Exporters should handle empty traces (#107)

* Add test for empty trace

* Skip setting common root span elements if there are no spans

* Add test for empty trace for ZipkinExporter

* Fix ZipkinExporter when the trace is empty

Author: chingor13

src/Trace/Exporter/StackdriverExporter.php

@@ -156,15 +156,16 @@ public function __construct(array $options = [])
     public function report(TracerInterface $tracer)
     {
         $this->processSpans($tracer);
-        $trace = self::$client->trace(
-            $tracer->spanContext()->traceId()
-        );
-        $spans = $this->convertSpans($tracer, $trace);
+        $spans = $this->convertSpans($tracer);
 
         if (empty($spans)) {
             return false;
         }
 
+        $trace = self::$client->trace(
+            $tracer->spanContext()->traceId()
+        );
+
         // build a Trace object and assign Spans
         $trace->setSpans($spans);
 
@@ -235,7 +236,11 @@ protected function getCallback()
     private function addCommonAttributes(&$tracer, $headers = null)
     {
         $headers = $headers ?: $_SERVER;
-        $rootSpan = $tracer->spans()[0];
+        $spans = $tracer->spans();
+        if (empty($spans)) {
+            return;
+        }
+        $rootSpan = $spans[0];
 
         $attributeMap = [
             self::HTTP_URL => ['REQUEST_URI'],

src/Trace/Exporter/ZipkinExporter.php

@@ -115,15 +115,14 @@ public function convertSpans(TracerInterface $tracer, $headers = null)
     {
         $headers = $headers ?: $_SERVER;
         $spans = $tracer->spans();
-        $rootSpan = $spans[0];
         $traceId = $tracer->spanContext()->traceId();
 
         // True is a request to store this span even if it overrides sampling policy.
         // This is true when the X-B3-Flags header has a value of 1.
         $isDebug = array_key_exists('HTTP_X_B3_FLAGS', $headers) && $headers['HTTP_X_B3_FLAGS'] == '1';
 
         // True if we are contributing to a span started by another tracer (ex on a different host).
-        $isShared = $rootSpan && $rootSpan->parentSpanId() != null;
+        $isShared = !empty($spans) && $spans[0]->parentSpanId() != null;
 
         $localEndpoint = [
             'serviceName' => $this->name,

tests/unit/Trace/Exporter/StackdriverExporterTest.php

@@ -134,4 +134,12 @@ public function testStacktrace()
         $data = $spans[0]->jsonSerialize();
         $this->assertArrayHasKey('stackTrace', $data);
     }
+
+    public function testEmptyTrace()
+    {
+        $tracer = new ContextTracer(new SpanContext('testtraceid'));
+
+        $reporter = new StackdriverExporter(['client' => $this->client->reveal()]);
+        $this->assertFalse($reporter->report($tracer));
+    }
 }

tests/unit/Trace/Exporter/ZipkinExporterTest.php

@@ -127,4 +127,13 @@ public function testSpanShared()
         $this->assertCount(1, $spans);
         $this->assertTrue($spans[0]['shared']);
     }
+
+    public function testEmptyTrace()
+    {
+        $spanContext = new SpanContext('testtraceid', 12345);
+        $tracer = new ContextTracer($spanContext);
+        $reporter = new ZipkinExporter('myapp', 'localhost', 9411);
+        $spans = $reporter->convertSpans($tracer);
+        $this->assertEmpty($spans);
+    }
 }