Module jmwallet.backends.neutrino

Neutrino (BIP157/BIP158) light client blockchain backend.

Lightweight alternative to running a full Bitcoin node. Uses compact block filters for privacy-preserving SPV operation.

The Neutrino client runs as a separate Go process and communicates via gRPC. This backend wraps the neutrino gRPC API for the JoinMarket wallet.

Reference: https://github.com/lightninglabs/neutrino

Neutrino-compatible Protocol Support: This backend implements verify_utxo_with_metadata() for Neutrino-compatible UTXO verification. When peers provide scriptPubKey and blockheight hints (via neutrino_compat feature flag), this backend can verify UTXOs without arbitrary queries by: 1. Adding the scriptPubKey to the watch list 2. Rescanning from the hinted blockheight 3. Downloading matching blocks via compact block filters 4. Extracting and verifying the UTXO

Classes

class NeutrinoBackend (neutrino_url: str = 'http://127.0.0.1:8334',
network: str = 'mainnet',
connect_peers: list[str] | None = None,
data_dir: str = '/data/neutrino')

Expand source code

class NeutrinoBackend(BlockchainBackend):
    """
    Blockchain backend using Neutrino light client.

    Neutrino is a privacy-preserving Bitcoin light client that uses
    BIP157/BIP158 compact block filters instead of traditional SPV.

    Communication with the neutrino daemon is via REST API.
    The neutrino daemon should be running alongside this client.
    """

    def __init__(
        self,
        neutrino_url: str = "http://127.0.0.1:8334",
        network: str = "mainnet",
        connect_peers: list[str] | None = None,
        data_dir: str = "/data/neutrino",
    ):
        """
        Initialize Neutrino backend.

        Args:
            neutrino_url: URL of the neutrino REST API (default port 8334)
            network: Bitcoin network (mainnet, testnet, regtest, signet)
            connect_peers: List of peer addresses to connect to (optional)
            data_dir: Directory for neutrino data (headers, filters)
        """
        self.neutrino_url = neutrino_url.rstrip("/")
        self.network = network
        self.connect_peers = connect_peers or []
        self.data_dir = data_dir
        self.client = httpx.AsyncClient(timeout=60.0)

        # Cache for watched addresses (neutrino needs to know what to scan for)
        self._watched_addresses: set[str] = set()
        self._watched_outpoints: set[tuple[str, int]] = set()

        # Security limits to prevent DoS via excessive watch list / rescan abuse
        self._max_watched_addresses: int = 10000  # Maximum addresses to track
        self._max_rescan_depth: int = 100000  # Maximum blocks to rescan (roughly 2 years)
        self._min_valid_blockheight: int = 481824  # SegWit activation (mainnet)
        # For testnet/regtest, this will be adjusted based on network

        # Block filter cache
        self._filter_header_tip: int = 0
        self._synced: bool = False

        # Track if we've done the initial rescan
        self._initial_rescan_done: bool = False

        # Adjust minimum blockheight based on network
        if network == "regtest":
            self._min_valid_blockheight = 0  # Regtest can have any height
        elif network == "testnet":
            self._min_valid_blockheight = 834624  # Approximate SegWit on testnet
        elif network == "signet":
            self._min_valid_blockheight = 0  # Signet started with SegWit

    async def _api_call(
        self,
        method: str,
        endpoint: str,
        params: dict[str, Any] | None = None,
        data: dict[str, Any] | None = None,
    ) -> Any:
        """Make an API call to the neutrino daemon."""
        url = f"{self.neutrino_url}/{endpoint}"

        try:
            if method == "GET":
                response = await self.client.get(url, params=params)
            elif method == "POST":
                response = await self.client.post(url, json=data)
            else:
                raise ValueError(f"Unsupported HTTP method: {method}")

            response.raise_for_status()
            return response.json()

        except httpx.HTTPError as e:
            logger.error(f"Neutrino API call failed: {endpoint} - {e}")
            raise

    async def wait_for_sync(self, timeout: float = 300.0) -> bool:
        """
        Wait for neutrino to sync block headers and filters.

        Args:
            timeout: Maximum time to wait in seconds

        Returns:
            True if synced, False if timeout
        """
        start_time = asyncio.get_event_loop().time()

        while True:
            try:
                status = await self._api_call("GET", "v1/status")
                synced = status.get("synced", False)
                block_height = status.get("block_height", 0)
                filter_height = status.get("filter_height", 0)

                if synced and block_height == filter_height:
                    self._synced = True
                    self._filter_header_tip = block_height
                    logger.info(f"Neutrino synced at height {block_height}")
                    return True

                logger.debug(f"Syncing... blocks: {block_height}, filters: {filter_height}")

            except Exception as e:
                logger.warning(f"Waiting for neutrino daemon: {e}")

            elapsed = asyncio.get_event_loop().time() - start_time
            if elapsed > timeout:
                logger.error("Neutrino sync timeout")
                return False

            await asyncio.sleep(2.0)

    async def add_watch_address(self, address: str) -> None:
        """
        Add an address to the local watch list.

        In neutrino-api v0.4, address watching is implicit - you just query
        UTXOs or do rescans with the addresses you care about. This method
        tracks addresses locally for convenience.

        Security: Limits the number of watched addresses to prevent memory
        exhaustion attacks.

        Args:
            address: Bitcoin address to watch

        Raises:
            ValueError: If watch list limit exceeded
        """
        if address in self._watched_addresses:
            return

        if len(self._watched_addresses) >= self._max_watched_addresses:
            logger.warning(
                f"Watch list limit reached ({self._max_watched_addresses}). "
                f"Cannot add address: {address[:20]}..."
            )
            raise ValueError(f"Watch list limit ({self._max_watched_addresses}) exceeded")

        self._watched_addresses.add(address)
        logger.debug(f"Watching address: {address}")

    async def add_watch_outpoint(self, txid: str, vout: int) -> None:
        """
        Add an outpoint to the local watch list.

        In neutrino-api v0.4, outpoint watching is done via UTXO queries
        with the address parameter. This method tracks outpoints locally.

        Args:
            txid: Transaction ID
            vout: Output index
        """
        outpoint = (txid, vout)
        if outpoint in self._watched_outpoints:
            return

        self._watched_outpoints.add(outpoint)
        logger.debug(f"Watching outpoint: {txid}:{vout}")

    async def get_utxos(self, addresses: list[str]) -> list[UTXO]:
        """
        Get UTXOs for given addresses using neutrino's rescan capability.

        Neutrino will scan the blockchain using compact block filters
        to find transactions relevant to the watched addresses.

        On first call, triggers a full blockchain rescan from genesis to ensure
        all historical UTXOs are found (critical for wallets funded before neutrino started).
        """
        utxos: list[UTXO] = []

        # Add addresses to watch list
        for address in addresses:
            await self.add_watch_address(address)

        # On first UTXO query, trigger a full blockchain rescan to find existing UTXOs
        # This is critical for wallets that were funded before neutrino was watching them
        logger.debug(
            f"get_utxos: _initial_rescan_done={self._initial_rescan_done}, "
            f"watched_addresses={len(self._watched_addresses)}"
        )
        if not self._initial_rescan_done and self._watched_addresses:
            logger.info(
                f"Performing initial blockchain rescan for {len(self._watched_addresses)} "
                "watched addresses (this may take a moment)..."
            )
            try:
                # Trigger rescan from block 0 for all watched addresses
                await self._api_call(
                    "POST",
                    "v1/rescan",
                    data={
                        "addresses": list(self._watched_addresses),
                        "start_height": 0,
                    },
                )
                # Wait for rescan to complete (neutrino processes this asynchronously)
                # On regtest with ~3000 blocks, this typically takes 5-10 seconds
                await asyncio.sleep(10.0)
                self._initial_rescan_done = True
                logger.info("Initial blockchain rescan completed")
            except Exception as e:
                logger.warning(f"Initial rescan failed (will retry on next sync): {e}")
        else:
            # Wait a moment for filter matching to complete
            await asyncio.sleep(0.5)

        try:
            # Request UTXO scan for addresses
            result = await self._api_call(
                "POST",
                "v1/utxos",
                data={"addresses": addresses},
            )

            tip_height = await self.get_block_height()

            for utxo_data in result.get("utxos", []):
                height = utxo_data.get("height", 0)
                confirmations = 0
                if height > 0:
                    confirmations = tip_height - height + 1

                utxo = UTXO(
                    txid=utxo_data["txid"],
                    vout=utxo_data["vout"],
                    value=utxo_data["value"],
                    address=utxo_data.get("address", ""),
                    confirmations=confirmations,
                    scriptpubkey=utxo_data.get("scriptpubkey", ""),
                    height=height if height > 0 else None,
                )
                utxos.append(utxo)

            logger.debug(f"Found {len(utxos)} UTXOs for {len(addresses)} addresses")

        except Exception as e:
            logger.error(f"Failed to fetch UTXOs: {e}")

        return utxos

    async def get_address_balance(self, address: str) -> int:
        """Get balance for an address in satoshis."""
        utxos = await self.get_utxos([address])
        balance = sum(utxo.value for utxo in utxos)
        logger.debug(f"Balance for {address}: {balance} sats")
        return balance

    async def broadcast_transaction(self, tx_hex: str) -> str:
        """
        Broadcast transaction via neutrino to the P2P network.

        Neutrino maintains P2P connections and can broadcast transactions
        directly to connected peers.
        """
        try:
            result = await self._api_call(
                "POST",
                "v1/tx/broadcast",
                data={"tx_hex": tx_hex},
            )
            txid = result.get("txid", "")
            logger.info(f"Broadcast transaction: {txid}")
            return txid

        except Exception as e:
            logger.error(f"Failed to broadcast transaction: {e}")
            raise ValueError(f"Broadcast failed: {e}") from e

    async def get_transaction(self, txid: str) -> Transaction | None:
        """
        Get transaction by txid.

        Note: Neutrino uses compact block filters (BIP158) and can only fetch
        transactions for addresses it has rescanned. It cannot fetch arbitrary
        transactions by txid alone. This method always returns None.

        For verification after broadcast, rely on UTXO checks with known addresses
        and block heights instead.
        """
        # Neutrino doesn't support fetching arbitrary transactions by txid
        # It can only work with UTXOs for known addresses via compact filters
        return None

    async def verify_tx_output(
        self,
        txid: str,
        vout: int,
        address: str,
        start_height: int | None = None,
    ) -> bool:
        """
        Verify that a specific transaction output exists using neutrino's UTXO endpoint.

        Uses GET /v1/utxo/{txid}/{vout}?address=...&start_height=... to check if
        the output exists. This works because neutrino uses compact block filters
        that can match on addresses.

        Args:
            txid: Transaction ID to verify
            vout: Output index to check
            address: The address that should own this output
            start_height: Block height hint for efficient scanning (recommended)

        Returns:
            True if the output exists, False otherwise
        """
        try:
            params: dict[str, str | int] = {"address": address}
            if start_height is not None:
                params["start_height"] = start_height

            result = await self._api_call(
                "GET",
                f"v1/utxo/{txid}/{vout}",
                params=params,
            )

            # If we got a response with unspent status, the output exists
            # Note: Even spent outputs confirm the transaction was broadcast
            if result is not None:
                logger.debug(
                    f"Verified tx output {txid}:{vout} exists "
                    f"(unspent={result.get('unspent', 'unknown')})"
                )
                return True

            return False

        except httpx.HTTPStatusError as e:
            if e.response.status_code == 404:
                # Output not found
                logger.debug(f"Tx output {txid}:{vout} not found")
                return False
            logger.warning(f"Error verifying tx output {txid}:{vout}: {e}")
            return False
        except Exception as e:
            logger.warning(f"Error verifying tx output {txid}:{vout}: {e}")
            return False

    async def estimate_fee(self, target_blocks: int) -> int:
        """
        Estimate fee in sat/vbyte for target confirmation blocks.

        Neutrino can estimate fees based on observed mempool/block data.
        Falls back to reasonable defaults if estimation unavailable.
        """
        try:
            result = await self._api_call(
                "GET",
                "v1/fees/estimate",
                params={"target_blocks": target_blocks},
            )

            fee_rate = result.get("fee_rate", 0)
            if fee_rate > 0:
                logger.debug(f"Estimated fee for {target_blocks} blocks: {fee_rate} sat/vB")
                return int(fee_rate)

        except Exception as e:
            logger.warning(f"Fee estimation failed: {e}")

        # Fallback fee rates based on target
        if target_blocks <= 1:
            return 20
        elif target_blocks <= 3:
            return 10
        elif target_blocks <= 6:
            return 5
        else:
            return 2

    async def get_block_height(self) -> int:
        """Get current blockchain height from neutrino."""
        try:
            result = await self._api_call("GET", "v1/status")
            height = result.get("block_height", 0)
            logger.debug(f"Current block height: {height}")
            return height

        except Exception as e:
            logger.error(f"Failed to fetch block height: {e}")
            raise

    async def get_block_time(self, block_height: int) -> int:
        """Get block time (unix timestamp) for given height."""
        try:
            result = await self._api_call(
                "GET",
                f"v1/block/{block_height}/header",
            )
            timestamp = result.get("timestamp", 0)
            logger.debug(f"Block {block_height} timestamp: {timestamp}")
            return timestamp

        except Exception as e:
            logger.error(f"Failed to fetch block time for height {block_height}: {e}")
            raise

    async def get_block_hash(self, block_height: int) -> str:
        """Get block hash for given height."""
        try:
            result = await self._api_call(
                "GET",
                f"v1/block/{block_height}/header",
            )
            block_hash = result.get("hash", "")
            logger.debug(f"Block hash for height {block_height}: {block_hash}")
            return block_hash

        except Exception as e:
            logger.error(f"Failed to fetch block hash for height {block_height}: {e}")
            raise

    async def get_utxo(self, txid: str, vout: int) -> UTXO | None:
        """Get a specific UTXO from the blockchain.
        Returns None if the UTXO does not exist or has been spent."""
        try:
            result = await self._api_call(
                "GET",
                f"v1/utxo/{txid}/{vout}",
            )

            if not result or result.get("spent", False):
                logger.debug(f"UTXO {txid}:{vout} not found or spent")
                return None

            tip_height = await self.get_block_height()
            height = result.get("height", 0)
            confirmations = 0
            if height > 0:
                confirmations = tip_height - height + 1

            return UTXO(
                txid=txid,
                vout=vout,
                value=result.get("value", 0),
                address=result.get("address", ""),
                confirmations=confirmations,
                scriptpubkey=result.get("scriptpubkey", ""),
                height=height if height > 0 else None,
            )

        except httpx.HTTPStatusError as e:
            if e.response.status_code == 404:
                logger.debug(f"UTXO {txid}:{vout} not found")
                return None
            logger.error(f"Failed to get UTXO {txid}:{vout}: {e}")
            return None
        except Exception as e:
            logger.error(f"Failed to get UTXO {txid}:{vout}: {e}")
            return None

    def requires_neutrino_metadata(self) -> bool:
        """
        Neutrino backend requires metadata for arbitrary UTXO verification.

        Without scriptPubKey and blockheight hints, Neutrino cannot verify
        UTXOs that it hasn't been watching from the start.

        Returns:
            True - Neutrino always requires metadata for counterparty UTXOs
        """
        return True

    def can_provide_neutrino_metadata(self) -> bool:
        """
        Neutrino backend cannot reliably provide metadata for all UTXOs.

        Light clients can only provide metadata for UTXOs they've been watching.
        They cannot provide metadata for arbitrary addresses like full nodes can.

        Returns:
            False - Neutrino cannot provide metadata for arbitrary UTXOs
        """
        return False

    async def verify_utxo_with_metadata(
        self,
        txid: str,
        vout: int,
        scriptpubkey: str,
        blockheight: int,
    ) -> UTXOVerificationResult:
        """
        Verify a UTXO using provided metadata (neutrino_compat feature).

        This is the key method that enables Neutrino light clients to verify
        counterparty UTXOs in CoinJoin without arbitrary blockchain queries.

        Uses the neutrino-api v0.4 UTXO check endpoint which requires:
        - address: The Bitcoin address that owns the UTXO (derived from scriptPubKey)
        - start_height: Block height to start scanning from (for efficiency)

        The API scans from start_height to chain tip using compact block filters
        to determine if the UTXO exists and whether it has been spent.

        Security: Validates blockheight to prevent rescan abuse attacks where
        malicious peers provide very low blockheights to trigger expensive rescans.

        Args:
            txid: Transaction ID
            vout: Output index
            scriptpubkey: Expected scriptPubKey (hex) - used to derive address
            blockheight: Block height where UTXO was confirmed - scan start hint

        Returns:
            UTXOVerificationResult with verification status and UTXO data
        """
        # Security: Validate blockheight to prevent rescan abuse
        tip_height = await self.get_block_height()

        if blockheight < self._min_valid_blockheight:
            return UTXOVerificationResult(
                valid=False,
                error=f"Blockheight {blockheight} is below minimum valid height "
                f"{self._min_valid_blockheight} for {self.network}",
            )

        if blockheight > tip_height:
            return UTXOVerificationResult(
                valid=False,
                error=f"Blockheight {blockheight} is in the future (tip: {tip_height})",
            )

        # Limit rescan depth to prevent DoS
        rescan_depth = tip_height - blockheight
        if rescan_depth > self._max_rescan_depth:
            return UTXOVerificationResult(
                valid=False,
                error=f"Rescan depth {rescan_depth} exceeds max {self._max_rescan_depth}. "
                f"UTXO too old for efficient verification.",
            )

        logger.debug(
            f"Verifying UTXO {txid}:{vout} with metadata "
            f"(scriptpubkey={scriptpubkey[:20]}..., blockheight={blockheight})"
        )

        # Step 1: Derive address from scriptPubKey
        # The neutrino-api v0.4 requires the address for UTXO lookup
        address = self._scriptpubkey_to_address(scriptpubkey)
        if not address:
            return UTXOVerificationResult(
                valid=False,
                error=f"Could not derive address from scriptPubKey: {scriptpubkey[:40]}...",
            )

        logger.debug(f"Derived address {address} from scriptPubKey")

        try:
            # Step 2: Query the specific UTXO using the v0.4 API
            # GET /v1/utxo/{txid}/{vout}?address=...&start_height=...
            #
            # The start_height parameter is critical for performance:
            # - Scanning 1 block takes ~0.01s
            # - Scanning 100 blocks takes ~0.5s
            # - Scanning 10,000+ blocks can take minutes
            #
            # We use blockheight - 1 as a safety margin in case of reorgs
            start_height = max(0, blockheight - 1)

            result = await self._api_call(
                "GET",
                f"v1/utxo/{txid}/{vout}",
                params={"address": address, "start_height": start_height},
            )

            # Check if UTXO is unspent
            if not result.get("unspent", False):
                spending_txid = result.get("spending_txid", "unknown")
                spending_height = result.get("spending_height", "unknown")
                return UTXOVerificationResult(
                    valid=False,
                    error=f"UTXO has been spent in tx {spending_txid} at height {spending_height}",
                )

            # Step 3: Verify scriptPubKey matches
            actual_scriptpubkey = result.get("scriptpubkey", "")
            scriptpubkey_matches = actual_scriptpubkey.lower() == scriptpubkey.lower()

            if not scriptpubkey_matches:
                return UTXOVerificationResult(
                    valid=False,
                    value=result.get("value", 0),
                    error=f"ScriptPubKey mismatch: expected {scriptpubkey[:20]}..., "
                    f"got {actual_scriptpubkey[:20]}...",
                    scriptpubkey_matches=False,
                )

            # Step 4: Calculate confirmations
            tip_height = await self.get_block_height()
            # The blockheight parameter is the confirmation height hint from the peer
            confirmations = tip_height - blockheight + 1 if blockheight > 0 else 0

            logger.info(
                f"UTXO {txid}:{vout} verified: value={result.get('value', 0)}, "
                f"confirmations={confirmations}"
            )

            return UTXOVerificationResult(
                valid=True,
                value=result.get("value", 0),
                confirmations=confirmations,
                scriptpubkey_matches=True,
            )

        except httpx.HTTPStatusError as e:
            if e.response.status_code == 404:
                return UTXOVerificationResult(
                    valid=False,
                    error="UTXO not found - may not exist or address derivation failed",
                )
            return UTXOVerificationResult(
                valid=False,
                error=f"UTXO query failed: {e}",
            )
        except Exception as e:
            return UTXOVerificationResult(
                valid=False,
                error=f"Verification failed: {e}",
            )

    def _scriptpubkey_to_address(self, scriptpubkey: str) -> str | None:
        """
        Convert scriptPubKey to address for watch list.

        Supports common script types:
        - P2WPKH: 0014<20-byte-hash> -> bc1q...
        - P2WSH: 0020<32-byte-hash> -> bc1q...
        - P2PKH: 76a914<20-byte-hash>88ac -> 1...
        - P2SH: a914<20-byte-hash>87 -> 3...

        Args:
            scriptpubkey: Hex-encoded scriptPubKey

        Returns:
            Bitcoin address or None if conversion fails
        """
        try:
            script_bytes = bytes.fromhex(scriptpubkey)

            # P2WPKH: OP_0 <20 bytes>
            if len(script_bytes) == 22 and script_bytes[0] == 0x00 and script_bytes[1] == 0x14:
                # Use bech32 encoding
                return self._encode_bech32_address(script_bytes[2:], 0)

            # P2WSH: OP_0 <32 bytes>
            if len(script_bytes) == 34 and script_bytes[0] == 0x00 and script_bytes[1] == 0x20:
                return self._encode_bech32_address(script_bytes[2:], 0)

            # P2PKH: OP_DUP OP_HASH160 <20 bytes> OP_EQUALVERIFY OP_CHECKSIG
            if (
                len(script_bytes) == 25
                and script_bytes[0] == 0x76
                and script_bytes[1] == 0xA9
                and script_bytes[2] == 0x14
                and script_bytes[23] == 0x88
                and script_bytes[24] == 0xAC
            ):
                return self._encode_base58check_address(script_bytes[3:23], 0x00)

            # P2SH: OP_HASH160 <20 bytes> OP_EQUAL
            if (
                len(script_bytes) == 23
                and script_bytes[0] == 0xA9
                and script_bytes[1] == 0x14
                and script_bytes[22] == 0x87
            ):
                return self._encode_base58check_address(script_bytes[2:22], 0x05)

            logger.warning(f"Unknown scriptPubKey format: {scriptpubkey[:20]}...")
            return None

        except Exception as e:
            logger.warning(f"Failed to convert scriptPubKey to address: {e}")
            return None

    def _encode_bech32_address(self, witness_program: bytes, witness_version: int) -> str:
        """Encode witness program as bech32 address."""
        # Simplified bech32 encoding - in production use a proper library
        hrp = "bc" if self.network == "mainnet" else "bcrt" if self.network == "regtest" else "tb"

        # Convert witness program to 5-bit groups
        def convertbits(data: bytes, frombits: int, tobits: int, pad: bool = True) -> list[int]:
            acc = 0
            bits = 0
            ret = []
            maxv = (1 << tobits) - 1
            for value in data:
                acc = (acc << frombits) | value
                bits += frombits
                while bits >= tobits:
                    bits -= tobits
                    ret.append((acc >> bits) & maxv)
            if pad and bits:
                ret.append((acc << (tobits - bits)) & maxv)
            return ret

        charset = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"

        def bech32_polymod(values: list[int]) -> int:
            gen = [0x3B6A57B2, 0x26508E6D, 0x1EA119FA, 0x3D4233DD, 0x2A1462B3]
            chk = 1
            for v in values:
                b = chk >> 25
                chk = ((chk & 0x1FFFFFF) << 5) ^ v
                for i in range(5):
                    chk ^= gen[i] if ((b >> i) & 1) else 0
            return chk

        def bech32_hrp_expand(hrp: str) -> list[int]:
            return [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]

        def bech32_create_checksum(hrp: str, data: list[int]) -> list[int]:
            values = bech32_hrp_expand(hrp) + data
            polymod = bech32_polymod(values + [0, 0, 0, 0, 0, 0]) ^ 1
            return [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]

        data = [witness_version] + convertbits(witness_program, 8, 5)
        checksum = bech32_create_checksum(hrp, data)
        return hrp + "1" + "".join(charset[d] for d in data + checksum)

    def _encode_base58check_address(self, payload: bytes, version: int) -> str:
        """Encode payload as base58check address."""
        import hashlib

        versioned = bytes([version]) + payload
        checksum = hashlib.sha256(hashlib.sha256(versioned).digest()).digest()[:4]
        data = versioned + checksum

        ALPHABET = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"  # noqa: N806
        n = int.from_bytes(data, "big")
        result = ""
        while n > 0:
            n, r = divmod(n, 58)
            result = ALPHABET[r] + result

        # Add leading zeros
        for byte in data:
            if byte == 0:
                result = "1" + result
            else:
                break

        return result

    async def get_filter_header(self, block_height: int) -> str:
        """
        Get compact block filter header for given height.

        BIP157 filter headers form a chain for validation.
        """
        try:
            result = await self._api_call(
                "GET",
                f"v1/block/{block_height}/filter_header",
            )
            return result.get("filter_header", "")

        except Exception as e:
            logger.error(f"Failed to fetch filter header for height {block_height}: {e}")
            raise

    async def get_connected_peers(self) -> list[dict[str, Any]]:
        """Get list of connected P2P peers."""
        try:
            result = await self._api_call("GET", "v1/peers")
            return result.get("peers", [])

        except Exception as e:
            logger.warning(f"Failed to fetch peers: {e}")
            return []

    async def rescan_from_height(
        self,
        start_height: int,
        addresses: list[str] | None = None,
        outpoints: list[tuple[str, int]] | None = None,
    ) -> None:
        """
        Rescan blockchain from a specific height for addresses.

        This triggers neutrino to re-check compact block filters from
        the specified height for relevant transactions.

        Uses the neutrino-api v0.4 rescan endpoint:
        POST /v1/rescan with {"start_height": N, "addresses": [...]}

        Note: The v0.4 API only supports address-based rescans.
        Outpoints are tracked via address watches instead.

        Args:
            start_height: Block height to start rescan from
            addresses: List of addresses to scan for (required for v0.4)
            outpoints: List of (txid, vout) outpoints - not directly supported,
                      will be ignored (use add_watch_outpoint instead)

        Raises:
            ValueError: If start_height is invalid or rescan depth exceeds limits
        """
        if not addresses:
            logger.warning("Rescan called without addresses - nothing to scan")
            return

        # Security: Validate start_height to prevent rescan abuse
        if start_height < self._min_valid_blockheight:
            raise ValueError(
                f"start_height {start_height} is below minimum valid height "
                f"{self._min_valid_blockheight} for {self.network}"
            )

        tip_height = await self.get_block_height()
        if start_height > tip_height:
            raise ValueError(f"start_height {start_height} is in the future (tip: {tip_height})")

        rescan_depth = tip_height - start_height
        if rescan_depth > self._max_rescan_depth:
            raise ValueError(
                f"Rescan depth {rescan_depth} exceeds maximum {self._max_rescan_depth} blocks"
            )

        # Track addresses locally (with limit check)
        for addr in addresses:
            await self.add_watch_address(addr)

        # Note: v0.4 API doesn't support outpoints in rescan
        if outpoints:
            logger.debug(
                "Outpoints parameter ignored in v0.4 rescan API. "
                "Use address-based watching instead."
            )
            for txid, vout in outpoints:
                self._watched_outpoints.add((txid, vout))

        try:
            await self._api_call(
                "POST",
                "v1/rescan",
                data={
                    "start_height": start_height,
                    "addresses": addresses,
                },
            )
            logger.info(f"Started rescan from height {start_height} for {len(addresses)} addresses")

        except Exception as e:
            logger.error(f"Failed to start rescan: {e}")
            raise

    async def close(self) -> None:
        """Close the HTTP client connection."""
        await self.client.aclose()

Blockchain backend using Neutrino light client.

Neutrino is a privacy-preserving Bitcoin light client that uses BIP157/BIP158 compact block filters instead of traditional SPV.

Communication with the neutrino daemon is via REST API. The neutrino daemon should be running alongside this client.

Initialize Neutrino backend.

Args

neutrino_url

URL of the neutrino REST API (default port 8334)

network

Bitcoin network (mainnet, testnet, regtest, signet)

connect_peers

List of peer addresses to connect to (optional)

data_dir

Directory for neutrino data (headers, filters)

Ancestors

• BlockchainBackend
• abc.ABC

Methods

async def add_watch_address(self, address: str) ‑> None

Expand source code

async def add_watch_address(self, address: str) -> None:
    """
    Add an address to the local watch list.

    In neutrino-api v0.4, address watching is implicit - you just query
    UTXOs or do rescans with the addresses you care about. This method
    tracks addresses locally for convenience.

    Security: Limits the number of watched addresses to prevent memory
    exhaustion attacks.

    Args:
        address: Bitcoin address to watch

    Raises:
        ValueError: If watch list limit exceeded
    """
    if address in self._watched_addresses:
        return

    if len(self._watched_addresses) >= self._max_watched_addresses:
        logger.warning(
            f"Watch list limit reached ({self._max_watched_addresses}). "
            f"Cannot add address: {address[:20]}..."
        )
        raise ValueError(f"Watch list limit ({self._max_watched_addresses}) exceeded")

    self._watched_addresses.add(address)
    logger.debug(f"Watching address: {address}")

Add an address to the local watch list.

In neutrino-api v0.4, address watching is implicit - you just query UTXOs or do rescans with the addresses you care about. This method tracks addresses locally for convenience.

Security: Limits the number of watched addresses to prevent memory exhaustion attacks.

Args

address

Bitcoin address to watch

Raises

ValueError

If watch list limit exceeded

async def add_watch_outpoint(self, txid: str, vout: int) ‑> None

Expand source code

async def add_watch_outpoint(self, txid: str, vout: int) -> None:
    """
    Add an outpoint to the local watch list.

    In neutrino-api v0.4, outpoint watching is done via UTXO queries
    with the address parameter. This method tracks outpoints locally.

    Args:
        txid: Transaction ID
        vout: Output index
    """
    outpoint = (txid, vout)
    if outpoint in self._watched_outpoints:
        return

    self._watched_outpoints.add(outpoint)
    logger.debug(f"Watching outpoint: {txid}:{vout}")

Add an outpoint to the local watch list.

In neutrino-api v0.4, outpoint watching is done via UTXO queries with the address parameter. This method tracks outpoints locally.

Args

txid

Transaction ID

vout

Output index

async def broadcast_transaction(self, tx_hex: str) ‑> str

Expand source code

async def broadcast_transaction(self, tx_hex: str) -> str:
    """
    Broadcast transaction via neutrino to the P2P network.

    Neutrino maintains P2P connections and can broadcast transactions
    directly to connected peers.
    """
    try:
        result = await self._api_call(
            "POST",
            "v1/tx/broadcast",
            data={"tx_hex": tx_hex},
        )
        txid = result.get("txid", "")
        logger.info(f"Broadcast transaction: {txid}")
        return txid

    except Exception as e:
        logger.error(f"Failed to broadcast transaction: {e}")
        raise ValueError(f"Broadcast failed: {e}") from e

Broadcast transaction via neutrino to the P2P network.

Neutrino maintains P2P connections and can broadcast transactions directly to connected peers.

def can_provide_neutrino_metadata(self) ‑> bool

Expand source code

def can_provide_neutrino_metadata(self) -> bool:
    """
    Neutrino backend cannot reliably provide metadata for all UTXOs.

    Light clients can only provide metadata for UTXOs they've been watching.
    They cannot provide metadata for arbitrary addresses like full nodes can.

    Returns:
        False - Neutrino cannot provide metadata for arbitrary UTXOs
    """
    return False

Neutrino backend cannot reliably provide metadata for all UTXOs.

Light clients can only provide metadata for UTXOs they've been watching. They cannot provide metadata for arbitrary addresses like full nodes can.

Returns

False - Neutrino cannot provide metadata for arbitrary UTXOs

async def close(self) ‑> None

Expand source code

async def close(self) -> None:
    """Close the HTTP client connection."""
    await self.client.aclose()

Close the HTTP client connection.

async def estimate_fee(self, target_blocks: int) ‑> int

Expand source code

async def estimate_fee(self, target_blocks: int) -> int:
    """
    Estimate fee in sat/vbyte for target confirmation blocks.

    Neutrino can estimate fees based on observed mempool/block data.
    Falls back to reasonable defaults if estimation unavailable.
    """
    try:
        result = await self._api_call(
            "GET",
            "v1/fees/estimate",
            params={"target_blocks": target_blocks},
        )

        fee_rate = result.get("fee_rate", 0)
        if fee_rate > 0:
            logger.debug(f"Estimated fee for {target_blocks} blocks: {fee_rate} sat/vB")
            return int(fee_rate)

    except Exception as e:
        logger.warning(f"Fee estimation failed: {e}")

    # Fallback fee rates based on target
    if target_blocks <= 1:
        return 20
    elif target_blocks <= 3:
        return 10
    elif target_blocks <= 6:
        return 5
    else:
        return 2

Estimate fee in sat/vbyte for target confirmation blocks.

Neutrino can estimate fees based on observed mempool/block data. Falls back to reasonable defaults if estimation unavailable.

async def get_address_balance(self, address: str) ‑> int

Expand source code

async def get_address_balance(self, address: str) -> int:
    """Get balance for an address in satoshis."""
    utxos = await self.get_utxos([address])
    balance = sum(utxo.value for utxo in utxos)
    logger.debug(f"Balance for {address}: {balance} sats")
    return balance

Get balance for an address in satoshis.

async def get_block_hash(self, block_height: int) ‑> str

Expand source code

async def get_block_hash(self, block_height: int) -> str:
    """Get block hash for given height."""
    try:
        result = await self._api_call(
            "GET",
            f"v1/block/{block_height}/header",
        )
        block_hash = result.get("hash", "")
        logger.debug(f"Block hash for height {block_height}: {block_hash}")
        return block_hash

    except Exception as e:
        logger.error(f"Failed to fetch block hash for height {block_height}: {e}")
        raise

Get block hash for given height.

async def get_block_height(self) ‑> int

Expand source code

async def get_block_height(self) -> int:
    """Get current blockchain height from neutrino."""
    try:
        result = await self._api_call("GET", "v1/status")
        height = result.get("block_height", 0)
        logger.debug(f"Current block height: {height}")
        return height

    except Exception as e:
        logger.error(f"Failed to fetch block height: {e}")
        raise

Get current blockchain height from neutrino.

async def get_block_time(self, block_height: int) ‑> int

Expand source code

async def get_block_time(self, block_height: int) -> int:
    """Get block time (unix timestamp) for given height."""
    try:
        result = await self._api_call(
            "GET",
            f"v1/block/{block_height}/header",
        )
        timestamp = result.get("timestamp", 0)
        logger.debug(f"Block {block_height} timestamp: {timestamp}")
        return timestamp

    except Exception as e:
        logger.error(f"Failed to fetch block time for height {block_height}: {e}")
        raise

Get block time (unix timestamp) for given height.

async def get_connected_peers(self) ‑> list[dict[str, typing.Any]]

Expand source code

async def get_connected_peers(self) -> list[dict[str, Any]]:
    """Get list of connected P2P peers."""
    try:
        result = await self._api_call("GET", "v1/peers")
        return result.get("peers", [])

    except Exception as e:
        logger.warning(f"Failed to fetch peers: {e}")
        return []

Get list of connected P2P peers.

async def get_filter_header(self, block_height: int) ‑> str

Expand source code

async def get_filter_header(self, block_height: int) -> str:
    """
    Get compact block filter header for given height.

    BIP157 filter headers form a chain for validation.
    """
    try:
        result = await self._api_call(
            "GET",
            f"v1/block/{block_height}/filter_header",
        )
        return result.get("filter_header", "")

    except Exception as e:
        logger.error(f"Failed to fetch filter header for height {block_height}: {e}")
        raise

Get compact block filter header for given height.

BIP157 filter headers form a chain for validation.

async def get_transaction(self, txid: str) ‑> Transaction | None

Expand source code

async def get_transaction(self, txid: str) -> Transaction | None:
    """
    Get transaction by txid.

    Note: Neutrino uses compact block filters (BIP158) and can only fetch
    transactions for addresses it has rescanned. It cannot fetch arbitrary
    transactions by txid alone. This method always returns None.

    For verification after broadcast, rely on UTXO checks with known addresses
    and block heights instead.
    """
    # Neutrino doesn't support fetching arbitrary transactions by txid
    # It can only work with UTXOs for known addresses via compact filters
    return None

Get transaction by txid.

Note: Neutrino uses compact block filters (BIP158) and can only fetch transactions for addresses it has rescanned. It cannot fetch arbitrary transactions by txid alone. This method always returns None.

For verification after broadcast, rely on UTXO checks with known addresses and block heights instead.

async def get_utxo(self, txid: str, vout: int) ‑> UTXO | None

Expand source code

async def get_utxo(self, txid: str, vout: int) -> UTXO | None:
    """Get a specific UTXO from the blockchain.
    Returns None if the UTXO does not exist or has been spent."""
    try:
        result = await self._api_call(
            "GET",
            f"v1/utxo/{txid}/{vout}",
        )

        if not result or result.get("spent", False):
            logger.debug(f"UTXO {txid}:{vout} not found or spent")
            return None

        tip_height = await self.get_block_height()
        height = result.get("height", 0)
        confirmations = 0
        if height > 0:
            confirmations = tip_height - height + 1

        return UTXO(
            txid=txid,
            vout=vout,
            value=result.get("value", 0),
            address=result.get("address", ""),
            confirmations=confirmations,
            scriptpubkey=result.get("scriptpubkey", ""),
            height=height if height > 0 else None,
        )

    except httpx.HTTPStatusError as e:
        if e.response.status_code == 404:
            logger.debug(f"UTXO {txid}:{vout} not found")
            return None
        logger.error(f"Failed to get UTXO {txid}:{vout}: {e}")
        return None
    except Exception as e:
        logger.error(f"Failed to get UTXO {txid}:{vout}: {e}")
        return None

Get a specific UTXO from the blockchain. Returns None if the UTXO does not exist or has been spent.

async def get_utxos(self, addresses: list[str]) ‑> list[UTXO]

Expand source code

async def get_utxos(self, addresses: list[str]) -> list[UTXO]:
    """
    Get UTXOs for given addresses using neutrino's rescan capability.

    Neutrino will scan the blockchain using compact block filters
    to find transactions relevant to the watched addresses.

    On first call, triggers a full blockchain rescan from genesis to ensure
    all historical UTXOs are found (critical for wallets funded before neutrino started).
    """
    utxos: list[UTXO] = []

    # Add addresses to watch list
    for address in addresses:
        await self.add_watch_address(address)

    # On first UTXO query, trigger a full blockchain rescan to find existing UTXOs
    # This is critical for wallets that were funded before neutrino was watching them
    logger.debug(
        f"get_utxos: _initial_rescan_done={self._initial_rescan_done}, "
        f"watched_addresses={len(self._watched_addresses)}"
    )
    if not self._initial_rescan_done and self._watched_addresses:
        logger.info(
            f"Performing initial blockchain rescan for {len(self._watched_addresses)} "
            "watched addresses (this may take a moment)..."
        )
        try:
            # Trigger rescan from block 0 for all watched addresses
            await self._api_call(
                "POST",
                "v1/rescan",
                data={
                    "addresses": list(self._watched_addresses),
                    "start_height": 0,
                },
            )
            # Wait for rescan to complete (neutrino processes this asynchronously)
            # On regtest with ~3000 blocks, this typically takes 5-10 seconds
            await asyncio.sleep(10.0)
            self._initial_rescan_done = True
            logger.info("Initial blockchain rescan completed")
        except Exception as e:
            logger.warning(f"Initial rescan failed (will retry on next sync): {e}")
    else:
        # Wait a moment for filter matching to complete
        await asyncio.sleep(0.5)

    try:
        # Request UTXO scan for addresses
        result = await self._api_call(
            "POST",
            "v1/utxos",
            data={"addresses": addresses},
        )

        tip_height = await self.get_block_height()

        for utxo_data in result.get("utxos", []):
            height = utxo_data.get("height", 0)
            confirmations = 0
            if height > 0:
                confirmations = tip_height - height + 1

            utxo = UTXO(
                txid=utxo_data["txid"],
                vout=utxo_data["vout"],
                value=utxo_data["value"],
                address=utxo_data.get("address", ""),
                confirmations=confirmations,
                scriptpubkey=utxo_data.get("scriptpubkey", ""),
                height=height if height > 0 else None,
            )
            utxos.append(utxo)

        logger.debug(f"Found {len(utxos)} UTXOs for {len(addresses)} addresses")

    except Exception as e:
        logger.error(f"Failed to fetch UTXOs: {e}")

    return utxos

Get UTXOs for given addresses using neutrino's rescan capability.

Neutrino will scan the blockchain using compact block filters to find transactions relevant to the watched addresses.

On first call, triggers a full blockchain rescan from genesis to ensure all historical UTXOs are found (critical for wallets funded before neutrino started).

def requires_neutrino_metadata(self) ‑> bool

Expand source code

def requires_neutrino_metadata(self) -> bool:
    """
    Neutrino backend requires metadata for arbitrary UTXO verification.

    Without scriptPubKey and blockheight hints, Neutrino cannot verify
    UTXOs that it hasn't been watching from the start.

    Returns:
        True - Neutrino always requires metadata for counterparty UTXOs
    """
    return True

Neutrino backend requires metadata for arbitrary UTXO verification.

Without scriptPubKey and blockheight hints, Neutrino cannot verify UTXOs that it hasn't been watching from the start.

Returns

True - Neutrino always requires metadata for counterparty UTXOs

async def rescan_from_height(self,
start_height: int,
addresses: list[str] | None = None,
outpoints: list[tuple[str, int]] | None = None) ‑> None

Expand source code

async def rescan_from_height(
    self,
    start_height: int,
    addresses: list[str] | None = None,
    outpoints: list[tuple[str, int]] | None = None,
) -> None:
    """
    Rescan blockchain from a specific height for addresses.

    This triggers neutrino to re-check compact block filters from
    the specified height for relevant transactions.

    Uses the neutrino-api v0.4 rescan endpoint:
    POST /v1/rescan with {"start_height": N, "addresses": [...]}

    Note: The v0.4 API only supports address-based rescans.
    Outpoints are tracked via address watches instead.

    Args:
        start_height: Block height to start rescan from
        addresses: List of addresses to scan for (required for v0.4)
        outpoints: List of (txid, vout) outpoints - not directly supported,
                  will be ignored (use add_watch_outpoint instead)

    Raises:
        ValueError: If start_height is invalid or rescan depth exceeds limits
    """
    if not addresses:
        logger.warning("Rescan called without addresses - nothing to scan")
        return

    # Security: Validate start_height to prevent rescan abuse
    if start_height < self._min_valid_blockheight:
        raise ValueError(
            f"start_height {start_height} is below minimum valid height "
            f"{self._min_valid_blockheight} for {self.network}"
        )

    tip_height = await self.get_block_height()
    if start_height > tip_height:
        raise ValueError(f"start_height {start_height} is in the future (tip: {tip_height})")

    rescan_depth = tip_height - start_height
    if rescan_depth > self._max_rescan_depth:
        raise ValueError(
            f"Rescan depth {rescan_depth} exceeds maximum {self._max_rescan_depth} blocks"
        )

    # Track addresses locally (with limit check)
    for addr in addresses:
        await self.add_watch_address(addr)

    # Note: v0.4 API doesn't support outpoints in rescan
    if outpoints:
        logger.debug(
            "Outpoints parameter ignored in v0.4 rescan API. "
            "Use address-based watching instead."
        )
        for txid, vout in outpoints:
            self._watched_outpoints.add((txid, vout))

    try:
        await self._api_call(
            "POST",
            "v1/rescan",
            data={
                "start_height": start_height,
                "addresses": addresses,
            },
        )
        logger.info(f"Started rescan from height {start_height} for {len(addresses)} addresses")

    except Exception as e:
        logger.error(f"Failed to start rescan: {e}")
        raise

Rescan blockchain from a specific height for addresses.

This triggers neutrino to re-check compact block filters from the specified height for relevant transactions.

Uses the neutrino-api v0.4 rescan endpoint: POST /v1/rescan with {"start_height": N, "addresses": […]}

Note: The v0.4 API only supports address-based rescans. Outpoints are tracked via address watches instead.

Args

start_height

Block height to start rescan from

addresses

List of addresses to scan for (required for v0.4)

outpoints

List of (txid, vout) outpoints - not directly supported, will be ignored (use add_watch_outpoint instead)

Raises

ValueError

If start_height is invalid or rescan depth exceeds limits

async def verify_tx_output(self, txid: str, vout: int, address: str, start_height: int | None = None) ‑> bool

Expand source code

async def verify_tx_output(
    self,
    txid: str,
    vout: int,
    address: str,
    start_height: int | None = None,
) -> bool:
    """
    Verify that a specific transaction output exists using neutrino's UTXO endpoint.

    Uses GET /v1/utxo/{txid}/{vout}?address=...&start_height=... to check if
    the output exists. This works because neutrino uses compact block filters
    that can match on addresses.

    Args:
        txid: Transaction ID to verify
        vout: Output index to check
        address: The address that should own this output
        start_height: Block height hint for efficient scanning (recommended)

    Returns:
        True if the output exists, False otherwise
    """
    try:
        params: dict[str, str | int] = {"address": address}
        if start_height is not None:
            params["start_height"] = start_height

        result = await self._api_call(
            "GET",
            f"v1/utxo/{txid}/{vout}",
            params=params,
        )

        # If we got a response with unspent status, the output exists
        # Note: Even spent outputs confirm the transaction was broadcast
        if result is not None:
            logger.debug(
                f"Verified tx output {txid}:{vout} exists "
                f"(unspent={result.get('unspent', 'unknown')})"
            )
            return True

        return False

    except httpx.HTTPStatusError as e:
        if e.response.status_code == 404:
            # Output not found
            logger.debug(f"Tx output {txid}:{vout} not found")
            return False
        logger.warning(f"Error verifying tx output {txid}:{vout}: {e}")
        return False
    except Exception as e:
        logger.warning(f"Error verifying tx output {txid}:{vout}: {e}")
        return False

Verify that a specific transaction output exists using neutrino's UTXO endpoint.

Uses GET /v1/utxo/{txid}/{vout}?address=…&start_height=… to check if the output exists. This works because neutrino uses compact block filters that can match on addresses.

Args

txid

Transaction ID to verify

vout

Output index to check

address

The address that should own this output

start_height

Block height hint for efficient scanning (recommended)

Returns

True if the output exists, False otherwise

async def verify_utxo_with_metadata(self, txid: str, vout: int, scriptpubkey: str, blockheight: int) ‑> UTXOVerificationResult

Expand source code

async def verify_utxo_with_metadata(
    self,
    txid: str,
    vout: int,
    scriptpubkey: str,
    blockheight: int,
) -> UTXOVerificationResult:
    """
    Verify a UTXO using provided metadata (neutrino_compat feature).

    This is the key method that enables Neutrino light clients to verify
    counterparty UTXOs in CoinJoin without arbitrary blockchain queries.

    Uses the neutrino-api v0.4 UTXO check endpoint which requires:
    - address: The Bitcoin address that owns the UTXO (derived from scriptPubKey)
    - start_height: Block height to start scanning from (for efficiency)

    The API scans from start_height to chain tip using compact block filters
    to determine if the UTXO exists and whether it has been spent.

    Security: Validates blockheight to prevent rescan abuse attacks where
    malicious peers provide very low blockheights to trigger expensive rescans.

    Args:
        txid: Transaction ID
        vout: Output index
        scriptpubkey: Expected scriptPubKey (hex) - used to derive address
        blockheight: Block height where UTXO was confirmed - scan start hint

    Returns:
        UTXOVerificationResult with verification status and UTXO data
    """
    # Security: Validate blockheight to prevent rescan abuse
    tip_height = await self.get_block_height()

    if blockheight < self._min_valid_blockheight:
        return UTXOVerificationResult(
            valid=False,
            error=f"Blockheight {blockheight} is below minimum valid height "
            f"{self._min_valid_blockheight} for {self.network}",
        )

    if blockheight > tip_height:
        return UTXOVerificationResult(
            valid=False,
            error=f"Blockheight {blockheight} is in the future (tip: {tip_height})",
        )

    # Limit rescan depth to prevent DoS
    rescan_depth = tip_height - blockheight
    if rescan_depth > self._max_rescan_depth:
        return UTXOVerificationResult(
            valid=False,
            error=f"Rescan depth {rescan_depth} exceeds max {self._max_rescan_depth}. "
            f"UTXO too old for efficient verification.",
        )

    logger.debug(
        f"Verifying UTXO {txid}:{vout} with metadata "
        f"(scriptpubkey={scriptpubkey[:20]}..., blockheight={blockheight})"
    )

    # Step 1: Derive address from scriptPubKey
    # The neutrino-api v0.4 requires the address for UTXO lookup
    address = self._scriptpubkey_to_address(scriptpubkey)
    if not address:
        return UTXOVerificationResult(
            valid=False,
            error=f"Could not derive address from scriptPubKey: {scriptpubkey[:40]}...",
        )

    logger.debug(f"Derived address {address} from scriptPubKey")

    try:
        # Step 2: Query the specific UTXO using the v0.4 API
        # GET /v1/utxo/{txid}/{vout}?address=...&start_height=...
        #
        # The start_height parameter is critical for performance:
        # - Scanning 1 block takes ~0.01s
        # - Scanning 100 blocks takes ~0.5s
        # - Scanning 10,000+ blocks can take minutes
        #
        # We use blockheight - 1 as a safety margin in case of reorgs
        start_height = max(0, blockheight - 1)

        result = await self._api_call(
            "GET",
            f"v1/utxo/{txid}/{vout}",
            params={"address": address, "start_height": start_height},
        )

        # Check if UTXO is unspent
        if not result.get("unspent", False):
            spending_txid = result.get("spending_txid", "unknown")
            spending_height = result.get("spending_height", "unknown")
            return UTXOVerificationResult(
                valid=False,
                error=f"UTXO has been spent in tx {spending_txid} at height {spending_height}",
            )

        # Step 3: Verify scriptPubKey matches
        actual_scriptpubkey = result.get("scriptpubkey", "")
        scriptpubkey_matches = actual_scriptpubkey.lower() == scriptpubkey.lower()

        if not scriptpubkey_matches:
            return UTXOVerificationResult(
                valid=False,
                value=result.get("value", 0),
                error=f"ScriptPubKey mismatch: expected {scriptpubkey[:20]}..., "
                f"got {actual_scriptpubkey[:20]}...",
                scriptpubkey_matches=False,
            )

        # Step 4: Calculate confirmations
        tip_height = await self.get_block_height()
        # The blockheight parameter is the confirmation height hint from the peer
        confirmations = tip_height - blockheight + 1 if blockheight > 0 else 0

        logger.info(
            f"UTXO {txid}:{vout} verified: value={result.get('value', 0)}, "
            f"confirmations={confirmations}"
        )

        return UTXOVerificationResult(
            valid=True,
            value=result.get("value", 0),
            confirmations=confirmations,
            scriptpubkey_matches=True,
        )

    except httpx.HTTPStatusError as e:
        if e.response.status_code == 404:
            return UTXOVerificationResult(
                valid=False,
                error="UTXO not found - may not exist or address derivation failed",
            )
        return UTXOVerificationResult(
            valid=False,
            error=f"UTXO query failed: {e}",
        )
    except Exception as e:
        return UTXOVerificationResult(
            valid=False,
            error=f"Verification failed: {e}",
        )

Verify a UTXO using provided metadata (neutrino_compat feature).

This is the key method that enables Neutrino light clients to verify counterparty UTXOs in CoinJoin without arbitrary blockchain queries.

Uses the neutrino-api v0.4 UTXO check endpoint which requires: - address: The Bitcoin address that owns the UTXO (derived from scriptPubKey) - start_height: Block height to start scanning from (for efficiency)

The API scans from start_height to chain tip using compact block filters to determine if the UTXO exists and whether it has been spent.

Security: Validates blockheight to prevent rescan abuse attacks where malicious peers provide very low blockheights to trigger expensive rescans.

Args

txid

Transaction ID

vout

Output index

scriptpubkey

Expected scriptPubKey (hex) - used to derive address

blockheight

Block height where UTXO was confirmed - scan start hint

Returns

UTXOVerificationResult with verification status and UTXO data

async def wait_for_sync(self, timeout: float = 300.0) ‑> bool

Expand source code

async def wait_for_sync(self, timeout: float = 300.0) -> bool:
    """
    Wait for neutrino to sync block headers and filters.

    Args:
        timeout: Maximum time to wait in seconds

    Returns:
        True if synced, False if timeout
    """
    start_time = asyncio.get_event_loop().time()

    while True:
        try:
            status = await self._api_call("GET", "v1/status")
            synced = status.get("synced", False)
            block_height = status.get("block_height", 0)
            filter_height = status.get("filter_height", 0)

            if synced and block_height == filter_height:
                self._synced = True
                self._filter_header_tip = block_height
                logger.info(f"Neutrino synced at height {block_height}")
                return True

            logger.debug(f"Syncing... blocks: {block_height}, filters: {filter_height}")

        except Exception as e:
            logger.warning(f"Waiting for neutrino daemon: {e}")

        elapsed = asyncio.get_event_loop().time() - start_time
        if elapsed > timeout:
            logger.error("Neutrino sync timeout")
            return False

        await asyncio.sleep(2.0)

Wait for neutrino to sync block headers and filters.

Args

timeout

Maximum time to wait in seconds

Returns

True if synced, False if timeout

Inherited members

• BlockchainBackend:
  • scan_descriptors

class NeutrinoConfig (network: str = 'mainnet',
data_dir: str = '/data/neutrino',
listen_port: int = 8334,
peers: list[str] | None = None,
tor_socks: str | None = None)

Expand source code

class NeutrinoConfig:
    """
    Configuration for running a neutrino daemon.

    This configuration can be used to start a neutrino process
    programmatically or generate a config file.
    """

    def __init__(
        self,
        network: str = "mainnet",
        data_dir: str = "/data/neutrino",
        listen_port: int = 8334,
        peers: list[str] | None = None,
        tor_socks: str | None = None,
    ):
        """
        Initialize neutrino configuration.

        Args:
            network: Bitcoin network (mainnet, testnet, regtest, signet)
            data_dir: Directory for neutrino data
            listen_port: Port for REST API
            peers: List of peer addresses to connect to
            tor_socks: Tor SOCKS5 proxy address (e.g., "127.0.0.1:9050")
        """
        self.network = network
        self.data_dir = data_dir
        self.listen_port = listen_port
        self.peers = peers or []
        self.tor_socks = tor_socks

    def get_chain_params(self) -> dict[str, Any]:
        """Get chain-specific parameters."""
        params = {
            "mainnet": {
                "default_port": 8333,
                "dns_seeds": [
                    "seed.bitcoin.sipa.be",
                    "dnsseed.bluematt.me",
                    "dnsseed.bitcoin.dashjr.org",
                    "seed.bitcoinstats.com",
                    "seed.bitcoin.jonasschnelli.ch",
                    "seed.btc.petertodd.net",
                ],
            },
            "testnet": {
                "default_port": 18333,
                "dns_seeds": [
                    "testnet-seed.bitcoin.jonasschnelli.ch",
                    "seed.tbtc.petertodd.net",
                    "testnet-seed.bluematt.me",
                ],
            },
            "signet": {
                "default_port": 38333,
                "dns_seeds": [
                    "seed.signet.bitcoin.sprovoost.nl",
                ],
            },
            "regtest": {
                "default_port": 18444,
                "dns_seeds": [],
            },
        }
        return params.get(self.network, params["mainnet"])

    def to_args(self) -> list[str]:
        """Generate command-line arguments for neutrino daemon."""
        args = [
            f"--datadir={self.data_dir}",
            f"--{self.network}",
            f"--restlisten=0.0.0.0:{self.listen_port}",
        ]

        if self.tor_socks:
            args.append(f"--proxy={self.tor_socks}")

        for peer in self.peers:
            args.append(f"--connect={peer}")

        return args

Configuration for running a neutrino daemon.

This configuration can be used to start a neutrino process programmatically or generate a config file.

Initialize neutrino configuration.

Args

network

Bitcoin network (mainnet, testnet, regtest, signet)

data_dir

Directory for neutrino data

listen_port

Port for REST API

peers

List of peer addresses to connect to

tor_socks

Tor SOCKS5 proxy address (e.g., "127.0.0.1:9050")

Methods

def get_chain_params(self) ‑> dict[str, typing.Any]

Expand source code

def get_chain_params(self) -> dict[str, Any]:
    """Get chain-specific parameters."""
    params = {
        "mainnet": {
            "default_port": 8333,
            "dns_seeds": [
                "seed.bitcoin.sipa.be",
                "dnsseed.bluematt.me",
                "dnsseed.bitcoin.dashjr.org",
                "seed.bitcoinstats.com",
                "seed.bitcoin.jonasschnelli.ch",
                "seed.btc.petertodd.net",
            ],
        },
        "testnet": {
            "default_port": 18333,
            "dns_seeds": [
                "testnet-seed.bitcoin.jonasschnelli.ch",
                "seed.tbtc.petertodd.net",
                "testnet-seed.bluematt.me",
            ],
        },
        "signet": {
            "default_port": 38333,
            "dns_seeds": [
                "seed.signet.bitcoin.sprovoost.nl",
            ],
        },
        "regtest": {
            "default_port": 18444,
            "dns_seeds": [],
        },
    }
    return params.get(self.network, params["mainnet"])

Get chain-specific parameters.

def to_args(self) ‑> list[str]

Expand source code

def to_args(self) -> list[str]:
    """Generate command-line arguments for neutrino daemon."""
    args = [
        f"--datadir={self.data_dir}",
        f"--{self.network}",
        f"--restlisten=0.0.0.0:{self.listen_port}",
    ]

    if self.tor_socks:
        args.append(f"--proxy={self.tor_socks}")

    for peer in self.peers:
        args.append(f"--connect={peer}")

    return args

Generate command-line arguments for neutrino daemon.