fix: Fix SpanId generation for interoperability (#126)

* Fix SpanId formatting for interoperability

SpanIds in opencensus-node are currently generated, sent in traces, and
propagated to other services as numeric values. This isn't consistent
with other opencensus libraries (e.g.:
[opencensus-java](https://github.com/census-instrumentation/opencensus-java/blob/master/api/src/main/java/io/opencensus/trace/SpanId.java)
serializes the span id as lowercase base16). When opencensus-node is
setup with B3 propagation, this SpanId format violates the [B3
specification](https://github.com/openzipkin/b3-propagation#spanid-1)
which mandates lowercase base16 encoding. Generally speaking,
opencensus-java only accepts spans in this format so it will fail to
correctly link to any span generated by opencensus-node. The best case
scenario is a shared trace id with a missing parent span link.

This PR removes the integer parsing, and leaves it as lowercase hex
characters. I tested locally with B3 propagation where node creates the
root span and propagates it to a Java service instrumented with
opencensus-java, and verified the data is correctly ingested and
correlated in Jaeger.

* Convert spanId into a numeric value for stackdriver

Using the hex2dec library also used by
https://github.com/googleapis/cloud-trace-nodejs/ , so assuming this
dependency is okay.

* Fix formatting

packages/opencensus-core/src/internal/util.ts

@@ -19,8 +19,7 @@
 
 import * as crypto from 'crypto';
 
-// Use 6 bytes of randomness only as JS numbers are doubles not 64-bit ints.
-const SPAN_ID_RANDOM_BYTES = 6;
+const SPAN_ID_RANDOM_BYTES = 8;
 
 // Use the faster crypto.randomFillSync when available (Node 7+) falling back to
 // using crypto.randomBytes.
@@ -32,6 +31,5 @@ const spanRandomBuffer = randomFillSync ?
     () => randomBytes(SPAN_ID_RANDOM_BYTES);
 
 export function randomSpanId() {
-  // tslint:disable-next-line:ban Needed to parse hexadecimal.
-  return parseInt(spanRandomBuffer().toString('hex'), 16).toString();
-}
+  return spanRandomBuffer().toString('hex');
+}

packages/opencensus-propagation-b3/src/b3-format.ts

@@ -76,8 +76,7 @@ export class B3Format implements Propagation {
   generate(): SpanContext {
     return {
       traceId: uuid.v4().split('-').join(''),
-      // tslint:disable-next-line:ban Needed to parse hexadecimal.
-      spanId: parseInt(crypto.randomBytes(6).toString('hex'), 16).toString(),
+      spanId: crypto.randomBytes(8).toString('hex'),
       options: SAMPLED_VALUE
     } as SpanContext;
   }

packages/opencensus-propagation-jaeger/src/jaeger-format.ts

@@ -97,8 +97,7 @@ export class JaegerFormat implements Propagation {
   generate(): SpanContext {
     return {
       traceId: uuid.v4().split('-').join(''),
-      // tslint:disable-next-line:ban Needed to parse hexadecimal.
-      spanId: parseInt(crypto.randomBytes(6).toString('hex'), 16).toString(),
+      spanId: crypto.randomBytes(8).toString('hex'),
       options: SAMPLED_VALUE
     } as SpanContext;
   }