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Use the query start block for ReplyChannelRange response messages #961

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Jul 8, 2021
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Use the query start block for ReplyChannelRange response messages #961

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90 changes: 60 additions & 30 deletions lightning/src/routing/network_graph.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -373,23 +373,39 @@ impl<C: Deref , L: Deref > RoutingMessageHandler for NetGraphMsgHandler<C, L> wh

let mut pending_events = self.pending_events.lock().unwrap();
let batch_count = batches.len();
let mut prev_batch_endblock = msg.first_blocknum;
for (batch_index, batch) in batches.into_iter().enumerate() {
// Per spec, the initial first_blocknum needs to be <= the query's first_blocknum and subsequent
// must be >= the prior reply. We'll simplify this by using zero since its still spec compliant and
// sequence completion is now explicitly.
let first_blocknum = 0;

// Per spec, the final end_blocknum needs to be >= the query's end_blocknum, so we'll use the
// query's value. Prior batches must use the number of blocks that fit into the message. We'll
// base this off the last SCID in the batch since we've somewhat abusing first_blocknum.
let number_of_blocks = if batch_index == batch_count-1 {
msg.end_blocknum()
} else {
block_from_scid(batch.last().unwrap()) + 1
// Per spec, the initial `first_blocknum` needs to be <= the query's `first_blocknum`
// and subsequent `first_blocknum`s must be >= the prior reply's `first_blocknum`.
//
// Additionally, c-lightning versions < 0.10 require that the `first_blocknum` of each
// reply is >= the previous reply's `first_blocknum` and either exactly the previous
// reply's `first_blocknum + number_of_blocks` or exactly one greater. This is a
// significant diversion from the requirements set by the spec, and, in case of blocks
// with no channel opens (e.g. empty blocks), requires that we use the previous value
// and *not* derive the first_blocknum from the actual first block of the reply.
let first_blocknum = prev_batch_endblock;

// Each message carries the number of blocks (from the `first_blocknum`) its contents
// fit in. Though there is no requirement that we use exactly the number of blocks its
// contents are from, except for the bogus requirements c-lightning enforces, above.
//
// Per spec, the last end block (ie `first_blocknum + number_of_blocks`) needs to be
// >= the query's end block. Thus, for the last reply, we calculate the difference
// between the query's end block and the start of the reply.
//
// Overflow safe since end_blocknum=msg.first_block_num+msg.number_of_blocks and
// first_blocknum will be either msg.first_blocknum or a higher block height.
let (sync_complete, number_of_blocks) = if batch_index == batch_count-1 {
(true, msg.end_blocknum() - first_blocknum)
}
// Prior replies should use the number of blocks that fit into the reply. Overflow
// safe since first_blocknum is always <= last SCID's block.
else {
(false, block_from_scid(batch.last().unwrap()) - first_blocknum)
};

// Only true for the last message in a sequence
let sync_complete = batch_index == batch_count - 1;
prev_batch_endblock = first_blocknum + number_of_blocks;

pending_events.push(MessageSendEvent::SendReplyChannelRange {
node_id: their_node_id.clone(),
Expand Down Expand Up @@ -2235,8 +2251,8 @@ mod tests {
vec![
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 0x01000000,
first_blocknum: 0xffffff,
number_of_blocks: 1,
sync_complete: true,
short_channel_ids: vec![]
},
Expand All @@ -2256,8 +2272,8 @@ mod tests {
vec![
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 2000,
first_blocknum: 1000,
number_of_blocks: 1000,
sync_complete: true,
short_channel_ids: vec![],
}
Expand All @@ -2277,8 +2293,8 @@ mod tests {
vec![
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 0xffffffff,
first_blocknum: 0xfe0000,
number_of_blocks: 0xffffffff - 0xfe0000,
sync_complete: true,
short_channel_ids: vec![
0xfffffe_ffffff_ffff, // max
Expand All @@ -2300,8 +2316,8 @@ mod tests {
vec![
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 108000,
first_blocknum: 100000,
number_of_blocks: 8000,
sync_complete: true,
short_channel_ids: (100000..=107999)
.map(|block| scid_from_parts(block, 0, 0).unwrap())
Expand All @@ -2323,17 +2339,17 @@ mod tests {
vec![
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 108000,
first_blocknum: 100000,
number_of_blocks: 7999,
sync_complete: false,
short_channel_ids: (100000..=107999)
.map(|block| scid_from_parts(block, 0, 0).unwrap())
.collect(),
},
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 108001,
first_blocknum: 107999,
number_of_blocks: 2,
sync_complete: true,
short_channel_ids: vec![
scid_from_parts(108000, 0, 0).unwrap(),
Expand All @@ -2355,17 +2371,17 @@ mod tests {
vec![
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 108002,
first_blocknum: 100002,
number_of_blocks: 7999,
sync_complete: false,
short_channel_ids: (100002..=108001)
.map(|block| scid_from_parts(block, 0, 0).unwrap())
.collect(),
},
ReplyChannelRange {
chain_hash: chain_hash.clone(),
first_blocknum: 0,
number_of_blocks: 108002,
first_blocknum: 108001,
number_of_blocks: 1,
sync_complete: true,
short_channel_ids: vec![
scid_from_parts(108001, 1, 0).unwrap(),
Expand All @@ -2382,6 +2398,9 @@ mod tests {
expected_ok: bool,
expected_replies: Vec<ReplyChannelRange>
) {
let mut max_firstblocknum = msg.first_blocknum.saturating_sub(1);
let mut c_lightning_0_9_prev_end_blocknum = max_firstblocknum;
let query_end_blocknum = msg.end_blocknum();
let result = net_graph_msg_handler.handle_query_channel_range(test_node_id, msg);

if expected_ok {
Expand All @@ -2403,6 +2422,17 @@ mod tests {
assert_eq!(msg.number_of_blocks, expected_reply.number_of_blocks);
assert_eq!(msg.sync_complete, expected_reply.sync_complete);
assert_eq!(msg.short_channel_ids, expected_reply.short_channel_ids);

// Enforce exactly the sequencing requirements present on c-lightning v0.9.3
assert!(msg.first_blocknum == c_lightning_0_9_prev_end_blocknum || msg.first_blocknum == c_lightning_0_9_prev_end_blocknum.saturating_add(1));
assert!(msg.first_blocknum >= max_firstblocknum);
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  • Since we're checking for >=, wouldn't it be min_firstblocknum?
  • Is it fair to say that max_firstblocknum is checking that the msg's first_blocknum is at least the first_blocknum of the previous msg?

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Its the maximum-seen-firstblocknum, which each new message must be greater than.

Is it fair to say that max_firstblocknum is checking that the msg's first_blocknum is at least the first_blocknum of the previous msg?
Yes

max_firstblocknum = msg.first_blocknum;
c_lightning_0_9_prev_end_blocknum = msg.first_blocknum.saturating_add(msg.number_of_blocks);

// Check that the last block count is >= the query's end_blocknum
if i == events.len() - 1 {
assert!(msg.first_blocknum.saturating_add(msg.number_of_blocks) >= query_end_blocknum);
}
},
_ => panic!("expected MessageSendEvent::SendReplyChannelRange"),
}
Expand Down