sign-psbt.py example does not support electrum's testnet xpub encoding for p2wsh

[kanzure]

For regtest/testnet mode, bitcointx raises an error when attempting to sign an electrum-generated PSBT because of the presence of an xpub with prefix 0x043587cf (tpub) and does not accept an xpub with prefix 0x02575483 (Vpub).

https://electrum.readthedocs.io/en/latest/xpub_version_bytes.html#specification

I think the simplest solution here would be some xpub type coercion when the user calls the signer with a special flag? Or even type coercion based on --regtest/--mainnet flags.

That said, @darosior mentions:

hardcoding of specific script types inside the encoding of an extended public key is an unscalable and terrible layer violation

[dgpv]

The exception should be raised within deserialization code, not within the signing code.

Please check if the following PR would fix your problem: #72

in that PR, PartiallySignedTransaction.deserialize() accepts optional arg acceptable_xpub_prefixes which is the list of 4-byte prefixes acceptable for xpubs. The example sign-psbt.py is also updated (use --acceptable-xpub-prefixes).

[dgpv]

Please note that the serialization will use standard prefixes, so when PSBT with non-standard prefixes is deserialized and then serialized again the result will differ from the original

[dgpv]

@kanzure, has #72 fixed the problem ?