Getting TraceID from an OpenTracing DatadogSpanContext can throw "Cannot read properties of undefined (reading 'toString')

[davidalpert]

Calling this DatadogSpanContext.toTraceId() method on what appears to be a valid span can sometimes error out with an undefined inner this._traceId value:

dd-trace-js/packages/dd-trace/src/opentracing/span_context.js

Lines 33 to 40 in 497c0b0

	toTraceId (get128bitId = false) {
	if (get128bitId) {
	return this._traceId.toBuffer().length <= 8 && this._trace.tags[TRACE_ID_128]
	? this._trace.tags[TRACE_ID_128] + this._traceId.toString(16).padStart(16, '0')
	: this._traceId.toString(16).padStart(32, '0')
	}
	return this._traceId.toString(10)
	}

Suggested Solution

• While I am not sure what might cause this scenario, a quick fix would be to make the dot property access of this._traceId a bit more defensive:

   toTraceId (get128bitId = false) {
      if (this._traceId && get128bitId) {
        return this._traceId.toBuffer().length <= 8 && this._trace.tags[TRACE_ID_128]
          ? this._trace.tags[TRACE_ID_128] + this._traceId.toString(16).padStart(16, '0')
          : this._traceId.toString(16).padStart(32, '0')
      }
      return this._traceId?.toString(10)
    }
  

Replication Steps

• Using:

      "dd-trace": "5.25.0",
  

• Initialize the tracer on startup:

  import tracer from 'dd-trace';
  import { version } from '../../package.json';
  import { buildVars } from '#root/.build/buildVars';
  
  tracer.init({
    service: process.env.DD_SERVICE || 'my-fe-app',
    version: version ? `${version}-${buildVars.GIT_SHA}` : '0.0.0',
    tags: {
      pid: process.pid,
    },
    runtimeMetrics: true,
    logInjection: true,
  });
  

• Try to defensively get the active span's traceID at runtime

  import tracer from 'dd-trace';
  
  ...
  
      const span = tracer.scope().active();
      const traceID = span?.context()?.toTraceId() ?? 'n/a';
  
  ...
  

Expected result

• traceID is either a valid Trace ID from the current span or undefined in which case we default to 'n/a/ based on the code above

Actual result

• We regularly encounter an error whereby we seem to have a defined span (i.e. not null or undefined) with an empty or missing DatadogSpanContext._traceID property such that when we call toTraceId() on it we get the following error:

  .../my_app/node_modules/dd-trace/packages/dd-trace/src/opentracing/span_context.js:39
       return this._traceId.toString(10)
                                        ^
  TypeError: Cannot read properties of undefined (reading 'toString')
       at DatadogSpanContext.toTraceId (.../my_app/packages/dd-trace/src/opentracing/span_context.js:39:26)
  

Unit Tests

• Here is a failing test we can add to packages/dd-trace/test/opentracing/span_context.spec.js to demonstrate the issue

  'use strict'
  
  require('../setup/tap')
  
  const { expect } = require('chai')
  const id = require('../../src/id')
  
  describe('SpanContext', () => {
    let SpanContext
    let TraceState
  
    beforeEach(() => {
      SpanContext = require('../../src/opentracing/span_context')
      TraceState = require('../../src/opentracing/propagation/tracestate')
    })
   
    ...
    describe('toTraceparent()', () => {
    ...
  
      it('should allow nullsafe access to trace ID', () => {
        const spanContext = new SpanContext({
          traceId: undefined,
          spanId: id('456', 16)
        })
  
        spanContext._trace.tags['_dd.p.tid'] = null
  
        expect(spanContext.toTraceId()).to.equal(undefined)
      })
    })
  })
  

[mtgto]

We too are having trouble with this error sometimes after we upgraded from v5.24.0 to v5.25.0.
Here are a portion of our code.

import tracer from 'dd-trace'

const serviceName = process.env['DD_SERVICE']

if (serviceName) {
  tracer.init({
    logInjection: true,
    service: serviceName,
  })
}

...

export function logger() {
  // Set req.traceId to http access log
  return (req: Request, res: Response, next: NextFunction) => {
    // dd-trace v5.25.0 sometimes raise error `Cannot read properties of undefined (reading 'toString')`
    // in https://github.com/DataDog/dd-trace-js/blob/497c0b0d4333b6a7e7a434fb4de275595e5950c9/packages/dd-trace/src/opentracing/span_context.js#L39
    req.traceId = tracer?.scope().active()?.context().toTraceId()
    delegate(req, res, next)
  }
}

const app = express()
app.use(logger())

...