elastic-apm-trace-context

This is a basic implementation of the W3C trace context header spec.

Installation

npm install elastic-apm-trace-context

Example Usage

const crypto = require('crypto')
const TraceContext = require('elastic-apm-trace-context')
 
const version = Buffer.alloc(1).toString('hex')
const traceId = crypto.randomBytes(16).toString('hex')
const id = crypto.randomBytes(8).toString('hex')
const flags = '01'
 
const header = `${version}-${traceId}-${id}-${flags}`
 
const context = TraceContext.fromString(header)

API

new TraceContext(buffer)

Construct a new TraceContext instance from an existing buffer. The contents are binary data that corresponds to the structure of the W3C traceparent header format, with separators removed.

TraceContext.fromString(header)

Reconstruct a TraceContext instance from a formatted W3C traceparent header string.

TraceContext.startOrResume(parent, settings)

Resume from a parent context, if given, or start a new context. Accepts another TraceContext instance, a W3C traceparent header string, or a Span or Transaction instance from elastic-apm-node.

Requires a settings object with a transactionSampleRate value from 0.0 to 1.0 to generate a sampling decision for the context. This will only be applied when starting a new context. When continuing an existing context, the sampling decision will be propagated into all child contexts.

context.recorded

Returns true if this TraceContext is sampled.

context.traceId

The traceId property will propagate through all children in the tree to link them all together.

context.id

The id property is used to uniquely identify a given TraceContext instance within the tree.

context.parentId

The parentId property links this context to its direct parent in the tree.

context.flags

The flags property is used to store metadata such as the sampling decision.

context.version

The version property corresponds to the version segment of the W3C traceparent header.

context.child()

Create a new TraceContext instance that is a child of this one.

context.toString()

Formats the TraceContext instance as a W3C traceparent header.

context.ensureParentId()

Return the parent ID, if there is none, generate one. This is useful in browser instrumentation to produce a starting span around a browser request which was not instrumented prior to page load.

License

MIT