feat(span): use inject and extract for span context

Author: Peter Marton

Diff for: src/instrumentation/express.js

@@ -29,11 +29,7 @@ function patchModuleRoot (express, tracer) {
   function middleware (req, res, next) {
     // start
     const url = `${req.protocol}://${req.hostname}${req.originalUrl}`
-    const parentSpanContextStr = req.headers['trace-span-context']
-    const parentSpanContext = parentSpanContextStr
-      ? SpanContext.fromString(parentSpanContextStr)
-      : undefined
-
+    const parentSpanContext = tracer.extract(opentracing.FORMAT_HTTP_HEADERS, req.headers)
     const span = cls.startRootSpan(tracer, OPERATION_NAME, parentSpanContext)
 
     span.setTag(opentracing.Tags.HTTP_URL, url)

Diff for: src/instrumentation/httpClient.js

@@ -54,7 +54,7 @@ function patchHttp (http, tracer) {
       options = _.isString(options) ? url.parse(options) : _.merge({}, options)
       options.headers = options.headers || {}
 
-      options.headers['trace-span-context'] = span.context().toString()
+      tracer.inject(span, opentracing.FORMAT_HTTP_HEADERS, options.headers)
 
       const uri = extractUrl(options)
       span.setTag(opentracing.Tags.HTTP_URL, uri)