tbc: add lazy block reader for zero-copy per-tx access

CHANGELOG.md

@@ -27,6 +27,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add `BlockRawByHash` to DB interface and `lazyBlock` type for zero-copy
+  per-tx block access without full deserialization
+  ([#1051](https://github.com/hemilabs/heminetwork/pull/1051)).
 - Add generic `lru` package with cost-based LRU cache (`lru.Cache[K,V]`)
   ([#1034](https://github.com/hemilabs/heminetwork/pull/1034)).
 - Add utxo read LRU cache (`TBC_UTXO_READ_CACHE_SIZE`) to reduce LevelDB

database/tbcd/database.go

@@ -112,6 +112,7 @@ type Database interface {
 	BlockInsert(ctx context.Context, b *btcutil.Block) (int64, error)
 	// BlocksInsert(ctx context.Context, bs []*btcutil.Block) (int64, error)
 	BlockByHash(ctx context.Context, hash chainhash.Hash) (*btcutil.Block, error)
+	BlockRawByHash(ctx context.Context, hash chainhash.Hash) ([]byte, error)
 	BlockExistsByHash(ctx context.Context, hash chainhash.Hash) (bool, error)
 	BlockCacheStats() CacheStats
 

database/tbcd/level/level.go

@@ -1589,6 +1589,23 @@ func (l *ldb) BlockByHash(ctx context.Context, hash chainhash.Hash) (*btcutil.Bl
 	return b, nil
 }
 
+// BlockRawByHash returns the raw block bytes. Not cached, unlike BlockByHash.
+func (l *ldb) BlockRawByHash(ctx context.Context, hash chainhash.Hash) ([]byte, error) {
+	log.Tracef("BlockRawByHash")
+	defer log.Tracef("BlockRawByHash exit")
+
+	bDB := l.rawPool[level.BlocksDB]
+	eb, err := bDB.Get(hash[:])
+	if err != nil {
+		if errors.Is(err, leveldb.ErrNotFound) {
+			return nil, database.BlockNotFoundError{Hash: hash}
+		}
+		return nil, fmt.Errorf("block raw get: %w", err)
+	}
+
+	return eb, nil
+}
+
 func (l *ldb) BlockExistsByHash(ctx context.Context, hash chainhash.Hash) (bool, error) {
 	log.Tracef("BlockExistsByHash")
 	defer log.Tracef("BlockExistsByHash exit")

service/tbc/cpfp_test.go

@@ -82,6 +82,10 @@ func (stubDB) BlockByHash(context.Context, chainhash.Hash) (*btcutil.Block, erro
 	panic("stub")
 }
 
+func (stubDB) BlockRawByHash(context.Context, chainhash.Hash) ([]byte, error) {
+	panic("stub")
+}
+
 func (stubDB) BlockExistsByHash(context.Context, chainhash.Hash) (bool, error) {
 	panic("stub")
 }