feat: derive a fallback for service.name if not set

by finding the application's main package.json file and using its name
and version attribute.

package.json

@@ -71,6 +71,7 @@
     "sinon": "^17.0.1",
     "ts-node": "^10.9.2",
     "ts-proto": "^1.172.0",
+    "type-fest": "^4.18.2",
     "typescript": "^5.4.5",
     "typescript-eslint": "^7.7.1"
   }

src/detectors/node/opentelemetry-resource-detector-kubernetes-pod/index_test.ts

@@ -96,7 +96,7 @@ const procSelfMountInfoContentWithPodUid2 = `2317 1432 0:473 / / rw,relatime mas
 1456 2318 0:476 /null /proc/sched_debug rw,nosuid - tmpfs tmpfs rw,size=65536k,mode=755
 1457 2322 0:480 / /sys/firmware ro,relatime - tmpfs tmpfs ro`;
 
-describe('podUidDetector', () => {
+describe('pod ui detection', () => {
   const sandbox = sinon.createSandbox();
   let readFileStub: sinon.SinonStub;
   let podUidDetector: PodUidDetector;

src/detectors/node/opentelemetry-resource-detector-service-name-fallback/index.ts

@@ -0,0 +1,59 @@
+// SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+import { DetectorSync, Resource } from '@opentelemetry/resources';
+import { SEMRESATTRS_SERVICE_NAME } from '@opentelemetry/semantic-conventions';
+
+import { readPackageJson } from './packageJsonUtil';
+
+export default class ServiceNameFallbackDetector implements DetectorSync {
+  detect(): Resource {
+    return new Resource({}, this.detectServiceNameFallback());
+  }
+
+  private async detectServiceNameFallback(): Promise<any> {
+    if (
+      hasOptedOutOfServiceNameFallbackDetection() ||
+      hasOTelServiceNameSet() ||
+      hasServiceNameSetViaResourceAttributesThing()
+    ) {
+      return {};
+    }
+
+    const packageJson = await readPackageJson();
+    if (!packageJson) {
+      return {};
+    }
+    return { [SEMRESATTRS_SERVICE_NAME]: `${packageJson.name}@${packageJson.version}` };
+  }
+}
+
+function hasOptedOutOfServiceNameFallbackDetection() {
+  const automaticServiceName = process.env.DASH0_AUTOMATIC_SERVICE_NAME;
+  return automaticServiceName && automaticServiceName.trim().toLowerCase() === 'false';
+}
+
+function hasOTelServiceNameSet() {
+  const otelServiceName = process.env.OTEL_SERVICE_NAME;
+  return otelServiceName && otelServiceName.trim() !== '';
+}
+
+function hasServiceNameSetViaResourceAttributesThing() {
+  const otelResourceAttributes = process.env.OTEL_RESOURCE_ATTRIBUTES;
+  if (otelResourceAttributes) {
+    const rawAttributes: string[] = otelResourceAttributes.split(',');
+    for (const rawAttribute of rawAttributes) {
+      const keyValuePair: string[] = rawAttribute.split('=');
+      if (keyValuePair.length !== 2) {
+        continue;
+      }
+      const [key, value] = keyValuePair;
+      if (key.trim() === SEMRESATTRS_SERVICE_NAME) {
+        if (value != null && value.trim().split(/^"|"$/).join('').trim().length > 0) {
+          return true;
+        }
+      }
+    }
+  }
+  return false;
+}

src/detectors/node/opentelemetry-resource-detector-service-name-fallback/index_test.ts

@@ -0,0 +1,129 @@
+// SPDX-FileCopyrightText: Copyright 2024 Dash0 Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+import { Resource } from '@opentelemetry/resources';
+import { SEMRESATTRS_SERVICE_NAME } from '@opentelemetry/semantic-conventions';
+import { expect } from 'chai';
+import Sinon from 'sinon';
+import sinon from 'sinon';
+
+import ServiceNameFallbackDetector from './index';
+import * as packageJsonUtil from './packageJsonUtil';
+
+const packageJson = {
+  name: '@example/app-under-test',
+  version: '2.13.47',
+  description: 'a Node.js application',
+  main: 'src/index.js',
+};
+
+const envVarNames = [
+  //
+  'DASH0_AUTOMATIC_SERVICE_NAME',
+  'OTEL_SERVICE_NAME',
+  'OTEL_RESOURCE_ATTRIBUTES',
+];
+
+interface Dict<T> {
+  [key: string]: T | undefined;
+}
+
+describe('service name fallback', () => {
+  const sandbox = sinon.createSandbox();
+  let readPackageJsonStub: Sinon.SinonStub;
+  let serviceNameFallback: ServiceNameFallbackDetector;
+
+  const originalEnvVarValues: Dict<string> = {};
+
+  before(() => {
+    envVarNames.forEach(envVarName => {
+      originalEnvVarValues[envVarName] = process.env[envVarName];
+    });
+  });
+
+  beforeEach(() => {
+    readPackageJsonStub = sandbox.stub(packageJsonUtil, 'readPackageJson');
+    serviceNameFallback = new ServiceNameFallbackDetector();
+  });
+
+  afterEach(() => {
+    sandbox.restore();
+    envVarNames.forEach(envVarName => {
+      if (originalEnvVarValues[envVarName] === undefined) {
+        delete process.env[envVarName];
+      } else {
+        process.env[envVarName] = originalEnvVarValues[envVarName];
+      }
+    });
+  });
+
+  it('sets a service name based on package.json attributes', async () => {
+    givenAValidPackageJsonFile();
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.have.property(SEMRESATTRS_SERVICE_NAME, '@example/[email protected]');
+  });
+
+  it('does not set a service name if DASH0_AUTOMATIC_SERVICE_NAME is false', async () => {
+    givenAValidPackageJsonFile();
+    process.env.DASH0_AUTOMATIC_SERVICE_NAME = 'false';
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.be.empty;
+  });
+
+  it('does not set a service name if OTEL_SERVICE_NAME is set', async () => {
+    givenAValidPackageJsonFile();
+    process.env.OTEL_SERVICE_NAME = 'already-set';
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.be.empty;
+  });
+
+  it('sets a service name if OTEL_SERVICE_NAME is set to an empty string', async () => {
+    givenAValidPackageJsonFile();
+    process.env.OTEL_SERVICE_NAME = '   ';
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.have.property(SEMRESATTRS_SERVICE_NAME, '@example/[email protected]');
+  });
+
+  it('does not set a service name if OTEL_RESOURCE_ATTRIBUTES has the service.name key', async () => {
+    givenAValidPackageJsonFile();
+    process.env.OTEL_RESOURCE_ATTRIBUTES = 'key1=value,service.name=already-set,key2=valu,key2=valuee';
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.be.empty;
+  });
+
+  it('sets a service name if OTEL_RESOURCE_ATTRIBUTES is set but does not have the service.name key', async () => {
+    givenAValidPackageJsonFile();
+    process.env.OTEL_RESOURCE_ATTRIBUTES = 'key1=value,key2=value';
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.have.property(SEMRESATTRS_SERVICE_NAME, '@example/[email protected]');
+  });
+
+  it('does not set a service name if no package.json can be found', async () => {
+    givenThereIsNoPackageJsonFile();
+    const result = serviceNameFallback.detect();
+    const attributes = await waitForAsyncDetection(result);
+    expect(attributes).to.be.empty;
+  });
+
+  function givenThereIsNoPackageJsonFile() {
+    readPackageJsonStub.returns(null);
+  }
+
+  function givenAValidPackageJsonFile() {
+    readPackageJsonStub.returns(null).returns(packageJson);
+  }
+
+  async function waitForAsyncDetection(result: Resource) {
+    expect(result).to.exist;
+    expect(result.asyncAttributesPending).to.be.true;
+    // @ts-expect-error required
+    await result.waitForAsyncAttributes();
+    return result.attributes;
+  }
+});