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External Calls.md

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49 - External Calls

Call/Delegatecall/Staticcall: In order to interface with contracts that do not adhere to the ABI, or to get more direct control over the encoding, the functions call, delegatecall and staticcall are provided.

They all take a single bytes memory parameter and return the success condition (as a bool) and the returned data (bytes memory).

The functions abi.encode, abi.encodePacked, abi.encodeWithSelector and abi.encodeWithSignature can be used to encode structured data.

  1. gas and value modifiers can be used with these functions (delegatecall doesn’t support value) to specify the amount of gas and Ether value passed to the callee.

  2. With delegatecall, only the code of the given address is used but all other aspects (storage, balance, msg.sender etc.) are taken from the current contract. The purpose of delegatecall is to use library/logic code which is stored in callee contract but operate on the state of the caller contract

  3. With staticcall, the execution will revert if the called function modifies the state in any way

Slide Screenshot

049.jpg

Slide Deck

  • call, delegatecall, staticcall
  • Parameters: bytes memory
  • Return: success, bytes memory
  • abi.\* -> Functions, gas/value
  • delegatecall -> State/Modify
  • staticcall -> State/Use
  • Security: Low-level Call, Untrusted Contract, Reentrancy, Return Value Check

References

Tags

System Operations ABI Encoding-Decoding