--- a/lib/Protobuf-PHP/library/DrSlump/Protobuf/AnnotatedMessage.php
+++ b/lib/Protobuf-PHP/library/DrSlump/Protobuf/AnnotatedMessage.php
@@ -1,1 +1,116 @@
+<?php
 
+namespace DrSlump\Protobuf;
+
+use DrSlump\Protobuf;
+
+abstract class AnnotatedMessage extends Message
+{
+    static public function descriptor()
+    {
+        $class = get_called_class();
+
+        // Instantiate a new descriptor
+        $descriptor = new Descriptor($class);
+
+        $rflClass = new \ReflectionClass($class);
+        $props = $rflClass->getProperties();
+        foreach ($props as $prop) {
+            $doc = $prop->getDocComment();
+            if (empty($doc)) {
+                continue;
+            }
+
+            // Format: @protobuf(tag=X, type=bool, required=true)
+
+            // Extract annotation from the comment
+            if (!preg_match('/@protobuf\s?\(([^\)]+)\)/', $doc, $m)) {
+                continue;
+            }
+
+            // Parse params
+            $params = explode(',', $m[1]);
+            $params = array_filter(array_map('trim', $params));
+
+            $options = array();
+            foreach ($params as $param) {
+                $parts = explode('=', $param);
+                $parts = array_filter(array_map('trim', $parts));
+                $options[$parts[0]] = count($parts) < 2
+                                    ? true
+                                    : $parts[1];
+            }
+
+            // Check if we have the minimum required options
+            if (empty($options['tag'])) {
+                throw new \InvalidArgumentException('The tag option is required for property ' . $prop->getName());
+            }
+            if (empty($options['type'])) {
+                throw new \InvalidArgumentException('The type option is required for property ' . $prop->getName());
+            }
+
+            // Normalize boolean values
+            foreach(array('required', 'optional', 'repeated', 'packed') as $opt) {
+                if (isset($options[$opt])) {
+                    $options[$opt] = filter_var($options[$opt], FILTER_VALIDATE_BOOLEAN);
+                }
+            }
+
+            // Build a field descriptor
+            $f = new Protobuf\Field();
+            $f->number    = (int)$options['tag'];
+            $f->name      = $prop->getName();
+
+            // Convert type name to its numeric constant
+            switch (strtolower($options['type'])) {
+            case 'double'  : $f->type = Protobuf::TYPE_DOUBLE; break;
+            case 'float'   : $f->type = Protobuf::TYPE_FLOAT; break;
+            case 'int64'   : $f->type = Protobuf::TYPE_INT64; break;
+            case 'uint64'  : $f->type = Protobuf::TYPE_UINT64; break;
+            case 'int32'   : $f->type = Protobuf::TYPE_INT32; break;
+            case 'fixed64' : $f->type = Protobuf::TYPE_FIXED64; break;
+            case 'fixed32' : $f->type = Protobuf::TYPE_FIXED32; break;
+            case 'bool'    : $f->type = Protobuf::TYPE_BOOL; break;
+            case 'string'  : $f->type = Protobuf::TYPE_STRING; break;
+            case 'message' : $f->type = Protobuf::TYPE_MESSAGE; break;
+            case 'bytes'   : $f->type = Protobuf::TYPE_BYTES; break;
+            case 'uint32'  : $f->type = Protobuf::TYPE_UINT32; break;
+            case 'enum'    : $f->type = Protobuf::TYPE_ENUM; break;
+            case 'sfixed32': $f->type = Protobuf::TYPE_SFIXED32; break;
+            case 'sfixed64': $f->type = Protobuf::TYPE_SFIXED64; break;
+            case 'sint32'  : $f->type = Protobuf::TYPE_SINT32; break;
+            case 'sint64'  : $f->type = Protobuf::TYPE_SINT64; break;
+            default:
+                throw new \InvalidArgumentException('Type ' . $options['type'] . ' is not recognized as valid for property ' . $prop->getName());
+            }
+
+            // Define the rule type
+            $f->rule = Protobuf::RULE_OPTIONAL;
+            if (!empty($options['required'])) $f->rule = Protobuf::RULE_REQUIRED;
+            if (!empty($options['repeated'])) $f->rule = Protobuf::RULE_REPEATED;
+
+            // Check if it's flagged as packed
+            if (isset($options['packed'])) {
+                $f->packed = $options['packed'];
+            }
+
+            // Get the reference
+            if (isset($options['reference'])) {
+                $f->reference = $options['reference'];
+            } else if ($f->type === Protobuf::TYPE_MESSAGE || $f->type === Protobuf::TYPE_ENUM) {
+                throw new \InvalidArgumentException('Property ' . $prop->getName() . ' requires the "reference" option');
+            }
+
+            if (isset($options['default'])) {
+                $f->default = $options['default'];
+            }
+
+            // Add the field to the message descriptor
+            $descriptor->addField($f);
+        }
+
+        return $descriptor;
+    }
+
+}
+