find the cached version that's closest to a given spec

index.js

'use strict'

const BB = require('bluebird')

const cacache = require('cacache')
const npa = require('npm-package-arg')
const pickManifest = require('npm-pick-manifest')
const ssri = require('ssri')

module.exports = cachedVersions
async function cachedVersions (cache, spec, opts) {
  spec = npa(spec)
  opts = opts || {}
  const registry = opts.registry || 'https://registry.npmjs.org'
  if (!spec.registry) {
    throw new Error('Only registry specs are supported')
  }
  let res
  try {
    res = await cacache.get(cache, `make-fetch-happen:request-cache:${
      registry
    }/${
      spec.escapedName
    }`)
  } catch (err) {
    if (err.code === 'ENOENT') { return null }
    throw err
  }
  const packument = JSON.parse(res.data.toString('utf8'))
  const versions = Object.keys(packument.versions)
  let bestMatch
  try {
    bestMatch = pickManifest(packument, spec.rawSpec)
  } catch (e) {
    if (e.code === 'ETARGET') {
      bestMatch = packument.versions[versions[versions.length - 1]]
    } else {
      throw e
    }
  }
  const bestMatchIdx = versions.indexOf(bestMatch.version)
  for (
    let i = 0;
    // If we haven't gone past the beginning
    (bestMatchIdx - i) > 0 ||
    // Or we haven't gone past the end
    (bestMatchIdx + i) < versions.length;
    i++
  ) {
    const back = packument.versions[versions[bestMatchIdx - i]]
    const forth = packument.versions[versions[bestMatchIdx + i]]
    const promises = []
    if (back) {
      promises.push(
        cacache.get.hasContent(cache, back.dist.integrity),
        cacache.get.hasContent(cache, ssri.fromHex(back.dist.shasum), 'sha1')
      )
    }
    if (forth) {
      promises.push(
        cacache.get.hasContent(cache, forth.dist.integrity),
        cacache.get.hasContent(cache, ssri.fromHex(forth.dist.shasum), 'sha1')
      )
    }
    if (!promises.length) { continue }
    try {
      const existing = await BB.some(promises, 1)
      return existing[0] && existing[0].sri.toString()
    } catch (e) {
      if (e instanceof BB.AggregateError) { continue }
      throw e
    }
  }
}

package.json

{
  "name": "nearest-cached-hash",
  "version": "0.0.0",
  "dependencies": {
    "ssri": "^5.0.0",
    "npm-pick-manifest": "^2.1.0",
    "npm-package-arg": "^6.0.0",
    "cacache": "^10.0.1"
  }
}