I am trying to run a forked version of the Stellar-Laboratory, I have forked the js-stellar-base and js-stellar-sdk accordingly, basically what I am trying to do is add a new operation on the Laboratory UI.

The new operation is mimicking every aspect of the BumpSequence operation.

I modified js-stellar-base, then published it to npm as a separate package. Then, in js-stellar-sdk I updated the version of js-stellar-base inside the package.json file.

Then I published the js-stellar-sdk(my version) also to npm.

Now I am using my own version of js-stellar-sdk in the modified version of stellar-laboratory.

And I am not able to generate XDR for any operation, neither for the one I added, nor for the older ones and it is returning this error:

"- XDR Write Error: undefined is not a Hyper "

If anyone can provide any resolution or hint to get rid of this error.

If any other info is required, feel free to ask.

Note: All the changes that are made are mentioned in the above description, they are very minimal changes and it is more like building on top of the existing structure.

1 Answer 1


You should debug the XDR serialisation stage. Something that should be a 64-bit integer is null. The one hint you get is that the field type is Hyper. This refers to 64-bit signed or unsigned integers in the XDR scheme. You can see the Hyper fields in the XDR serialisation code.

  • I was able to remove the errors related to "XDR write error", only one error is remaining which states "Error: Bad Union Switch -789528406". Any idea how this can be resolved.
    – Deb
    Commented Jan 4, 2019 at 11:58
  • 1
    The union switches are discriminants for the type Discriminated Union tools.ietf.org/html/rfc4506#section-4.15. They're usually a very small neg or pos integer. If you get a large number, then there's been a problem parsing the previous fields. I would debug the serialisation, so you can view the fields as they are serialised to make sure they look correct as per the XDR RFC and the Stellar definition: github.com/stellar/js-stellar-base/tree/master/xdr
    – Synesso
    Commented Jan 5, 2019 at 23:51
  • This is the test that is failing: TransactionEnvelope calculates correct hash with non-utf8 strings: Error: Bad union switch: -789528406
    – Deb
    Commented Jan 7, 2019 at 6:12

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