Introduce the `EVM.dryCall` method #6838

m-Peter · 2024-12-27T15:19:17Z

This new method can be used instead of COA.call, in a Cadence transaction, when the user wants to execute a contract call, without committing any state changes. This is useful for reading a contract's state.

codecov-commenter · 2024-12-27T15:22:32Z

Codecov Report

Attention: Patch coverage is 70.00000% with 27 lines in your changes missing coverage. Please review.

Project coverage is 41.19%. Comparing base (72adf9e) to head (02715e9).

Files with missing lines	Patch %	Lines
fvm/evm/impl/impl.go	69.51%	16 Missing and 9 partials ⚠️
utils/unittest/execution_state.go	0.00%	2 Missing ⚠️

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@@            Coverage Diff             @@
##           master    #6838      +/-   ##
==========================================
+ Coverage   41.18%   41.19%   +0.01%     
==========================================
  Files        2109     2109              
  Lines      185660   185716      +56     
==========================================
+ Hits        76460    76505      +45     
- Misses     102788   102794       +6     
- Partials     6412     6417       +5

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This new method can be used instead of COA.call, in a Cadence transaction, when the users wants to execute a contract call, without committing any state changes. This is useful for reading a contract's state.

janezpodhostnik

Nice work. Left some comments.

janezpodhostnik · 2025-01-06T16:56:14Z

fvm/evm/evm_test.go

+			json.MustEncode(cadence.NewUInt64(tx.Gas())),
+			json.MustEncode(cadence.NewUInt(uint(tx.Value().Uint64()))),
+		)
+		_, output, err := vm.Run(


can you return the execution snapshot out of dryCall and in "test dryCall has no side-effects" verify that no changes were made on the EVM state register?

Good point 👍 Added some assertions in 20c84f4

janezpodhostnik · 2025-01-06T17:01:16Z

fvm/evm/stdlib/contract.go

@@ -178,6 +178,37 @@ var InternalEVMTypeDryRunFunctionType = &sema.FunctionType{
 	ReturnTypeAnnotation: sema.NewTypeAnnotation(sema.AnyStructType),
 }

+// InternalEVM.dryCall


nit: can you move it after call?

Updated in d1e1e8e

janezpodhostnik · 2025-01-06T17:06:36Z

fvm/evm/impl/impl.go

+			inter := invocation.Interpreter
+			locationRange := invocation.LocationRange
+
+			// Get from address
+
+			fromAddressValue, ok := invocation.Arguments[0].(*interpreter.ArrayValue)
+			if !ok {
+				panic(errors.NewUnreachableError())
+			}
+
+			fromAddress, err := AddressBytesArrayValueToEVMAddress(inter, locationRange, fromAddressValue)
+			if err != nil {
+				panic(err)
+			}
+
+			// Get to address
+
+			toAddressValue, ok := invocation.Arguments[1].(*interpreter.ArrayValue)
+			if !ok {
+				panic(errors.NewUnreachableError())
+			}
+
+			toAddress, err := AddressBytesArrayValueToEVMAddress(inter, locationRange, toAddressValue)
+			if err != nil {
+				panic(err)
+			}
+
+			to := toAddress.ToCommon()
+
+			// Get data
+
+			dataValue, ok := invocation.Arguments[2].(*interpreter.ArrayValue)
+			if !ok {
+				panic(errors.NewUnreachableError())
+			}
+
+			data, err := interpreter.ByteArrayValueToByteSlice(inter, dataValue, locationRange)
+			if err != nil {
+				panic(err)
+			}
+
+			// Get gas limit
+
+			gasLimitValue, ok := invocation.Arguments[3].(interpreter.UInt64Value)
+			if !ok {
+				panic(errors.NewUnreachableError())
+			}
+
+			gasLimit := types.GasLimit(gasLimitValue)
+
+			// Get balance
+
+			balanceValue, ok := invocation.Arguments[4].(interpreter.UIntValue)
+			if !ok {
+				panic(errors.NewUnreachableError())
+			}


This first part is exactly the same as a call function with makes sense. Can you create a common function for that?

Good idea 👍 Added in 02715e9

janezpodhostnik · 2025-01-06T17:06:37Z

fvm/evm/impl/impl.go

+
+			// call contract function
+
+			res := handler.DryRun(txPayload, fromAddress)


DryRun? should this be called dry call? Is this equivalent?

DryCall under the hood works the same way as DryRun. The only difference is the the API. For example:

// EVM.dryRun EVM.dryRun(tx: tx, from: EVM.EVMAddress(...)) // where tx is an RLP-encoded tx // EVM.dryCall EVM.dryCall( from: EVM.EVMAddress(bytes: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 0, 0, 0, 0, 0, 0, 0, 0, 15]), to: EVM.addressFromString(to), data: data, gasLimit: gasLimit, value: EVM.Balance(attoflow: value) )

Right now EVM.dryRun is basically only used from the EVM Gateway, for facilitating Cadence Arch Calls in eth_call / eth_estimateGas etc.

The new EVM.dryCall is supposed to be used from within Cadence transactions, and replace the coa.call, so that we do not form EVM transactions, when the developer simply wants to read a contract's state.

That's why I am making use of the already existing handler.DryRun method, which provides the functionality we need. There's no need to add another function.

janezpodhostnik

Nice! Looks great.

sisyphusSmiling · 2025-01-08T20:13:14Z

fvm/evm/stdlib/contract.cdc

+        gasLimit: UInt64,
+        value: Balance,
+    ): Result {
+        return InternalEVM.dryCall(


Who is the msg.sender and txn.origin in this instance? I would expect dryCall to be exposed on the COA - coa.call and dryCall - but maybe that's just a matter of verbiage.

Who is the msg.sender and txn.origin in this instance?

The msg.sender for the top-level call, is the from address. The tx.origin is also the from address.

I would expect dryCall to be exposed on the COA - coa.call and dryCall - but maybe that's just a matter of verbiage.

There are a couple of issues with that approach. Most of the APIs for the COA resource, use as from the COA address. This means that users will have to first create a COA resource, in order to be able to call dryCall. Even if the said COA resource is destroyed after, the COA contract is still deployed in Flow EVM, so we're left with a dead account.
The second issue, is that users do not have any control over the randomly-generated address of a COA, so they are not able to simulate/debug with an EOA of their choice.

I think exposing it additionally on the COA makes sense for convenience

I think exposing it additionally on the COA makes sense for convenience

Ah right, to have it additionally there makes sense indeed. As long as it doesn't force users to create a COA in the first place.

m-Peter added Feature Flow EVM labels Dec 27, 2024

m-Peter self-assigned this Dec 27, 2024

m-Peter force-pushed the mpeter/implement-evm-dry-call branch from efd6cc6 to 56eeb97 Compare December 29, 2024 12:05

m-Peter marked this pull request as ready for review December 30, 2024 11:46

m-Peter requested review from janezpodhostnik and zhangchiqing as code owners December 30, 2024 11:46

janezpodhostnik requested a review from peterargue January 3, 2025 15:42

m-Peter added 3 commits January 6, 2025 12:35

Introduce the EVM.dryCall method

3facc3f

This new method can be used instead of COA.call, in a Cadence transaction, when the users wants to execute a contract call, without committing any state changes. This is useful for reading a contract's state.

Update state commitment expected values

8c25560

Add test cases for EVM.dryCall method

cd3d0ca

m-Peter force-pushed the mpeter/implement-evm-dry-call branch from bcfb56f to cd3d0ca Compare January 6, 2025 10:38

janezpodhostnik reviewed Jan 6, 2025

View reviewed changes

zhangchiqing approved these changes Jan 6, 2025

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m-Peter added 3 commits January 7, 2025 12:53

Move EVM.dryCall definition after coa.call

d1e1e8e

Add state register assertions for EVM.dryRun test cases

20c84f4

Extract logic for parsing call arguments to its own function

02715e9

janezpodhostnik approved these changes Jan 7, 2025

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sisyphusSmiling reviewed Jan 8, 2025

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Introduce the `EVM.dryCall` method #6838

Introduce the `EVM.dryCall` method #6838

m-Peter commented Dec 27, 2024

codecov-commenter commented Dec 27, 2024 •

edited

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m-Peter Jan 9, 2025


		// call contract function

		res := handler.DryRun(txPayload, fromAddress)

Introduce the EVM.dryCall method #6838

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Introduce the EVM.dryCall method #6838

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Introduce the `EVM.dryCall` method #6838

Introduce the `EVM.dryCall` method #6838

codecov-commenter commented Dec 27, 2024 •

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