Error: Cannot find external module "buffer" - what to do?

[dckc]

In hindley-milner-systems/dapp-ertp-airdrop#72 (comment) , we see

Error {
    message: 'Cannot find external module "buffer" in package file:///Users/tgreco/merkle-airdrop-resources/dapp-ertp-airdrop/node_modules/merkletreejs/',
}

What's going on? What do we do?

cc @tgrecojs @Jovonni

[dckc]

Buffer is a Node.js host API...

The conventional globals defined by browser or Node.js hosts are not available by default... Buffer ...
-- Hardening JavaScript: Limiting Globals with Compartments

I think npm has a number of libraries that provide the buffer API in a browser context. Some of them are probably suitable for use in contracts. @Jovonni I wonder if you have a favorite?

@kriskowal I wonder if an @endo/buffer API would be cost-effective.

[tgrecojs]

With a bit of digging, i've traced the string Cannot find external module <package name> back to @endo/compartment-mapper. Here's a link to all files that mention it.

[dckc]

Yes, the compartment mapper is correctly complaining that the merkletreejs package refers to a buffer package:

import { Buffer } from 'buffer'

-- https://github.com/merkletreejs/merkletreejs/blob/13b886e0f02c5b90369e5bf0f539aa3fdc769f8b/src/MerkleTree.ts#L1

but it does not declare a dependency on any such package:

  "dependencies": {
    "bignumber.js": "^9.0.1",
    "buffer-reverse": "^1.0.1",
    "crypto-js": "^4.2.0",
    "treeify": "^1.1.0",
    "web3-utils": "^1.3.4"
  },

-- https://github.com/merkletreejs/merkletreejs/blob/13b886e0f02c5b90369e5bf0f539aa3fdc769f8b/package.json#L87-L93

The merkletreejs package assumes the Node.js buffer host API. That Node.js host API is not provided by the Agoric smart contract runtime.