[bitcoin-dev] An efficient re-implementation of Electrum Server in Rust

[Roman Zeyde <me@romanzey.de>]

Hello all,

I was working on this project for the last few months, so a user could run his own Electrum server, with required hardware resources not much beyond those of a full node (using ideas from ElectrumX [1], Electrum Personal Server [2] and bitcoincore-indexd [3]).

The code and usage instructions can be found here:
https://github.com/romanz/electrs

The server indexes the entire Bitcoin blockchain, and the resulting index [4] enables fast queries for any given user wallet, allowing the user to keep real-time track of his balances and his transaction history using the Electrum wallet [5].
Since it runs on the user's own machine, there is no need for the wallet to communicate with external Electrum servers, thus preserving the privacy of the user's addresses and balances.

Features:
 * Supports latest Electrum protocol [6].
 * Maintains an index of transaction inputs and outputs, allowing fast balance queries
 * Fast synchronization of the Bitcoin blockchain (~2.5 hours for ~185GB @ June 2018) on modest hardware [7]
 * Low CPU & memory usage (after initial indexing)
 * Low index storage overhead (~20%), relying on a local full node for transaction retrieval
 * Efficient mempool tracker allowing better fee estimation [8].
 * `-txindex` is not required for the Bitcoin node
 * Uses `rust-bitcoin` library [9] for efficient serialization/deserialization of Bitcoin transactions
 * Uses a single RocksDB [10] database, for better consistency and crash recovery

Hope you'll find it useful :)
Questions, suggestions and pull requests are welcome!

[1] https://github.com/kyuupichan/electrumx
[2] https://github.com/chris-belcher/electrum-personal-server
[3] https://github.com/jonasschnelli/bitcoincore-indexd
[4] https://github.com/romanz/electrs/blob/master/doc/schema.md
[5] https://electrum.org
[6] https://electrumx.readthedocs.io/en/latest/protocol.html
[7] https://gist.github.com/romanz/cd9324474de0c2f121198afe3d063548
[8] https://github.com/spesmilo/electrum/blob/59c1d03f018026ac301c4e74facfc64da8ae4708/RELEASE-NOTES#L34-L46)
[9] https://github.com/rust-bitcoin/rust-bitcoin
[10] https://github.com/spacejam/rust-rocksdb