refactor(context): use shared buffer and string getters

Author: Stephen Belanger

lib/instrumentation/context.js

@@ -2,74 +2,57 @@
 
 const crypto = require('crypto')
 
-function fromHex (hex) {
-  return Buffer.from(hex, 'hex')
-}
-
-function toHex (buffer) {
-  return buffer.toString('hex')
+const OFFSETS = {
+  version: 0,
+  traceId: 1,
+  id: 17,
+  flags: 25
 }
 
 class TraceContext {
-  constructor ({ version, traceId, id, flags, parentId } = {}) {
-    // 1 byte
-    this.version = version
-    // 16 bytes
-    this.traceId = traceId
-    // 8 bytes
-    this.id = id
-    // 1 byte
-    this.flags = flags
-    // 8 bytes
-    this.parentId = parentId
+  constructor (buffer) {
+    this.buffer = buffer
   }
 
-  static create (sampled = false) {
-    const bytes = crypto.randomBytes(24)
-    const flags = Buffer.alloc(1)
-
-    // Load sampled flag into first bit of flags
-    if (sampled) {
-      flags[0] |= 0x01
-    } else {
-      flags[0] &= ~0x01
-    }
-
-    return new TraceContext({
-      version: Buffer.alloc(1),
-      traceId: bytes.slice(0, 16),
-      id: bytes.slice(16),
-      flags: flags
-    })
+  get version () {
+    return this.buffer.slice(
+      OFFSETS.version,
+      OFFSETS.traceId
+    ).toString('hex')
+  }
+  get traceId () {
+    return this.buffer.slice(
+      OFFSETS.traceId,
+      OFFSETS.id
+    ).toString('hex')
+  }
+  get id () {
+    return this.buffer.slice(
+      OFFSETS.id,
+      OFFSETS.flags
+    ).toString('hex')
+  }
+  get flags () {
+    return this.buffer.slice(
+      OFFSETS.flags
+    ).toString('hex')
   }
 
-  static fromString (header) {
-    const [
-      version,
-      traceId,
-      id,
-      flags
-    ] = header.split('-').map(fromHex)
-
-    return new TraceContext({
-      version,
-      traceId,
-      id,
-      flags
-    })
+  static create (sampled = false) {
+    const buffer = Buffer.alloc(26)
+    crypto.randomFillSync(buffer, 1, 24)
+    if (sampled) buffer[26] = 0x01
+    return new TraceContext(buffer)
   }
 
   child () {
-    const { version, traceId, id: parentId, flags } = this
-    const id = crypto.randomBytes(8)
+    const buffer = Buffer.from(this.buffer)
+    crypto.randomFillSync(buffer, 17, 8)
+    return new TraceContext(buffer)
+  }
 
-    return new TraceContext({
-      version,
-      traceId,
-      id,
-      flags,
-      parentId
-    })
+  static fromString (header) {
+    return new TraceContext(Buffer.from(header.replace(/-/g, ''), 'hex'))
   }
 
   toString () {
@@ -80,16 +63,16 @@ class TraceContext {
       this.flags
     ]
 
-    return parts.map(toHex).join('-')
+    return parts.join('-')
   }
 
   toJSON () {
     return {
-      version: this.version.toString('hex'),
-      traceId: this.traceId.toString('hex'),
-      id: this.id.toString('hex'),
-      flags: this.flags.toString('hex'),
-      parentId: this.parentId && this.parentId.toString('hex')
+      version: this.version,
+      traceId: this.traceId,
+      id: this.id,
+      flags: this.flags,
+      header: this.toString()
     }
   }
 }

test/instrumentation/context.js

@@ -12,31 +12,18 @@ const flags = Buffer.alloc(1)
 
 const header = `00-${traceId.toString('hex')}-${id.toString('hex')}-00`
 
-test('constructor', t => {
-  const context = new TraceContext({
-    version,
-    traceId,
-    id,
-    flags
-  })
-
-  t.ok(context instanceof TraceContext, 'has a trace context object')
-  t.ok(version.equals(context.version), 'version matches')
-  t.ok(traceId.equals(context.traceId), 'traceId matches')
-  t.ok(id.equals(context.id), 'id matches')
-  t.ok(flags.equals(context.flags), 'flags matches')
-
-  t.end()
-})
+function toHex (buffer) {
+  return buffer.toString('hex')
+}
 
 test('fromString', t => {
   const context = TraceContext.fromString(header)
 
   t.ok(context instanceof TraceContext, 'has a trace context object')
-  t.ok(version.equals(context.version), 'version matches')
-  t.ok(traceId.equals(context.traceId), 'traceId matches')
-  t.ok(id.equals(context.id), 'id matches')
-  t.ok(flags.equals(context.flags), 'flags matches')
+  t.equal(version.toString('hex'), context.version, 'version matches')
+  t.equal(traceId.toString('hex'), context.traceId, 'traceId matches')
+  t.equal(id.toString('hex'), context.id, 'id matches')
+  t.equal(flags.toString('hex'), context.flags, 'flags matches')
 
   t.end()
 })
@@ -55,7 +42,12 @@ test('toJSON', t => {
     traceId: traceId.toString('hex'),
     id: id.toString('hex'),
     flags: flags.toString('hex'),
-    parentId: undefined
+    header: [
+      version,
+      traceId,
+      id,
+      flags
+    ].map(toHex).join('-')
   }, 'trace context serializes fields to hex strings, in JSON form')
 
   t.end()
@@ -65,10 +57,10 @@ test('create', t => {
   const context = TraceContext.create()
 
   t.ok(context instanceof TraceContext, 'has a trace context object')
-  t.ok(version.equals(context.version), 'version matches')
-  t.notOk(traceId.equals(context.traceId), 'has new traceId')
-  t.notOk(id.equals(context.id), 'has new spanId')
-  t.ok(flags.equals(context.flags), 'flags matches')
+  t.equal(version.toString('hex'), context.version, 'version matches')
+  t.notEqual(traceId.toString('hex'), context.traceId, 'has new traceId')
+  t.notEqual(id.toString('hex'), context.id, 'has new id')
+  t.equal(flags.toString('hex'), context.flags, 'flags matches')
 
   t.end()
 })
@@ -78,11 +70,10 @@ test('child', t => {
   const context = parent.child()
 
   t.ok(context instanceof TraceContext, 'has a trace context object')
-  t.ok(version.equals(context.version), 'version matches')
-  t.ok(traceId.equals(context.traceId), 'traceId matches')
-  t.notOk(id.equals(context.id), 'has new id')
-  t.ok(flags.equals(context.flags), 'flags matches')
-  t.ok(parent.id.equals(context.parentId), 'parentId matches parent.id')
+  t.equal(version.toString('hex'), context.version, 'version matches')
+  t.equal(traceId.toString('hex'), context.traceId, 'has new traceId')
+  t.notEqual(id.toString('hex'), context.id, 'has new id')
+  t.equal(flags.toString('hex'), context.flags, 'flags matches')
 
   t.end()
 })