diff --git a/lib/cpp/src/TReflectionLocal.h b/lib/cpp/src/TReflectionLocal.h
index 414a0eb..df6e706 100644
--- a/lib/cpp/src/TReflectionLocal.h
+++ b/lib/cpp/src/TReflectionLocal.h
@@ -22,7 +22,7 @@
  */
 
 struct FieldMeta {
-  int16_t tags;
+  int16_t tag;
   bool is_optional;
 };
 
diff --git a/lib/cpp/src/protocol/TBinaryProtocol.h b/lib/cpp/src/protocol/TBinaryProtocol.h
index 01f7c3b..89958ec 100644
--- a/lib/cpp/src/protocol/TBinaryProtocol.h
+++ b/lib/cpp/src/protocol/TBinaryProtocol.h
@@ -23,6 +23,7 @@
  protected:
   static const int32_t VERSION_MASK = 0xffff0000;
   static const int32_t VERSION_1 = 0x80010000;
+  // VERSION_2 (0x80020000)  is taken by TDenseProtocol.
 
  public:
   TBinaryProtocol(boost::shared_ptr<TTransport> trans) :
@@ -175,7 +176,6 @@
  protected:
   uint32_t readStringBody(std::string& str, int32_t sz);
 
- private:
   int32_t string_limit_;
   int32_t container_limit_;
 
diff --git a/lib/cpp/src/protocol/TDenseProtocol.cpp b/lib/cpp/src/protocol/TDenseProtocol.cpp
new file mode 100644
index 0000000..095dd64
--- /dev/null
+++ b/lib/cpp/src/protocol/TDenseProtocol.cpp
@@ -0,0 +1,480 @@
+// Copyright (c) 2006- Facebook
+// Distributed under the Thrift Software License
+//
+// See accompanying file LICENSE or visit the Thrift site at:
+// http://developers.facebook.com/thrift/
+
+#include "TDenseProtocol.h"
+#include "TReflectionLocal.h"
+
+// XXX for debugging (duh)
+#define DEBUG_TDENSEPROTOCOL
+
+// The XXX above does not apply to this.
+#ifdef DEBUG_TDENSEPROTOCOL
+#undef NDEBUG
+#endif
+#include <cassert>
+
+using std::string;
+
+namespace facebook { namespace thrift { namespace protocol {
+
+// Top TypeSpec.  TypeSpec of the structure being encoded.
+#define TTS  (ts_stack_.back())  // type = TypeSpec*
+// InDeX.  Index into TTS of the current/next field to encode.
+#define IDX (idx_stack_.back())  // type = int
+// Field TypeSpec.  TypeSpec of the current/next field to encode.
+#define FTS (TTS->tstruct.specs[IDX])  // type = TypeSpec*
+// Field MeTa.  Metadata of the current/next field to encode.
+#define FMT (TTS->tstruct.metas[IDX])  // type = FieldMeta
+// SubType 1/2.  TypeSpec of the first/second subtype of this container.
+#define ST1 (TTS->tcontainer.subtype1)
+#define ST2 (TTS->tcontainer.subtype2)
+
+
+inline void TDenseProtocol::checkTType(const TType ttype) {
+  assert(!ts_stack_.empty());
+  assert(TTS->ttype == ttype);
+}
+
+inline void TDenseProtocol::stateTransition() {
+  TypeSpec* old_tts = ts_stack_.back();
+  ts_stack_.pop_back();
+
+  if (ts_stack_.empty()) {
+    assert(old_tts = type_spec_);
+    return;
+  }
+
+  switch (TTS->ttype) {
+
+    case T_STRUCT:
+      assert(old_tts == FTS);
+      break;
+
+    case T_LIST:
+    case T_SET:
+      assert(old_tts == ST1);
+      ts_stack_.push_back(old_tts);
+      break;
+
+    case T_MAP:
+      assert(old_tts == (mkv_stack_.back() ? ST1 : ST2));
+      mkv_stack_.back() = !mkv_stack_.back();
+      ts_stack_.push_back(mkv_stack_.back() ? ST1 : ST2);
+      break;
+
+    default:
+      assert(!"Invalid TType in stateTransition.");
+      break;
+
+  }
+}
+
+uint32_t TDenseProtocol::writeMessageBegin(const std::string& name,
+                                           const TMessageType messageType,
+                                           const int32_t seqid) {
+  int32_t version = (VERSION_2) | ((int32_t)messageType);
+  uint32_t wsize = 0;
+  wsize += subWriteI32(version);
+  wsize += subWriteString(name);
+  wsize += subWriteI32(seqid);
+  return wsize;
+}
+
+uint32_t TDenseProtocol::writeMessageEnd() {
+  return 0;
+}
+
+// Also implements readStructBegin.
+uint32_t TDenseProtocol::writeStructBegin(const string& name) {
+  if (ts_stack_.empty()) {
+    if (type_spec_ == NULL) {
+      throw TApplicationException("TDenseProtocol: No type specified.");
+    } else {
+      ts_stack_.push_back(type_spec_);
+    }
+  }
+
+  idx_stack_.push_back(0);
+  return 0;
+}
+
+uint32_t TDenseProtocol::writeStructEnd() {
+  idx_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::writeFieldBegin(const string& name,
+                                         const TType fieldType,
+                                         const int16_t fieldId) {
+  uint32_t xfer = 0;
+
+  while (FMT.tag != fieldId) {
+    // TODO(dreiss): Old meta here.
+    assert(FTS->ttype != T_STOP);
+    assert(FMT.is_optional);
+    xfer += subWriteBool(false);
+    IDX++;
+  }
+
+  // TODO(dreiss): give a better exception.
+  assert(FTS->ttype == fieldType);
+
+  if (FMT.is_optional) {
+    subWriteBool(true);
+    xfer += 1;
+  }
+
+  // OMG I'm so gross.  XXX
+  if (FTS->ttype != T_STOP) {
+    ts_stack_.push_back(FTS);
+  }
+  return xfer;
+}
+
+uint32_t TDenseProtocol::writeFieldEnd() {
+  IDX++;
+  return 0;
+}
+
+uint32_t TDenseProtocol::writeFieldStop() {
+  return writeFieldBegin("", T_STOP, 0);
+}
+
+uint32_t TDenseProtocol::writeMapBegin(const TType keyType,
+                                       const TType valType,
+                                       const uint32_t size) {
+  checkTType(T_MAP);
+
+  assert(keyType == ST1->ttype);
+  assert(valType == ST2->ttype);
+
+  ts_stack_.push_back(ST1);
+  mkv_stack_.push_back(true);
+
+  return subWriteI32((int32_t)size);
+}
+
+uint32_t TDenseProtocol::writeMapEnd() {
+  ts_stack_.pop_back();
+  mkv_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::writeListBegin(const TType elemType,
+                                        const uint32_t size) {
+  checkTType(T_LIST);
+
+  assert(elemType == ST1->ttype);
+  ts_stack_.push_back(ST1);
+  return subWriteI32((int32_t)size);
+}
+
+uint32_t TDenseProtocol::writeListEnd() {
+  ts_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::writeSetBegin(const TType elemType,
+                                       const uint32_t size) {
+  checkTType(T_SET);
+
+  assert(elemType == ST1->ttype);
+  ts_stack_.push_back(ST1);
+  return subWriteI32((int32_t)size);
+}
+
+uint32_t TDenseProtocol::writeSetEnd() {
+  ts_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::writeBool(const bool value) {
+  checkTType(T_BOOL);
+  stateTransition();
+  return TBinaryProtocol::writeBool(value);
+}
+
+uint32_t TDenseProtocol::writeByte(const int8_t byte) {
+  checkTType(T_BYTE);
+  stateTransition();
+  return TBinaryProtocol::writeByte(byte);
+}
+
+
+
+// XXX Remove this code for collecting statistics.
+static int vli_size(uint64_t towrite) {
+  int count = 0;
+  while (true) {
+    towrite = towrite >> 7;
+    if (towrite == 0) {
+      return count+1;
+    }
+  }
+}
+
+uint32_t TDenseProtocol::writeI16(const int16_t i16) {
+  vli_save_16 += 2 - vli_size(i16);
+  if (i16 < 0) negs++;
+
+  checkTType(T_I16);
+  stateTransition();
+  return TBinaryProtocol::writeI16(i16);
+}
+
+uint32_t TDenseProtocol::writeI32(const int32_t i32) {
+  vli_save_32 += 4 - vli_size(i32);
+  if (i32 < 0) negs++;
+
+  checkTType(T_I32);
+  stateTransition();
+  return TBinaryProtocol::writeI32(i32);
+}
+
+uint32_t TDenseProtocol::writeI64(const int64_t i64) {
+  vli_save_64 += 8 - vli_size(i64);
+  if (i64 < 0) negs++;
+
+  checkTType(T_I64);
+  stateTransition();
+  return TBinaryProtocol::writeI64(i64);
+}
+
+uint32_t TDenseProtocol::writeDouble(const double dub) {
+  checkTType(T_DOUBLE);
+  stateTransition();
+  return TBinaryProtocol::writeDouble(dub);
+}
+
+uint32_t TDenseProtocol::writeString(const std::string& str) {
+  checkTType(T_STRING);
+  stateTransition();
+  return subWriteString(str);
+}
+
+// XXX this can go into .h when we delete instrumentaion.  (See subWritebool)
+inline uint32_t TDenseProtocol::subWriteI32(const int32_t i32) {
+  vli_save_sub += 4 - vli_size(i32);
+  if (i32 < 0) negs++;
+
+  int32_t net = (int32_t)htonl(i32);
+  trans_->write((uint8_t*)&net, 4);
+  return 4;
+}
+
+// XXX Delete when subWriteI32 goes into .h
+uint32_t TDenseProtocol::subWriteString(const std::string& str) {
+  uint32_t size = str.size();
+  uint32_t xfer = subWriteI32((int32_t)size);
+  if (size > 0) {
+    trans_->write((uint8_t*)str.data(), size);
+  }
+  return xfer + size;
+}
+
+
+/**
+ * Reading functions
+ */
+
+uint32_t TDenseProtocol::readMessageBegin(std::string& name,
+                                          TMessageType& messageType,
+                                          int32_t& seqid) {
+  uint32_t xfer = 0;
+  int32_t sz;
+  xfer += subReadI32(sz);
+
+  if (sz < 0) {
+    // Check for correct version number
+    int32_t version = sz & VERSION_MASK;
+    if (version != VERSION_2) {
+      throw TProtocolException(TProtocolException::BAD_VERSION, "Bad version identifier");
+    }
+    messageType = (TMessageType)(sz & 0x000000ff);
+    xfer += subReadString(name);
+    xfer += subReadI32(seqid);
+  } else {
+    throw TProtocolException(TProtocolException::BAD_VERSION, "No version identifier... old protocol client in strict mode?");
+  }
+  return xfer;
+}
+
+uint32_t TDenseProtocol::readMessageEnd() {
+  return 0;
+}
+
+uint32_t TDenseProtocol::readStructBegin(string& name) {
+  // TODO(dreiss): Any chance this gets inlined?
+  return TDenseProtocol::writeStructBegin(name);
+}
+
+uint32_t TDenseProtocol::readStructEnd() {
+  idx_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::readFieldBegin(string& name,
+                                        TType& fieldType,
+                                        int16_t& fieldId) {
+  uint32_t xfer = 0;
+
+  while (FMT.is_optional) {
+    bool is_present;
+    xfer += subReadBool(is_present);
+    if (is_present) {
+      break;
+    }
+    IDX++;
+  }
+
+  fieldId   = FMT.tag;
+  fieldType = FTS->ttype;
+
+  // OMG I'm so gross.  XXX
+  if (FTS->ttype != T_STOP) {
+    ts_stack_.push_back(FTS);
+  }
+  return xfer;
+}
+
+uint32_t TDenseProtocol::readFieldEnd() {
+  IDX++;
+  return 0;
+}
+
+uint32_t TDenseProtocol::readMapBegin(TType& keyType,
+                                      TType& valType,
+                                      uint32_t& size) {
+  checkTType(T_MAP);
+
+  uint32_t xfer = 0;
+  int32_t sizei;
+  xfer += subReadI32(sizei);
+  if (sizei < 0) {
+    throw TProtocolException(TProtocolException::NEGATIVE_SIZE);
+  } else if (container_limit_ && sizei > container_limit_) {
+    throw TProtocolException(TProtocolException::SIZE_LIMIT);
+  }
+  size = (uint32_t)sizei;
+
+  keyType = ST1->ttype;
+  valType = ST2->ttype;
+
+  ts_stack_.push_back(ST1);
+  mkv_stack_.push_back(true);
+
+  return xfer;
+}
+
+uint32_t TDenseProtocol::readMapEnd() {
+  ts_stack_.pop_back();
+  mkv_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::readListBegin(TType& elemType,
+                                       uint32_t& size) {
+  checkTType(T_LIST);
+
+  uint32_t xfer = 0;
+  int32_t sizei;
+  xfer += subReadI32(sizei);
+  if (sizei < 0) {
+    throw TProtocolException(TProtocolException::NEGATIVE_SIZE);
+  } else if (container_limit_ && sizei > container_limit_) {
+    throw TProtocolException(TProtocolException::SIZE_LIMIT);
+  }
+  size = (uint32_t)sizei;
+
+  elemType = ST1->ttype;
+
+  ts_stack_.push_back(ST1);
+
+  return xfer;
+}
+
+uint32_t TDenseProtocol::readListEnd() {
+  ts_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::readSetBegin(TType& elemType,
+                                      uint32_t& size) {
+  checkTType(T_SET);
+
+  uint32_t xfer = 0;
+  int32_t sizei;
+  xfer += subReadI32(sizei);
+  if (sizei < 0) {
+    throw TProtocolException(TProtocolException::NEGATIVE_SIZE);
+  } else if (container_limit_ && sizei > container_limit_) {
+    throw TProtocolException(TProtocolException::SIZE_LIMIT);
+  }
+  size = (uint32_t)sizei;
+
+  elemType = ST1->ttype;
+
+  ts_stack_.push_back(ST1);
+
+  return xfer;
+}
+
+uint32_t TDenseProtocol::readSetEnd() {
+  ts_stack_.pop_back();
+  stateTransition();
+  return 0;
+}
+
+uint32_t TDenseProtocol::readBool(bool& value) {
+  checkTType(T_BOOL);
+  stateTransition();
+  return TBinaryProtocol::readBool(value);
+}
+
+uint32_t TDenseProtocol::readByte(int8_t& byte) {
+  checkTType(T_BYTE);
+  stateTransition();
+  return TBinaryProtocol::readByte(byte);
+}
+
+uint32_t TDenseProtocol::readI16(int16_t& i16) {
+  checkTType(T_I16);
+  stateTransition();
+  return TBinaryProtocol::readI16(i16);
+}
+
+uint32_t TDenseProtocol::readI32(int32_t& i32) {
+  checkTType(T_I32);
+  stateTransition();
+  return TBinaryProtocol::readI32(i32);
+}
+
+uint32_t TDenseProtocol::readI64(int64_t& i64) {
+  checkTType(T_I64);
+  stateTransition();
+  return TBinaryProtocol::readI64(i64);
+}
+
+uint32_t TDenseProtocol::readDouble(double& dub) {
+  checkTType(T_DOUBLE);
+  stateTransition();
+  return TBinaryProtocol::readDouble(dub);
+}
+
+uint32_t TDenseProtocol::readString(std::string& str) {
+  checkTType(T_STRING);
+  stateTransition();
+  return subReadString(str);
+}
+
+}}} // facebook::thrift::protocol
diff --git a/lib/cpp/src/protocol/TDenseProtocol.h b/lib/cpp/src/protocol/TDenseProtocol.h
new file mode 100644
index 0000000..ffc6afa
--- /dev/null
+++ b/lib/cpp/src/protocol/TDenseProtocol.h
@@ -0,0 +1,247 @@
+// Copyright (c) 2006- Facebook
+// Distributed under the Thrift Software License
+//
+// See accompanying file LICENSE or visit the Thrift site at:
+// http://developers.facebook.com/thrift/
+
+#ifndef _THRIFT_PROTOCOL_TDENSEPROTOCOL_H_
+#define _THRIFT_PROTOCOL_TDENSEPROTOCOL_H_ 1
+
+#include "TBinaryProtocol.h"
+
+namespace facebook { namespace thrift { namespace protocol {
+
+/**
+ * The dense protocol is designed to use as little space as possible.
+ *
+ * !!!WARNING!!!
+ * This class is still highly experimental.  Incompatible changes
+ * WILL be made to it without notice.  DO NOT USE IT YET unless
+ * you are coordinating your testing with the author.
+ *
+ * TODO(dreiss): New class write with old meta.
+ *
+ * We override all of TBinaryProtocol's methods.
+ * We inherit so that we can can explicitly call TBPs's primitive-writing
+ * methods within our versions.
+ *
+ * @author David Reiss <dreiss@facebook.com>
+ */
+class TDenseProtocol : public TBinaryProtocol {
+ protected:
+  static const int32_t VERSION_MASK = 0xffff0000;
+  // VERSION_2 (0x80010000)  is taken by TBinaryProtocol.
+  static const int32_t VERSION_2 = 0x80020000;
+
+ public:
+  typedef facebook::thrift::reflection::local::TypeSpec TypeSpec;
+
+  TDenseProtocol(boost::shared_ptr<TTransport> trans,
+                 TypeSpec* type_spec = NULL) :
+    TBinaryProtocol(trans),
+    type_spec_(type_spec) {
+      vli_save_16 = 0;
+      vli_save_32 = 0;
+      vli_save_64 = 0;
+      vli_save_sub = 0;
+      negs = 0;
+    }
+
+  TDenseProtocol(boost::shared_ptr<TTransport> trans,
+                  TypeSpec* type_spec,
+                  int32_t string_limit,
+                  int32_t container_limit) :
+    TBinaryProtocol(trans,
+                    string_limit,
+                    container_limit,
+                    true,
+                    true),
+    type_spec_(type_spec) {
+      vli_save_16 = 0;
+      vli_save_32 = 0;
+      vli_save_64 = 0;
+      vli_save_sub = 0;
+      negs = 0;
+    }
+
+  void setTypeSpec(TypeSpec* type_spec) {
+    type_spec_ = type_spec;
+  }
+  TypeSpec* getTypeSpec() {
+    return type_spec_;
+  }
+
+
+  /*
+   * Writing functions.
+   */
+
+  virtual uint32_t writeMessageBegin(const std::string& name,
+                                     const TMessageType messageType,
+                                     const int32_t seqid);
+
+  virtual uint32_t writeMessageEnd();
+
+
+  virtual uint32_t writeStructBegin(const std::string& name);
+
+  virtual uint32_t writeStructEnd();
+
+  virtual uint32_t writeFieldBegin(const std::string& name,
+                                   const TType fieldType,
+                                   const int16_t fieldId);
+
+  virtual uint32_t writeFieldEnd();
+
+  virtual uint32_t writeFieldStop();
+
+  virtual uint32_t writeMapBegin(const TType keyType,
+                                 const TType valType,
+                                 const uint32_t size);
+
+  virtual uint32_t writeMapEnd();
+
+  virtual uint32_t writeListBegin(const TType elemType,
+                                  const uint32_t size);
+
+  virtual uint32_t writeListEnd();
+
+  virtual uint32_t writeSetBegin(const TType elemType,
+                                 const uint32_t size);
+
+  virtual uint32_t writeSetEnd();
+
+  virtual uint32_t writeBool(const bool value);
+
+  virtual uint32_t writeByte(const int8_t byte);
+
+  virtual uint32_t writeI16(const int16_t i16);
+
+  virtual uint32_t writeI32(const int32_t i32);
+
+  virtual uint32_t writeI64(const int64_t i64);
+
+  virtual uint32_t writeDouble(const double dub);
+
+  virtual uint32_t writeString(const std::string& str);
+
+
+  /*
+   * Helper writing functions (don't do state transitions).
+   */
+  inline uint32_t subWriteI32(const int32_t i32);
+
+  uint32_t subWriteBool(const bool value) {
+    return TBinaryProtocol::writeBool(value);
+  }
+
+#if 0
+  // Use this version when subWriteI32 is moved in here.
+  uint32_t subWriteString(const std::string& str) {
+    uint32_t size = str.size();
+    uint32_t xfer = subWriteI32((int32_t)size);
+    if (size > 0) {
+      trans_->write((uint8_t*)str.data(), size);
+    }
+    return xfer + size;
+  }
+#else
+  inline uint32_t subWriteString(const std::string& str);
+#endif
+
+
+  /*
+   * Reading functions
+   */
+
+  uint32_t readMessageBegin(std::string& name,
+                            TMessageType& messageType,
+                            int32_t& seqid);
+
+  uint32_t readMessageEnd();
+
+  uint32_t readStructBegin(std::string& name);
+
+  uint32_t readStructEnd();
+
+  uint32_t readFieldBegin(std::string& name,
+                          TType& fieldType,
+                          int16_t& fieldId);
+
+  uint32_t readFieldEnd();
+
+  uint32_t readMapBegin(TType& keyType,
+                        TType& valType,
+                        uint32_t& size);
+
+  uint32_t readMapEnd();
+
+  uint32_t readListBegin(TType& elemType,
+                         uint32_t& size);
+
+  uint32_t readListEnd();
+
+  uint32_t readSetBegin(TType& elemType,
+                        uint32_t& size);
+
+  uint32_t readSetEnd();
+
+  uint32_t readBool(bool& value);
+
+  uint32_t readByte(int8_t& byte);
+
+  uint32_t readI16(int16_t& i16);
+
+  uint32_t readI32(int32_t& i32);
+
+  uint32_t readI64(int64_t& i64);
+
+  uint32_t readDouble(double& dub);
+
+  uint32_t readString(std::string& str);
+
+
+  /*
+   * Helper reading functions (don't do state transitions).
+   */
+  uint32_t subReadI32(int32_t& i32) {
+    return TBinaryProtocol::readI32(i32);
+  }
+
+  uint32_t subReadBool(bool& value) {
+    return TBinaryProtocol::readBool(value);
+  }
+
+  uint32_t subReadString(std::string& str) {
+    uint32_t xfer;
+    int32_t size;
+    xfer = subReadI32(size);
+    return xfer + readStringBody(str, size);
+  }
+
+
+
+ private:
+
+  inline void checkTType(const TType ttype);
+  inline void stateTransition();
+
+  TypeSpec* type_spec_;
+
+  std::vector<TypeSpec*> ts_stack_;   // TypeSpec stack.
+  std::vector<int>       idx_stack_;  // InDeX stack.
+  std::vector<bool>      mkv_stack_;  // Map Key/Vlue stack.
+                                      // True = key, False = value.
+
+  // XXX Remove these when wire format is finalized.
+ public:
+  int vli_save_16;
+  int vli_save_32;
+  int vli_save_64;
+  int vli_save_sub;
+  int negs;
+};
+
+}}} // facebook::thrift::protocol
+
+#endif // #ifndef _THRIFT_PROTOCOL_TDENSEPROTOCOL_H_