reg/src/nodejs/loader.mjs

`reg` is a package manager for native ES Modules. It's built to enable dependency management for Universal JavaScript (JavaScript that can run in the Browser and in Node.js w/o a compiler).

import path from 'path'
import process from 'process'
import Module from 'module'
import fs from 'fs'
import { promisify } from 'util'
import { fileURLToPath } from 'url'

const require = Module.createRequire(import.meta.url)
const CID = require('cids')
const { local } = require('./storage.js')
const createTypes = require('./types.js')
const mkdirp = promisify(require('mkdirp'))

const { readFile } = fs.promises
const __filename = fileURLToPath(import.meta.url)
const __dirname = path.dirname(__filename)

const builtins = Module.builtinModules
const JS_EXTENSIONS = new Set(['.js', '.mjs'])

const baseURL = new URL(`${process.cwd()}/`, 'file://')

const store = local()
const types = createTypes({getBlock: store.get})
const cache = path.join(process.env.HOME, '.reg', 'deflate')

const { createWriteStream } = fs

let globals = {}

export async function resolve (specifier, parentModuleURL = baseURL, defaultResolve) {
  if (specifier.startsWith('@') || specifier.startsWith('@')) {
    throw new Error("Unsupported: The Node.js ESM loader has bugs in loader IO so we can't yet do dynamic loading")
  } else if (specifier.startsWith('/@reg/')) {
    const stage = parentModuleURL.slice(0, parentModuleURL.lastIndexOf('/'))
    let filename = specifier.slice('/@reg/'.length)
    return { url: stage + '/' + filename, format: 'module' }
  } else {
    if (!specifier.startsWith('./') &&
        !specifier.startsWith('../') &&
        !specifier.startsWith('/') &&
        !specifier.startsWith('file://')){
      throw new Error(`Unknown import: "${specifier}`)
    }
    let url = specifier.startsWith('file://') ? specifier : 'file://' + specifier
    return { url, format: 'module' }
    throw new Error("not implemented")
  }

  /* Fallback */
  if (builtins.includes(specifier)) {
    return {
      url: specifier,
      format: 'builtin'
    }
  }
  if (/^\.{0,2}[/]/.test(specifier) !== true && !specifier.startsWith('file:')) {
    // For node_modules support:
    // return defaultResolve(specifier, parentModuleURL);
    throw new Error(
      `imports must begin with '/', './', or '../'; '${specifier}' does not`)
  }
  const resolved = new URL(specifier, parentModuleURL)
  const ext = path.extname(resolved.pathname)
  if (!JS_EXTENSIONS.has(ext)) {
    throw new Error(
      `Cannot load file with non-JavaScript file extension ${ext}.`)
  }
  return {
    url: resolved.href,
    format: 'module'
  }
}