Neutrino: Privacy-Preserving Bitcoin Light Client
Neutrino is a Bitcoin light client written in Go and designed with mobile Lightning Network clients in mind. It uses a new proposal for compact block filters to minimize bandwidth and storage use on the client side, while attempting to preserve privacy and minimize processor load on full nodes serving light clients.
Mechanism of operation
The light client synchronizes only block headers and a chain of compact block filter headers specifying the correct filters for each block. Filters are loaded lazily and stored in the database upon request; blocks are loaded lazily and not saved.
Usage
The client is instantiated as an object using NewChainService and then
started. Upon start, the client sets up its database and other relevant files
and connects to the p2p network. At this point, it becomes possible to query the
client.
Queries
There are various types of queries supported by the client. There are many ways
to access the database, for example, to get block headers by height and hash; in
addition, it's possible to get a full block from the network using
GetBlockFromNetwork by hash. However, the most useful methods are specifically
tailored to scan the blockchain for data relevant to a wallet or a smart
contract platform such as a Lightning Network node like
lnd. These are described below.
Rescan
Rescan allows a wallet to scan a chain for specific TXIDs, outputs, and
addresses. A start and end block may be specified along with other options. If
no end block is specified, the rescan continues until stopped. If no start block
is specified, the rescan begins with the latest known block. While a rescan
runs, it notifies the client of each connected and disconnected block; the
notifications follow the
btcjson
format with the option to use any of the relevant notifications. It's important
to note that "recvtx" and "redeemingtx" notifications are only sent when a
transaction is confirmed, not when it enters the mempool; the client does not
currently support accepting 0-confirmation transactions.
GetUtxo
GetUtxo allows a wallet or smart contract platform to check that a UTXO exists
on the blockchain and has not been spent. It is highly recommended to
specify a start block; otherwise, in the event that the UTXO doesn't exist on
the blockchain, the client will download all the filters back to block 1
searching for it. The client scans from the tip of the chain backwards, stopping
when it finds the UTXO having been either spent or created; if it finds neither,
it keeps scanning backwards until it hits the specified start block or, if a
start block isn't specified, the first block in the blockchain. It returns a
SpendReport containing either a TxOut including the PkScript required to
spend the output, or containing information about the spending transaction,
spending input, and block height in which the spending transaction was seen.
Stopping the client
Calling Stop on the ChainService client allows the user to stop the client;
the method doesn't return until the ChainService is cleanly shut down.