index.js

var lodashMap = require("lodash.map")
var lodashTrimStart = require("lodash.trimstart")
var lodashTrimEnd = require("lodash.trimend")
var assert = require("assert")

module.exports = function(options) {
  assert(options && typeof options.bucket === "string")
  var bucket = options.bucket
  var s3 =
    options.s3 || new (require("aws-sdk")).S3({ apiVersion: "2006-03-01" })

  return {
    ls: function ls(path) {
      var prefix = lodashTrimStart(lodashTrimEnd(path, "/") + "/", "/")
      var result = { files: [], folders: [] }

      function s3ListCheckTruncated(data) {
        result.files = result.files.concat(lodashMap(data.Contents, "Key"))
        result.folders = result.folders.concat(
          lodashMap(data.CommonPrefixes, "Prefix")
        )

        if (data.IsTruncated) {
          return s3
            .listObjectsV2({
              Bucket: bucket,
              MaxKeys: 2147483647, // Maximum allowed by S3 API
              Delimiter: "/",
              Prefix: prefix,
              ContinuationToken: data.NextContinuationToken
            })
            .promise()
            .then(s3ListCheckTruncated)
        }

        return result
      }

      return s3
        .listObjectsV2({
          Bucket: bucket,
          MaxKeys: 2147483647, // Maximum allowed by S3 API
          Delimiter: "/",
          Prefix: prefix,
          StartAfter: prefix // removes the folder name from listing
        })
        .promise()
        .then(s3ListCheckTruncated)
    }
  }
}