How to customize your Orbit chain's precompiles
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The tutorial only works when you use eth_call to call the new precompiles, if you want to add non-view/pure methods or call from other contracts, it will break validation, but we will have how to update the wasm module root tutorial to fix this soon. If you want to test modifying the STS before we have instructions for wasm module root generation, you can add command --node.staker.dangerous.without-block-validator when you start the node.
There are two ways to customize your chain's precompiles:
- Add new methods to an existing precompile.
- Create a new precompile.
Prerequisites
Clone the Nitro repository before you begin:
git clone --branch v2.1.1 <https://github.com/OffchainLabs/nitro.git>
cd nitro
git submodule update --init --recursive --force
Option 1: Add new methods to an existing precompile
Using your favorite code editor, open an existing precompile from the precompiles implementation directory, /precompiles. We'll use ArbSys.go as an example. Open the corresponding Go implementation file (ArbSys.go) and add a simple SayHi method:
func (con *ArbSys) SayHi(c ctx, evm mech) (string, error) {
return "hi", nil
}
Then, open the corresponding Solidity interface file (ArbSys.sol) from the precompiles interface directory, /src/precompiles, and add the required interface. Ensure that the method name on the interface matches the name of the function you introduced in the previous step, camelCased:
function sayHi() external view returns(string memory);
Next, build Nitro by following steps 3-7 of the instructions in How to build Nitro locally. Note that if you've already built the Docker image, you still need run the last step to rebuild.
Run Nitro with the following command:
docker run --rm -it -v /some/local/dir/arbitrum:/home/user/.arbitrum -p 0.0.0.0:8547:8547 -p 0.0.0.0:8548:8548 offchainlabs/nitro-node:v2.1.1-e9d8842 --parent-chain.connection.url=<YourParentChainUrl> --chain.id=<YourOrbitChainId> --http.api=net,web3,eth,debug --http.corsdomain=* --http.addr=0.0.0.0 --http.vhosts=*
Note that the instructions provided in How to run a full node will not work with your Orbit node. See Command-line options (Orbit) for Orbit-specific CLI flags.
Once your node is running, you can call ArbSys.sol either directly using curl, or through Foundry's cast call.
Call your function directly using curl
curl Your_IP_Address:8547\
-X POST \
-H "Content-Type: application/json" \
--data '{"method":"eth_call","params":[{"from":null,"to":"0x0000000000000000000000000000000000000064","data":"0x0c49c36c"}, "latest"],"id":1,"jsonrpc":"2.0"}'
You should see something like this:
{"jsonrpc":"2.0","id":1,"result":"0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000026869000000000000000000000000000000000000000000000000000000000000"}
0x6869 is the hex-encoded utf8 representation of hi, which you'll see embedded in the result hex string.
Call your function using Foundry's cast call
cast call 0x0000000000000000000000000000000000000064 "sayHi()(string)”
You should see something like this:
hi
Option 2: Create a new precompile
First, navigate to the precompiles implementation directory, /precompiles, and create a new precompile implementation file called ArbHi.go. We'll define a new method, and we'll give it an address:
package precompiles
// ArbGasInfo provides insight into the cost of using the rollup.
type ArbHi struct {
Address addr // 0x11a, for example
}
func (con *ArbHi) SayHi(c ctx, evm mech) (string, error) {
return "hi", nil
}
Then, update precompile.go to register the new precompile under the Precompiles() method:
insert(MakePrecompile(templates.ArbHiMetaData, &ArbHi{Address: hex("11a")})) // 0x011a here is an example address
Navigate to the precompiles interface directory, /src/precompiles, create ArbHi.sol, and add the required interface. Ensure that the method name on the interface matches the name of the function you introduced in the previous step, camelCased:
pragma solidity >=0.4.21 <0.9.0;
/// @title Say hi.
/// @notice just for test
/// This custom contract will set on 0x000000000000000000000000000000000000011a since we set it in precompile.go.
interface ArbHi {
function sayHi() external view returns(string memory);
}
Next, build Nitro by following the instructions in How to build Nitro locally. Note that if you've already built the Docker image, you still need run the last step to rebuild.
Run Nitro with the following command:
docker run --rm -it -v /some/local/dir/arbitrum:/home/user/.arbitrum -p 0.0.0.0:8547:8547 -p 0.0.0.0:8548:8548 offchainlabs/nitro-node:v2.1.1-e9d8842 --parent-chain.connection.url=<YourParentChainUrl> --chain.id=<YourOrbitChainId> --http.api=net,web3,eth,debug --http.corsdomain=* --http.addr=0.0.0.0 --http.vhosts=*
Note that the instructions provided in How to run a full node will not work with your Orbit node. See Command-line options (Orbit) for Orbit-specific CLI flags.
Once your node is running, you can call ArbHi.sol either directly using curl, or through Foundry's cast call.
Call your function directly using curl
curl Your_IP_Address:8547 \
-X POST \
-H "Content-Type: application/json" \
--data '{"method":"eth_call","params":[{"from":null,"to":"0x000000000000000000000000000000000000011a","data":"0x0c49c36c"}, "latest"],"id":1,"jsonrpc":"2.0"}'
You should see something like this:
{"jsonrpc":"2.0","id":1,"result":"0x000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000026869000000000000000000000000000000000000000000000000000000000000"}
Call your function using Foundry's cast call
cast call 0x000000000000000000000000000000000000011a "sayHi()(string)”
You should see something like this:
hi