zkApp composability #297

mitschabaude · 2022-07-22T09:54:50Z

This is the final PR for zkApp composability.

Implements the RFC here: zkApp composability RFC #303 (please read before reviewing this)
Stacked on top of zkApps composability, pt 3: witness Party #294
Closes Support interactions between 2 smart contracts (i.e. composability, call stack) #185

mitschabaude

some comments to help reviewing!

mitschabaude · 2022-07-25T19:03:47Z

src/examples/zkapps/composability.ts

@@ -0,0 +1,118 @@
+/**


this is the example that demonstrates composability

mitschabaude · 2022-07-25T19:09:37Z

src/lib/circuit_value.ts

@@ -533,3 +546,38 @@ Circuit.constraintSystem = function <T>(f: () => T) {
  );
  return result;
 };
+
+let memoizationContext = Context.create<{


new global context that is used to remember prover values which are created during createTransaction, to be reused in the prover for the same method. In snarkyjs, only used for the blindingValue right now, but I figured it would be nice to also expose that capability to the outside world -- that's what the memoizeWitness function below is for.

mitschabaude · 2022-07-25T19:10:56Z

src/lib/proof_system.ts

@@ -467,6 +472,43 @@ function synthesizeMethodArguments(
  return args;
 }

+function methodArgumentsToConstant(
+  { allArgs, proofArgs, witnessArgs }: MethodInterface,


two new helper functions we need to convert the input arguments of a zkapp call to inputs to our hash function

mitschabaude · 2022-07-25T19:14:06Z

src/lib/zkapp.ts

-          fetchMode: inProver() ? 'cached' : 'test',
-          isFinalRunOutsideCircuit: false,
-        },
+    if (!smartContractContext.has()) {


This function -- wrappedMethod -- is what always gets called when you call any smart contract method. It is where most of the new logic lives. The function is now quite complex!

This first, large if branch is handling the case that was supported already -- calling a zkApp method when you're not inside another zkApp method.

mitschabaude · 2022-07-25T19:15:57Z

src/lib/zkapp.ts

-          assertStatePrecondition(this);
-          return result;
+          if (inCheckedComputation()) {
+            // important to run this with a fresh party everytime, otherwise compile messes up our circuits


the code below didn't really change in its entirety. It's just marked green because there is more nesting, causing two more spaces on the left

mitschabaude · 2022-07-25T19:19:05Z

src/lib/zkapp.ts

+                }
+                callDataFields.push(getMethodId(methodIntf, methodIndex));
+                callDataFields.push(blindingValue);
+                party.body.callData = Poseidon.hash(callDataFields);


This whole code block is the case that we're in a circuit. So, these commands are what is added to the circuit on top of the user code in a @method. It is also how a called method is executed inside its own prover (but not in the prover of the caller -- that case is further below!). On this line, we're populating our own callData field -- as explained in the RFC, this is done every time, to make the method callable by default

mitschabaude · 2022-07-25T19:29:27Z

src/lib/zkapp.ts

    }
+    // if we're here, this method was called inside _another_ smart contract method


this is what happens inside the caller, inside calling another method. the code below has some comments to explain what's happening

ymekuria · 2022-07-26T04:11:56Z

src/examples/zkapps/composability.ts

+  if (!doProofs) zkapp.sign(zkappKey);
+});
+if (doProofs) {
+  console.log('proving (3 proofs.. can take a bit!)');


How long are the 3 proofs taking on your machine @mitschabaude?

takes 42 sec for me

ymekuria · 2022-07-26T04:12:48Z

src/examples/zkapps/composability.ts

@@ -0,0 +1,118 @@
+/**


This is a great intuitive example to demonstrate composability.

ymekuria · 2022-07-26T08:01:30Z

src/lib/zkapp.ts

+          `  // ...\n` +
+          `}\n\n` +
+          `Note: Only types built out of \`Field\` are valid return types. This includes snarkyjs primitive types and custom CircuitValues.`;
+        // if we're lucky, analyzeMethods was already run on the callee smart contract, and we can catch this error early


Clarifying question. When does analyzeMethods run for the first time on a contract?

It runs

in SmartContract.compile() (before actually compiling)

when computing the SmartContract.digest()

in a Mina.transaction block, it runs if one of the methods needs it under the hood; this is only the case when reducing sequence events right now.
So, it definitely runs when we're proving things (because we compile first), but likely not if we don't.

The code above will throw the helpful error message if we're not proving, so that case is covered.

The case that's problematic is when we compile the caller first, and the callee second. Then, the "if we're lucky" case above is not true in the caller circuit. Then, we won't be able to nicely catch the missing return type annotation, and the caller's compile will throw an ugly, unhelpful error instead.

Thanks for poking into this :D Maybe I should make it so that analyzeMethods figures out all the SmartContracts called inside a method, and also runs analyzeMethods on them. This way, the callee would definitely be analyzed already in the code above, so we'd avoid the "ugly error" case.

Update: I tried this out, but wasn't able to make it work. The ugly error is already thrown during analyzeMethods, so I have no way of finding the list of callees before. I think we'll have to live with a suboptimal error message in this edge case

Update: I tried this out, but wasn't able to make it work. The ugly error is already thrown during analyzeMethods, so I have no way of finding the list of callees before. I think we'll have to live with a suboptimal error message in this edge case

At least we are aware of the edge case error behavior.

mitschabaude · 2022-08-01T09:12:22Z

Update: Implemented callData hashing as proposed here: #303 (comment)
I think this is a solution that already makes sense, so leaving further tweaks to a separate PR

mitschabaude added 16 commits July 15, 2022 23:19

add account.isNew

a20146b

WIP manual composability

c7a0e56

fix public key from fields, remove debug logs

9fc8d3a

use method name for lazy proof, skip party.check

ec7ac47

get manual composability example working

89a55d2

support memoizing witnesses in methods for prover

c56d0c3

composability mvp

f669f6c

include return value in callData hash

4ea5c05

add random value into the callData hash for hiding

504f663

start handling calls inside calls

f8536e6

change composability example to do nested calls

48b9a7a

fix nested composability by witnessing calls hash

bcfab0f

fix example: deploy all contracts

8664529

clean up comments

e974cb7

delete manual composability example

4806e3a

minor change to party.test.ts

4ba97c1

jasongitmail assigned mitschabaude Jul 25, 2022

add method index + name to callData hash

2b30db8

mitschabaude commented Jul 25, 2022

View reviewed changes

minor

7b999e3

ymekuria reviewed Jul 26, 2022

View reviewed changes

Merge branch 'feature/composability' into tmp

4a93ee8

Base automatically changed from feature/composability to main July 26, 2022 10:15

Merge branch 'feature/is-new' into feature/composability-rebased

e9964a8

MartinMinkov approved these changes Jul 27, 2022

View reviewed changes

ymekuria approved these changes Jul 27, 2022

View reviewed changes

mitschabaude mentioned this pull request Jul 30, 2022

Hash inputs in JS #310

Merged

mitschabaude added 2 commits August 1, 2022 10:07

Merge branch 'main' into feature/composability-rebased

56a1283

compute callData s.t. it fixes method signature

58331ea

mitschabaude merged commit c0bd0de into main Aug 1, 2022

mitschabaude deleted the feature/composability-rebased branch August 1, 2022 09:12

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zkApp composability #297

zkApp composability #297

mitschabaude commented Jul 22, 2022 •

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mitschabaude commented Aug 1, 2022

		}
		// if we're here, this method was called inside _another_ smart contract method

zkApp composability #297

zkApp composability #297

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mitschabaude commented Jul 22, 2022 • edited

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mitschabaude commented Aug 1, 2022

mitschabaude commented Jul 22, 2022 •

edited