1 //! When fetching gossip from peers, lightning nodes need to validate that gossip against the
2 //! current UTXO set. This module defines an implementation of the LDK API required to do so
3 //! against a [`BlockSource`] which implements a few additional methods for accessing the UTXO set.
5 use crate::{AsyncBlockSourceResult, BlockData, BlockSource};
7 use bitcoin::blockdata::block::Block;
8 use bitcoin::blockdata::transaction::{TxOut, OutPoint};
9 use bitcoin::hash_types::BlockHash;
11 use lightning::sign::NodeSigner;
13 use lightning::ln::peer_handler::{CustomMessageHandler, PeerManager, SocketDescriptor};
14 use lightning::ln::msgs::{ChannelMessageHandler, OnionMessageHandler};
16 use lightning::routing::gossip::{NetworkGraph, P2PGossipSync};
17 use lightning::routing::utxo::{UtxoFuture, UtxoLookup, UtxoResult, UtxoLookupError};
19 use lightning::util::logger::Logger;
21 use std::sync::{Arc, Mutex};
22 use std::collections::VecDeque;
23 use std::future::Future;
26 /// A trait which extends [`BlockSource`] and can be queried to fetch the block at a given height
27 /// as well as whether a given output is unspent (i.e. a member of the current UTXO set).
29 /// Note that while this is implementable for a [`BlockSource`] which returns filtered block data
30 /// (i.e. [`BlockData::HeaderOnly`] for [`BlockSource::get_block`] requests), such an
31 /// implementation will reject all gossip as it is not fully able to verify the UTXOs referenced.
32 pub trait UtxoSource : BlockSource + 'static {
33 /// Fetches the block hash of the block at the given height.
35 /// This will, in turn, be passed to to [`BlockSource::get_block`] to fetch the block needed
36 /// for gossip validation.
37 fn get_block_hash_by_height<'a>(&'a self, block_height: u32) -> AsyncBlockSourceResult<'a, BlockHash>;
39 /// Returns true if the given output has *not* been spent, i.e. is a member of the current UTXO
41 fn is_output_unspent<'a>(&'a self, outpoint: OutPoint) -> AsyncBlockSourceResult<'a, bool>;
44 /// A generic trait which is able to spawn futures in the background.
46 /// If the `tokio` feature is enabled, this is implemented on `TokioSpawner` struct which
47 /// delegates to `tokio::spawn()`.
48 pub trait FutureSpawner : Send + Sync + 'static {
49 /// Spawns the given future as a background task.
51 /// This method MUST NOT block on the given future immediately.
52 fn spawn<T: Future<Output = ()> + Send + 'static>(&self, future: T);
55 #[cfg(feature = "tokio")]
56 /// A trivial [`FutureSpawner`] which delegates to `tokio::spawn`.
57 pub struct TokioSpawner;
58 #[cfg(feature = "tokio")]
59 impl FutureSpawner for TokioSpawner {
60 fn spawn<T: Future<Output = ()> + Send + 'static>(&self, future: T) {
65 /// A struct which wraps a [`UtxoSource`] and a few LDK objects and implements the LDK
66 /// [`UtxoLookup`] trait.
68 /// Note that if you're using this against a Bitcoin Core REST or RPC server, you likely wish to
69 /// increase the `rpcworkqueue` setting in Bitcoin Core as LDK attempts to parallelize requests (a
70 /// value of 1024 should more than suffice), and ensure you have sufficient file descriptors
71 /// available on both Bitcoin Core and your LDK application for each request to hold its own
73 pub struct GossipVerifier<S: FutureSpawner,
74 Blocks: Deref + Send + Sync + 'static + Clone,
75 L: Deref + Send + Sync + 'static,
76 Descriptor: SocketDescriptor + Send + Sync + 'static,
77 CM: Deref + Send + Sync + 'static,
78 OM: Deref + Send + Sync + 'static,
79 CMH: Deref + Send + Sync + 'static,
80 NS: Deref + Send + Sync + 'static,
82 Blocks::Target: UtxoSource,
84 CM::Target: ChannelMessageHandler,
85 OM::Target: OnionMessageHandler,
86 CMH::Target: CustomMessageHandler,
87 NS::Target: NodeSigner,
90 peer_manager: Arc<PeerManager<Descriptor, CM, Arc<P2PGossipSync<Arc<NetworkGraph<L>>, Self, L>>, OM, L, CMH, NS>>,
91 gossiper: Arc<P2PGossipSync<Arc<NetworkGraph<L>>, Self, L>>,
93 block_cache: Arc<Mutex<VecDeque<(u32, Block)>>>,
96 const BLOCK_CACHE_SIZE: usize = 5;
98 impl<S: FutureSpawner,
99 Blocks: Deref + Send + Sync + Clone,
100 L: Deref + Send + Sync,
101 Descriptor: SocketDescriptor + Send + Sync,
102 CM: Deref + Send + Sync,
103 OM: Deref + Send + Sync,
104 CMH: Deref + Send + Sync,
105 NS: Deref + Send + Sync,
106 > GossipVerifier<S, Blocks, L, Descriptor, CM, OM, CMH, NS> where
107 Blocks::Target: UtxoSource,
109 CM::Target: ChannelMessageHandler,
110 OM::Target: OnionMessageHandler,
111 CMH::Target: CustomMessageHandler,
112 NS::Target: NodeSigner,
114 /// Constructs a new [`GossipVerifier`].
116 /// This is expected to be given to a [`P2PGossipSync`] (initially constructed with `None` for
117 /// the UTXO lookup) via [`P2PGossipSync::add_utxo_lookup`].
118 pub fn new(source: Blocks, spawn: S, gossiper: Arc<P2PGossipSync<Arc<NetworkGraph<L>>, Self, L>>, peer_manager: Arc<PeerManager<Descriptor, CM, Arc<P2PGossipSync<Arc<NetworkGraph<L>>, Self, L>>, OM, L, CMH, NS>>) -> Self {
120 source, spawn, gossiper, peer_manager,
121 block_cache: Arc::new(Mutex::new(VecDeque::with_capacity(BLOCK_CACHE_SIZE))),
125 async fn retrieve_utxo(
126 source: Blocks, block_cache: Arc<Mutex<VecDeque<(u32, Block)>>>, short_channel_id: u64
127 ) -> Result<TxOut, UtxoLookupError> {
128 let block_height = (short_channel_id >> 5 * 8) as u32; // block height is most significant three bytes
129 let transaction_index = ((short_channel_id >> 2 * 8) & 0xffffff) as u32;
130 let output_index = (short_channel_id & 0xffff) as u16;
132 let (outpoint, output);
134 'tx_found: loop { // Used as a simple goto
135 macro_rules! process_block {
136 ($block: expr) => { {
137 if transaction_index as usize >= $block.txdata.len() {
138 return Err(UtxoLookupError::UnknownTx);
140 let transaction = &$block.txdata[transaction_index as usize];
141 if output_index as usize >= transaction.output.len() {
142 return Err(UtxoLookupError::UnknownTx);
145 outpoint = OutPoint::new(transaction.txid(), output_index.into());
146 output = transaction.output[output_index as usize].clone();
150 let recent_blocks = block_cache.lock().unwrap();
151 for (height, block) in recent_blocks.iter() {
152 if *height == block_height {
153 process_block!(block);
159 let block_hash = source.get_block_hash_by_height(block_height).await
160 .map_err(|_| UtxoLookupError::UnknownTx)?;
161 let block_data = source.get_block(&block_hash).await
162 .map_err(|_| UtxoLookupError::UnknownTx)?;
163 let block = match block_data {
164 BlockData::HeaderOnly(_) => return Err(UtxoLookupError::UnknownTx),
165 BlockData::FullBlock(block) => block,
167 process_block!(block);
169 let mut recent_blocks = block_cache.lock().unwrap();
170 let mut insert = true;
171 for (height, _) in recent_blocks.iter() {
172 if *height == block_height {
177 if recent_blocks.len() >= BLOCK_CACHE_SIZE {
178 recent_blocks.pop_front();
180 recent_blocks.push_back((block_height, block));
185 let outpoint_unspent =
186 source.is_output_unspent(outpoint).await.map_err(|_| UtxoLookupError::UnknownTx)?;
187 if outpoint_unspent {
190 Err(UtxoLookupError::UnknownTx)
195 impl<S: FutureSpawner,
196 Blocks: Deref + Send + Sync + Clone,
197 L: Deref + Send + Sync,
198 Descriptor: SocketDescriptor + Send + Sync,
199 CM: Deref + Send + Sync,
200 OM: Deref + Send + Sync,
201 CMH: Deref + Send + Sync,
202 NS: Deref + Send + Sync,
203 > Deref for GossipVerifier<S, Blocks, L, Descriptor, CM, OM, CMH, NS> where
204 Blocks::Target: UtxoSource,
206 CM::Target: ChannelMessageHandler,
207 OM::Target: OnionMessageHandler,
208 CMH::Target: CustomMessageHandler,
209 NS::Target: NodeSigner,
212 fn deref(&self) -> &Self { self }
216 impl<S: FutureSpawner,
217 Blocks: Deref + Send + Sync + Clone,
218 L: Deref + Send + Sync,
219 Descriptor: SocketDescriptor + Send + Sync,
220 CM: Deref + Send + Sync,
221 OM: Deref + Send + Sync,
222 CMH: Deref + Send + Sync,
223 NS: Deref + Send + Sync,
224 > UtxoLookup for GossipVerifier<S, Blocks, L, Descriptor, CM, OM, CMH, NS> where
225 Blocks::Target: UtxoSource,
227 CM::Target: ChannelMessageHandler,
228 OM::Target: OnionMessageHandler,
229 CMH::Target: CustomMessageHandler,
230 NS::Target: NodeSigner,
232 fn get_utxo(&self, _genesis_hash: &BlockHash, short_channel_id: u64) -> UtxoResult {
233 let res = UtxoFuture::new();
234 let fut = res.clone();
235 let source = self.source.clone();
236 let gossiper = Arc::clone(&self.gossiper);
237 let block_cache = Arc::clone(&self.block_cache);
238 let pm = Arc::clone(&self.peer_manager);
239 self.spawn.spawn(async move {
240 let res = Self::retrieve_utxo(source, block_cache, short_channel_id).await;
241 fut.resolve(gossiper.network_graph(), &*gossiper, res);
244 UtxoResult::Async(res)