Creating WebAssembly wrappers

In this guide, you will implement a custom Wasm wrapper.

Prerequisites

You'll need these dependencies installed globally own your machine before you begin:

• nvm
• yarn
• docker
• docker-compose

Setting up the template project

We'll use the Wasm wrapper template project as a starting point. Run:

```shell
npx polywrap create wasm assemblyscript my-wrapper
cd my-wrapper

Then install dependencies with:

nvm install && nvm use && yarn

Defining method types and fields

The ./src/schema.graphql file is where we define the types that your wrappers can have and fields on those types – this file controls the data that your wrappers can take and the data it can return.

Wrappers can import the methods and types of other deployed wrappers. We will now import the IPFS plugin wrapper by writing the import statement at the top of schema.graphql file:

#import { Module } into Ipfs from "wrap://ens/ipfs.polywrap.eth"

Add functions to get and set data to IPFS:

type Module {
  ...


getIpfsData(
    address: String!
    connection: Ethereum_Connection
  ): String!


setIpfsData(
    options: SetIpfsDataOptions!
    connection: Ethereum_Connection
  ): SetIpfsDataResult!
}


type SetIpfsDataOptions {
  address: String!
  data: String!
}


type SetIpfsDataResult {
  ipfsHash: String!
  txReceipt: String!
}

Implementing wrapper functions

In the ./src/index.ts file, import the new types we've defined:

import {
	...


  Ipfs_Module,
  Input_getIpfsData,
  Input_setIpfsData,
  SetIpfsDataResult,
} from './wrap';

Then implement the setIpfsData method:

export function setIpfsData(input: Input_setIpfsData): SetIpfsDataResult {
  // 1. Upload the data to IPFS
  const ipfsHash = Ipfs_Module.addFile({
    data: String.UTF8.encode(input.options.data),
  })


  // 2. Add the data's IPFS hash to SimpleStorage using `setHash(...)`
  const txReceipt = Ethereum_Module.callContractMethodAndWait({
    address: input.options.address,
    method: 'function setHash(string value)',
    args: [ipfsHash],
    connection: input.connection,
  })


  // 3. Return the result
  return {
    ipfsHash,
    txReceipt: txReceipt.transactionHash,
  }
}

And also the getIpfsData method:

export function getIpfsData(input: Input_getIpfsData): string {
  const hash = Ethereum_Module.callContractView({
    address: input.address,
    method: 'function getHash() view returns (string)',
    args: [],
    connection: input.connection,
  })


  return String.UTF8.decode(Ipfs_Module.catFile({ cid: hash }))
}

Run yarn build to confirm that this file can build successfully.