Add note export function

This function is the first step to get out data following GDPR about the
transportability of data.

Details: https://gdpr-info.eu/art-20-gdpr/
Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

lib/web/userRouter.js

@@ -1,5 +1,7 @@
 'use strict'
 
+const archiver = require('archiver')
+const async = require('async')
 const Router = require('express').Router
 
 const response = require('../response')
@@ -64,6 +66,60 @@ UserRouter.get('/me/delete/:token?', function (req, res) {
   }
 })
 
+// export the data of the authenticated user
+UserRouter.get('/me/export', function (req, res) {
+  if (req.isAuthenticated()) {
+    // let output = fs.createWriteStream(__dirname + '/example.zip');
+    let archive = archiver('zip', {
+      zlib: { level: 3 } // Sets the compression level.
+    })
+    res.setHeader('Content-Type', 'application/zip')
+    res.attachment('archive.zip')
+    archive.pipe(res)
+    archive.on('error', function (err) {
+      logger.error('export user data failed: ' + err)
+      return response.errorInternalError(res)
+    })
+    models.User.findOne({
+      where: {
+        id: req.user.id
+      }
+    }).then(function (user) {
+      models.Note.findAll({
+        where: {
+          ownerId: user.id
+        }
+      }).then(function (notes) {
+        let list = []
+        async.each(notes, function (note, callback) {
+          let title
+          let extension = ''
+          do {
+            title = note.title + extension
+            extension++
+          } while (list.indexOf(title) !== -1)
+
+          list.push(title)
+          logger.debug('Write: ' + title + '.md')
+          archive.append(Buffer.from(note.content), { name: title + '.md', date: note.lastchangeAt })
+          callback(null, null)
+        }, function (err) {
+          if (err) {
+            return response.errorInternalError(res)
+          }
+
+          archive.finalize()
+        })
+      })
+    }).catch(function (err) {
+      logger.error('export user data failed: ' + err)
+      return response.errorInternalError(res)
+    })
+  } else {
+    return response.errorForbidden(res)
+  }
+})
+
 UserRouter.get('/user/:username/avatar.svg', function (req, res, next) {
   res.setHeader('Content-Type', 'image/svg+xml')
   res.setHeader('Cache-Control', 'public, max-age=86400')