@sylphx/cat-tracing

W3C Trace Context support for @sylphx/cat logger

1.46 KB • W3C compliant • Distributed tracing • Auto trace ID generation

Installation

npm install @sylphx/cat @sylphx/cat-tracing

Description

Adds W3C Trace Context support to @sylphx/cat logger. Automatically generates and propagates trace IDs and span IDs for distributed tracing across microservices. Compatible with OpenTelemetry, Datadog, New Relic, and any W3C Trace Context-compliant system.

Usage Examples

Basic Tracing

import { createLogger } from '@sylphx/cat'
import { tracingPlugin } from '@sylphx/cat-tracing'

const logger = createLogger({
  plugins: [tracingPlugin()]
})

logger.info('Request processed')
// {"level":"info","message":"Request processed","traceId":"4bf92f3577b34da6a3ce929d0e0e4736","spanId":"00f067aa0ba902b7"}

HTTP Header Propagation (Express)

import { createLogger } from '@sylphx/cat'
import { TracingPlugin, tracingPlugin } from '@sylphx/cat-tracing'
import express from 'express'

const tracingPluginInstance = tracingPlugin()
const logger = createLogger({
  plugins: [tracingPluginInstance]
})

const app = express()

app.use((req, res, next) => {
  // Extract trace context from incoming request
  const context = TracingPlugin.fromHeaders(req.headers)
  if (context) {
    tracingPluginInstance.setTraceContext(context)
  }

  logger.info({ req }, 'Request received')
  next()
})

app.get('/api/users', async (req, res) => {
  // Make downstream request with trace context
  const context = tracingPluginInstance.getContext()
  const headers = context ? TracingPlugin.toHeaders(context) : {}

  const response = await fetch('http://downstream-service/users', {
    headers: {
      ...headers,  // Propagates traceparent header
      'Content-Type': 'application/json'
    }
  })

  res.json(await response.json())
})

Manual Trace Context

import { createLogger } from '@sylphx/cat'
import { tracingPlugin, createTraceContext } from '@sylphx/cat-tracing'

const tracing = tracingPlugin()
const logger = createLogger({
  plugins: [tracing]
})

// Create custom trace context
const context = createTraceContext({
  traceId: '4bf92f3577b34da6a3ce929d0e0e4736',
  spanId: '00f067aa0ba902b7',
  sampled: true
})

tracing.setTraceContext(context)
logger.info('Custom trace context')

API Reference

tracingPlugin(options?: TracingPluginOptions): Plugin

Creates a tracing plugin instance.

Options:

• enabled?: boolean - Enable tracing (default: true)
• generateTraceId?: boolean - Auto-generate trace IDs if not present (default: true)
• traceparentHeader?: string - Header name for trace parent (default: 'traceparent')
• getTraceContext?: () => TraceContext | null - Custom trace context getter
• includeTraceContext?: boolean - Include trace context in logs (default: true)

Example:

tracingPlugin({
  enabled: true,
  generateTraceId: true,
  getTraceContext: () => {
    // Custom logic to get trace context
    // e.g., from AsyncLocalStorage
    return asyncStorage.getStore()?.traceContext
  }
})

Trace Context Utilities

createTraceContext(options?: Partial<TraceContext>): TraceContext

Creates a new trace context with optional overrides.

import { createTraceContext } from '@sylphx/cat-tracing'

const context = createTraceContext()
// { traceId: '...', spanId: '...', traceFlags: 1 }

generateTraceId(): string

Generates a random 32-character hexadecimal trace ID.

import { generateTraceId } from '@sylphx/cat-tracing'

const traceId = generateTraceId()
// '4bf92f3577b34da6a3ce929d0e0e4736'

generateSpanId(): string

Generates a random 16-character hexadecimal span ID.

import { generateSpanId } from '@sylphx/cat-tracing'

const spanId = generateSpanId()
// '00f067aa0ba902b7'

parseTraceparent(traceparent: string): TraceContext | null

Parses a W3C traceparent header.

import { parseTraceparent } from '@sylphx/cat-tracing'

const context = parseTraceparent('00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01')
// { traceId: '4bf92f3577b34da6a3ce929d0e0e4736', spanId: '00f067aa0ba902b7', traceFlags: 1 }

formatTraceparent(context: TraceContext): string

Formats a trace context as a W3C traceparent header.

import { formatTraceparent } from '@sylphx/cat-tracing'

const header = formatTraceparent({
  traceId: '4bf92f3577b34da6a3ce929d0e0e4736',
  spanId: '00f067aa0ba902b7',
  traceFlags: 1
})
// '00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01'

Static Methods

TracingPlugin.fromHeaders(headers: Record<string, string | string[]>): TraceContext | null

Extracts trace context from HTTP headers.

const context = TracingPlugin.fromHeaders(request.headers)

TracingPlugin.toHeaders(context: TraceContext): Record<string, string>

Converts trace context to HTTP headers.

const headers = TracingPlugin.toHeaders(context)
// { traceparent: '00-...-...-01' }

Instance Methods

setTraceContext(context: TraceContext | null): void

Sets the current trace context.

const tracing = tracingPlugin()
tracing.setTraceContext(context)

getContext(): TraceContext | null

Gets the current trace context.

const tracing = tracingPlugin()
const context = tracing.getContext()

W3C Trace Context Format

The plugin follows the W3C Trace Context specification:

traceparent header format:

00-{trace-id}-{parent-id}-{trace-flags}

Example:

00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01
│  │                                │                │
│  │                                │                └─ flags (01 = sampled)
│  │                                └────────────────── parent-id (16 hex chars)
│  └───────────────────────────────────────────────── trace-id (32 hex chars)
└────────────────────────────────────────────────────── version (00)

Integration Examples

With OTLP Transport

import { createLogger } from '@sylphx/cat'
import { tracingPlugin } from '@sylphx/cat-tracing'
import { otlpTransport } from '@sylphx/cat-otlp'

const logger = createLogger({
  plugins: [tracingPlugin()],
  transports: [
    otlpTransport({
      endpoint: 'https://api.honeycomb.io/v1/logs',
      headers: { 'x-honeycomb-team': process.env.API_KEY }
    })
  ]
})

logger.info('Traced and exported to OTLP')
// Trace context automatically included in OTLP export

With AsyncLocalStorage (Node.js)

import { AsyncLocalStorage } from 'async_hooks'
import { createLogger } from '@sylphx/cat'
import { tracingPlugin } from '@sylphx/cat-tracing'

const asyncStorage = new AsyncLocalStorage()

const logger = createLogger({
  plugins: [
    tracingPlugin({
      getTraceContext: () => asyncStorage.getStore()?.traceContext
    })
  ]
})

// In your request handler
app.use((req, res, next) => {
  const context = TracingPlugin.fromHeaders(req.headers) || createTraceContext()
  asyncStorage.run({ traceContext: context }, () => {
    next()
  })
})

Package Size

• Minified: ~4.5 KB
• Minified + Gzipped: 1.46 KB
• No additional dependencies

Standards Compliance

• ✅ W3C Trace Context Specification
• ✅ OpenTelemetry compatible
• ✅ Distributed tracing ready

Links

• Main Documentation
• GitHub Repository
• npm Package
• W3C Trace Context Spec

Related Packages

• @sylphx/cat - Core logger
• @sylphx/cat-otlp - OpenTelemetry Protocol export
• @sylphx/cat-tail-sampling - Requires tracing for sampling

License

MIT © Kyle Zhu