Understanding the RunCode RPC

Context

Here we infer RunCode RPC semantics from Taquito Code.

References

• R1: runCode RPC

RunCode RPC

Reference R1 documentation for runCode RPC is “Run a piece of code in the current context”.

In Taquito the request inputs are described by:

RPCRunCodeParam
  Script: MichelsonV1ExpressionExtended[]
  Storage: MichelsonV1Expression
  Input: MichelsonV1Expression
  Amount: string
  Chain_id: string
  Source?: string
  Payer?: string
  Gas?: BigNumber
  Entrypoint?: string
  Balance?: string

The result is described by:

RunCodeResult
  Storage: MichelsonV1Expression
  Operations: InternalOperationResult[]
  Big_map_diff?: ContractBigMapDiff
  Lazy_storage_diff?: LazyStorageDiff

Taquito’s Use of RunCode

Taquito leverages the RunCode RPC to:

• Execute a tzip-16 Michelson Storage View
• Simulate execution of a Smart Contract’s OnChainView

These Taquito use cases make use of RunCode in a very similar way, enabling us to infer semantics.

Inferred Semantics

RunCode simulates execution of a specified Transaction against a specified (Michelson script, storage-value, balance) tuple as if that tuple is an Originated Account in the current Context.

This interpretation enables us to make sense of (most of) RPCRunCodeParam.

Some Parameters specify the virtual Smart Contract:

• Script - defines Params, Storage and Code elements of the virtual Smart Contract
• Storage - the storage state of the virtual Smart Contract
• Balance - the balance state of the virtual Smart Contract

Other Parameters specify the Transaction:

• Source - the “To” is implicitly the virtual Smart Contract address
• Amount
• Entrypoint
• Input - entrypoint arguments

The Chain_id seems redundant. We are talking to a particular RPC Node which is already bound to a particular chain_id. Moreover, we are tasking this node to execute as if our virtual smart contract is in the current context; the only current context an RPC node can service is for the chain-id that it is bound to.

This leaves two optional RPCRunCodeParam parameters that remain uninterpreted, namely: Payer and Gas. Taquito does not make use of these parameters.

We can now make sense of RunCodeResult:

• Storage - the value of the virtual smart contract’s storage after the transaction is executed
• Operations - the result of executing any Internal Operations left on the Michelson Stack after the transaction endpoint is executed. Taquito does not actually make use of this field since in both Taquito use cases, no Operations are left on the stack.

This leaves two optional RunCodeResult parameters that remain uninterpreted, namely: Big_map_diff and Lazy_storage_diff. Taquito does not make use of these parameters.