SpanData now implements stackTraceHashId() (#154)

* SpanData now implements stackTraceHashId()

* Workaround for intsize on 32-bit PHP

* Store and return the hashId as a hex string to preserve uint64 semantics

Author: chingor13

src/Trace/SpanData.php

@@ -136,6 +136,14 @@ class SpanData
      */
     private $kind;
 
+    /**
+     * An optional value to de-dup the stackTrace array. Represented as a
+     * hexadecimal string.
+     *
+     * @var string
+     */
+    private $stackTraceHashId;
+
     /**
      * Instantiate a new SpanData instance.
      *
@@ -303,6 +311,21 @@ public function stackTrace()
         return $this->stackTrace;
     }
 
+    /**
+     * Return a hash id for this span's stackTrace in hexadecimal
+     *
+     * @return string
+     */
+    public function stackTraceHashId()
+    {
+        if (!isset($this->stackTraceHashId)) {
+            // take the lower 16 digits of the md5
+            $md5 = md5(serialize($this->stackTrace));
+            $this->stackTraceHashId = substr($md5, 16);
+        }
+        return $this->stackTraceHashId;
+    }
+
     /**
      * Whether or not this span is in the same process as its parent.
      *

tests/unit/Trace/SpanDataTest.php

@@ -70,4 +70,22 @@ public function spanDataOptions()
             ['kind', Span::KIND_SERVER]
         ];
     }
+
+    public function testStackTraceHashIdIsRepeatable()
+    {
+        $stackTrace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
+        $startTime = new \DateTime();
+        $endTime = new \DateTime();
+        $spanData = new SpanData('span-name', 'aaa', 'bbb', $startTime, $endTime, [
+            'stackTrace' => $stackTrace
+        ]);
+
+        $spanData2 = new SpanData('span-name2', 'aaa', 'bbb', $startTime, $endTime, [
+            'stackTrace' => $stackTrace
+        ]);
+
+        $hashId = $spanData->stackTraceHashId();
+        $this->assertInternalType('string', $hashId);
+        $this->assertEquals($hashId, $spanData2->stackTraceHashId());
+    }
 }