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Capi

Capi is a framework for crafting interactions with Substrate chains. It consists of a development server and fluent API, which facilitates multichain interactions without compromising either performance or ease of use.

Installation

npm i capi
Deno Equivalent

import_map.json

{
  "imports": {
    "capi": "https://deno.land/x/capi/mod.ts",
    "capi/nets": "https://deno.land/x/capi/nets/mod.ts"
  }
}

Configuration

Create a nets.ts and specify the chains with which you’d like to interact.

import { bins, net } from "capi/nets"

const bin = bins({ polkadot: ["polkadot", "v0.9.38"] })

// A Polkadot development network
export const polkadotDev = net.dev({
  bin: bin.polkadot,
  chain: "polkadot-dev",
})

// The Polkadot relay chain
export const polkadot = net.ws({
  url: "wss://rpc.polkadot.io/",
  targets: { dev: polkadotDev },
})

Command Line Tool

In this documentation, we use Capi’s CLI via the alias “capi”, instead of via its full path:

./node_modules/.bin/capi
Deno Equivalent 
deno run -A https://deno.land/x/capi/main.ts

Codegen Chain-specific APIs

capi sync node
Deno Equivalent 
capi sync deno

Build Tool Integration

If you use a build tool such as Vite or Webpack during development, you’ll need to configure two environment variables.

vite.config.ts example 
import { defineConfig } from "vite"

export default defineConfig({
  define: {
    "process.env.CAPI_SERVER": process.env.CAPI_SERVER,
    "process.env.CAPI_TARGET": process.env.CAPI_TARGET,
  },
})
webpack.config.js example 
import webpack from "webpack"

export default {
  plugins: [
    new webpack.DefinePlugin({
      process: {
        env: {
          CAPI_SERVER: JSON.stringify(process.env.CAPI_SERVER),
          CAPI_TARGET: JSON.stringify(process.env.CAPI_TARGET),
        },
      },
    }),
  ],
}

At a Glance

Retrieve the first 10 entries from a storage map of Polkadot.

import { polkadot } from "@capi/polkadot"

const accounts = await polkadot.System.Account.entries({ limit: 10 }).run()

Development Networks

During development, we may want to swap out the underlying connection with that of a devnet. This can be achieved via targets — by specifying alternate targets in your nets.ts file, you can switch to them by wrapping your command with capi serve --target someTarget --. For example:

capi serve --target dev -- node main.js

Other examples:

  • capi serve --target dev -- npm run start
  • capi serve --target dev -- deno run -A ./main.ts

Running Examples

Within a fresh clone of this repository…

deno task sync # only needed once
deno task run examples/<example_path>

Rationale

In a likely future of specialized, interoperable chains, developers will need to make use of on-chain programs to satisfy varying use cases; the expertise required to interact with these on-chain programs is currently greater than that which should be expected of app developers. Does this mean that app developers must forgo integrating with this blossoming infrastructure? We think not; the open source community can use Capi to abstract over the atomics of the on-chain world. An interaction spanning several chains and dozens of methods can be described with a single Rune[^1].

As you read through this documentation, please consider use cases over which you might like to abstract; if you wish to add your use case to Capi’s standard library, please submit an issue.

Code of Conduct

Everyone interacting in this repo is expected to follow the code of conduct.

Contributing

Contributions are welcome and appreciated! Check out the contributing guide before you dive in.

License

Capi is Apache licensed.

[^1]: Rune is the unit of composition with which we model Capi programs.