We might be trying to send an invoice amount that's greater than the size of the channel, but once you factor in the custom channel logic, an actual HTLC can be sent over the channel to pay that larger payment.
As a result, we'll skip over this check if a have a custom HTLC.
The routing package implements authentication+validation of channel
announcements, pruning of the channel graph, path finding within the network,
sending outgoing payments into the network and synchronizing new peers to our
channel graph state.
Installation and Updating
$ go get -u github.com/lightningnetwork/lnd/routing