Fix file exporter serialization (#124)

* Init arrays as arrays

If we try to convert OpenCensus\Trace\Span
to Google\Cloud\Trace\Span and timeEvents
is null, we'll get an error while calling
json_encode on spans with null timeEvents.

As Google\Cloud\Trace\Span addTimeEvents
method expects array if we give null it
will raise an error.

* Fix FileExporter report serialization (#119)

The FileExporter report method uses json_encode
but pass an OpenCensus\Trace\Span array as arg.

As OpenCensus\Trace\Span does not implements
JsonSerializable it isn't serealizable.

Convert spans into arrays solves the issue.

Author: Arquivei

src/Trace/Exporter/FileExporter.php

@@ -17,6 +17,7 @@
 
 namespace OpenCensus\Trace\Exporter;
 
+use OpenCensus\Trace\Span;
 use OpenCensus\Trace\Tracer\TracerInterface;
 
 /**
@@ -57,6 +58,35 @@ public function __construct($filename)
      */
     public function report(TracerInterface $tracer)
     {
-        return file_put_contents($this->filename, json_encode($tracer->spans()) . PHP_EOL, FILE_APPEND) !== false;
+        $spans = $this->convertSpans($tracer);
+        return file_put_contents($this->filename, json_encode($spans) . PHP_EOL, FILE_APPEND) !== false;
+    }
+
+    /**
+     * Convert spans into array ready for serialization.
+     *
+     * @param TracerInterface $tracer
+     * @return array Representation of the collected trace spans ready for serialization
+     */
+    private function convertSpans(TracerInterface $tracer)
+    {
+        $traceId = $tracer->spanContext()->traceId();
+
+        return array_map(function (Span $span) use ($traceId) {
+            return [
+                'traceId' => $traceId,
+                'name' => $span->name(),
+                'spanId' => $span->spanId(),
+                'parentSpanId' => $span->parentSpanId(),
+                'stackTrace' => $span->stackTrace(),
+                'startTime' => $span->startTime(),
+                'endTime' => $span->endTime(),
+                'status' => $span->status(),
+                'attributes' => $span->attributes(),
+                'timeEvents' => $span->timeEvents(),
+                'links' => $span->links(),
+                'sameProcessAsParentSpan' => $span->sameProcessAsParentSpan(),
+            ];
+        }, $tracer->spans());
     }
 }

src/Trace/Span.php

@@ -88,7 +88,7 @@ class Span
      *
      * @var array
      */
-    private $stackTrace;
+    private $stackTrace = [];
 
     /**
      * A collection of `TimeEvent`s. A `TimeEvent` is a time-stamped annotation
@@ -97,15 +97,15 @@ class Span
      *
      * @var TimeEvent[]
      */
-    private $timeEvents;
+    private $timeEvents = [];
 
     /**
      * A collection of links, which are references from this span to a span
      * in the same or different trace.
      *
-     * @var Link
+     * @var Link[]
      */
-    private $links;
+    private $links = [];
 
     /**
      * An optional final status for this span.

tests/unit/Trace/Exporter/FileExporterTest.php

@@ -43,6 +43,8 @@ public function tearDown()
 
     public function testLogsTrace()
     {
+        $this->tracer->spanContext()->willReturn(new SpanContext());
+
         $spans = [
             new Span([
                 'name' => 'span',