Send server.version as first message to interact with Electrumx server

[worldwideward]

We are using bitcoinlib for our project.

I had installed up a bitcoin-core node + electrumx server, locally in regtest mode.
I had configured bitcoinlib's provider.json to connect to the electrumx server

However, when executing wallet.scan(), bitcoinlib would throw an error:

2026/04/17 17:39:18 DEBUG _provider_execute(221) Error Extra data: line 2 column 1 (char 1024) on provider bitcoin.electrumx
2026/04/17 17:39:18 ERROR __init__(40) No successful response from any serviceprovider: ['bitcoin.electrumx']

The electrumx server complained:

INFO:ElectrumX:[3] TCP 172.20.0.12:42954, 1 total
INFO:ElectrumX:[3] closing session: server.version must be first msg. got: blockchain.headers.subscribe

After reading the protocol docs (https://electrumx.readthedocs.io/en/latest/protocol-methods.html#server-version) it became clear the electrumx provider in bitcoinlib wasn't sending this required message.

I could see the second message being crafted:

# bitcoinlib/services/electrumx.py
    def blockcount(self):
        return self.compose_request('blockchain.headers.subscribe')['height']

I realized that before sending blockcount() or other methods, the server.version message should be sent. But I wasn't completely sure how to implement this. As a last resort I shared the codebase with an AI model from Mistral, and asked for help. The result is this PR.

I am happy because now electrumx responds the way I expect it to:

2026/04/17 17:45:51 DEBUG _provider_execute(210) Executed method blockcount from provider bitcoin.electrumx
2026/04/17 17:45:51 DEBUG _provider_execute(210) Executed method getutxos from provider bitcoin.electrumx
2026/04/17 17:45:51 INFO utxos_update(3323) Got 0 new UTXOs for account 0
2026/04/17 17:45:52 INFO _balance_update(3152) Got balance for 10 key(s)

Now, if there is feedback on the implementation it is certainly welcome! But hopefully this can get merged 🙂