feat: add tracecontext propagation (#97)

Based on w3c TraceContext spec: https://w3c.github.io/distributed-tracing/

The `traceparent` header is validated and propagated according to spec.
The only caveat is that the option flags are lost downstream and reset to
"0x1" by the tracer. This will require a refactor of how the tracer treats
the options as certain assumptions are being made that the least-significant
bit will always represent "sampled".

The `tracestate` is propagated downstream, but is currently not mutable by
the tracer. It is simply stored as a string, but types have been generated
to allow this to be refactored into a more structured type in the future,
allowing the tracer to update the tracestate as necessary.

This commit does not attempt to implement the `Correlation-Context` header.

README.md

@@ -28,6 +28,7 @@ OpenCensus collects distributed tracing. It is able to do so by propagating span
 
 - [B3 Propagation](https://github.com/census-instrumentation/opencensus-node/blob/master/packages/opencensus-propagation-b3/README.md)
 - [Stackdriver Propagation](https://github.com/census-instrumentation/opencensus-node/blob/master/packages/opencensus-propagation-stackdriver/README.md)
+- [Trace Context Propagation](https://github.com/census-instrumentation/opencensus-node/blob/master/packages/opencensus-propagation-tracecontext/README.md)
 
 ## Exporters
 

packages/opencensus-core/src/trace/model/root-span.ts

@@ -30,8 +30,10 @@ export class RootSpan extends SpanBase implements types.RootSpan {
   private tracer: types.Tracer;
   /** A list of child spans. */
   private spansLocal: types.Span[];
-  /** It's trace ID. */
+  /** Its trace ID. */
   private traceIdLocal: string;
+  /** Its trace state. */
+  private traceStateLocal: types.TraceState;
   /** set isRootSpan = true */
   readonly isRootSpan = true;
 
@@ -50,6 +52,7 @@ export class RootSpan extends SpanBase implements types.RootSpan {
     this.name = context && context.name ? context.name : 'undefined';
     if (context && context.spanContext) {
       this.parentSpanId = context.spanContext.spanId || '';
+      this.traceStateLocal = context.spanContext.traceState;
     }
     this.spansLocal = [];
     this.kind = context && context.kind ? context.kind : null;
@@ -66,12 +69,20 @@ export class RootSpan extends SpanBase implements types.RootSpan {
     return this.traceIdLocal;
   }
 
+  /** Gets trace state from rootspan instance */
+  get traceState(): types.TraceState {
+    return this.traceStateLocal;
+  }
+
   /** Starts a rootspan instance. */
   start() {
     super.start();
-    this.logger.debug(
-        'starting %s  %o', this.className,
-        {traceId: this.traceId, id: this.id, parentSpanId: this.parentSpanId});
+    this.logger.debug('starting %s  %o', this.className, {
+      traceId: this.traceId,
+      id: this.id,
+      parentSpanId: this.parentSpanId,
+      traceState: this.traceState
+    });
 
     this.tracer.onStartSpan(this);
   }

packages/opencensus-core/src/trace/model/span-base.ts

@@ -65,6 +65,8 @@ export abstract class SpanBase implements types.Span {
   /** Gets the trace ID. */
   abstract get traceId(): string;
 
+  /** Gets the trace state */
+  abstract get traceState(): types.TraceState;
 
   /** Indicates if span was started. */
   get started(): boolean {
@@ -120,7 +122,8 @@ export abstract class SpanBase implements types.Span {
     return {
       traceId: this.traceId,
       spanId: this.id,
-      options: 0x1  // always traced
+      options: 0x1,  // always traced
+      traceState: this.traceState
     };
   }
 

packages/opencensus-core/src/trace/model/span.ts

@@ -42,12 +42,19 @@ export class Span extends SpanBase implements types.Span {
     return this.root.traceId;
   }
 
+  get traceState(): string {
+    return this.root.traceState;
+  }
+
   /** Starts the span instance. */
   start() {
     super.start();
-    this.logger.debug(
-        'starting span  %o',
-        {traceId: this.traceId, spanId: this.id, name: this.name});
+    this.logger.debug('starting span  %o', {
+      traceId: this.traceId,
+      spanId: this.id,
+      name: this.name,
+      traceState: this.traceState
+    });
   }
 
 

packages/opencensus-core/src/trace/model/types.ts

@@ -73,6 +73,8 @@ export interface TraceOptions {
   kind?: string;
 }
 
+export type TraceState = string;
+
 /** Defines the span context */
 export interface SpanContext {
   /** Trace ID */
@@ -81,6 +83,8 @@ export interface SpanContext {
   spanId: string;
   /** Options */
   options?: number;
+  /** TraceState */
+  traceState?: TraceState;
 }
 
 /** Defines an end span event listener */
@@ -128,9 +132,12 @@ export interface Span {
   /** true if span is a RootSpan */
   isRootSpan: boolean;
 
-  /** Constructs a new SpanBaseModel instance. */
+  /** Trace id asscoiated with span. */
   readonly traceId: string;
 
+  /** Trace state associated with span */
+  readonly traceState: TraceState;
+
   /** Indicates if span was started. */
   readonly started: boolean;
 

packages/opencensus-propagation-tracecontext/AUTHORS

@@ -0,0 +1,8 @@
+# This is the list of OpenCensus authors for copyright purposes.
+#
+# This does not necessarily list everyone who has contributed code, since in
+# some cases, their employer may be the copyright holder.  To see the full list
+# of contributors, see the revision history in source control.
+
+Google LLC
+CESAR Team (www.cesar.org.br)

packages/opencensus-propagation-tracecontext/LICENSE

@@ -0,0 +1,202 @@
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packages/opencensus-propagation-tracecontext/README.md

@@ -0,0 +1,46 @@
+# OpenCensus Trace Context Format Propagation for Node.js
+[![Gitter chat][gitter-image]][gitter-url]
+
+OpenCensus Trace Context Format Propagation sends a span context on the wire in an HTTP request, allowing other services to create spans with the right context.
+
+This project is still at an early stage of development. It's subject to change.
+
+## Installation
+
+Install OpenCensus TraceContex Propagation with:
+```bash
+npm install @opencensus/propagation-tracecontext
+```
+
+## Usage
+
+To propagate span context arround services with Trace Context Propagation, pass an instance of Trace Context Propagation to your tracing instance. For Javascript:
+
+```javascript
+const tracing = require('@opencensus/nodejs');
+const propagation = require('@opencensus/propagation-tracecontext');
+
+const traceContext = new propagation.TraceContextFormat();
+
+tracing.start({propagation: traceContext});
+```
+
+Similarly for Typescript:
+
+```typescript
+import * as tracing from '@opencensus/nodejs';
+import { TraceContextFormat } from '@opencensus/propagation-tracecontext';
+
+const traceContext = new TraceContextFormat();
+
+tracing.start({propagation: traceContext});
+```
+
+## Useful links
+- To know more about Trace Context Format propagation, visit: <https://w3c.github.io/distributed-tracing/>
+- For more information on OpenCensus, visit: <https://opencensus.io/>
+- To checkout the OpenCensus for Node.js, visit: <https://github.com/census-instrumentation/opencensus-node>
+- For help or feedback on this project, join us on [gitter](https://gitter.im/census-instrumentation/Lobby)
+
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