Adds encoders.

src/DDTrace/Encoder.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace DDTrace;
+
+use Psr\Http\Message\StreamInterface;
+
+interface Encoder
+{
+    /**
+     * @param Span[][]|array $traces
+     * @return string|StreamInterface
+     */
+    public function encodeTraces(array $traces);
+
+    /**
+     * @return string
+     */
+    public function getContentType();
+}

src/DDTrace/Encoders/Json.php

@@ -0,0 +1,75 @@
+<?php
+
+namespace DDTrace\Encoders;
+
+use DDTrace\Encoder;
+use DDTrace\Span;
+
+final class Json implements Encoder
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function encodeTraces(array $traces)
+    {
+        return '[' . implode(',', array_map(function ($trace) {
+            return '[' . implode(',', array_map(function ($span) {
+                return $this->encodeSpan($span);
+            }, $trace)) . ']';
+        }, $traces))  . ']';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getContentType()
+    {
+        return 'application/json';
+    }
+
+    /**
+     * @param Span $span
+     * @return array
+     */
+    private function spanToArray(Span $span)
+    {
+        $arraySpan = [
+            'trace_id' => $span->getTraceId(),
+            'span_id' => $span->getSpanId(),
+            'name' => $span->getOperationName(),
+            'resource' => $span->getResource(),
+            'service' => $span->getService(),
+            'start_micro' => 0,
+            'error' => $span->hasError() ? 1 : 0,
+        ];
+
+        if ($span->getType() !== null) {
+            $arraySpan['type'] = $span->getType();
+        }
+
+        if ($span->isFinished()) {
+            $arraySpan['duration_micro'] = 0;
+        }
+
+        if ($span->getParentId() !== null) {
+            $arraySpan['parent_id'] = $span->getParentId();
+        }
+
+        if (!empty($span->getAllTags())) {
+            $arraySpan['meta'] = $span->getAllTags();
+        }
+
+        return $arraySpan;
+    }
+
+    private function encodeSpan(Span $span)
+    {
+        return str_replace([
+            '"start_micro":0',
+            '"duration_micro":0',
+        ], [
+            '"start":' . $span->getStartTime() . '000',
+            '"duration":' . $span->getDuration() . '000',
+        ], json_encode($this->spanToArray($span)));
+    }
+}

src/DDTrace/Encoders/Noop.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace DDTrace\Encoders;
+
+use DDTrace\Encoder;
+
+final class Noop implements Encoder
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function encodeTraces(array $traces)
+    {
+        return '';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getContentType()
+    {
+        return 'noop';
+    }
+}

src/DDTrace/Span.php

@@ -226,8 +226,8 @@ public function getAllTags()
     }
 
     /**
-     * Stores a Throwable object within the span meta. The error status is
-     * updated and the error.Error() string is included with a default meta key.
+     * Stores a Throwable object within the span tags. The error status is
+     * updated and the error.Error() string is included with a default tag key.
      * If the Span has been finished, it will not be modified by this method.
      *
      * @param Throwable|Exception $error

tests/Unit/Encoders/JsonTest.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace DDTrace\Tests\Unit\Encoders;
+
+use DDTrace\Encoders\Json;
+use DDTrace\Span;
+use DDTrace\SpanContext;
+use PHPUnit_Framework_TestCase;
+
+final class JsonTest extends PHPUnit_Framework_TestCase
+{
+    public function testEncodeTracesSuccess()
+    {
+        $expectedPayload = <<<JSON
+[[{"trace_id":"160e7072ff7bd5f1","span_id":"160e7072ff7bd5f2","name":"test_name","resource":"test_resource",
+JSON
+            .    <<<JSON
+"service":"test_service","start":1518038421211969000,"error":0}]]
+JSON;
+
+        $context = new SpanContext('160e7072ff7bd5f1', '160e7072ff7bd5f2');
+        $span = new Span(
+            'test_name',
+            $context,
+            'test_service',
+            'test_resource',
+            1518038421211969
+        );
+        $jsonEncoder = new Json();
+        $encodedTrace = $jsonEncoder->encodeTraces([[$span]]);
+        $this->assertEquals($expectedPayload, $encodedTrace);
+    }
+}