Connecting to a node with incompatible version

[mixmix]

The problem

I noticed a really unhelpful test when trialing the CLI. I told it to make a register an account and got this:

Attempting to register the address: 5CBCdVRZDw8zTvnVkcrwSriAuJKLTnajLpZkz2BU4aNWgGNs
file:///home/projects/ENTROPY/cli/node_modules/@polkadot/types/metadata/decorate/extrinsics/createUnchecked.js:11
            throw new Error(`Extrinsic ${section}.${funcName} expects ${expectedArgs.length} arguments, got ${args.length}.`);
                  ^

Error: Extrinsic registry.register expects 3 arguments, got 2.
    at extrinsicFn (file:///home/projects/ENTROPY/cli/node_modules/@polkadot/types/metadata/decorate/extrinsics/createUnchecked.js:11:19)
    at Object.decorated [as register] (file:///home/projects/ENTROPY/cli/node_modules/@polkadot/api/base/Decorate.js:539:50)
    at RegistrationManager.register (file:///home/projects/ENTROPY/cli/node_modules/@entropyxyz/sdk/dist/index.js:99:51)
    at Entropy.register (file:///home/projects/ENTROPY/cli/node_modules/@entropyxyz/sdk/dist/index.js:831:57)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

Very unhelpful response as a CLI user.

The actual problem is that the default endpoint it was connecting to is on an old version of Entropy core compared to CLI.

Questions

I'm wondering

• is this going to happen when there are changes to the network in the future?
• is there a way to ask an endpoint what version it is?

Obviously we would make less breaking changes, but as the CLI developer I'm wanting to make it clear/ safe for my users.

[ameba23]

I think you can get the current version number of the runtime from a subxt client by doing api.runtime_version().spec_version. I imagine polkadot js has something similar. But i don't know whether this is telling you the runtime version the client is expecting (from the entropy-metadata.scale file) or the runtime version of the connected chain endpoint (by actually doing a query).

Ideally you want to know both and be able to compare them.

Usually though with subxt i get a pretty clear error MetadataError::IncompatibleCodegen which can be shown to the user as 'you need to update your client'.