Defer transaction signing until user clicks Send #915

1. 
   151henry151 commented at 7:19 pm on November 22, 2025: contributor

   Fixes #30070

   When creating an unsigned PSBT from the GUI, the transaction was already signed during preparation, causing legacy inputs to have non-empty scriptSig fields. The PSBT parser then rejects them.

   This defers signing until the user clicks “Send” instead of signing during preparation. Fee calculation still works since transactions can be created without signing.

   Follows the approach suggested by @achow101 in the issue comments.

2. 
   DrahtBot commented at 7:19 pm on November 22, 2025: contributor

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   Concept ACK	achow101

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   Conflicts

   Reviewers, this pull request conflicts with the following ones:

   • #bitcoin/bitcoin/33112 (wallet: relax external_signer flag constraints by Sjors)

   If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

3. hebasto renamed this:
   qt: Defer transaction signing until user clicks Send
   Defer transaction signing until user clicks Send
   on Nov 22, 2025
4. DrahtBot added the label CI failed on Nov 22, 2025
5. 
   151henry151 commented at 6:02 pm on November 23, 2025: contributor

   It looks like the one failing check is a CI issue with disk space too low. I’m not sure how to address that. I think the code of the PR is correct.
6. 
   151henry151 commented at 9:51 pm on November 29, 2025: contributor

   @achow101 would you like to check this out and let me know if it looks OK?
7. maflcko closed this on Dec 17, 2025

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8. maflcko reopened this on Dec 17, 2025

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9. 
   151henry151 commented at 6:40 pm on January 18, 2026: contributor

   Should I push an empty commit to trigger a re-run of the CI here, or is there some other action needed?
10. 
    hebasto commented at 3:59 pm on January 19, 2026: member

    Should I push an empty commit to trigger a re-run of the CI here, or is there some other action needed?

    No action needed.

11. 
    hebasto commented at 3:59 pm on January 19, 2026: member

    cc @achow101 @furszy
12. hebasto removed the label CI failed on Jan 19, 2026
13. hebasto added the label Wallet on Jan 19, 2026
14. in src/qt/walletmodel.cpp:150 in 58adbcf88a

    146@@ -147,7 +147,7 @@ bool WalletModel::validateAddress(const QString& address) const
    147     return IsValidDestinationString(address.toStdString());
    148 }
    149 
    150-WalletModel::SendCoinsReturn WalletModel::prepareTransaction(WalletModelTransaction &transaction, const CCoinControl& coinControl)
    151+WalletModel::SendCoinsReturn WalletModel::prepareTransaction(WalletModelTransaction &transaction, const CCoinControl& coinControl, bool sign)
    

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    achow101 commented at 8:51 pm on January 19, 2026:

    prepareTransaction has only a single caller that already sets sign = false. I don’t think this needs to take a parameter, it can just always not sign.

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    151henry151 commented at 5:26 pm on January 20, 2026:

    suggestion implemented
15. in src/qt/sendcoinsdialog.cpp:551 in 58adbcf88a

    546+            // Sign the transaction now that the user has confirmed they want to send.
    547+            CMutableTransaction mtx = CMutableTransaction{*(m_current_transaction->getWtx())};
    548+            PartiallySignedTransaction psbtx(mtx);
    549+            bool complete = false;
    550+            // Fill and sign the PSBT
    551+            const auto err{model->wallet().fillPSBT(std::nullopt, /*sign=*/true, /*bip32derivs=*/false, /*n_signed=*/nullptr, psbtx, complete)};
    

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    achow101 commented at 8:53 pm on January 19, 2026:

    Creating the PSBT and calling fillPSBT on it is being done for all of the other cases in this function, and hence is now duplicated 3 times. This can be refactored so that the PSBT is always created and filled at the top of the function, and each action can do whatever specific thing it needs to do with that PSBT.

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    151henry151 commented at 5:26 pm on January 20, 2026:

    refactored as suggested
16. 
    achow101 commented at 8:54 pm on January 19, 2026: member

    Concept ACK
17. qt: Defer transaction signing until user clicks Send

    Fixes #30070
    
    When creating an unsigned PSBT from the GUI, the transaction was already signed during preparation, causing legacy inputs to have non-empty scriptSig fields. The PSBT parser then rejects them.
    
    This defers signing until the user clicks "Send" instead of signing during preparation. Fee calculation still works since transactions can be created without signing.
    
    Follows the approach suggested by @achow101 in the issue comments.

    3c61ba5df6
18. 151henry151 force-pushed on Jan 20, 2026
19. DrahtBot added the label CI failed on Jan 20, 2026

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151henry151 DrahtBot hebasto achow101

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