[1.0] Replace using levelup for caching with lowdb to avoid native de…

…pendency (#1142)

* Replace leveldb with lowdb to avoid native dependency

* Add missing slash

packages/gatsby/package.json

@@ -56,9 +56,10 @@
     "joi": "^9.1.1",
     "json-loader": "^0.5.2",
     "json5": "^0.5.0",
-    "level": "^1.6.0",
     "loader-utils": "^0.2.16",
     "lodash": "^4.17.4",
+    "lodash-id": "^0.14.0",
+    "lowdb": "^0.16.2",
     "markdown-it": "^7.0.1",
     "md5-file": "^3.1.1",
     "mime": "^1.3.4",

packages/gatsby/src/cache-dir/app.js

@@ -1,10 +1,12 @@
 const apiRunner = require(`./api-runner-browser`)
-// Let the site/plugins run code very early.
-apiRunner(`onClientEntry`)
 
 import React from "react"
 import ReactDOM from "react-dom"
 import { AppContainer as HotContainer } from "react-hot-loader"
+window.___emitter = require(`./emitter`)
+
+// Let the site/plugins run code very early.
+apiRunner(`onClientEntry`)
 
 /**
  * Service Workers are persistent by nature. They stick around,

packages/gatsby/src/cache-dir/root.js

@@ -15,7 +15,6 @@ import ComponentRenderer from "./component-renderer"
 import loader from "./loader"
 loader.addPagesArray(pages)
 loader.addDevRequires(syncRequires)
-
 window.___loader = loader
 
 const history = createHistory()

packages/gatsby/src/utils/__tests__/cache.js

@@ -0,0 +1,13 @@
+const cache = require(`../cache`)
+cache.initCache()
+
+describe(`site cache`, () => {
+  it(`can set and get cache items`, async () => {
+    await cache.set(`a key`, `value`)
+    await cache.set(`a boolean key`, true)
+    const value = await cache.get(`a key`)
+    const value2 = await cache.get(`a boolean key`)
+    expect(value).toBe(`value`)
+    expect(value2).toBe(true)
+  })
+})

packages/gatsby/src/utils/cache.js

@@ -1,44 +1,46 @@
-let levelup
-if (process.env.NODE_ENV !== `test`) {
-  levelup = require(`level`)
-}
 const Promise = require(`bluebird`)
+const low = require(`lowdb`)
 const fs = require(`fs-extra`)
 
 let db
 exports.initCache = () => {
   fs.ensureDirSync(`${process.cwd()}/.cache/cache`)
+  let directory
   if (process.env.NODE_ENV === `test`) {
-    db = {
-      get: () => false,
-      set: () => false,
-    }
+    directory = require(`os`).tmpdir()
   } else {
-    db = levelup(`${process.cwd()}/.cache/cache`, {
-      keyEncoding: `json`,
-      valueEncoding: `json`,
-    })
+    directory = process.cwd() + `/.cache/cache`
   }
+  db = low(`${directory}/site-cache.json`, {
+    storage: require("lowdb/lib/storages/file-async"),
+    format: {
+      serialize: obj => JSON.stringify(obj),
+      deserialize: str => JSON.parse(str),
+    },
+  })
+  db._.mixin(require("lodash-id"))
+
+  db.defaults({ keys: [] }).write()
 }
 
 exports.get = key =>
   new Promise((resolve, reject) => {
-    db.get(key, (err, value) => {
-      if (err && !err.notFound) {
-        reject(err)
-      } else {
-        resolve(value)
-      }
-    })
+    let pair
+    try {
+      pair = db.get(`keys`).getById(key).value()
+    } catch (e) {
+      // ignore
+    }
+
+    if (pair) {
+      resolve(pair.value)
+    } else {
+      resolve()
+    }
   })
 
 exports.set = (key, value) =>
   new Promise((resolve, reject) => {
-    db.put(key, value, err => {
-      if (err) {
-        reject(err)
-      } else {
-        resolve(`OK`)
-      }
-    })
+    db.get(`keys`).upsert({ id: key, value }).write()
+    resolve(`Ok`)
   })