Fix HTTP headers in fetch instrumentation (#489)

Author: juan-fernandez

features/support/tracer.ts

@@ -12,11 +12,15 @@ function wrap(method: any) {
     return tracer.trace(
       "fetch",
       { type: "http", resource: request.getUrl() },
-      (span: any) => {
+      (span: any, callback?: (error?: Error) => string) => {
         const spanId = span.context().toSpanId();
         const traceId = span.context().toTraceId();
         request.setHeaderParam("x-datadog-parent-id", spanId);
         request.setHeaderParam("x-datadog-trace-id", traceId);
+        // These headers are required to prevent the continuation of the trace from being dropped
+        request.setHeaderParam("x-datadog-origin", "ciapp-test");
+        request.setHeaderParam("x-datadog-sampling-priority", "1");
+        request.setHeaderParam("x-datadog-sampled", "1");
         const response = method(request);
 
         response.promise = response.promise.then((responseContext: any) => {
@@ -29,6 +33,13 @@ function wrap(method: any) {
           }
           return responseContext;
         });
+
+        response.promise.finally(() => {
+          if (callback) {
+            callback()
+          }
+        });
+
         return response;
       }
     );