v30rc2 createrawtransaction unable to create txns with multiple OP_RETURNs #33544

Is there an existing issue for this?

• I have searched the existing issues

Current behaviour

createrawtransaction in v30rc2 seems unable to create txns with multiple OP_RETURNs

Expected behaviour

Expected v30 cli to be able to generate transactions with multiple OP_RETURN outputs.

Steps to reproduce

$ bitcoin-cli -regtest createrawtransaction \
  '[{"txid":"0000000000000000000000000000000000000000000000000000000000000000","vout":0}]' \
  '[{"data":"68656c6c6f"},{"data":"776f726c64"}]'

# Error:
# error code: -8
# error message: Invalid parameter, duplicate key: data

Relevant log output

No response

How did you obtain Bitcoin Core

Pre-built binaries

What version of Bitcoin Core are you using?

v30rc2

Operating system and version

UNIX

Machine specifications

No response

Here's the offending lines

https://github.com/bitcoin/bitcoin/blob/30.x/src/rpc/rawtransaction_util.cpp#L109-L111

Is there an existing issue for this?

* [x]  I have searched the existing issues

See #32478?

@maflcko - apologies. Out of interest, is it a hard rule that RPC changes like this must follow a release later? Seems strange to relax standardness but not give users a straightforward way to make use of it

With policy changes, the expectation is that one release is needed to upgrade a sufficient portion of the network, until the wallet and RPC can offer them as features. Otherwise, users may not be able to propagate such transactions, or only intermittently.

@maflcko genuine question - why couldn't the approach be to accommodate policy changes in the same release but with a warning to users about potential propagation issues (and then remove it in the next release)?

Yeah, it is always a bit of a case-by-case decision. However, I don't think a pull request in a reviewable state exists to implement this? So nothing can be merged into 31.x, nor 30.x anyway.

Here's the offending lines

https://github.com/bitcoin/bitcoin/blob/30.x/src/rpc/rawtransaction_util.cpp#L109-L111 @maflcko this is all that needs removing and replacing with a warning. I assume there are standardness tests that will start failing and need changing too. Not sure if I'll have time to get to this myself. Also concerned there may be dragons here and it's not as simple as it appears - what do you think @petertodd or @murchandamus ?

There is https://github.com/bitcoin/bitcoin/pull/32790/files, but it is still in draft and has not received any code-review, only a conceptual feedback.

No strong opinion from my side, but I've removed the milestone from the issue and pull, so that reviewers (once there are any) can suggest a milestone, but I think it is clear that this missed 30.0 and it seems unlikely to make it into 30.1. Though, again, no strong opinion.

@maflcko I suppose if it's not going into 30.0 then it wont need warnings. It's a shame to not have it in 30.0 but if the ship has sailed it is what it is.