels. scid-alias chan-type channels are
required to be private. Two paths are available for opening a zero-conf
channel:
* explicit chan-type negotiation
* LDK carve-out where chan-types are not used, LND is on the
receiving end, and a ChannelAcceptor is used to enable zero-conf
When a zero-conf channel is negotiated, the funding manager:
* sends a FundingLocked with an alias
* waits for a FundingLocked from the remote peer
* calls addToRouterGraph to persist the channel using our alias in
the graph. The peer's alias is used to send them a ChannelUpdate.
* wait for six confirmations. If public, the alias edge in the
graph is deleted and replaced (not atomically) with the confirmed
edge. Our policy is also read-and-replaced, but the counterparty's
policy won't exist until they send it to us.
When a scid-alias-feature channel is negotiated, the funding manager:
* sends a FundingLocked with an alias:
* calls addToRouterGraph, sends ChannelUpdate with the confirmed SCID
since it exists.
* when six confirmations occurs, the edge is deleted and re-inserted
since the peer may have sent us an alias ChannelUpdate that we are
storing in the graph.
Since it is possible for a user to toggle the scid-alias-feature-bit
to on while channels exist in the funding manager, care has been taken
to ensure that an alias is ALWAYS sent in the funding_locked message
if this happens.
Add more fields to channel acceptor response so that users can have more
fine grained control over their incoming channels. With our chained
acceptor, it is possible that we get inconsistent responses from
multiple chained acceptors. We create a conjugate repsponse from all the
set fields in our various responses, but fail if we get different, non-
zero responses from our various acceptors. Separate merge functions are
used per type so that we avoid unexpected outcomes comparing interfaces
(panic on comparing types that aren't comparable), with casting used
where applicable to avoid code duplication.
This commit adds an optional error message to the channel acceptor's
reponse to allow operators to inform (or insult) unsuccessful channel
initiators as to the reason for their rejection.
This field is added in addition to the existing accept field to maintain
backwards compatibity. If we were to deprecate accept and interpret a
non-nil error as rejecting the channel, then received a response with
accept=false and a nil error, the server cannot tell whether this is a
legacy rejection or new mesage type acceptance (due to nil error),
so we keep both fields.
This commit introduces the chanacceptor package which is used
to determine, by a set of heuristics, which open channel messages
to accept and reject. Currently, two acceptors are implemented
via the ChannelAcceptor interface: ChainedAcceptor and RPCAcceptor.
The RPCAcceptor allows the RPC client to respond to the open channel
request, and the ChainedAcceptor allows a conjunction of acceptors
to be used.
