feat(sdk-trace-base): add util.inspect support for SpanImpl, Tracer, BasicTracerProvider

CHANGELOG.md

@@ -14,6 +14,8 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 
 ### :rocket: Features
 
+* feat(sdk-trace-base): pretty-print `SpanImpl`, `Tracer`, and `BasicTracerProvider` via `util.inspect` so they render through `diag` and `console.log` [#6690](https://github.com/open-telemetry/opentelemetry-js/pull/6690) @mcollina
+
 ### :bug: Bug Fixes
 
 ### :books: Documentation

packages/opentelemetry-sdk-trace-base/src/BasicTracerProvider.ts

@@ -13,6 +13,8 @@ import { loadDefaultConfig } from './config';
 import { MultiSpanProcessor } from './MultiSpanProcessor';
 import type { TracerConfig } from './types';
 import { reconfigureLimits } from './utility';
+import type { InspectFn, InspectStylizeOptions } from './inspect';
+import { formatInspect, inspectCustom } from './inspect';
 
 export enum ForceFlushState {
   'resolved',
@@ -125,4 +127,28 @@ export class BasicTracerProvider implements TracerProvider {
   shutdown(): Promise<void> {
     return this._activeSpanProcessor.shutdown();
   }
+
+  [inspectCustom](
+    depth: number,
+    options: InspectStylizeOptions | undefined,
+    inspect: InspectFn | undefined
+  ): unknown {
+    const processors = this._activeSpanProcessor[
+      '_spanProcessors'
+    ] as SpanProcessor[];
+    const payload = {
+      resource: { attributes: this._resource.attributes },
+      tracers: Array.from(this._tracers.keys()),
+      spanProcessors: processors.map(
+        p => p.constructor?.name ?? 'SpanProcessor'
+      ),
+    };
+    return formatInspect(
+      'BasicTracerProvider',
+      payload,
+      depth,
+      options,
+      inspect
+    );
+  }
 }

packages/opentelemetry-sdk-trace-base/src/Span.ts

@@ -41,6 +41,8 @@ import { ExceptionEventName } from './enums';
 import type { SpanProcessor } from './SpanProcessor';
 import type { TimedEvent } from './TimedEvent';
 import type { SpanLimits } from './types';
+import type { InspectFn, InspectStylizeOptions } from './inspect';
+import { formatInspect, inspectCustom } from './inspect';
 
 /**
  * This type provides the properties of @link{ReadableSpan} at the same time
@@ -524,4 +526,31 @@ export class SpanImpl implements Span {
     // Other types, no need to apply value length limit
     return value;
   }
+
+  [inspectCustom](
+    depth: number,
+    options: InspectStylizeOptions | undefined,
+    inspect: InspectFn | undefined
+  ): unknown {
+    const payload = {
+      name: this.name,
+      kind: this.kind,
+      spanContext: this._spanContext,
+      parentSpanContext: this.parentSpanContext,
+      status: this.status,
+      startTime: this.startTime,
+      endTime: this.endTime,
+      duration: this._duration,
+      ended: this._ended,
+      attributes: this.attributes,
+      events: this.events,
+      links: this.links,
+      droppedAttributesCount: this._droppedAttributesCount,
+      droppedEventsCount: this._droppedEventsCount,
+      droppedLinksCount: this._droppedLinksCount,
+      instrumentationScope: this.instrumentationScope,
+      resource: { attributes: this.resource.attributes },
+    };
+    return formatInspect('SpanImpl', payload, depth, options, inspect);
+  }
 }

packages/opentelemetry-sdk-trace-base/src/Tracer.ts

@@ -16,6 +16,8 @@ import { RandomIdGenerator } from './platform';
 import type { Resource } from '@opentelemetry/resources';
 import { TracerMetrics } from './TracerMetrics';
 import { VERSION } from './version';
+import type { InspectFn, InspectStylizeOptions } from './inspect';
+import { formatInspect, inspectCustom } from './inspect';
 
 /**
  * This class represents a basic tracer.
@@ -255,4 +257,18 @@ export class Tracer implements api.Tracer {
   getSpanLimits(): SpanLimits {
     return this._spanLimits;
   }
+
+  [inspectCustom](
+    depth: number,
+    options: InspectStylizeOptions | undefined,
+    inspect: InspectFn | undefined
+  ): unknown {
+    const payload = {
+      instrumentationScope: this.instrumentationScope,
+      resource: { attributes: this._resource.attributes },
+      spanLimits: this._spanLimits,
+      generalLimits: this._generalLimits,
+    };
+    return formatInspect('Tracer', payload, depth, options, inspect);
+  }
 }

packages/opentelemetry-sdk-trace-base/src/inspect.ts

@@ -0,0 +1,48 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Well-known symbol used by Node.js `util.inspect` (and `console.*`) to
+ * render an object via a custom representation. Defined as a global Symbol
+ * so it works without importing from `node:util`, keeping this module safe
+ * for browser builds (where the symbol is simply never looked up).
+ */
+export const inspectCustom = Symbol.for('nodejs.util.inspect.custom');
+
+export type InspectFn = (value: unknown, options: unknown) => string;
+
+export interface InspectStylizeOptions {
+  depth?: number | null;
+  stylize?: (text: string, styleType: string) => string;
+}
+
+/**
+ * Build a class-tagged inspect representation. Returns a stub like
+ * `[ClassName]` once the recursion budget is exhausted, otherwise returns
+ * `ClassName <inspected payload>` so nested fields keep proper coloring,
+ * indentation, and depth handling. In environments that don't supply an
+ * `inspect` callback (e.g. browsers), falls back to returning the raw
+ * payload object.
+ */
+export function formatInspect(
+  className: string,
+  payload: object,
+  depth: number,
+  options: InspectStylizeOptions | undefined,
+  inspect: InspectFn | undefined
+): unknown {
+  if (typeof depth === 'number' && depth < 0) {
+    const tag = `[${className}]`;
+    return options?.stylize ? options.stylize(tag, 'special') : tag;
+  }
+  if (typeof inspect !== 'function' || !options) {
+    return payload;
+  }
+  const childOptions = {
+    ...options,
+    depth: options.depth == null ? options.depth : options.depth - 1,
+  };
+  return `${className} ${inspect(payload, childOptions)}`;
+}

packages/opentelemetry-sdk-trace-base/test/node/inspect.test.ts

@@ -0,0 +1,87 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { SpanContext } from '@opentelemetry/api';
+import { ROOT_CONTEXT, SpanKind, TraceFlags } from '@opentelemetry/api';
+import * as assert from 'assert';
+import * as util from 'util';
+import { BasicTracerProvider } from '../../src';
+import { SpanImpl } from '../../src/Span';
+import type { Tracer } from '../../src/Tracer';
+
+describe('util.inspect', () => {
+  const tracerProvider = new BasicTracerProvider();
+  const tracer = tracerProvider.getTracer('default') as Tracer;
+  const spanContext: SpanContext = {
+    traceId: 'd4cda95b652f4a1592b449d5929fda1b',
+    spanId: '6e0c63257de34c92',
+    traceFlags: TraceFlags.SAMPLED,
+  };
+
+  describe('SpanImpl', () => {
+    it('should render with class tag and key fields', () => {
+      const span = new SpanImpl({
+        scope: tracer.instrumentationScope,
+        resource: tracer['_resource'],
+        context: ROOT_CONTEXT,
+        spanContext,
+        name: 'span1',
+        kind: SpanKind.CLIENT,
+        spanLimits: tracer.getSpanLimits(),
+        spanProcessor: tracer['_spanProcessor'],
+        attributes: { foo: 'bar' },
+      });
+
+      const out = util.inspect(span, { depth: 5, colors: false });
+      assert.ok(out.startsWith('SpanImpl '), `unexpected prefix: ${out}`);
+      assert.ok(out.includes("name: 'span1'"));
+      assert.ok(out.includes(spanContext.traceId));
+      assert.ok(out.includes(spanContext.spanId));
+      assert.ok(out.includes("foo: 'bar'"));
+    });
+
+    it('should collapse to a stub when depth budget is exhausted', () => {
+      const span = new SpanImpl({
+        scope: tracer.instrumentationScope,
+        resource: tracer['_resource'],
+        context: ROOT_CONTEXT,
+        spanContext,
+        name: 'span1',
+        kind: SpanKind.CLIENT,
+        spanLimits: tracer.getSpanLimits(),
+        spanProcessor: tracer['_spanProcessor'],
+      });
+
+      const out = util.inspect({ span }, { depth: 0, colors: false });
+      assert.ok(out.includes('[SpanImpl]'), `unexpected output: ${out}`);
+    });
+  });
+
+  describe('Tracer', () => {
+    it('should render with scope and resource', () => {
+      const t = tracerProvider.getTracer('debug-scope', '1.2.3');
+      const out = util.inspect(t, { depth: 4, colors: false });
+      assert.ok(out.startsWith('Tracer '), `unexpected prefix: ${out}`);
+      assert.ok(out.includes("name: 'debug-scope'"));
+      assert.ok(out.includes("version: '1.2.3'"));
+      assert.ok(out.includes('spanLimits'));
+    });
+  });
+
+  describe('BasicTracerProvider', () => {
+    it('should render with tracer keys', () => {
+      const provider = new BasicTracerProvider();
+      provider.getTracer('a');
+      provider.getTracer('b', '0.0.1');
+      const out = util.inspect(provider, { depth: 4, colors: false });
+      assert.ok(
+        out.startsWith('BasicTracerProvider '),
+        `unexpected prefix: ${out}`
+      );
+      assert.ok(out.includes("'a@:'"));
+      assert.ok(out.includes("'b@0.0.1:'"));
+    });
+  });
+});