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diff --git a/upb/google/bridge.h b/upb/google/bridge.h
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+//
+// upb - a minimalist implementation of protocol buffers.
+//
+// Copyright (c) 2011-2012 Google Inc.  See LICENSE for details.
+// Author: Josh Haberman <jhaberman@gmail.com>
+//
+// This file contains functionality for constructing upb Defs and Handlers
+// corresponding to proto2 messages.  Using this functionality, you can use upb
+// to dynamically generate parsing code that can behave exactly like proto2's
+// generated parsing code.  Alternatively, you can configure things to
+// read/write only a subset of the fields for higher performance when only some
+// fields are needed.
+//
+// Example usage (FIX XXX):
+//
+//   // Build a def that will have all fields and parse just like proto2 would.
+//   const upb::MessageDef* md = upb::proto2_bridge::NewMessageDef(&MyProto());
+//
+//   // JIT the parser; should only be done once ahead-of-time.
+//   upb::Handlers* handlers = upb::NewHandlersForMessage(md);
+//   upb::DecoderPlan* plan = upb::DecoderPlan::New(handlers);
+//   handlers->Unref();
+//
+//   // The actual parsing.
+//   MyProto proto;
+//   upb::Decoder decoder;
+//   upb::StringSource source(buf, len);
+//   decoder.ResetPlan(plan, 0);
+//   decoder.ResetInput(source.AllBytes(), &proto);
+//   CHECK(decoder.Decode() == UPB_OK) << decoder.status();
+//
+// To parse only one field and skip all others:
+//
+//   const upb::MessageDef* md =
+//       upb::proto2_bridge::NewEmptyMessageDef(MyProto().GetPrototype());
+//   upb::proto2_bridge::AddFieldDef(
+//       MyProto::descriptor()->FindFieldByName("my_field"), md);
+//   upb::Freeze(md);
+//
+//   // Now continue with "JIT the parser" from above.
+//
+// Note that there is currently no support for
+// CodedInputStream::SetExtensionRegistry(), which allows specifying a separate
+// DescriptorPool and MessageFactory for extensions.  Since this is a property
+// of the input in proto2, it's difficult to build a plan ahead-of-time that
+// can properly support this.  If it's an important use case, the caller should
+// probably build a upb plan explicitly.
+
+#ifndef UPB_GOOGLE_BRIDGE_H_
+#define UPB_GOOGLE_BRIDGE_H_
+
+namespace google {
+namespace protobuf { class Message; }
+}  // namespace google
+
+namespace proto2 { class Message; }
+
+namespace upb {
+
+class Handlers;
+
+namespace google {
+
+// Returns a upb::Handlers object that can be used to populate a proto2::Message
+// object of the same type as "m."
+//
+// TODO(haberman): Add handler caching functionality so that we don't use
+// O(n^2) memory in the worst case when incrementally building handlers.
+const upb::Handlers* NewWriteHandlers(const proto2::Message& m, void *owner);
+const upb::Handlers* NewWriteHandlers(const ::google::protobuf::Message& m,
+                                      void *owner);
+
+}  // namespace google
+}  // namespace upb
+
+#endif  // UPB_GOOGLE_BRIDGE_H_