This intent of this change is to prevent privacy leaks when routing
with aliases and also to allow routing when using an alias. The
aliases are our aliases.
Introduces are two maps:
* aliasToReal:
This is an N->1 mapping for a channel. The keys are the set of
aliases and the value is the confirmed, on-chain SCID.
* baseIndex:
This is also an N->1 mapping for a channel. The keys are the set
of aliases and the value is the "base" SCID (whatever is in the
OpenChannel.ShortChannelID field). There is also a base->base
mapping, so not all keys are aliases.
The above maps are populated when a link is added to the switch and
when the channel has confirmed on-chain. The maps are not removed
from if the link is removed, but this is fine since forwarding won't
occur.
* getLinkByMapping
This function is introduced to adhere to the spec requirements that
using the confirmed SCID of a private, scid-alias-feature-bit
channel does not work. Lnd implements a stricter version of the spec
and disallows this behavior if the feature-bit was negotiated, rather
than just the channel type. The old, privacy-leak behavior is
preserved.
The spec also requires that if we must fail back an HTLC, the
ChannelUpdate must use the SCID of whatever was in the onion, to avoid
a privacy leak. This is also done by passing in the relevant SCID to
the mailbox and link. Lnd will also cancel back on the "incoming" side
if the InterceptableSwitch was used or if the link failed to decrypt
the onion. In this case, we are cautious and replace the SCID if an
alias exists.
eugene
13c15e8038