[bug]: GetChanInfo returns an error for zero-conf channels

[alexbosworth]

Background

To update channel fees, you can use the UpdateChannelPolicy and then use GetChanInfo to confirm the fee rate update was applied, but for zero-conf channels the latter API call returns an error

So when looking up such a channel with GetChanInfo, it should return the channel info

Your environment

• LND 0.15.5-beta

Steps to reproduce

• Create a zero-conf channel
• Update the fee rate
• Check that the fee rate was applied

Expected behavior

• The fee rate should be returned

Actual behavior

• Error is returned

[yyforyongyu]

What's the returned error?

[alexbosworth]

edge not found

[Crypt-iQ]

Is the zero-conf channel confirmed? Which SCID are you using in the call to GetChanInfo?

[alexbosworth]

it is not confirmed

[Crypt-iQ]

I wasn't able to reproduce this following the steps above. The channel was an unconfirmed, zero-conf channel and GetChanInfo returned the expected info

[alexbosworth]

ok cool, must be due to using the wrong id then

[Crypt-iQ]

This happened due to a disconnected block notification which called

lnd/channeldb/graph.go

Lines 1519 to 1533 in d9c79d8

	func (c *ChannelGraph) DisconnectBlockAtHeight(height uint32) ([]*ChannelEdgeInfo,
	error) {
	// Every channel having a ShortChannelID starting at 'height'
	// will no longer be confirmed.
	startShortChanID := lnwire.ShortChannelID{
	BlockHeight: height,
	}
	// Delete everything after this height from the db.
	endShortChanID := lnwire.ShortChannelID{
	BlockHeight: math.MaxUint32 & 0x00ffffff,
	TxIndex: math.MaxUint32 & 0x00ffffff,
	TxPosition: math.MaxUint16,
	}

This leads to every SCID in the graph being deleted if it has a height after the disconnected height - meaning every zero-conf channel gets its edge deleted. The fix here would be set endShortChanID to right before the start of the alias SCID range. I'm not sure what can be done to remedy this if this has happened to live zero-conf channels without trying to close the channel or trying to surgically insert the edge