Fix inconsistent timestamp json encode/decode

php/src/Google/Protobuf/Internal/GPBUtil.php

@@ -485,6 +485,10 @@ class GPBUtil
                 $nanoseconds = substr($timestamp, $periodIndex + 1, $nanosecondsLength);
                 $nanoseconds = intval($nanoseconds);
 
+                if ($nanosecondsLength < 9) {
+                    $nanoseconds = $nanoseconds * pow(10, 9 - $nanosecondsLength);
+                }
+
                 // remove the nanoseconds and preceding period from the timestamp
                 $date = substr($timestamp, 0, $periodIndex);
                 $timezone = substr($timestamp, $periodIndex + $nanosecondsLength + 1);

php/tests/EncodeDecodeTest.php

@@ -992,6 +992,16 @@ class EncodeDecodeTest extends TestBase
                             $m->serializeToJsonString());
     }
 
+    public function testEncodeDecodeTimestampConsistency()
+    {
+        $m = new Google\Protobuf\Timestamp();
+        $m->setSeconds(946684800);
+        $m->setNanos(123000000);
+        $m->mergeFromJsonString($m->serializeToJsonString());
+        $this->assertEquals(946684800, $m->getSeconds());
+        $this->assertEquals(123000000, $m->getNanos());
+    }
+
     public function testDecodeTopLevelValue()
     {
         $m = new Value();