git.bitcoin.ninja Git - rust-lightning/blob - lightning-block-sync/src/poll.rs

   1 //! Adapters that make one or more [`BlockSource`]s simpler to poll for new chain tip transitions.
   2
   3 use crate::{AsyncBlockSourceResult, BlockHeaderData, BlockSource, BlockSourceError, BlockSourceResult};
   4
   5 use bitcoin::blockdata::block::Block;
   6 use bitcoin::hash_types::BlockHash;
   7 use bitcoin::network::constants::Network;
   8
   9 use std::ops::Deref;
  10
  11 /// The `Poll` trait defines behavior for polling block sources for a chain tip and retrieving
  12 /// related chain data. It serves as an adapter for `BlockSource`.
  13 ///
  14 /// [`ChainPoller`] adapts a single `BlockSource`, while any other implementations of `Poll` are
  15 /// required to be built in terms of it to ensure chain data validity.
  16 ///
  17 /// [`ChainPoller`]: ../struct.ChainPoller.html
  18 pub trait Poll {
  19         /// Returns a chain tip in terms of its relationship to the provided chain tip.
  20         fn poll_chain_tip<'a>(&'a self, best_known_chain_tip: ValidatedBlockHeader) ->
  21                 AsyncBlockSourceResult<'a, ChainTip>;
  22
  23         /// Returns the header that preceded the given header in the chain.
  24         fn look_up_previous_header<'a>(&'a self, header: &'a ValidatedBlockHeader) ->
  25                 AsyncBlockSourceResult<'a, ValidatedBlockHeader>;
  26
  27         /// Returns the block associated with the given header.
  28         fn fetch_block<'a>(&'a self, header: &'a ValidatedBlockHeader) ->
  29                 AsyncBlockSourceResult<'a, ValidatedBlock>;
  30 }
  31
  32 /// A chain tip relative to another chain tip in terms of block hash and chainwork.
  33 #[derive(Clone, Debug, PartialEq)]
  34 pub enum ChainTip {
  35         /// A chain tip with the same hash as another chain's tip.
  36         Common,
  37
  38         /// A chain tip with more chainwork than another chain's tip.
  39         Better(ValidatedBlockHeader),
  40
  41         /// A chain tip with less or equal chainwork than another chain's tip. In either case, the
  42         /// hashes of each tip will be different.
  43         Worse(ValidatedBlockHeader),
  44 }
  45
  46 /// The `Validate` trait defines behavior for validating chain data.
  47 ///
  48 /// This trait is sealed and not meant to be implemented outside of this crate.
  49 pub trait Validate: sealed::Validate {
  50         /// The validated data wrapper which can be dereferenced to obtain the validated data.
  51         type T: std::ops::Deref<Target = Self>;
  52
  53         /// Validates the chain data against the given block hash and any criteria needed to ensure that
  54         /// it is internally consistent.
  55         fn validate(self, block_hash: BlockHash) -> BlockSourceResult<Self::T>;
  56 }
  57
  58 impl Validate for BlockHeaderData {
  59         type T = ValidatedBlockHeader;
  60
  61         fn validate(self, block_hash: BlockHash) -> BlockSourceResult<Self::T> {
  62                 self.header
  63                         .validate_pow(&self.header.target())
  64                         .or_else(|e| Err(BlockSourceError::persistent(e)))?;
  65
  66                 // TODO: Use the result of validate_pow instead of recomputing the block hash once upstream.
  67                 if self.header.block_hash() != block_hash {
  68                         return Err(BlockSourceError::persistent("invalid block hash"));
  69                 }
  70
  71                 Ok(ValidatedBlockHeader { block_hash, inner: self })
  72         }
  73 }
  74
  75 impl Validate for Block {
  76         type T = ValidatedBlock;
  77
  78         fn validate(self, block_hash: BlockHash) -> BlockSourceResult<Self::T> {
  79                 self.header
  80                         .validate_pow(&self.header.target())
  81                         .or_else(|e| Err(BlockSourceError::persistent(e)))?;
  82
  83                 // TODO: Use the result of validate_pow instead of recomputing the block hash once upstream.
  84                 if self.block_hash() != block_hash {
  85                         return Err(BlockSourceError::persistent("invalid block hash"));
  86                 }
  87
  88                 if !self.check_merkle_root() {
  89                         return Err(BlockSourceError::persistent("invalid merkle root"));
  90                 }
  91
  92                 if !self.check_witness_commitment() {
  93                         return Err(BlockSourceError::persistent("invalid witness commitment"));
  94                 }
  95
  96                 Ok(ValidatedBlock { block_hash, inner: self })
  97         }
  98 }
  99
 100 /// A block header with validated proof of work and corresponding block hash.
 101 #[derive(Clone, Copy, Debug, PartialEq)]
 102 pub struct ValidatedBlockHeader {
 103         pub(crate) block_hash: BlockHash,
 104         inner: BlockHeaderData,
 105 }
 106
 107 impl std::ops::Deref for ValidatedBlockHeader {
 108         type Target = BlockHeaderData;
 109
 110         fn deref(&self) -> &Self::Target {
 111                 &self.inner
 112         }
 113 }
 114
 115 impl ValidatedBlockHeader {
 116         /// Checks that the header correctly builds on previous_header: the claimed work differential
 117         /// matches the actual PoW and the difficulty transition is possible, i.e., within 4x.
 118         fn check_builds_on(&self, previous_header: &ValidatedBlockHeader, network: Network) -> BlockSourceResult<()> {
 119                 if self.header.prev_blockhash != previous_header.block_hash {
 120                         return Err(BlockSourceError::persistent("invalid previous block hash"));
 121                 }
 122
 123                 if self.height != previous_header.height + 1 {
 124                         return Err(BlockSourceError::persistent("invalid block height"));
 125                 }
 126
 127                 let work = self.header.work();
 128                 if self.chainwork != previous_header.chainwork + work {
 129                         return Err(BlockSourceError::persistent("invalid chainwork"));
 130                 }
 131
 132                 if let Network::Bitcoin = network {
 133                         if self.height % 2016 == 0 {
 134                                 let previous_work = previous_header.header.work();
 135                                 if work > (previous_work << 2) || work < (previous_work >> 2) {
 136                                         return Err(BlockSourceError::persistent("invalid difficulty transition"))
 137                                 }
 138                         } else if self.header.bits != previous_header.header.bits {
 139                                 return Err(BlockSourceError::persistent("invalid difficulty"))
 140                         }
 141                 }
 142
 143                 Ok(())
 144         }
 145 }
 146
 147 /// A block with validated data against its transaction list and corresponding block hash.
 148 pub struct ValidatedBlock {
 149         pub(crate) block_hash: BlockHash,
 150         inner: Block,
 151 }
 152
 153 impl std::ops::Deref for ValidatedBlock {
 154         type Target = Block;
 155
 156         fn deref(&self) -> &Self::Target {
 157                 &self.inner
 158         }
 159 }
 160
 161 mod sealed {
 162         /// Used to prevent implementing [`super::Validate`] outside the crate but still allow its use.
 163         pub trait Validate {}
 164
 165         impl Validate for crate::BlockHeaderData {}
 166         impl Validate for bitcoin::blockdata::block::Block {}
 167 }
 168
 169 /// The canonical `Poll` implementation used for a single `BlockSource`.
 170 ///
 171 /// Other `Poll` implementations should be built using `ChainPoller` as it provides the simplest way
 172 /// of validating chain data and checking consistency.
 173 pub struct ChainPoller<B: Deref<Target=T> + Sized, T: BlockSource> {
 174         block_source: B,
 175         network: Network,
 176 }
 177
 178 impl<B: Deref<Target=T> + Sized, T: BlockSource> ChainPoller<B, T> {
 179         /// Creates a new poller for the given block source.
 180         ///
 181         /// If the `network` parameter is mainnet, then the difficulty between blocks is checked for
 182         /// validity.
 183         pub fn new(block_source: B, network: Network) -> Self {
 184                 Self { block_source, network }
 185         }
 186 }
 187
 188 impl<B: Deref<Target=T> + Sized + Send + Sync, T: BlockSource> Poll for ChainPoller<B, T> {
 189         fn poll_chain_tip<'a>(&'a self, best_known_chain_tip: ValidatedBlockHeader) ->
 190                 AsyncBlockSourceResult<'a, ChainTip>
 191         {
 192                 Box::pin(async move {
 193                         let (block_hash, height) = self.block_source.get_best_block().await?;
 194                         if block_hash == best_known_chain_tip.header.block_hash() {
 195                                 return Ok(ChainTip::Common);
 196                         }
 197
 198                         let chain_tip = self.block_source
 199                                 .get_header(&block_hash, height).await?
 200                                 .validate(block_hash)?;
 201                         if chain_tip.chainwork > best_known_chain_tip.chainwork {
 202                                 Ok(ChainTip::Better(chain_tip))
 203                         } else {
 204                                 Ok(ChainTip::Worse(chain_tip))
 205                         }
 206                 })
 207         }
 208
 209         fn look_up_previous_header<'a>(&'a self, header: &'a ValidatedBlockHeader) ->
 210                 AsyncBlockSourceResult<'a, ValidatedBlockHeader>
 211         {
 212                 Box::pin(async move {
 213                         if header.height == 0 {
 214                                 return Err(BlockSourceError::persistent("genesis block reached"));
 215                         }
 216
 217                         let previous_hash = &header.header.prev_blockhash;
 218                         let height = header.height - 1;
 219                         let previous_header = self.block_source
 220                                 .get_header(previous_hash, Some(height)).await?
 221                                 .validate(*previous_hash)?;
 222                         header.check_builds_on(&previous_header, self.network)?;
 223
 224                         Ok(previous_header)
 225                 })
 226         }
 227
 228         fn fetch_block<'a>(&'a self, header: &'a ValidatedBlockHeader) ->
 229                 AsyncBlockSourceResult<'a, ValidatedBlock>
 230         {
 231                 Box::pin(async move {
 232                         self.block_source
 233                                 .get_block(&header.block_hash).await?
 234                                 .validate(header.block_hash)
 235                 })
 236         }
 237 }
 238
 239 #[cfg(test)]
 240 mod tests {
 241         use crate::*;
 242         use crate::test_utils::Blockchain;
 243         use super::*;
 244         use bitcoin::util::uint::Uint256;
 245
 246         #[tokio::test]
 247         async fn poll_empty_chain() {
 248                 let mut chain = Blockchain::default().with_height(0);
 249                 let best_known_chain_tip = chain.tip();
 250                 chain.disconnect_tip();
 251
 252                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 253                 match poller.poll_chain_tip(best_known_chain_tip).await {
 254                         Err(e) => {
 255                                 assert_eq!(e.kind(), BlockSourceErrorKind::Transient);
 256                                 assert_eq!(e.into_inner().as_ref().to_string(), "empty chain");
 257                         },
 258                         Ok(_) => panic!("Expected error"),
 259                 }
 260         }
 261
 262         #[tokio::test]
 263         async fn poll_chain_without_headers() {
 264                 let chain = Blockchain::default().with_height(1).without_headers();
 265                 let best_known_chain_tip = chain.at_height(0);
 266
 267                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 268                 match poller.poll_chain_tip(best_known_chain_tip).await {
 269                         Err(e) => {
 270                                 assert_eq!(e.kind(), BlockSourceErrorKind::Persistent);
 271                                 assert_eq!(e.into_inner().as_ref().to_string(), "header not found");
 272                         },
 273                         Ok(_) => panic!("Expected error"),
 274                 }
 275         }
 276
 277         #[tokio::test]
 278         async fn poll_chain_with_invalid_pow() {
 279                 let mut chain = Blockchain::default().with_height(1);
 280                 let best_known_chain_tip = chain.at_height(0);
 281
 282                 // Invalidate the tip by changing its target.
 283                 chain.blocks.last_mut().unwrap().header.bits =
 284                         BlockHeader::compact_target_from_u256(&Uint256::from_be_bytes([0; 32]));
 285
 286                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 287                 match poller.poll_chain_tip(best_known_chain_tip).await {
 288                         Err(e) => {
 289                                 assert_eq!(e.kind(), BlockSourceErrorKind::Persistent);
 290                                 assert_eq!(e.into_inner().as_ref().to_string(), "block target correct but not attained");
 291                         },
 292                         Ok(_) => panic!("Expected error"),
 293                 }
 294         }
 295
 296         #[tokio::test]
 297         async fn poll_chain_with_malformed_headers() {
 298                 let chain = Blockchain::default().with_height(1).malformed_headers();
 299                 let best_known_chain_tip = chain.at_height(0);
 300
 301                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 302                 match poller.poll_chain_tip(best_known_chain_tip).await {
 303                         Err(e) => {
 304                                 assert_eq!(e.kind(), BlockSourceErrorKind::Persistent);
 305                                 assert_eq!(e.into_inner().as_ref().to_string(), "invalid block hash");
 306                         },
 307                         Ok(_) => panic!("Expected error"),
 308                 }
 309         }
 310
 311         #[tokio::test]
 312         async fn poll_chain_with_common_tip() {
 313                 let chain = Blockchain::default().with_height(0);
 314                 let best_known_chain_tip = chain.tip();
 315
 316                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 317                 match poller.poll_chain_tip(best_known_chain_tip).await {
 318                         Err(e) => panic!("Unexpected error: {:?}", e),
 319                         Ok(tip) => assert_eq!(tip, ChainTip::Common),
 320                 }
 321         }
 322
 323         #[tokio::test]
 324         async fn poll_chain_with_uncommon_tip_but_equal_chainwork() {
 325                 let mut chain = Blockchain::default().with_height(1);
 326                 let best_known_chain_tip = chain.tip();
 327
 328                 // Change the nonce to get a different block hash with the same chainwork.
 329                 chain.blocks.last_mut().unwrap().header.nonce += 1;
 330                 let worse_chain_tip = chain.tip();
 331                 assert_eq!(best_known_chain_tip.chainwork, worse_chain_tip.chainwork);
 332
 333                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 334                 match poller.poll_chain_tip(best_known_chain_tip).await {
 335                         Err(e) => panic!("Unexpected error: {:?}", e),
 336                         Ok(tip) => assert_eq!(tip, ChainTip::Worse(worse_chain_tip)),
 337                 }
 338         }
 339
 340         #[tokio::test]
 341         async fn poll_chain_with_worse_tip() {
 342                 let mut chain = Blockchain::default().with_height(1);
 343                 let best_known_chain_tip = chain.tip();
 344
 345                 chain.disconnect_tip();
 346                 let worse_chain_tip = chain.tip();
 347
 348                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 349                 match poller.poll_chain_tip(best_known_chain_tip).await {
 350                         Err(e) => panic!("Unexpected error: {:?}", e),
 351                         Ok(tip) => assert_eq!(tip, ChainTip::Worse(worse_chain_tip)),
 352                 }
 353         }
 354
 355         #[tokio::test]
 356         async fn poll_chain_with_better_tip() {
 357                 let chain = Blockchain::default().with_height(1);
 358                 let best_known_chain_tip = chain.at_height(0);
 359
 360                 let better_chain_tip = chain.tip();
 361
 362                 let poller = ChainPoller::new(&chain, Network::Bitcoin);
 363                 match poller.poll_chain_tip(best_known_chain_tip).await {
 364                         Err(e) => panic!("Unexpected error: {:?}", e),
 365                         Ok(tip) => assert_eq!(tip, ChainTip::Better(better_chain_tip)),
 366                 }
 367         }
 368 }