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Add section documenting the safety of txindex upon reorganizations

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This commit is contained in:
Luke Parker 2024-09-11 11:58:27 -04:00
parent 9b8c8f8231
commit 3ac0265f07
2 changed files with 32 additions and 6 deletions
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8
processor/bitcoin/src/scan.rs
View file

@ -16,7 +16,7 @@ use serai_client::networks::bitcoin::Address;
use serai_db::Get;
use primitives::OutputType;
use crate::{db, hash_bytes};
use crate::hash_bytes;
const KEY_DST: &[u8] = b"Serai Bitcoin Processor Key Offset";
static BRANCH_BASE_OFFSET: LazyLock<<Secp256k1 as Ciphersuite>::F> =
@ -62,9 +62,9 @@ pub(crate) fn presumed_origin(getter: &impl Get, tx: &Transaction) -> Option<Add
for input in &tx.input {
let txid = hash_bytes(input.previous_output.txid.to_raw_hash());
let vout = input.previous_output.vout;
if let Some(address) = Address::new(ScriptBuf::from_bytes(
db::ScriptPubKey::get(getter, txid, vout).expect("unknown output being spent by input"),
)) {
if let Some(address) =
Address::new(crate::txindex::script_pubkey_for_on_chain_output(getter, txid, vout))
{
return Some(address);
}
}

30
processor/bitcoin/src/txindex.rs
View file

@ -14,13 +14,27 @@
This task builds that index.
*/
use serai_db::{DbTxn, Db};
use bitcoin_serai::bitcoin::ScriptBuf;
use serai_db::{Get, DbTxn, Db};
use primitives::task::ContinuallyRan;
use scanner::ScannerFeed;
use crate::{db, rpc::Rpc, hash_bytes};
pub(crate) fn script_pubkey_for_on_chain_output(
getter: &impl Get,
txid: [u8; 32],
vout: u32,
) -> ScriptBuf {
// We index every single output on the blockchain, so this shouldn't be possible
ScriptBuf::from_bytes(
db::ScriptPubKey::get(getter, txid, vout)
.expect("requested script public key for unknown output"),
)
}
pub(crate) struct TxIndexTask<D: Db>(Rpc<D>);
#[async_trait::async_trait]
@ -40,6 +54,18 @@ impl<D: Db> ContinuallyRan for TxIndexTask<D> {
Rpc::<D>::CONFIRMATIONS
))?;
/*
`finalized_block_number` is the latest block number minus confirmations. The blockchain may
undetectably re-organize though, as while the scanner will maintain an index of finalized
blocks and panics on reorganization, this runs prior to the scanner and that index.
A reorganization of `CONFIRMATIONS` blocks is still an invariant. Even if that occurs, this
saves the script public keys *by the transaction hash an output index*. Accordingly, it isn't
invalidated on reorganization. The only risk would be if the new chain reorganized to
include a transaction to Serai which we didn't index the parents of. If that happens, we'll
panic when we scan the transaction, causing the invariant to be detected.
*/
let finalized_block_number_in_db = db::LatestBlockToYieldAsFinalized::get(&self.0.db);
let next_block = finalized_block_number_in_db.map_or(0, |block| block + 1);
@ -63,7 +89,7 @@ impl<D: Db> ContinuallyRan for TxIndexTask<D> {
let mut txn = self.0.db.txn();
for tx in &block.txdata[1 ..] {
for tx in &block.txdata {
let txid = hash_bytes(tx.compute_txid().to_raw_hash());
for (o, output) in tx.output.iter().enumerate() {
let o = u32::try_from(o).unwrap();