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htlcswitch: perform fee related checks at forwarding time

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In this commit, we fix a very old, lingering bug within the link. When
accepting an HTLC we are meant to validate the fee against the
constraints of the *outgoing* link. This is due to the fact that we're
offering a payment transit service on our outgoing link. Before this
commit, we would use the policies of the *incoming* link. This would at
times lead to odd routing errors as we would go to route, get an error
update and then route again, repeating the process.

With this commit, we'll properly use the incoming link for timelock
related constraints, and the outgoing link for fee related constraints.
We do this by introducing a new HtlcSatisfiesPolicy method in the link.
This method should return a non-nil error if the link can carry the HTLC
as it satisfies its current forwarding policy. We'll use this method now
at *forwarding* time to ensure that we only forward to links that
actually accept the policy. This fixes a number of bugs that existed
before that could result in a link accepting an HTLC that actually
violated its policy. In the case that the policy is violated for *all*
links, we take care to return the error returned by the *target* link so
the caller can update their sending accordingly.

In this commit, we also remove the prior linkControl channel in the
channelLink. Instead, of sending a message to update the internal link
policy, we'll use a mutex in place. This simplifies the code, and also
adds some necessary refactoring in anticipation of the next follow up
commit.
This commit is contained in:
Olaoluwa Osuntokun
2018-04-03 19:51:40 -07:00
parent 9d4cea93f0
commit 7037d55f65
3 changed files with 181 additions and 134 deletions
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8
htlcswitch/interfaces.go
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@@ -76,6 +76,14 @@ type ChannelLink interface {
// policy to govern if it an incoming HTLC should be forwarded or not.
UpdateForwardingPolicy(ForwardingPolicy)
// HtlcSatifiesPolicy should return a nil error if the passed HTLC
// details satisfy the current forwarding policy fo the target link.
// Otherwise, a valid protocol failure message should be returned in
// order to signal to the source of the HTLC, the policy consistency
// issue.
HtlcSatifiesPolicy(payHash [32]byte,
incomingAmt, amtToForward lnwire.MilliSatoshi) lnwire.FailureMessage
// Bandwidth returns the amount of milli-satoshis which current link
// might pass through channel link. The value returned from this method
// represents the up to date available flow through the channel. This