Offline experiments with Remix and local RSKJ Node

4 min readNov 20, 2020

The Remix IDE is a popular environment to experiment with and deploy smart contracts written in Solidity for Ethereum-like blockchains including RSK. In this post we go over a few simple steps to run Remix IDE locally along with a local RSKJ node. A local setup is useful for offline testing and can also serve as an alternative to the Ethereum foundation’s service.

Components

Remix users work with the following components

A blockchain: This may be a local blockchain e.g. ganache,geth, rskj, or a public blockchain endpoint e.g. https://public-node.testnet.rsk.co.
A wallet to manage blockchain credentials (accounts, private keys, signatures). This is often a browser extension e.g. Nifty or Metamask. Users can also use a hardware wallet.
Remix IDE in a Web Browser, typically https://remix.ethereum.org via Chrome or Firefox.

To use Remix, users connect their browser wallet to a relevant blockchain. This is only needed if users wish to deploy or administer smart contracts. Those using Remix IDE just to compile contracts (no deployment) do not have to use a wallet or connect to any blockchain.

In the current exercise we run two of the above components within separate docker containers: one to run a blockchain (a local RSKJ node) and another to serve Remix. We then connect to these services as before — through a browser (with a wallet) on the host machine. I used Google Chrome with Nifty wallet extension enabled.

A Ubuntu 20.04 LTS machine served as the host system. I used a docker image with Ubuntu 18.04 LTS base for both containers. The process is quite straightforward and largely follows instructions from respective docs (RSKJ and Remix).

Steps in brief

Follow these instructions to install RSKJ. Start the node in regtest mode
Follow these instructions to install Remix IDE. Start the service.
Enable a wallet extension in your browser. Connect wallet to the local RSK blockchain (custom RPC endpoint, with CORS enabled)
Use [JSON RPC] to fund the account in the wallet so we can pay for gas costs of deploying contracts from Remix

#use eth_accounts() to
#find out pre-funded accounts on the node (regtest)curl localhost:4444     -X POST     -H "Content-Type: application/json"     --data '{"jsonrpc":"2.0","method":"eth_accounts","params": [],"id":1}' #use eth_sendTransaction() to fund the wallet account#change "to", "from", "value" as neededcurl localhost:4444 -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_sendTransaction","params":[{"from":"0xcd2a3d9f938e13cd947ec05abc7fe734df8dd826","to": "0xf87594Cb9036302G1081753D2d6D4Fb7e9127Ac5","gas":"0x76c0","gasPrice": "0x9184e72a000","value": "0xb6255df5f50080000","data": "0x"}],"id":1}'

Now we can use our own Remix service to compile and deploy contracts on our own local (experimental) blockchain.

Steps in more detail

Note: Depending on your user account (user id), you may need to use sudo when installing.

Install RSKJ

RSKJ is a Java implementation of an RSK node. Use the general steps described here or this reproducible build. Some steps are reproduced here for convenience. I suggest you follow those from source links as they are more likely to be up to date. Binaries are also available for some systems. An x64 system, with at least 2 cores and 8GB RAM is recommended.

apt-get update -y && \
    apt-get install -y git curl gnupg openjdk-8-jdk && \
    rm -rf /var/lib/apt/lists/* && \
    apt-get autoremove -y && \
    apt-get cleangpg --keyserver https://secchannel.rsk.co/release.asc --recv-keys 1A92D8942171AFA951A857365DECF4415E3B8FA4
gpg --finger 1A92D8942171AFA951A857365DECF4415E3B8FA4# clone the project into a local directory
git clone --single-branch --depth 1 --branch PAPYRUS-2.1.0 https://github.com/rsksmart/rskj.git /code/rskj# switch to the directory
cd /code/rskj
gpg --verify SHA256SUMS.asc
sha256sum --check SHA256SUMS.asc#run the config script, changing persmission with chmod +x as needed
./configure.sh# build the project, automated tests can be run later if desired
./gradlew clean build -x test
#The built JARS will be in the directory `rskj-core/build/libs/`
# For a quick check of the installation, we can start the node in `regtest` mode.java -cp rskj-core/build/libs/rskj-core-2.1.0-SNAPSHOT-all.jar co.rsk.Start --regtest

Cross Origin Resource Sharing: In order to connect to the node from a browser based wallet, we should run the node with CORS enabled. See node configuration for details. One way to do this is to start a node with this option (instead of the one above)

java -cp rskj-core/build/libs/rskj-core-2.1.0-SNAPSHOT-all.jar  -Drpc.providers.web.cors=* co.rsk.Start --regtest

If the node starts normally, then there will be no messages. This can seem odd the first time. But the node is working! It can be accessed via http://localhost:4444 from another terminal attached to the container. This is also the URL to use for custom RPC endpoint for browser wallets.

Test the node with a JSON remote procedure call (RPC) using curl such as

curl localhost:4444/1.1.0/ -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

the response should be something like

{"jsonrpc":"2.0","id":1,"result":"0x10b"}

For later use, forward the port from docker container to host machine. Using an environment such as Visual Studio Code — with extensions for docker — makes this really simple.

Install Remix IDE

Remix IDE is open source with installation instructions here. There is a desktop version available as well (that I have not tested).

Assuming we already have curl, git, wget, yarn etc installed. Run commands with sudo as needed.

# Install a recent version of node from debsource .. 
curl -sL https://deb.nodesource.com/setup_15.x -o nodesource_setup.sh# make it executable and execute
bash chmod +x node*.sh# Install the nx CLI
npm install -g @nrwl/cli # to enable nx executable commands# Install Yarn package manager
curl -sL https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add - echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.listapt-get update && sudo apt-get install yarn# Clone the Remix repo (needs wget)
apt-get install wgetgit clone https://github.com/ethereum/remix-project.gitcd remix-project# install and serve
npm install
nx build remix-ide --with-deps
nx serve

If using docker, forward the port so we can access the service from browser on host machine.