This looks great and is obviously useful. I will review and get feedback to you asap.

@Sjors Please review my test case (testing/test_export.py) and if you can tighten it, please submit a PR for that. Thanks again for adding this feature.

Thanks! The test looks OK, but maybe you want to add a test that interacts with bitcoind, and checks that getnewaddress returns the correct first address.

Another useful feature I think would be to print the first couple of addresses in the txt file, so users can more easily check that they didn't mess up the import.

Yes, on both counts.

Also, if you want to add support for airgapped transaction signing, you could add support for reading a plain text file with the base64 encoded PSBT.

And for the signed result, you could even add the required command, I believe the GUI console lets you nest stuff: sendrawtransaction(finalizepsbt(PSBT))
But I haven't tried

Coldcard supports binary PSBT files coming from MicroSD already. If the result is a finalized transaction (as in typical single-signer case), then the hex-encoded transaction is also saved to MicroSD card.

I can import the keys into bitcoind, but I don't have a good way to test they got in there.

• getnewaddress ... theres lots of crap in my bitcoind, and I don't expect it to return same thing everytime; I don't see a way to control what pool of addresses it draws from.
• getaddressinfo ... did not return anything useful:

{'address': 'tb1qxvzlcjr2djne6n60q0ytzet49mcqumpdqmluzm',
 'ischange': False,
 'ismine': False,
 'isscript': False,
 'iswatchonly': False,
 'iswitness': True,
 'labels': [],
 'scriptPubKey': '00143305fc486a6ca79d4f4f03c8b165752ef00e6c2d',
 'solvable': False,
 'witness_program': '3305fc486a6ca79d4f4f03c8b165752ef00e6c2d',
 'witness_version': 0}

In particular:

• label isn't set, but perhaps that's because no label was set first time I imported these keys?
• ismine and/or iswatchonly aren't true?

I am using 0.18.1

You should create a fresh bitcoind wallet for this, and it needs to be watch-only (see createwallet wallet command in the docs that I added). In order to select that wallet from RPC, you need to add -rpcwallet=... to the command. You should also rm -f it before the start of the test run.

Coldcard supports binary PSBT files coming from MicroSD already.

But Bitcoin Core doesn't. So users can only put a (unsigned) base58 encoded PSBT on the SD card.

If the result is a finalized transaction (as in typical single-signer case), then the hex-encoded transaction is also saved to MicroSD card.

Ok, so then the user can call sendrawtransaction on that.

• I've created a text fixture to make a temp wallet, and added that to the test case
• support for Base64 PSBT files will come in a future version of Coldcard

a2329cf looks good to me. If you use #32 in the commit description, Github will automatically add a comment to this thread linking to it.

You could use this to make the tests works on Windows and Linux: https://github.com/cryptoadvance/specter-desktop/blob/aa0513f5521f672bc24e6e615d07dd5bd8c6a103/src/rpc.py#L8-L16