SafeCall

Git Source

Title: SafeCall

Performs a call or a static call that caps the returndata copied into memory, so that a callee returning or reverting with oversized returndata cannot inflate the gas cost of the calling contract.

Copied from LayerZero at commit 592625b9e5967643853476445ffe0e777360b906, path packages/layerzero-v2/evm/messagelib/contracts/libs/SafeCall.sol, which is itself a copy of the nomad-xyz ExcessivelySafeCall library at commit 81cd99ce3e69117d665d7601c330ea03b97acce0, path src/ExcessivelySafeCall.sol. Copyright (c) Illusory Systems Inc. and LayerZero Labs Ltd., licensed MIT OR Apache-2.0.

LayerZero changed the nomad original as follows: added the extcodesize guard that returns (false, "") when the target holds no code, renamed excessivelySafeCall to safeCall and excessivelySafeStaticCall to safeStaticCall, dropped the swapSelector helper, and raised the pragma from >=0.7.6 to ^0.8.20.

This copy changes the LayerZero source as follows: widened uint to uint256 in the extcodesize guard, corrected two stale comments that named a fixed byte count where the code caps at _maxCopy, and added the lint suppressions. The executable code is otherwise unchanged.

Neither function propagates the revert reason. Both return the returndata truncated to _maxCopy bytes, which the caller must bubble up itself if it wants to revert. An Error(string) payload needs 100 bytes to survive intact, and a callee that runs out of gas returns no data at all, which a caller cannot tell apart from a bare revert().

Functions

safeCall

calls a contract with a specified gas limit and value and captures the return data

function safeCall(
        address _target,
        uint256 _gas,
        uint256 _value,
        uint16 _maxCopy,
        bytes memory _calldata
    ) internal returns (bool, bytes memory);

Parameters

Name	Type	Description
_target	address	The address to call
_gas	uint256	The amount of gas to forward to the remote contract
_value	uint256	The value in wei to send to the remote contract to memory.
_maxCopy	uint16	The maximum number of bytes of returndata to copy to memory.
_calldata	bytes	The data to send to the remote contract

Returns

Name	Type	Description
<none>	bool	success and returndata, as .call(). Returndata is capped to _maxCopy bytes.
<none>	bytes

safeStaticCall

Use when you really really really don't trust the called contract. This prevents the called contract from causing reversion of the caller in as many ways as we can.

The main difference between this and a solidity low-level call is that we limit the number of bytes that the callee can cause to be copied to caller memory. This prevents stupid things like malicious contracts returning 10,000,000 bytes causing a local OOG when copying to memory.

function safeStaticCall(
        address _target,
        uint256 _gas,
        uint16 _maxCopy,
        bytes memory _calldata
    ) internal view returns (bool, bytes memory);

Parameters

Name	Type	Description
_target	address	The address to call
_gas	uint256	The amount of gas to forward to the remote contract
_maxCopy	uint16	The maximum number of bytes of returndata to copy to memory.
_calldata	bytes	The data to send to the remote contract

Returns

Name	Type	Description
<none>	bool	success and returndata, as .call(). Returndata is capped to _maxCopy bytes.
<none>	bytes