Basic happy path

client.js

@@ -0,0 +1,53 @@
+const { once } = require('events')
+const ReadyResource = require('ready-resource')
+const safetyCatch = require('safety-catch')
+const RPC = require('protomux-rpc')
+const { MetricsReplyEnc } = require('dht-prom-client/lib/encodings')
+
+class ScraperClient extends ReadyResource {
+  constructor (dht, promClientPublicKey) {
+    super()
+
+    this.dht = dht
+    this.key = promClientPublicKey
+    this.rpc = null
+    this.socket = null
+  }
+
+  async _open () {
+    // TODO: auto reconnect
+    // TODO: retry on failure
+    // TODO: define a keepAlive
+    // TODO: handle error paths (peer not available etc)
+    this.socket = this.dht.connect(this.key)
+    this.socket.on('error', safetyCatch)
+
+    await this.socket.opened
+
+    if (!this.socket.connected) {
+      throw new Error('Could not open socket')
+    }
+
+    this.rpc = new RPC(this.socket, { protocol: 'prometheus-metrics' })
+    await once(this.rpc, 'open')
+  }
+
+  async _close () {
+    this.rpc?.destroy()
+    this.socket?.destroy()
+  }
+
+  async lookup () {
+    if (!this.opened) await this.ready()
+
+    const res = await this.rpc.request(
+      'metrics',
+      null,
+      { responseEncoding: MetricsReplyEnc }
+    )
+
+    return res
+  }
+}
+
+module.exports = ScraperClient

index.js

@@ -0,0 +1,70 @@
+const ScraperClient = require('./client')
+const ReadyResource = require('ready-resource')
+const idEnc = require('hypercore-id-encoding')
+const b4a = require('b4a')
+const safetyCatch = require('safety-catch')
+
+class PrometheusDhtBridge extends ReadyResource {
+  constructor (dht, server) {
+    super()
+
+    this.dht = dht
+
+    this.server = server
+    this.server.get(
+      '/scrape/:alias/metrics',
+      { logLevel: 'info' },
+      this._handleGet.bind(this)
+    )
+
+    this.aliases = new Map() // alias->scrapeClient
+  }
+
+  get publicKey () {
+    return this.dht.defaultKeyPair.publicKey
+  }
+
+  async _close () {
+    await Promise.all([
+      [...this.aliases.values()].map(a => a.close())
+    ])
+  }
+
+  putAlias (alias, targetPubKey) {
+    targetPubKey = idEnc.decode(idEnc.normalize(targetPubKey))
+    const current = this.aliases.get(alias)
+
+    if (current) {
+      if (b4a.equals(current.key, targetPubKey)) {
+        return // Idempotent
+      }
+
+      current.close().catch(safetyCatch)
+    }
+
+    const scrapeClient = new ScraperClient(this.dht, targetPubKey)
+    this.aliases.set(alias, scrapeClient)
+  }
+
+  async _handleGet (req, reply) {
+    const alias = req.params.alias
+
+    const scrapeClient = this.aliases.get(alias)
+
+    if (!scrapeClient) {
+      // TODO: 404 code
+      throw new Error('Unkown alias')
+    }
+
+    if (!scrapeClient.opened) await scrapeClient.ready()
+
+    const res = await scrapeClient.lookup()
+    if (res.success) {
+      reply.send(res.metrics)
+    } else {
+      // TODO:
+    }
+  }
+}
+
+module.exports = PrometheusDhtBridge

package.json

@@ -4,7 +4,7 @@
   "description": "Bridge to scrape Prometheus metrics exposed over hyperdht",
   "main": "index.js",
   "scripts": {
-    "test": "standard"
+    "test": "standard && brittle test.js"
   },
   "repository": {
     "type": "git",
@@ -24,6 +24,18 @@
   },
   "homepage": "https://github.com/HDegroote/dht-prometheus#readme",
   "devDependencies": {
+    "axios": "^1.7.2",
+    "brittle": "^3.5.2",
+    "hyperdht": "^6.15.1",
+    "prom-client": "^15.1.2",
     "standard": "^17.1.0"
+  },
+  "dependencies": {
+    "dht-prom-client": "^0.0.1-alpha.1",
+    "fastify": "^4.28.0",
+    "hypercore-id-encoding": "^1.3.0",
+    "protomux-rpc": "^1.5.2",
+    "ready-resource": "^1.1.1",
+    "safety-catch": "^1.0.2"
   }
 }

test.js

@@ -0,0 +1,72 @@
+const test = require('brittle')
+const PrometheusDhtBridge = require('./index')
+const promClient = require('prom-client')
+const DhtPromClient = require('dht-prom-client')
+const createTestnet = require('hyperdht/testnet')
+const HyperDHT = require('hyperdht')
+const fastify = require('fastify')
+const axios = require('axios')
+
+test('put alias + lookup happy flow', async t => {
+  const { bridge, dhtPromClient } = await setup(t)
+
+  await dhtPromClient.ready()
+  await bridge.ready()
+
+  const baseUrl = await bridge.server.listen({ host: '127.0.0.1', port: 0 })
+
+  bridge.putAlias('dummy', dhtPromClient.publicKey)
+
+  const res = await axios.get(`${baseUrl}/scrape/dummy/metrics`)
+  t.is(res.status, 200, 'correct status')
+  t.is(
+    res.data.includes('process_cpu_user_seconds_total'),
+    true,
+    'Successfully scraped metrics'
+  )
+})
+
+test('No new alias if adding same key', async t => {
+  const { bridge } = await setup(t)
+  const key = 'a'.repeat(64)
+  const key2 = 'b'.repeat(64)
+
+  await bridge.ready()
+  bridge.putAlias('dummy', key)
+  const clientA = bridge.aliases.get('dummy')
+
+  t.is(clientA != null, true, 'sanity check')
+  bridge.putAlias('dummy', key)
+  t.is(clientA, bridge.aliases.get('dummy'), 'no new client')
+
+  t.is(clientA.closing == null, true, 'sanity check')
+  bridge.putAlias('dummy', key2)
+  t.not(clientA, bridge.aliases.get('dummy'), 'sanity check')
+  t.is(clientA.closing != null, true, 'lifecycle ok')
+})
+
+async function setup (t) {
+  promClient.collectDefaultMetrics() // So we have something to scrape
+  t.teardown(() => promClient.register.clear())
+
+  const testnet = await createTestnet()
+  const bootstrap = testnet.bootstrap
+
+  const dht = new HyperDHT({ bootstrap })
+  const server = fastify({ logger: false })
+  const bridge = new PrometheusDhtBridge(dht, server, { address: '127.0.0.1', port: 30000 })
+  const scraperPubKey = bridge.publicKey
+
+  const dhtClient = new HyperDHT({ bootstrap })
+  const dhtPromClient = new DhtPromClient(dhtClient, promClient, scraperPubKey)
+
+  t.teardown(async () => {
+    await server.close()
+    await bridge.close()
+    await dhtPromClient.close()
+    await dht.destroy()
+    await testnet.destroy()
+  })
+
+  return { dhtPromClient, bridge, bootstrap }
+}