Getting started with Ethereum: connecting geth, Remix and Metamask for local development

#blockchain #ethereum #solidity #web3

What I thought would have been an easy task turned out to be a good challenge.

I'm just getting started with Ethereum and Solidity development, I know that there are frameworks out there that can help you get started faster, but for me, it's also quite important to understand what is going on behind the scenes before moving to a framework that abstracts those things away.

My goal was:

run an Ethereum node locally
connect a wallet to my local node, so I can see what's going on
deploy a "test" smart contract

In the end, I chose geth as the Ethereum node, Metamask as the wallet and Remix as the tool to help me deploy a smart contract.

I'm not going to enter the merit about I chose those tools above, they just seem reasonably good at first glance, and most of them are often mentioned in tutorials out there

The challenge here was to connect those things together. Since there's no framework behind it, you have to figure out some things on your own.

The first step is to run geth with the appropriate configuration for development.

Geth

You can run geth in development mode by following the steps mentioned here however, it's not clear how to connect to other tools like Metamask.

I ended up running geth with the following options:

--datadir: location for the database and keystores, avoids losing the state when restarting geth
--dev: changes geth to "local" mode, it does not connect to external nodes and also bootstraps an account with eth
--http: enables HTTP server
--http.api web3,eth,debug,personal,net: enables the following APIs via HTTP - safe for development only
--ws: enables websockets server
--ws.api web3,eth,debug,personal,net: enables the following APIs via websockets - again, safe only for development
--vmdebug: enable debugging
--http.corsdomain: enable requests to the geth process via HTTP only for some specific domains.

The full command will depend on the URL of the Metamask in your browser.

Getting the Metamask URL

Metamask is not obligatory to develop locally, but if you're getting started (like me), it helps you understand some basic concepts.

To connect Metamask to your local geth, you need to add the URL of the browser extension. To get the URL:

Open the Metamask extension (this will show a popup in the browser)
Click on the three dots next to your account and "expand view", this will open a new tab/window.
Copy the URL of the new window. If you're using Firefox, it may look like this: moz-extension://aaac9e04-2a0d-45a8-bb45-7ad026ae5536

The full command

I prefer to start geth node together with the console on, to do that, run:

geth --datadir geth-test-chain-dir \
     --dev \
     --http \
     --http.corsdomain "https://remix.ethereum.org,moz-extension://aaac9e04-2a0d-45a8-bb45-7ad026ae5536" 
     --http.api web3,eth,debug,personal,net \
     --ws \
     --ws.api web3,eth,debug,personal,net \
     --vmdebug \
     console

To check if everything is running correctly, you can run on the console:

> eth.accounts
["0xaaa..."]

Connecting Metamask

To connect your local geth to Metamask, you need to change it to use the "test networks".

Click on the dropdown next to your account icon and choose "Localhost 8545". If you don't see it, you need to change the settings to display "test networks".

Note: sometimes it takes a while to connect. Usually after a refresh of the Metamask extension page a few times it works, but sometimes closing and opening the browser helps.

Test transaction

If you started geth in dev mode together with console, you can run:

> personal.newAccount()

This will prompt for a passphrase, remember that.

After that, you can transfer some eth:

> eth.accounts[1]
"0xaaa..."
> eth.sendTransaction({from: eth.coinbase, to: eth.accounts[1], value: web3.toWei(1, "ether")})

This will send 1 ETH from the default account created by development mode to the newly created account (you can also use the string address instead of the array position).

You can now import this account into Metamask.

Click on the account icon and choose "Import Account".
Choose the JSON type for import and upload the file from your geth-test-chain-dir/keystore/...aaa...
Put the passphrase you typed in the prompt before

You now should see the account you just created with 1 ETH. If something is not working correctly:

make sure you're connected to Localhost node
make sure you're importing the proper JSON file, there might be two or more files
make sure you're using the correct passphrase

That's it, good luck!