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[FR] - Balance existing transaction

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#867 19 comments 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Quiet
Tech stack
haskell
Domain
blockchain, cli

Research direction

Start by reviewing the existing cardano-cli transaction build workflow and how transaction envelopes, redeemers, and signing keys are handled. Done means balancing an externally drafted transaction by calculating script costs and fees, selecting fee inputs, adding change, and writing the result to disk or stdout using node data.

Written by the indexing model from the issue text.

Description

needs investigation Stale

Internal (anyone could benefit though)

Area
Transaction building

Describe the feature you'd like

I would like to use the cardano-cli to balance a transaction that was drafted by another application. Assuming we have a transaction already built with body and witnesses (redeemers) by a DApp in a transaction envelope tx.json and some signing key wallet.sk which owns ADA to pay fees:

 cardano-cli transaction balance \
   --socket-path ... \ #
   --testnet-magic 2 \
   --unbalanced-tx tx.json \
   --cardano-signing-key wallet.sk \
   --out-file tx.json

Would connect to the cardano-node as usual to fetch various information (utxo owned by user, protocol parameters, system start and era history) and balance the transaction. That is:

  • (Re-)calculate script costs using redeemers from the tx
  • Estimate fees
  • Find and add input to cover fees
  • Add a change output
  • Write the balanced transaction to disk (or stdout)

Alternative with slightly smaller scope: Take only an input to use for paying fees and change address, very much like transaction build.

Describe alternatives you've considered
Obvious alternative is to do all this in the DApp itself, but balancing a transaction is a generic process and not application-specific. Also, this would tie the transaction creating code very much to the "source" of where UTxO, protocol parameters etc. are fetched from. Having it in the cardano-cli, a dedicated client to the cardano-node, would keep it separated from e.g. an alternative workflow that uses blockfrost.

Additional context / screenshots
We encountered this while designing a command line tool to create certain smart contract transactions in the Hydra protocol. More details here: https://github.com/cardano-scaling/hydra/issues/1574

Dominant language
Haskell
Stars
72
Forks
25
Avg merge
2d 1h
Merged PRs (30d)
8

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  4. Open a pull request that references the issue number.

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