Initial commit: snapshot of spesmilo/electrumx 2.0.0

Unmodified source tree of upstream commit 280cb339aa158e099eb936033eecd15719770651
("Merge pull request #389 from SomberNight/202607_release_2_0",
https://github.com/spesmilo/electrumx, release 2.0.0, 3 July 2026).

All Palladium-specific changes are in the commits that follow.

docs/features.rst

@@ -0,0 +1,59 @@
+Features
+========
+
+- Efficient, lightweight reimplementation of electrum-server
+- Fast synchronization of bitcoin mainnet from Genesis.  Recent
+  hardware should synchronize in well under 24 hours.  The fastest
+  time to height 448k (mid January 2017) reported is under 4h 30m.  On
+  the same hardware JElectrum would take around 4 days and
+  electrum-server probably around 1 month.
+- Various configurable means of controlling resource consumption and
+  handling bad clients and denial of service attacks.  These include
+  maximum connection counts, subscription limits per-connection and
+  across all connections, maximum response size, per-session bandwidth
+  limits, and session timeouts.
+- Minimal resource usage once caught up and serving clients; tracking the
+  transaction mempool appears to be the most expensive part.
+- Mostly asynchronous processing of new blocks, mempool updates, and
+  client requests.  Busy clients should not noticeably impede other
+  clients' requests and notifications, nor the processing of incoming
+  blocks and mempool updates.
+- Daemon failover.  More than one daemon can be specified, and
+  ElectrumX will failover round-robin style if the current one fails
+  for any reason.
+- Peer discovery protocol removes need for IRC
+- Coin abstraction makes compatible altcoin and testnet support easy.
+
+Implementation
+==============
+
+ElectrumX does not do any pruning or throwing away of history.  I want
+to retain this property for as long as it is feasible, and it appears
+efficiently achievable for the foreseeable future with plain Python.
+
+The following all play a part in making it efficient as a Python
+blockchain indexer:
+
+- aggressive caching and batching of DB writes
+- more compact and efficient representation of UTXOs, address index,
+  and history.  Electrum Server stores full transaction hash and
+  height for each UTXO, and does the same in its pruned history.  In
+  contrast ElectrumX just stores the transaction number in the linear
+  history of transactions.  ElectrumX can determine block
+  height from a simple binary search of tx counts stored on disk.
+  ElectrumX stores historical transaction hashes in a linear array on
+  disk.
+- placing static append-only metadata indexable by position on disk
+  rather than in levelDB.  It would be nice to do this for histories
+  but I cannot think of a way.
+- avoiding unnecessary or redundant computations, such as converting
+  address hashes to human-readable ASCII strings with expensive bignum
+  arithmetic, and then back again.
+- better choice of Python data structures giving lower memory usage as
+  well as faster traversal
+- leveraging asyncio for asynchronous prefetch of blocks to mostly
+  eliminate CPU idling.  As a Python program ElectrumX is unavoidably
+  single-threaded in its essence; we must keep that CPU core busy.
+
+Python's :mod:`asyncio` means ElectrumX has no (direct) use for threads
+and associated complications.