Retrieve CHAIN_ID of the executing chain from a Solidity contract

Question

Is there a way to directly be able to retrieve CHAIN_ID information about the executing chain from a smart contract?

I know that for any chain that has EIP-155 implemented, CHAIN_IDs are retrievable from the v component of a signature but would require the passing of one for extraction.

Since CHAIN_ID is information about the chain I suspect that there should be a way to access this. Is there a way for Solidity to directly get this information?

Alternative: Because you are deploying the contract on a different chain you can give the chain id as a constructor parameter. — Mikko Ohtamaa, Aug 17 '18 at 14:40

taijusanagi · Answer 1 · 2021-04-16T19:36:54.683

34

chainid is available in native solidity 0.8.0. So you can get chain id like block timestamp or block number.

Here is the code.

block.chainid;

Documentation https://docs.soliditylang.org/en/v0.8.0/units-and-global-variables.html

Solidity update PR is here. https://github.com/ethereum/solidity/pull/10557

edited Apr 16 '21 at 19:36

answered Mar 14 '21 at 06:01

taijusanagi

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TypeError: "chainid" is not supported by the VM version (v0.8.0) – Jim Nov 24 '21 at 19:56
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FYI "Chain ID is a 256-bit value." - https://eips.ethereum.org/EIPS/eip-1344 – Stiin Jan 12 '22 at 20:43
I think the VM version and solidity version is a different thing. Solidity version v0.8.0 has "block.chainId" but VM implements eip-1344. – taijusanagi Feb 03 '22 at 11:15
That's seems like the better answer – Roy Toledo Apr 08 '22 at 16:29
CompileError: TypeError: "chainid" is not supported by the VM version. pragma solidity ^0.8.4; – Barney Chambers Dec 01 '22 at 14:46
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@Barney Chambers, solidity version and EVM version are two different things, you need to make sure the selected EVM version is at least Istanbul for block.chainid to compile. – hellopeach Dec 28 '22 at 12:42

score 18 · Accepted Answer · answered Nov 16 '19 at 11:12

18

As of version 0.5.12, Solidity includes an assembly function chainid() that provides access to the new CHAINID opcode:

function getChainID() external view returns (uint256) {
    uint256 id;
    assembly {
        id := chainid()
    }
    return id;
}

To use it, ensure you set the compiler's EVM version to Istanbul with the --evm-version istanbul flag.

Related documentation: Solidity Assembly - v0.5.12

answered Nov 16 '19 at 11:12

iamdefinitelyahuman

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very useful answer, thanks! note: for those using ganache: this needs v6.9.1 as eg v6.7.0 doesn't support the CHAINID opcode – oberstet Feb 24 '20 at 09:43
Is there an equivalent function in Vyper? – Paul Razvan Berg Jun 14 '20 at 09:57
@PaulRazvanBerg for Vyper - https://ethereum.stackexchange.com/questions/84261/does-vyper-have-an-equivalent-chainid-assembly-function/84264#84264 – iamdefinitelyahuman Jun 14 '20 at 10:17

score 3 · Answer 3 · answered Oct 16 '19 at 15:25

There isn't as of yet, but Istanbul (the upcoming hardfork) includes eip-1344, which includes a CHAINID opcode that pushes the chain id to the stack. I assume Solidity will add block.chainId or something similar, or at least add it to Solidity Assembly so that libraries can access it.

Retrieve CHAIN_ID of the executing chain from a Solidity contract

3 Answers3

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