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discovery: properly set FirstBlockHeight and NumBlocks in responses

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In this commit we fix in a bug in `lnd` that could cause other
implementations which implement a strict version of the spec to
disconnect when trying to sync their channel graph using the gossip
query feature. Before this commit, we would embed the request to a
`QueryChannelRange` in the response, causing some clients to reject the
response as the `FirstBlockHeight` and `NumBlocks` field would be
identical for each chunk of the response.

In order to remedy this, we now properly set these two fields with each
returned chunk. Note that even after this commit, we keep our existing
behavior surrounding the `Complete` field as is. Otherwise, current
`lnd` clients which rely on this field (rather than the two
aforementioned fields) wouldn't be able to properly detect when a set of
responses to their query was "complete".

Partially fixes #3728.
This commit is contained in:
Olaoluwa Osuntokun
2019-12-02 19:21:10 -08:00
parent 699bb193e4
commit 6a9b96122d
2 changed files with 90 additions and 17 deletions
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34
discovery/syncer.go
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@@ -824,6 +824,14 @@ func (g *GossipSyncer) replyChanRangeQuery(query *lnwire.QueryChannelRange) erro
// TODO(roasbeef): means can't send max uint above?
// * or make internal 64
// In the base case (no actual response) the first block and the last
// block in the query will be the same. In the loop below, we'll update
// these two variables incrementally with each chunk to properly
// compute the starting block for each response and the number of
// blocks in a response.
firstBlockHeight := query.FirstBlockHeight
lastBlockHeight := query.FirstBlockHeight
numChannels := int32(len(channelRange))
numChansSent := int32(0)
for {
@@ -854,13 +862,31 @@ func (g *GossipSyncer) replyChanRangeQuery(query *lnwire.QueryChannelRange) erro
"size=%v", g.cfg.peerPub[:], len(channelChunk))
}
// If we have any channels at all to return, then we need to
// update our pointers to the first and last blocks for each
// response.
if len(channelChunk) > 0 {
firstBlockHeight = channelChunk[0].BlockHeight
lastBlockHeight = channelChunk[len(channelChunk)-1].BlockHeight
}
// The number of blocks contained in this response (the total
// span) is the difference between the last channel ID and the
// first in the range. We add one as even if all channels
// returned are in the same block, we need to count that.
numBlocksInResp := lastBlockHeight - firstBlockHeight + 1
// With our chunk assembled, we'll now send to the remote peer
// the current chunk.
replyChunk := lnwire.ReplyChannelRange{
QueryChannelRange: *query,
Complete: 0,
EncodingType: g.cfg.encodingType,
ShortChanIDs: channelChunk,
QueryChannelRange: lnwire.QueryChannelRange{
ChainHash: query.ChainHash,
NumBlocks: numBlocksInResp,
FirstBlockHeight: firstBlockHeight,
},
Complete: 0,
EncodingType: g.cfg.encodingType,
ShortChanIDs: channelChunk,
}
if isFinalChunk {
replyChunk.Complete = 1