Bitcoin: mandatory-script-verify-flag-failed (Script evaluated without error but finished with a false/empty top stack element) on wrapped SegWit input

Here is a draft of the article:

Mandatory script validation tag failed: Debugging wrapped SegWit inputs

Ducat Protocol has been working on building reliable digital asset solutions. One of the challenges we are currently facing is debugging transactions that use wrapped Segwit inputs. Specifically, one of our tests resulted in a bug that puzzled us – the “mandatory script validation-tag failed” error.

To find out what this error means and how to debug it:

Error

When a transaction attempts to issue a wrapped Segwit input, the system should evaluate whether the script provided by the sender actually matches the script used for that input. This validation process is based on two tags: “script-verify” and “optional-space-pat”.

However, when the mandatory script verification flag fails (as indicated by the error message “mandatory-script-verify-flag-failed”), it indicates that the script evaluation failed without raising an error. In other words, the system encountered some problem with the provided script.

Wrapped FromWit Inputs

Wrapped Segwit inputs are a type of digital asset built on top of Bitcoin that allows for more efficient storage and transfer of assets. These inputs have their own unique characteristics, including additional space for metadata. The process of verifying wrapped Segwit inputs requires that the transaction field “optional-space-pat” be properly defined and match the script used to create the input.

Debugging the Issue

In our case, we noticed that a certain transaction was throwing the error “mandatory-script-verify-flag-failed” when we tried to issue a wrapped Segwit input. To fix this issue, I performed the following steps:

• Check Script: I first reviewed the script used for the transactions and verified that it was correctly defined in the wallet or validator configuration.

• Check Input Metadata: I then ensured that the transaction field “optional-space-pat” was properly set to match the input script.

• Evaluate Script Without Errors: After checking both tags, I evaluated the script without errors and saw that it followed the intended behavior.

Conclusion

In this article, we discussed the issue of the “mandatory script validation-markup failed” error when issuing packaged Segwit inputs in the Ducat protocol development environment. After performing the above steps and carefully checking each component involved in the transaction validation process, we were able to successfully debug the issue and identify the root cause.

If you are experiencing similar difficulties with your transactions or wallet configuration, the goal of this article is to provide useful insights and tuning strategies to address such issues in the future.

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Please note that this is a hypothetical example article, not a real case study. Feel free to modify it to fit your specific use case or topic if necessary. Also, I have used local token names and information (e.g. Ducat Protocol) for illustrative purposes only.

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