feat(otel): Add OpenTelemetry middleware

Close https://github.com/honojs/hono/issues/1864

.changeset/famous-starfishes-change.md

@@ -0,0 +1,5 @@
+---
+'@hono/otel': minor
+---
+
+Initial OpenTelemetry support with Hono

.github/workflows/ci-otel.yml

@@ -0,0 +1,25 @@
+name: ci-otel
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'packages/otel/**'
+  pull_request:
+    branches: ['*']
+    paths:
+      - 'packages/otel/**'
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: ./packages/otel
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20.x
+      - run: yarn install --frozen-lockfile
+      - run: yarn build
+      - run: yarn test

package.json

@@ -42,6 +42,7 @@
     "build:tsyringe": "yarn workspace @hono/tsyringe build",
     "build:cloudflare-access": "yarn workspace @hono/cloudflare-access build",
     "build:standard-validator": "yarn workspace @hono/standard-validator build",
+    "build:otel": "yarn workspace @hono/otel build",
     "build": "run-p 'build:*'",
     "lint": "eslint 'packages/**/*.{ts,tsx}'",
     "lint:fix": "eslint --fix 'packages/**/*.{ts,tsx}'",

packages/otel/README.md

@@ -0,0 +1,66 @@
+# OpenTelemetry middleware for Hono
+
+This package provides a [Hono](https://hono.dev/) middleware that instruments your application with [OpenTelemetry](https://opentelemetry.io/).
+
+## Usage
+
+```ts
+import { otel } from '@hono/otel'
+import { NodeSDK } from '@opentelemetry/sdk-node'
+import { ConsoleSpanExporter } from '@opentelemetry/sdk-trace-node'
+import { Hono } from 'hono'
+
+const sdk = new NodeSDK({
+  traceExporter: new ConsoleSpanExporter(),
+})
+
+sdk.start()
+
+const app = new Hono()
+
+app.use('*', otel())
+app.get('/', (c) => c.text('foo'))
+
+export default app
+```
+
+## Usage on Cloudflare Workers
+
+Since @opentelemetry/sdk-node is not supported on [Cloudflare Workers](https://workers.cloudflare.com/), you need to use [@microlabs/otel-cf-workers](https://github.com/evanderkoogh/otel-cf-workers) instead.
+
+The following example shows how to use @microlabs/otel-cf-workers with [Honeycomb](https://www.honeycomb.io/):
+
+```ts
+import { otel } from '@hono/otel'
+import { instrument, ResolveConfigFn } from '@microlabs/otel-cf-workers'
+import { Hono } from 'hono'
+
+const app = new Hono()
+
+app.use('*', otel())
+app.get('/', (c) => c.text('foo'))
+
+const config: ResolveConfigFn = (env: Env, _trigger) => {
+  return {
+    exporter: {
+      url: 'https://api.honeycomb.io/v1/traces',
+      headers: { 'x-honeycomb-team': env.HONEYCOMB_API_KEY },
+    },
+    service: { name: 'greetings' },
+  }
+}
+
+export default instrument(app, config)
+```
+
+## Limitation
+
+Since this instrumentation is based on Hono's middleware system, it instruments the entire request-response lifecycle. This means that it doesn't provide fine-grained instrumentation for individual middleware.
+
+## Author
+
+Hong Minhee <https://hongminhee.org/>
+
+## License
+
+MIT

packages/otel/package.json

@@ -0,0 +1,53 @@
+{
+  "name": "@hono/otel",
+  "version": "0.0.0",
+  "description": "OpenTelemetry middleware for Hono",
+  "type": "module",
+  "module": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "files": [
+    "dist"
+  ],
+  "scripts": {
+    "test": "vitest --run",
+    "build": "tsup ./src/index.ts --format esm,cjs --dts",
+    "publint": "publint",
+    "release": "yarn build && yarn test && yarn publint && yarn publish"
+  },
+  "exports": {
+    ".": {
+      "import": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/index.js"
+      },
+      "require": {
+        "types": "./dist/index.d.cts",
+        "default": "./dist/index.cjs"
+      }
+    }
+  },
+  "license": "MIT",
+  "publishConfig": {
+    "registry": "https://registry.npmjs.org",
+    "access": "public"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/honojs/middleware.git"
+  },
+  "homepage": "https://github.com/honojs/middleware",
+  "peerDependencies": {
+    "hono": "*"
+  },
+  "dependencies": {
+    "@opentelemetry/api": "^1.9.0",
+    "@opentelemetry/semantic-conventions": "^1.28.0"
+  },
+  "devDependencies": {
+    "@opentelemetry/sdk-trace-base": "^1.30.0",
+    "@opentelemetry/sdk-trace-node": "^1.30.0",
+    "hono": "^4.4.12",
+    "tsup": "^8.1.0",
+    "vitest": "^1.6.0"
+  }
+}

packages/otel/src/index.test.ts

@@ -0,0 +1,74 @@
+import { SpanKind, SpanStatusCode } from '@opentelemetry/api'
+import { InMemorySpanExporter, SimpleSpanProcessor } from '@opentelemetry/sdk-trace-base'
+import { NodeTracerProvider } from '@opentelemetry/sdk-trace-node'
+import {
+  ATTR_HTTP_REQUEST_METHOD,
+  ATTR_HTTP_RESPONSE_HEADER,
+  ATTR_HTTP_RESPONSE_STATUS_CODE,
+  ATTR_URL_FULL,
+  ATTR_HTTP_ROUTE,
+} from '@opentelemetry/semantic-conventions'
+import { Hono } from 'hono'
+import { otel } from '../src'
+
+describe('OpenTelemetry middleware', () => {
+  const app = new Hono()
+
+  const memoryExporter = new InMemorySpanExporter()
+  const spanProcessor = new SimpleSpanProcessor(memoryExporter)
+  const tracerProvider = new NodeTracerProvider({
+    spanProcessors: [spanProcessor],
+  })
+
+  app.use(otel({ tracerProvider }))
+  app.get('/foo', (c) => c.text('foo'))
+  app.post('/error', (_) => {
+    throw new Error('error message')
+  })
+
+  it('Should make a span', async () => {
+    memoryExporter.reset()
+    const response = await app.request('http://localhost/foo')
+    const spans = memoryExporter.getFinishedSpans()
+    expect(spans.length).toBe(1)
+    const [span] = spans
+    expect(span.name).toBe('GET /foo')
+    expect(span.kind).toBe(SpanKind.SERVER)
+    expect(span.status.code).toBe(SpanStatusCode.UNSET)
+    expect(span.status.message).toBeUndefined()
+    expect(span.attributes[ATTR_HTTP_REQUEST_METHOD]).toBe('GET')
+    expect(span.attributes[ATTR_URL_FULL]).toBe('http://localhost/foo')
+    expect(span.attributes[ATTR_HTTP_ROUTE]).toBe('/foo')
+    expect(span.attributes[ATTR_HTTP_RESPONSE_STATUS_CODE]).toBe(200)
+    for (const [name, value] of response.headers.entries()) {
+      expect(span.attributes[ATTR_HTTP_RESPONSE_HEADER(name)]).toBe(value)
+    }
+  })
+
+  it('Should make a span with error', async () => {
+    memoryExporter.reset()
+    await app.request('http://localhost/error', { method: 'POST' })
+    const spans = memoryExporter.getFinishedSpans()
+    expect(spans.length).toBe(1)
+    const [span] = spans
+    expect(span.name).toBe('POST /error')
+    expect(span.kind).toBe(SpanKind.SERVER)
+    expect(span.status.code).toBe(SpanStatusCode.ERROR)
+    expect(span.status.message).toBe('Error: error message')
+    expect(span.attributes[ATTR_HTTP_REQUEST_METHOD]).toBe('POST')
+    expect(span.attributes[ATTR_URL_FULL]).toBe('http://localhost/error')
+    expect(span.attributes[ATTR_HTTP_ROUTE]).toBe('/error')
+  })
+
+  it('Should update the active span', async () => {
+    memoryExporter.reset()
+    await tracerProvider.getTracer('test').startActiveSpan('existing span', async () => {
+      await app.request('http://localhost/foo')
+    })
+    const spans = memoryExporter.getFinishedSpans()
+    expect(spans.length).toBe(1)
+    const [span] = spans
+    expect(span.name).toBe('GET /foo')
+    expect(span.attributes[ATTR_HTTP_ROUTE]).toBe('/foo')
+  })
+})

packages/otel/src/index.ts

@@ -0,0 +1,75 @@
+import { SpanKind, SpanStatusCode, type TracerProvider, trace } from '@opentelemetry/api'
+import {
+  ATTR_HTTP_REQUEST_HEADER,
+  ATTR_HTTP_REQUEST_METHOD,
+  ATTR_HTTP_RESPONSE_HEADER,
+  ATTR_HTTP_RESPONSE_STATUS_CODE,
+  ATTR_URL_FULL,
+  ATTR_HTTP_ROUTE,
+} from '@opentelemetry/semantic-conventions'
+import type { Env, Input } from 'hono'
+import { createMiddleware } from 'hono/factory'
+import metadata from '../package.json' with { type: 'json'}
+
+const PACKAGE_NAME = metadata.name
+const PACKAGE_VERSION = metadata.version
+
+export type OtelOptions = {
+  augmentSpan?: false;
+  tracerProvider?: TracerProvider
+} | {
+  augmentSpan: true;
+}
+
+export const otel = <E extends Env = any, P extends string = any, I extends Input = {}>(
+  options: OtelOptions = {}
+) => {
+  if (options.augmentSpan) {
+    return createMiddleware<E, P, I>(async (c, next) => {
+      const result = await next()
+      const span = trace.getActiveSpan()
+      if (span != null) {
+        const route = c.req.matchedRoutes[c.req.matchedRoutes.length - 1]
+        span.setAttribute(ATTR_HTTP_ROUTE, route.path)
+        span.updateName(`${c.req.method} ${route.path}`)
+      }
+      return result
+    })
+  }
+  const tracerProvider = options.tracerProvider ?? trace.getTracerProvider()
+  const tracer = tracerProvider.getTracer(PACKAGE_NAME, PACKAGE_VERSION)
+  return createMiddleware<E, P, I>(async (c, next) => {
+    const route = c.req.matchedRoutes[c.req.matchedRoutes.length - 1]
+    await tracer.startActiveSpan(
+      `${c.req.method} ${route.path}`,
+      {
+        kind: SpanKind.SERVER,
+        attributes: {
+          [ATTR_HTTP_REQUEST_METHOD]: c.req.method,
+          [ATTR_URL_FULL]: c.req.url,
+          [ATTR_HTTP_ROUTE]: route.path,
+        },
+      },
+      async (span) => {
+        for (const [name, value] of Object.entries(c.req.header())) {
+          span.setAttribute(ATTR_HTTP_REQUEST_HEADER(name), value)
+        }
+        try {
+          await next()
+          span.setAttribute(ATTR_HTTP_RESPONSE_STATUS_CODE, c.res.status)
+          for (const [name, value] of c.res.headers.entries()) {
+            span.setAttribute(ATTR_HTTP_RESPONSE_HEADER(name), value)
+          }
+          if (c.error) {
+            span.setStatus({ code: SpanStatusCode.ERROR, message: String(c.error) })
+          }
+        } catch (e) {
+          span.setStatus({ code: SpanStatusCode.ERROR, message: String(e) })
+          throw e
+        } finally {
+          span.end()
+        }
+      }
+    )
+  })
+}

packages/otel/tsconfig.json

@@ -0,0 +1,10 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "rootDir": "./src",
+    "outDir": "./dist",
+    "module": "ESNext",
+    "resolveJsonModule": true
+  },
+  "include": ["src/**/*.ts"]
+}

packages/otel/vitest.config.ts

@@ -0,0 +1,8 @@
+/// <reference types="vitest" />
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    globals: true,
+  },
+})

yarn.lock

@@ -2677,6 +2677,22 @@ __metadata:
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+    vitest: "npm:^1.6.0"
+  peerDependencies:
+    hono: "*"
+  languageName: unknown
+  linkType: soft
+
 "@hono/prometheus@workspace:packages/prometheus":
   version: 0.0.0-use.local
   resolution: "@hono/prometheus@workspace:packages/prometheus"
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