feat: auto register(#22)

Author: kinolaev

README.md

@@ -68,6 +68,19 @@ app.register((instance, opts, done) => {
 }, { prefix: '/nested' })
 ```
 
+### Automatic plugin registration
+
+The plugin can be automatically registered with `registerOnInitialization` option set to `true`.
+In this case, it is necessary to await fastify instance.
+```js
+// ... in your OTEL setup
+const fastifyOtelInstrumentation = new FastifyOtelInstrumentation({ registerOnInitialization: true });
+
+// ... in your Fastify definition
+const Fastify = require('fastify');
+const app = await fastify();
+```
+
 > **Notes**:
 >
 > - This instrumentation requires `@opentelemetry/instrumentation-http` to be able to propagate the traces all the way back to upstream

index.d.ts

@@ -6,6 +6,7 @@ import { FastifyInstance } from 'fastify'
 export interface FastifyOtelOptions {}
 export interface FastifyOtelInstrumentationOpts extends InstrumentationConfig {
   servername?: string
+  registerOnInitialization?: boolean
 }
 
 declare class FastifyOtelInstrumentation<Config extends FastifyOtelInstrumentationOpts = FastifyOtelInstrumentationOpts> extends InstrumentationBase<Config> {

index.js

@@ -1,4 +1,5 @@
 'use strict'
+const dc = require('node:diagnostics_channel')
 const { context, trace, SpanStatusCode } = require('@opentelemetry/api')
 const { getRPCMetadata, RPCType } = require('@opentelemetry/core')
 const {
@@ -56,6 +57,25 @@ class FastifyOtelInstrumentation extends InstrumentationBase {
     this.servername = config?.servername ?? process.env.OTEL_SERVICE_NAME ?? 'fastify'
   }
 
+  enable () {
+    if (this._handleInitialization === undefined && this.getConfig().registerOnInitialization) {
+      const FastifyInstrumentationPlugin = this.plugin()
+      this._handleInitialization = (message) => {
+        message.fastify.register(FastifyInstrumentationPlugin)
+      }
+      dc.subscribe('fastify.initialization', this._handleInitialization)
+    }
+    return super.enable()
+  }
+
+  disable () {
+    if (this._handleInitialization) {
+      dc.unsubscribe('fastify.initialization', this._handleInitialization)
+      this._handleInitialization = undefined
+    }
+    return super.disable()
+  }
+
   // We do not do patching in this instrumentation
   init () {
     return []

test/index.test.js

@@ -91,6 +91,27 @@ describe('FastifyInstrumentation', () => {
       memoryExporter.reset()
     })
 
+    test('should attach plugin if registerOnInitialization is true', async () => {
+      const instrumentation = new FastifyInstrumentation({ registerOnInitialization: true })
+      assert.notEqual(instrumentation._handleInitialization, undefined)
+
+      const app = await Fastify()
+      assert.ok(app.hasPlugin('@fastify/otel'))
+      app.close()
+
+      instrumentation.disable()
+      assert.equal(instrumentation._handleInitialization, undefined)
+    })
+
+    test('shouldn\'t attach plugin if registerOnInitialization isn\'t set', async () => {
+      const instrumentation = new FastifyInstrumentation()
+      assert.equal(instrumentation._handleInitialization, undefined)
+
+      const app = await Fastify()
+      assert.equal(app.hasPlugin('@fastify/otel'), false)
+      app.close()
+    })
+
     test('should create anonymous span (simple case)', async t => {
       const app = Fastify()
       const plugin = instrumentation.plugin()