Add atomic pushView function

Author: mxstbr

README.md

@@ -2,7 +2,7 @@
 
 Public analytics as a Node.js microservice.
 
-With less than 50 lines of code this service is the smallest analytics you'll ever need. It does nothing except count the views of something and making the views accessible via an API.
+With less than 100 lines of code this service is the smallest analytics you'll ever need. It does nothing except count the views of something and making the views accessible via an API.
 
 (there is currently no frontend to consume the statistics, though writing one is on the to-do list)
 
@@ -39,10 +39,6 @@ This is how you'd track pageviews for a website: (though note that this can be u
 </script>
 ```
 
-## Gotchas
-
-Currently this uses promisified `level` for data storage, which doesn't have atomic operations. If you have a recommendation for a filesystem-based data storage module for Node that has atomic operations, please let us know!
-
 ## Contributing
 
 If you run `npm run dev` the server will restart every time you edit the code. Perfect for development of `micro-analytics`!

db.js

@@ -3,7 +3,7 @@ const promise = require('promise')
 
 const db = flatfile.sync('views')
 
-module.exports = {
+const promisifiedDb = {
   // Promisify async operations
   put: promise.denodeify(db.put.bind(db)),
   del: promise.denodeify(db.del.bind(db)),
@@ -14,3 +14,32 @@ module.exports = {
   keys: db.keys.bind(db),
   close: db.close.bind(db),
 }
+
+// Atomic view pushing method, can safely be called multiple times without the
+// db messing up.
+const pushView = async (key, view) => {
+  const locks = {}
+  await push()
+
+  async function push() {
+    if (locks[key]) return setImmediate(push)
+    locks[key] = true
+
+    let views
+    if (promisifiedDb.has(key)) {
+      views = promisifiedDb.get(key).views
+    } else {
+      views = []
+    }
+
+    try {
+      await promisifiedDb.put(key, { views: views.concat([view]) })
+      delete locks[key]
+    } catch (err) {
+      throw err
+    }
+  }
+}
+
+module.exports = exports = promisifiedDb
+exports.pushView = pushView

index.js

@@ -14,28 +14,14 @@ module.exports = async function (req, res) {
   }
   const shouldIncrement = query.inc !== 'false' && query.inc !== false
   try {
-    if (db.has(pathname)) {
-      const { views } = await db.get(pathname)
-      // Add a view and send the total views back to the client
-      if (shouldIncrement) {
-        views.push({ time: Date.now() })
-        await db.put(pathname, { views })
-      }
-      if (req.method === 'GET') {
-        send(res, 200, { views: views.length })
-      } else {
-        send(res, 200)
-      }
+    // Add a view and send the total views back to the client
+    if (shouldIncrement) {
+      await db.pushView(pathname, { time: Date.now() })
+    }
+    if (req.method === 'GET') {
+      send(res, 200, { views: db.get(pathname).views.length })
     } else {
-      // Initialise the page with one view
-      if (shouldIncrement) {
-        await db.put(pathname, { views: [{ time: Date.now() }] })
-      }
-      if (req.method === 'GET') {
-        send(res, 200, { views: shouldIncrement ? 1 : 0 })
-      } else {
-        send(res, 200)
-      }
+      send(res, 200)
     }
   } catch (err) {
     console.log(err)