add remote datastore

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 testdb
+localdb

fetch.js

@@ -0,0 +1 @@
+module.exports = window.fetch

package.json

@@ -21,6 +21,7 @@
   "devDependencies": {
     "coveralls": "^3.0.0",
     "documentation": "^6.1.0",
+    "fs-extra": "^5.0.0",
     "level-browserify": "^1.1.2",
     "nyc": "^11.6.0",
     "standard": "^11.0.1",
@@ -29,9 +30,13 @@
   "dependencies": {
     "borc": "git+https://github.com/dignifiedquire/borc.git#fix/nested-array",
     "ipld-graph-builder": "^1.3.8",
+    "node-fetch": "^2.1.2",
     "text-encoding": "^0.6.4",
     "uint1array": "^1.0.5"
   },
+  "browser": {
+    "node-fetch": "./fetch.js"
+  },
   "standard": {
     "ignore": [
       "/benchmark/"

remoteDatastore.js

@@ -0,0 +1,52 @@
+const Buffer = require('safe-buffer').Buffer
+const TreeDAG = require('./datastore.js')
+const fetch = require('node-fetch')
+
+module.exports = class RemoteTreeDAG extends TreeDAG {
+  /**
+   * @param dag {object} a level db instance
+   * @param remoteOpts
+   * @param remoteOpts.uri {string} the HTTP uri which has an interface: GET /:key -> value
+   * @param remoteOpts.encoding {string} the encoding of the reponse
+   * @param opts.decoder {object} a cbor decoder
+   */
+  constructor (dag, remoteOpts, decoder) {
+    super(dag, decoder)
+    this.remoteOpts = Object.assign({
+      uri: null,
+      encoding: 'base64'
+    }, remoteOpts)
+  }
+
+  async get (link) {
+    try {
+      return await super.get(link)
+    } catch (e) {
+      if (this.remoteOpts.uri) {
+        await this.fetchRemote(link)
+        return super.get(link)
+      }
+    }
+  }
+
+  fetchRemote (key) {
+    if (!Buffer.isBuffer(key)) {
+      key = Buffer.from(key.buffer)
+    }
+
+    const route = `${this.remoteOpts.uri}/${key.toString('hex')}`
+    return fetch(route)
+      .then(res => res.text())
+      .then(text => {
+        const encoded = Buffer.from(text, this.remoteOpts.encoding)
+        return new Promise((resolve, reject) => {
+          this._dag.put(key, encoded.toString('hex'), () => {
+            resolve(key)
+          })
+        })
+      })
+      .catch(err => {
+        console.warn(`error fetching ${route}:`, err.message)
+      })
+  }
+}

tests/index.js

@@ -1,7 +1,10 @@
+const fs = require('fs-extra')
 const tape = require('tape')
 const crypto = require('crypto')
 const level = require('level-browserify')
 const RadixTree = require('../')
+const RemoteDataStore = require('../remoteDatastore')
+const remote = require('./remote')
 const db = level('./testdb')
 
 tape('root existance', async t => {
@@ -203,3 +206,34 @@ tape('random', async t => {
 
   t.end()
 })
+
+tape('remote', async t => {
+  // remote
+  const remoteTree = new RadixTree({
+    db: db
+  })
+  const server = remote.listen(db)
+
+  const entries = 100
+  for (let i = 0; i < entries; i++) {
+    const key = crypto.createHash('sha256').update(i.toString()).digest().slice(0, 20)
+    remoteTree.set(key, Buffer.from([i]))
+  }
+  const stateRoot = await remoteTree.flush()
+
+  // local
+  fs.removeSync('./localdb')
+  const localTree = new RadixTree({
+    dag: new RemoteDataStore(level('./localdb'), {uri: 'http://localhost:3000'})
+  })
+  localTree.root = stateRoot
+
+  for (let i = 0; i < entries; i++) {
+    const key = crypto.createHash('sha256').update(i.toString()).digest().slice(0, 20)
+    const value = await localTree.get(key)
+    t.equals(value.value[0], i)
+  }
+
+  server.close()
+  t.end()
+})

tests/remote.js

@@ -0,0 +1,26 @@
+const RadixTree = require('../')
+
+const cbor = require('borc')
+const http = require('http')
+
+let tree
+
+const server = http.createServer(async (req, res) => {
+  const key = Buffer.from(req.url.slice(1), 'hex')
+  const value = await tree.graph._dag.get(key)
+  res.end(cbor.encode(value).toString('base64'))
+})
+
+module.exports = {
+  listen: (db, port = 3000) => {
+    server.listen(port, (err) => {
+      if (err) { return console.error(err) }
+
+      tree = new RadixTree({db})
+
+      console.log(`server is listening on ${port}`)
+    })
+
+    return server
+  }
+}