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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:
+//
+//   // JIT the parser; should only be done once ahead-of-time.
+//   upb::reffed_ptr<const upb::Handlers> write_myproto(
+//       upb::google::NewWriteHandlers(MyProto()));
+//   upb::reffed_ptr<const upb::Handlers> parse_myproto(
+//       upb::Decoder::NewDecoderHandlers(write_myproto.get(), true));
+//
+//   // The actual parsing.
+//   MyProto proto;
+//   upb::SeededPipeline<8192> pipeline(upb_realloc, NULL);
+//   upb::Sink* write_sink = pipeline.NewSink(write_myproto.get());
+//   upb::Sink* parse_sink = pipeline.NewSink(parse_myproto.get());
+//   upb::pb::Decoder* decoder = decoder_sink->GetObject<upb::pb::Decoder>();
+//   upb::pb::ResetDecoderSink(decoder, write_sink);
+//   write_sink->Reset(&proto);
+//
+// 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_
+
+#include <map>
+#include <vector>
+#include "upb/handlers.h"
+#include "upb/upb.h"
+
+namespace google {
+namespace protobuf {
+class FieldDescriptor;
+class Descriptor;
+class EnumDescriptor;
+class Message;
+}  // namespace protobuf
+}  // namespace google
+
+namespace proto2 {
+class FieldDescriptor;
+class Descriptor;
+class EnumDescriptor;
+class Message;
+}
+
+namespace upb {
+
+namespace googlepb {
+
+// Returns a upb::Handlers object that can be used to populate a proto2::Message
+// object of the same type as "m."  For more control over handler caching and
+// reuse, instantiate a CodeCache object below.
+upb::reffed_ptr<const upb::Handlers> NewWriteHandlers(const proto2::Message& m);
+upb::reffed_ptr<const upb::Handlers> NewWriteHandlers(
+    const ::google::protobuf::Message& m);
+
+// Builds upb::Defs from proto2::Descriptors, and caches all built Defs for
+// reuse.  CodeCache (below) uses this internally; there is no need to use this
+// class directly unless you only want Defs without corresponding Handlers.
+//
+// This class is NOT thread-safe.
+class DefBuilder {
+ public:
+  // Functions to get or create a Def from a corresponding proto2 Descriptor.
+  // The returned def will be frozen.
+  //
+  // The caller must take a ref on the returned value if it needs it long-term.
+  // The DefBuilder will retain a ref so it can keep the Def cached, but
+  // garbage-collection functionality may be added to DefBuilder later that
+  // could unref the returned pointer.
+  const EnumDef* GetEnumDef(const proto2::EnumDescriptor* d);
+  const EnumDef* GetEnumDef(const ::google::protobuf::EnumDescriptor* d);
+  const MessageDef* GetMessageDef(const proto2::Descriptor* d);
+  const MessageDef* GetMessageDef(const ::google::protobuf::Descriptor* d);
+
+  // Gets or creates a frozen MessageDef, properly expanding weak fields.
+  //
+  // Weak fields are only represented as BYTES fields in the Descriptor (unless
+  // you construct your descriptors in a somewhat complicated way; see
+  // https://goto.google.com/weak-field-descriptor), but we can get their true
+  // definitions relatively easily from the proto Message class.
+  const MessageDef* GetMessageDefExpandWeak(const proto2::Message& m);
+  const MessageDef* GetMessageDefExpandWeak(
+      const ::google::protobuf::Message& m);
+
+  // Static methods for converting a def without building a DefBuilder.
+  static reffed_ptr<const MessageDef> NewMessageDef(
+      const proto2::Descriptor* d) {
+    DefBuilder builder;
+    return reffed_ptr<const MessageDef>(builder.GetMessageDef(d));
+  }
+
+ private:
+  // Like GetMessageDef*(), except the returned def might not be frozen.
+  // We need this function because circular graphs of MessageDefs need to all
+  // be frozen together, to we have to create the graphs of defs in an unfrozen
+  // state first.
+  //
+  // If m is non-NULL, expands weak message fields.
+  const MessageDef* GetMaybeUnfrozenMessageDef(const proto2::Descriptor* d,
+                                               const proto2::Message* m);
+  const MessageDef* GetMaybeUnfrozenMessageDef(
+      const ::google::protobuf::Descriptor* d,
+      const ::google::protobuf::Message* m);
+
+  // Returns a new-unfrozen FieldDef corresponding to this FieldDescriptor.
+  // The return value is always newly created (never cached) and the returned
+  // pointer is the only owner of it.
+  //
+  // If "m" is non-NULL, expands the weak field if it is one, and populates
+  // *subm_prototype with a prototype of the submessage if this is a weak or
+  // non-weak MESSAGE or GROUP field.
+  reffed_ptr<FieldDef> NewFieldDef(const proto2::FieldDescriptor* f,
+                                   const proto2::Message* m);
+  reffed_ptr<FieldDef> NewFieldDef(const ::google::protobuf::FieldDescriptor* f,
+                                   const ::google::protobuf::Message* m);
+
+  // Freeze all defs that haven't been frozen yet.
+  void Freeze();
+
+  template <class T>
+  T* AddToCache(const void *proto2_descriptor, reffed_ptr<T> def) {
+    assert(def_cache_.find(proto2_descriptor) == def_cache_.end());
+    def_cache_[proto2_descriptor] = def;
+    return def.get();  // Continued lifetime is guaranteed by cache.
+  }
+
+  template <class T>
+  const T* FindInCache(const void *proto2_descriptor) {
+    DefCache::iterator iter = def_cache_.find(proto2_descriptor);
+    return iter == def_cache_.end() ? NULL :
+        upb::down_cast<const T*>(iter->second.get());
+  }
+
+ private:
+  // Maps a proto2 descriptor to the corresponding upb Def we have constructed.
+  // The proto2 descriptor is void* because the proto2 descriptor types do not
+  // share a common base.
+  typedef std::map<const void*, reffed_ptr<upb::Def> > DefCache;
+  DefCache def_cache_;
+
+  // Defs that have not been frozen yet.
+  std::vector<Def*> to_freeze_;
+};
+
+// Builds and caches upb::Handlers for populating proto2 generated classes.
+//
+// This class is NOT thread-safe.
+class CodeCache {
+ public:
+  // Gets or creates handlers for populating messages of the given message type.
+  //
+  // The caller must take a ref on the returned value if it needs it long-term.
+  // The CodeCache will retain a ref so it can keep the Def cached, but
+  // garbage-collection functionality may be added to CodeCache later that could
+  // unref the returned pointer.
+  const Handlers* GetWriteHandlers(const proto2::Message& m);
+  const Handlers* GetWriteHandlers(const ::google::protobuf::Message& m);
+
+ private:
+  const Handlers* GetMaybeUnfrozenWriteHandlers(const MessageDef* md,
+                                                const proto2::Message& m);
+  const Handlers* GetMaybeUnfrozenWriteHandlers(
+      const MessageDef* md, const ::google::protobuf::Message& m);
+
+  Handlers* AddToCache(const MessageDef* md, reffed_ptr<Handlers> handlers) {
+    assert(handlers_cache_.find(md) == handlers_cache_.end());
+    handlers_cache_[md] = handlers;
+    return handlers.get();  // Continue lifetime is guaranteed by the cache.
+  }
+
+  const Handlers* FindInCache(const MessageDef* md) {
+    HandlersCache::iterator iter = handlers_cache_.find(md);
+    return iter == handlers_cache_.end() ? NULL : iter->second.get();
+  }
+
+  DefBuilder def_builder_;
+
+  typedef std::map<const MessageDef*, upb::reffed_ptr<const Handlers> >
+      HandlersCache;
+  HandlersCache handlers_cache_;
+
+  std::vector<Handlers*> to_freeze_;
+};
+
+}  // namespace googlepb
+}  // namespace upb
+
+#endif  // UPB_GOOGLE_BRIDGE_H_