Substrate API playground in a Deno 🦕 repl, using Polkadot.js extension wallet as remote signer ✍️. Say goodbye to hardcoded mnemonics / seeds in dev scripts 👋!

Subshell at its core is a TypeScript repl with these preloaded lines:

import {
  ApiPromise,
  WsProvider,
} from "https://deno.land/x/polkadot@0.0.3/api/mod.ts";

const provider = new WsProvider(`wss://polkadot.api.onfinality.io/public-ws`);

const api = await ApiPromise.create({ provider });

In addition, it supports signing with your Polkadot.js wallet extension when accessed from the web ui. ✨

Use Subshell.extension.selectAccount() to show an account selection prompt:

Calls to api.sign, tx.signAndSend are proxied to your browser wallet extension:

Visiting homepage will connect you to Polkadot.

Use one of the following links to connect to a different chain:
Polkadot | Kusama | Moonbeam | Acala | Litentry | Parallel | Phala | Aleph Zero | Darwinia | ChainX | Edgeware | NFTMart | ...

Read the cheatsheet to get a basic idea of how to use the repl.

Maintainers of Polkadot.js libraries have made a preview release for Deno under the deno.land/x/polkadot namespace.

You can import them like this in the Deno repl:

import { stringToU8a } from 'https://deno.land/x/polkadot@0.0.3/util/mod.ts';

Subshell sessions run in patched denoland/deno to provide better repl experience. The frontend is based on polkadot-js/apps. The modified code will be published soon.

As a long term *nix user who does distro hopping from time to time, I often see (para)chains in the DotSama ecosystem as distros of Parity/Substrate, in the same sense that Arch, Debian, Gentoo, chromeOS and Android are different flavors of GNU/Linux.

(Guess which Linux distro I use the most?)

Taking the analogy a step further, in Linux based systems, once you have mastered the art of shell scripting, it becomes easy to switch between distros.

Likewise, if you are familiar with the Polkadot.js api, you will quickly learn how to play with new chains based on Substrate when they come out.

For the Linux kernel, we have a lot of shells: bash, zsh, fish, ash, dash, csh, ksh, etc. , in which we interactively type commands to perform various kinds of tasks.

While for Substrate, has there been anything like a shell? Yes, quite a few on the Node.js runtime, but at the same time they all feel somewhat lacking to me.

Reasons:

• You cannot add new imports on demand from a Node.js repl. You have to npm install or add them to your local NODE_PATH first.
• It's painful to deal with cjs / esm incompatibility.
• Hard coding mnemonics / seeds in scripts could lead to potential leak.
• None of those projects are actively maintained. Polkadot.js libraries version are out of date
• Node.js is not cool any more. It got rejected by its original creator.

Subshell is trying to avoid aforementioned problems by leveraging the power of Deno, a modern runtime for JavaScript and TypeScript.

Here are Subshell's advantages over existing Node.js based shells.

• Available as a web app, no installation required
• One click away from a drop-in dev terminal in browser

• Works out of the box with most chains in the DotSama ecosystem
• Plays nice with existing projects, like Substrate Playground. For example: use https://subshell.xyz/?rpc=wss://btwiuse.playground.substrate.dev/wss to connect to my playground dev node.
• --compat is turned on by default, so you can still use built-in modules from Node.js
• Added patches to improve the repl experience. The runtime is kept inact. Any Subshell scripts are also valid Deno scripts

In fact, you can load the Subshell init script in Deno.

$　deno repl --unstable --compat --eval-file=https://deno.land/x/subshell@0.0.3-7/init.ts
...
Deno 1.23.2
exit using ctrl+d or close()
> api.tx. # Here tab completion won't show up

But it won't tab complete in some circumstances (see denoland/deno#14967). Subshell used a custom patch to fix that. Plus you lose the ability to sign messages / transactions with browser wallet extension. So the recommend way is to access Subshell from the web ui.

• You can override the init script (soon)
• Custom types can be added the same way in Polkadot.js Apps
• You can easily load your custom scripts to decorate the api, in the way you want. For example: HackathonApi

• The decentralized nature of Deno's package import system allows you to load dependencies from url in the repl. You are not limited to deno.land/std, deno.land/x. The only limit is your imagination.

• Sign messages / transactions with Polkadot.js wallet extension. Never make keys leave your wallet again!
• Filesystem / network access can be disabled when you run scripts written by untrusted parties, thanks to sandboxing in Deno

At first glance, you might think that the Deno repl is running directly inside your browser. That's only an illusion. In fact, there are three parties involved in a Subshell session:

• 🦕: Deno (Rust)
• 🕸️: Relay server (Golang)
• 🌐: Frontend web ui (TypeScript)

First, Deno is running as a remote process on a worker container, inside a Pod on Kubernetes, with a persistent bidirectional JSON RPC connection over WebSocket to the relay server.

🦕⇆🕸️

Once you open the web ui from your browser, it will similarly establish a connection to the relay.

🌐⇆🕸️

These two connections are then spliced together by the relay server,

🌐⇆🕸️⇆🦕

creating an illusion that your browser is directly connected to Deno, full duplex:

🌐⇆⇆🦕

In full duplex communication, both ends can send and receive data to the other end at the same time.

Since both ends speak JSON RPC, the browser 🌐 can invoke methods available on the Deno 🦕 side, and vice versa.

You might ask, when could the browser 🌐 become a server? And how is this useful? That is covered in the next section.

When Subshell starts, the api object is created from the Deno repl context.

With an api object, you can query on-chain data using api.consts.*.*, api.query.*.* etc.

But it becomes clumsy when you want to send transactions with api.tx.*.*, because api does not come with a default signer.

What if you want to sign data with your own keys?

In your local dev environment it's fine to create a keyring, import your mnemonics / seed and set it as the signer:

import { Keyring } from '@polkadot/api';

// Create a keyring instance
const keyring = new Keyring({ type: 'sr25519' });

// Add an account
const alice = keyring.addFromUri('//Alice');

// Set default signer
api.setSigner(alice)

But keep in mind:

1. Private keys are supposed to be private.
2. Subshell is running in the cloud.
3. The cloud is just someone else's computer.

Therefore, you should never import your keys to Subshell.

Is there any approach to secure signing in an untrusted environment? Fortunately, there is a workaround.

Thanks to the work started by Ian He in polkadot-js/api#660, the Signer is now an interface, and the polkadot.js extension provides an implementation to it.

We can expose the implementation through the browser 🌐 side JSON RPC server, and use RemoteSignerBridge as the Signer implementation in Deno 🦕 repl context, where signing requests will be forwarded to the wallet extension via JSON RPC calls.

Pseudocode:

class RemoteSignerBridge implements Signer {
  signPayload (payload: SignerPayloadJSON) => Promise<SignerResult> {
    return jsonRpcClient.signPayload(payload)
  }
  signRaw (raw: SignerPayloadRaw) => Promise<SignerResult> {
    return jsonRpcClient.signRaw(raw)
  }
  ...
}

api.setSigner(new RemoteSignerBridge())

By applying this technique, you can safely do api.sign, api.tx.*.*.signAndSend in the remote Deno 🦕 repl, and sign it with the Polkadot.js wallet extension in your browser🌐.

No, it doesn't. The repl is running in a remote worker, not in our brower.

Currently no, but it's on the roadmap.

Yes. It is currently implemented as a module in btwiuse/k0s (Golang). I'm planning on porting it to Deno/TypeScript. I will probably borrow some ideas from the old paritytech/substrate-telemetry backend.

I will make an all-in-one Docker image that hold everything in one place. It should will be available soon. Stay tuned.

• https://github.com/halva-suite/halva
• https://github.com/cennznet/cli
• https://github.com/compound-finance/gateway/tree/develop/chains
• https://github.com/cryptolab-network/polkadot-api-cli

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