BIP152: Add basic Compact Block structures

src/consensus/encode.rs

@@ -27,6 +27,7 @@ use crate::io::{self, Cursor, Read};
 
 use crate::util::endian;
 use crate::util::psbt;
+use crate::util::bip152::{ShortId, PrefilledTransaction};
 use crate::util::taproot::TapLeafHash;
 use crate::hashes::hex::ToHex;
 
@@ -558,6 +559,7 @@ macro_rules! impl_array {
 
 impl_array!(2);
 impl_array!(4);
+impl_array!(6);
 impl_array!(8);
 impl_array!(10);
 impl_array!(12);
@@ -629,6 +631,9 @@ impl_vec!(TxIn);
 impl_vec!(Vec<u8>);
 impl_vec!(u64);
 impl_vec!(TapLeafHash);
+impl_vec!(VarInt);
+impl_vec!(ShortId);
+impl_vec!(PrefilledTransaction);
 
 #[cfg(feature = "std")] impl_vec!(Inventory);
 #[cfg(feature = "std")] impl_vec!((u32, Address));

src/util/bip152.rs

@@ -0,0 +1,417 @@
+// SPDX-License-Identifier: CC0-1.0
+
+//! BIP152 Compact Blocks
+//!
+//! Implementation of compact blocks data structure and algorithms.
+//!
+
+use crate::prelude::*;
+
+use crate::io;
+use core::{convert, convert::TryFrom, fmt, mem};
+#[cfg(feature = "std")]
+use std::error;
+
+use crate::consensus::encode::{self, Decodable, Encodable, VarInt};
+use crate::hashes::{sha256, siphash24, Hash};
+use crate::internal_macros::{impl_array_newtype, impl_bytes_newtype, impl_consensus_encoding};
+use crate::util::endian;
+use crate::{Block, BlockHash, BlockHeader, Transaction};
+
+/// A BIP-152 error
+#[derive(Clone, PartialEq, Eq, Debug, Copy, PartialOrd, Ord, Hash)]
+pub enum Error {
+    /// An unknown version number was used.
+    UnknownVersion,
+    /// The prefill slice provided was invalid.
+    InvalidPrefill,
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Error::UnknownVersion => write!(f, "an unknown version number was used"),
+            Error::InvalidPrefill => write!(f, "the prefill slice provided was invalid"),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl error::Error for Error {}
+
+/// A [PrefilledTransaction] structure is used in [HeaderAndShortIds] to
+/// provide a list of a few transactions explicitly.
+#[derive(PartialEq, Eq, Clone, Debug, PartialOrd, Ord, Hash)]
+pub struct PrefilledTransaction {
+    /// The index of the transaction in the block.
+    ///
+    /// This field is differentially encoded relative to the previous
+    /// prefilled transaction as described as follows:
+    ///
+    /// > Several uses of CompactSize below are "differentially encoded". For
+    /// > these, instead of using raw indexes, the number encoded is the
+    /// > difference between the current index and the previous index, minus one.
+    /// > For example, a first index of 0 implies a real index of 0, a second
+    /// > index of 0 thereafter refers to a real index of 1, etc.
+    pub idx: u16,
+    /// The actual transaction.
+    pub tx: Transaction,
+}
+
+impl convert::AsRef<Transaction> for PrefilledTransaction {
+    fn as_ref(&self) -> &Transaction {
+        &self.tx
+    }
+}
+
+impl Encodable for PrefilledTransaction {
+    #[inline]
+    fn consensus_encode<S: io::Write + ?Sized>(&self, mut s: &mut S) -> Result<usize, io::Error> {
+        Ok(VarInt(self.idx as u64).consensus_encode(&mut s)? + self.tx.consensus_encode(&mut s)?)
+    }
+}
+
+impl Decodable for PrefilledTransaction {
+    #[inline]
+    fn consensus_decode<D: io::Read + ?Sized>(
+        mut d: &mut D,
+    ) -> Result<PrefilledTransaction, encode::Error> {
+        let idx = VarInt::consensus_decode(&mut d)?.0;
+        let idx = u16::try_from(idx)
+            .map_err(|_| encode::Error::ParseFailed("BIP152 prefilled tx index out of bounds"))?;
+        let tx = Transaction::consensus_decode(&mut d)?;
+        Ok(PrefilledTransaction { idx, tx })
+    }
+}
+
+/// Short transaction IDs are used to represent a transaction without sending a full 256-bit hash.
+#[derive(PartialEq, Eq, Clone, Copy, Hash, Default, PartialOrd, Ord)]
+pub struct ShortId([u8; 6]);
+impl_array_newtype!(ShortId, u8, 6);
+impl_bytes_newtype!(ShortId, 6);
+
+impl ShortId {
+    /// Calculate the SipHash24 keys used to calculate short IDs.
+    pub fn calculate_siphash_keys(header: &BlockHeader, nonce: u64) -> (u64, u64) {
+        // 1. single-SHA256 hashing the block header with the nonce appended (in little-endian)
+        let h = {
+            let mut engine = sha256::Hash::engine();
+            header.consensus_encode(&mut engine).expect("engines don't error");
+            nonce.consensus_encode(&mut engine).expect("engines don't error");
+            sha256::Hash::from_engine(engine)
+        };
+
+        // 2. Running SipHash-2-4 with the input being the transaction ID and the keys (k0/k1)
+        // set to the first two little-endian 64-bit integers from the above hash, respectively.
+        (endian::slice_to_u64_le(&h[0..8]), endian::slice_to_u64_le(&h[8..16]))
+    }
+
+    /// Calculate the short ID with the given (w)txid and using the provided SipHash keys.
+    pub fn with_siphash_keys<T: AsRef<[u8]>>(txid: &T, siphash_keys: (u64, u64)) -> ShortId {
+        // 2. Running SipHash-2-4 with the input being the transaction ID and the keys (k0/k1)
+        // set to the first two little-endian 64-bit integers from the above hash, respectively.
+        let hash = siphash24::Hash::hash_with_keys(siphash_keys.0, siphash_keys.1, txid.as_ref());
+
+        // 3. Dropping the 2 most significant bytes from the SipHash output to make it 6 bytes.
+        let mut id = ShortId([0; 6]);
+        id.0.copy_from_slice(&hash[0..6]);
+        id
+    }
+}
+
+impl Encodable for ShortId {
+    #[inline]
+    fn consensus_encode<S: io::Write + ?Sized>(&self, s: &mut S) -> Result<usize, io::Error> {
+        self.0.consensus_encode(s)
+    }
+}
+
+impl Decodable for ShortId {
+    #[inline]
+    fn consensus_decode<D: io::Read + ?Sized>(d: &mut D) -> Result<ShortId, encode::Error> {
+        Ok(ShortId(Decodable::consensus_decode(d)?))
+    }
+}
+
+/// A [HeaderAndShortIds] structure is used to relay a block header, the short
+/// transactions IDs used for matching already-available transactions, and a
+/// select few transactions which we expect a peer may be missing.
+#[derive(PartialEq, Eq, Clone, Debug, PartialOrd, Ord, Hash)]
+pub struct HeaderAndShortIds {
+    /// The header of the block being provided.
+    pub header: BlockHeader,
+    ///  A nonce for use in short transaction ID calculations.
+    pub nonce: u64,
+    ///  The short transaction IDs calculated from the transactions
+    ///  which were not provided explicitly in prefilled_txs.
+    pub short_ids: Vec<ShortId>,
+    ///  Used to provide the coinbase transaction and a select few
+    ///  which we expect a peer may be missing.
+    pub prefilled_txs: Vec<PrefilledTransaction>,
+}
+impl_consensus_encoding!(HeaderAndShortIds, header, nonce, short_ids, prefilled_txs);
+
+impl HeaderAndShortIds {
+    /// Create a new [HeaderAndShortIds] from a full block.
+    ///
+    /// The version number must be either 1 or 2.
+    ///
+    /// The `prefill` slice indicates which transactions should be prefilled in
+    /// the block. It should contain the indexes in the block of the txs to
+    /// prefill. It must be ordered. 0 should not be included as the
+    /// coinbase tx is always prefilled.
+    ///
+    /// > Nodes SHOULD NOT use the same nonce across multiple different blocks.
+    pub fn from_block(
+        block: &Block,
+        nonce: u64,
+        version: u32,
+        mut prefill: &[usize],
+    ) -> Result<HeaderAndShortIds, Error> {
+        if version != 1 && version != 2 {
+            return Err(Error::UnknownVersion);
+        }
+
+        let siphash_keys = ShortId::calculate_siphash_keys(&block.header, nonce);
+
+        let mut prefilled = Vec::with_capacity(prefill.len() + 1); // +1 for coinbase tx
+        let mut short_ids = Vec::with_capacity(block.txdata.len() - prefill.len());
+        let mut last_prefill = 0;
+        for (idx, tx) in block.txdata.iter().enumerate() {
+            // Check if we should prefill this tx.
+            let prefill_tx = if prefill.get(0) == Some(&idx) {
+                prefill = &prefill[1..];
+                true
+            } else {
+                idx == 0 // Always prefill coinbase.
+            };
+
+            if prefill_tx {
+                let diff_idx = idx - last_prefill;
+                last_prefill = idx + 1;
+                prefilled.push(PrefilledTransaction {
+                    idx: diff_idx as u16,
+                    tx: match version {
+                        // >  As encoded in "tx" messages sent in response to getdata MSG_TX
+                        1 => {
+                            // strip witness for version 1
+                            let mut no_witness = tx.clone();
+                            no_witness.input.iter_mut().for_each(|i| i.witness.clear());
+                            no_witness
+                        }
+                        // > Transactions inside cmpctblock messages (both those used as direct
+                        // > announcement and those in response to getdata) and in blocktxn should
+                        // > include witness data, using the same format as responses to getdata
+                        // > MSG_WITNESS_TX, specified in BIP144.
+                        2 => tx.clone(),
+                        _ => unreachable!(),
+                    },
+                });
+            } else {
+                short_ids.push(ShortId::with_siphash_keys(
+                    &match version {
+                        1 => tx.txid().as_hash(),
+                        2 => tx.wtxid().as_hash(),
+                        _ => unreachable!(),
+                    },
+                    siphash_keys,
+                ));
+            }
+        }
+
+        if !prefill.is_empty() {
+            return Err(Error::InvalidPrefill);
+        }
+
+        Ok(HeaderAndShortIds {
+            header: block.header,
+            nonce,
+            // Provide coinbase prefilled.
+            prefilled_txs: prefilled,
+            short_ids,
+        })
+    }
+}
+
+/// A [BlockTransactionsRequest] structure is used to list transaction indexes
+/// in a block being requested.
+#[derive(PartialEq, Eq, Clone, Debug, PartialOrd, Ord, Hash)]
+pub struct BlockTransactionsRequest {
+    ///  The blockhash of the block which the transactions being requested are in.
+    pub block_hash: BlockHash,
+    ///  The indexes of the transactions being requested in the block.
+    ///
+    ///  Warning: Encoding panics with [`u64::MAX`] values. See [`BlockTransactionsRequest::consensus_encode()`]
+    pub indexes: Vec<u64>,
+}
+
+impl Encodable for BlockTransactionsRequest {
+    /// # Panics
+    ///
+    /// Panics if the index overflows [`u64::MAX`]. This happens when [`BlockTransactionsRequest::indexes`]
+    /// contains an entry with the value [`u64::MAX`] as `u64` overflows during differential encoding.
+    fn consensus_encode<S: io::Write + ?Sized>(&self, mut s: &mut S) -> Result<usize, io::Error> {
+        let mut len = self.block_hash.consensus_encode(&mut s)?;
+        // Manually encode indexes because they are differentially encoded VarInts.
+        len += VarInt(self.indexes.len() as u64).consensus_encode(&mut s)?;
+        let mut last_idx = 0;
+        for idx in &self.indexes {
+            len += VarInt(*idx - last_idx).consensus_encode(&mut s)?;
+            last_idx = *idx + 1; // can panic here
+        }
+        Ok(len)
+    }
+}
+
+impl Decodable for BlockTransactionsRequest {
+    fn consensus_decode<D: io::Read + ?Sized>(
+        mut d: &mut D,
+    ) -> Result<BlockTransactionsRequest, encode::Error> {
+        Ok(BlockTransactionsRequest {
+            block_hash: BlockHash::consensus_decode(&mut d)?,
+            indexes: {
+                // Manually decode indexes because they are differentially encoded VarInts.
+                let nb_indexes = VarInt::consensus_decode(&mut d)?.0 as usize;
+
+                // Since the number of indices ultimately represent transactions,
+                // we can limit the number of indices to the maximum number of
+                // transactions that would be allowed in a vector.
+                let byte_size = (nb_indexes as usize)
+                    .checked_mul(mem::size_of::<Transaction>())
+                    .ok_or(encode::Error::ParseFailed("Invalid length"))?;
+                if byte_size > encode::MAX_VEC_SIZE {
+                    return Err(encode::Error::OversizedVectorAllocation {
+                        requested: byte_size,
+                        max: encode::MAX_VEC_SIZE,
+                    });
+                }
+
+                let mut indexes = Vec::with_capacity(nb_indexes);
+                let mut last_index: u64 = 0;
+                for _ in 0..nb_indexes {
+                    let differential: VarInt = Decodable::consensus_decode(&mut d)?;
+                    last_index = match last_index.checked_add(differential.0) {
+                        Some(r) => r,
+                        None => return Err(encode::Error::ParseFailed("block index overflow")),
+                    };
+                    indexes.push(last_index);
+                    last_index = match last_index.checked_add(1) {
+                        Some(r) => r,
+                        None => return Err(encode::Error::ParseFailed("block index overflow")),
+                    };
+                }
+                indexes
+            },
+        })
+    }
+}
+
+/// A transaction index is requested that is out of range from the
+/// corresponding block.
+#[derive(Clone, PartialEq, Eq, Debug, Copy, PartialOrd, Ord, Hash)]
+pub struct TxIndexOutOfRangeError(u64);
+
+impl fmt::Display for TxIndexOutOfRangeError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "a transaction index is requested that is \
+            out of range from the corresponding block: {}",
+            self.0,
+        )
+    }
+}
+
+#[cfg(feature = "std")]
+impl error::Error for TxIndexOutOfRangeError {}
+
+/// A [BlockTransactions] structure is used to provide some of the transactions
+/// in a block, as requested.
+#[derive(PartialEq, Eq, Clone, Debug, PartialOrd, Ord, Hash)]
+pub struct BlockTransactions {
+    ///  The blockhash of the block which the transactions being provided are in.
+    pub block_hash: BlockHash,
+    ///  The transactions provided.
+    pub transactions: Vec<Transaction>,
+}
+impl_consensus_encoding!(BlockTransactions, block_hash, transactions);
+
+impl BlockTransactions {
+    /// Construct a [BlockTransactions] from a [BlockTransactionsRequest] and
+    /// the corresponsing full [Block] by providing all requested transactions.
+    pub fn from_request(
+        request: &BlockTransactionsRequest,
+        block: &Block,
+    ) -> Result<BlockTransactions, TxIndexOutOfRangeError> {
+        Ok(BlockTransactions {
+            block_hash: request.block_hash,
+            transactions: {
+                let mut txs = Vec::with_capacity(request.indexes.len());
+                for idx in &request.indexes {
+                    if *idx >= block.txdata.len() as u64 {
+                        return Err(TxIndexOutOfRangeError(*idx));
+                    }
+                    txs.push(block.txdata[*idx as usize].clone());
+                }
+                txs
+            },
+        })
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::{
+        Block, BlockHash, BlockHeader, OutPoint, Script, Sequence, Transaction, TxIn, TxMerkleNode,
+        TxOut, Txid, Witness,
+    };
+
+    fn dummy_tx(nonce: &[u8]) -> Transaction {
+        Transaction {
+            version: 1,
+            lock_time: 2,
+            input: vec![TxIn {
+                previous_output: OutPoint::new(Txid::hash(nonce), 0),
+                script_sig: Script::new(),
+                sequence: Sequence(1),
+                witness: Witness::new(),
+            }],
+            output: vec![TxOut { value: 1, script_pubkey: Script::new() }],
+        }
+    }
+
+    fn dummy_block() -> Block {
+        Block {
+            header: BlockHeader {
+                version: 1,
+                prev_blockhash: BlockHash::hash(&[0]),
+                merkle_root: TxMerkleNode::hash(&[1]),
+                time: 2,
+                bits: 3,
+                nonce: 4,
+            },
+            txdata: vec![dummy_tx(&[2]), dummy_tx(&[3]), dummy_tx(&[4])],
+        }
+    }
+
+    #[test]
+    fn test_header_and_short_ids_from_block() {
+        let block = dummy_block();
+
+        let compact = HeaderAndShortIds::from_block(&block, 42, 2, &[]).unwrap();
+        assert_eq!(compact.nonce, 42);
+        assert_eq!(compact.short_ids.len(), 2);
+        assert_eq!(compact.prefilled_txs.len(), 1);
+        assert_eq!(compact.prefilled_txs[0].idx, 0);
+        assert_eq!(&compact.prefilled_txs[0].tx, &block.txdata[0]);
+
+        let compact = HeaderAndShortIds::from_block(&block, 42, 2, &[0, 1, 2]).unwrap();
+        let idxs = compact.prefilled_txs.iter().map(|t| t.idx).collect::<Vec<_>>();
+        assert_eq!(idxs, vec![0, 0, 0]);
+
+        let compact = HeaderAndShortIds::from_block(&block, 42, 2, &[2]).unwrap();
+        let idxs = compact.prefilled_txs.iter().map(|t| t.idx).collect::<Vec<_>>();
+        assert_eq!(idxs, vec![0, 1]);
+    }
+}

src/util/mod.rs

@@ -14,6 +14,7 @@ pub mod amount;
 pub mod base58;
 pub mod bip32;
 pub mod bip143;
+pub mod bip152;
 pub mod hash;
 pub mod merkleblock;
 pub mod misc;