Cannot identify the number of signers in adapter layer

[areshand]

🚀 Feature Request

Motivation

When trying to use the latest move, come across a problem.

We automatically add signer to the script function call if we find the function requires signers (here

move/language/move-vm/runtime/src/runtime.rs

Line 280 in c113ea1

fn create_signers_and_arguments(

). This checks happens at VM runtime. It has access to the loader, which can load the script or script function to read the script/script_function parameter to determine how many signers are needed. But this loader seems not exposed to adapter layer.

With the new move revision (https://github.com/diem/move/pull/175/files), to use the new execute_entry_function, it only take args, which could contains both signer and txn args. we need to determine the number of signers to add to args at adapter layer now. However, some script function requires one signer and some doesn’t (eg: create_account). since loader is not exposed in the adapter’s session, I currently don’t find a way to calculate the number of signer in script or script function from adapter. Any suggestions or workarounds?

Pitch

Need to expose either the loader to adapter layers or functions in session to help determine the number of signers in the the script function or script

[areshand]

Hi @tnowacki, could you please take a look at this issue?
do you have a recommendation on the right way to identify the number of signer in script / script function at adapter layer?

cc: @zekun000 @msmouse

[tnowacki]

I sort of anticipated issues like this, but not this issue exactly. I just added a new API in #197. You should be able to use the new load_function function in Session to

• Add the function to the VM's cache
• View the signature of the function.
  See

  move/language/move-vm/runtime/src/session.rs

  Line 217 in 42cdb1b

  pub fn load_function(

So for this particular problem, you should be able to make a session, call load function, and then find out how to manage signer arguments as needed

Keep in mind the VM no longer verifies the signature of script functions at all, so the signers can appear in any position. You can use

move/language/move-bytecode-verifier/src/script_signature.rs

Line 153 in 42cdb1b

pub fn legacy_script_signature_checks(

to enforce the legacy rules

[areshand]

Thank you for such detailed reply. Close the issue now.

[areshand]

@tnowacki is there a way to provide a similar load_script function so that

[areshand]

@tnowacki Could there be a similar load_function for script to read the signature of the