Patch internal change 111557819.

Defer calls to mutable_unknown_fields() until it is actually required to
save memory for C++ lite runtime.

Change-Id: Ica9c1fd276cdb164942d1e7b6e098c83ee3ffdc5

src/google/protobuf/compiler/cpp/cpp_message.cc

@@ -1772,6 +1772,17 @@ GenerateShutdownCode(io::Printer* printer) {
 
 void MessageGenerator::
 GenerateClassMethods(io::Printer* printer) {
+  // mutable_unknown_fields wrapper function for LazyStringOutputStream
+  // callback.
+  if (!UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(
+        "static ::std::string* MutableUnknownFieldsFor$classname$(\n"
+        "    $classname$* ptr) {\n"
+        "  return ptr->mutable_unknown_fields();\n"
+        "}\n"
+        "\n",
+        "classname", classname_);
+  }
   if (IsAnyMessage(descriptor_)) {
     printer->Print(
       "void $classname$::PackFrom(const ::google::protobuf::Message& message) {\n"
@@ -2814,7 +2825,9 @@ GenerateMergeFrom(io::Printer* printer) {
         "}\n");
     } else {
       printer->Print(
-        "mutable_unknown_fields()->append(from.unknown_fields());\n");
+        "if (!from.unknown_fields().empty()) {\n"
+        "  mutable_unknown_fields()->append(from.unknown_fields());\n"
+        "}\n");
     }
   }
 
@@ -2889,11 +2902,16 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
     "classname", classname_);
 
   if (!UseUnknownFieldSet(descriptor_->file())) {
+    // Use LazyStringOutputString to avoid initializing unknown fields string
+    // unless it is actually needed. For the same reason, disable eager refresh
+    // on the CodedOutputStream.
     printer->Print(
-      "  ::google::protobuf::io::StringOutputStream unknown_fields_string(\n"
+      "  ::google::protobuf::io::LazyStringOutputStream unknown_fields_string(\n"
-      "      mutable_unknown_fields());\n"
+      "      ::google::protobuf::internal::NewPermanentCallback(\n"
+      "          &MutableUnknownFieldsFor$classname$, this));\n"
       "  ::google::protobuf::io::CodedOutputStream unknown_fields_stream(\n"
-      "      &unknown_fields_string);\n");
+      "      &unknown_fields_string, false);\n",
+      "classname", classname_);
   }
 
   printer->Print(

src/google/protobuf/io/coded_stream.cc

@@ -629,6 +629,24 @@ CodedOutputStream::CodedOutputStream(ZeroCopyOutputStream* output)
   had_error_ = false;
 }
 
+CodedOutputStream::CodedOutputStream(ZeroCopyOutputStream* output,
+                                     bool do_eager_refresh)
+  : output_(output),
+    buffer_(NULL),
+    buffer_size_(0),
+    total_bytes_(0),
+    had_error_(false),
+    aliasing_enabled_(false) {
+  if (do_eager_refresh) {
+    // Eagerly Refresh() so buffer space is immediately available.
+    Refresh();
+    // The Refresh() may have failed. If the client doesn't write any data,
+    // though, don't consider this an error. If the client does write data, then
+    // another Refresh() will be attempted and it will set the error once again.
+    had_error_ = false;
+  }
+}
+
 CodedOutputStream::~CodedOutputStream() {
   Trim();
 }

src/google/protobuf/io/coded_stream.h

@@ -666,6 +666,7 @@ class LIBPROTOBUF_EXPORT CodedOutputStream {
  public:
   // Create an CodedOutputStream that writes to the given ZeroCopyOutputStream.
   explicit CodedOutputStream(ZeroCopyOutputStream* output);
+  CodedOutputStream(ZeroCopyOutputStream* output, bool do_eager_refresh);
 
   // Destroy the CodedOutputStream and position the underlying
   // ZeroCopyOutputStream immediately after the last byte written.

src/google/protobuf/io/zero_copy_stream_impl_lite.cc

@@ -157,6 +157,7 @@ StringOutputStream::~StringOutputStream() {
 }
 
 bool StringOutputStream::Next(void** data, int* size) {
+  GOOGLE_CHECK_NE(NULL, target_);
   int old_size = target_->size();
 
   // Grow the string.
@@ -188,14 +189,44 @@ bool StringOutputStream::Next(void** data, int* size) {
 
 void StringOutputStream::BackUp(int count) {
   GOOGLE_CHECK_GE(count, 0);
+  GOOGLE_CHECK_NE(NULL, target_);
   GOOGLE_CHECK_LE(count, target_->size());
   target_->resize(target_->size() - count);
 }
 
 int64 StringOutputStream::ByteCount() const {
+  GOOGLE_CHECK_NE(NULL, target_);
   return target_->size();
 }
 
+void StringOutputStream::SetString(string* target) {
+  target_ = target;
+}
+
+// ===================================================================
+
+LazyStringOutputStream::LazyStringOutputStream(
+    ResultCallback<string*>* callback)
+    : StringOutputStream(NULL),
+      callback_(GOOGLE_CHECK_NOTNULL(callback)),
+      string_is_set_(false) {
+}
+
+LazyStringOutputStream::~LazyStringOutputStream() {
+}
+
+bool LazyStringOutputStream::Next(void** data, int* size) {
+  if (!string_is_set_) {
+    SetString(callback_->Run());
+    string_is_set_ = true;
+  }
+  return StringOutputStream::Next(data, size);
+}
+
+int64 LazyStringOutputStream::ByteCount() const {
+  return string_is_set_ ? StringOutputStream::ByteCount() : 0;
+}
+
 // ===================================================================
 
 CopyingInputStream::~CopyingInputStream() {}

src/google/protobuf/io/zero_copy_stream_impl_lite.h

@@ -148,6 +148,9 @@ class LIBPROTOBUF_EXPORT StringOutputStream : public ZeroCopyOutputStream {
   void BackUp(int count);
   int64 ByteCount() const;
 
+ protected:
+  void SetString(string* target);
+
  private:
   static const int kMinimumSize = 16;
 
@@ -156,6 +159,27 @@ class LIBPROTOBUF_EXPORT StringOutputStream : public ZeroCopyOutputStream {
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringOutputStream);
 };
 
+// LazyStringOutputStream is a StringOutputStream with lazy acquisition of
+// the output string from a callback. The string is owned externally, and not
+// deleted in the stream destructor.
+class LIBPROTOBUF_EXPORT LazyStringOutputStream : public StringOutputStream {
+ public:
+  // Callback should be permanent (non-self-deleting). Ownership is transferred
+  // to the LazyStringOutputStream.
+  explicit LazyStringOutputStream(ResultCallback<string*>* callback);
+  ~LazyStringOutputStream();
+
+  // implements ZeroCopyOutputStream, overriding StringOutputStream -----------
+  bool Next(void** data, int* size);
+  int64 ByteCount() const;
+
+ private:
+  const scoped_ptr<ResultCallback<string*> > callback_;
+  bool string_is_set_;
+
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(LazyStringOutputStream);
+};
+
 // Note:  There is no StringInputStream.  Instead, just create an
 // ArrayInputStream as follows:
 //   ArrayInputStream input(str.data(), str.size());

src/google/protobuf/stubs/callback.h

@@ -78,6 +78,18 @@ class LIBPROTOBUF_EXPORT Closure {
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(Closure);
 };
 
+template<typename R>
+class LIBPROTOBUF_EXPORT ResultCallback {
+ public:
+  ResultCallback() {}
+  virtual ~ResultCallback() {}
+
+  virtual R Run() = 0;
+
+ private:
+  GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ResultCallback);
+};
+
 template<typename R, typename A1>
 class LIBPROTOBUF_EXPORT ResultCallback1 {
  public:
@@ -240,6 +252,50 @@ class MethodClosure2 : public Closure {
   Arg2 arg2_;
 };
 
+template<typename R>
+class FunctionResultCallback_0_0 : public ResultCallback<R> {
+ public:
+  typedef R (*FunctionType)();
+
+  FunctionResultCallback_0_0(FunctionType function, bool self_deleting)
+      : function_(function), self_deleting_(self_deleting) {}
+  ~FunctionResultCallback_0_0() {}
+
+  R Run() {
+    bool needs_delete = self_deleting_;  // read in case callback deletes
+    R result = function_();
+    if (needs_delete) delete this;
+    return result;
+  }
+
+ private:
+  FunctionType function_;
+  bool self_deleting_;
+};
+
+template<typename R, typename P1>
+class FunctionResultCallback_1_0 : public ResultCallback<R> {
+ public:
+  typedef R (*FunctionType)(P1);
+
+  FunctionResultCallback_1_0(FunctionType function, bool self_deleting,
+                             P1 p1)
+      : function_(function), self_deleting_(self_deleting), p1_(p1) {}
+  ~FunctionResultCallback_1_0() {}
+
+  R Run() {
+    bool needs_delete = self_deleting_;  // read in case callback deletes
+    R result = function_(p1_);
+    if (needs_delete) delete this;
+    return result;
+  }
+
+ private:
+  FunctionType function_;
+  bool self_deleting_;
+  P1 p1_;
+};
+
 template<typename R, typename Arg1>
 class FunctionResultCallback_0_1 : public ResultCallback1<R, Arg1> {
  public:
@@ -408,6 +464,33 @@ inline Closure* NewPermanentCallback(
     object, method, false, arg1, arg2);
 }
 
+// See ResultCallback
+template<typename R>
+inline ResultCallback<R>* NewCallback(R (*function)()) {
+  return new internal::FunctionResultCallback_0_0<R>(function, true);
+}
+
+// See ResultCallback
+template<typename R>
+inline ResultCallback<R>* NewPermanentCallback(R (*function)()) {
+  return new internal::FunctionResultCallback_0_0<R>(function, false);
+}
+
+// See ResultCallback
+template<typename R, typename P1>
+inline ResultCallback<R>* NewCallback(R (*function)(P1), P1 p1) {
+  return new internal::FunctionResultCallback_1_0<R, P1>(
+      function, true, p1);
+}
+
+// See ResultCallback
+template<typename R, typename P1>
+inline ResultCallback<R>* NewPermanentCallback(
+    R (*function)(P1), P1 p1) {
+  return new internal::FunctionResultCallback_1_0<R, P1>(
+      function, false, p1);
+}
+
 // See ResultCallback1
 template<typename R, typename A1>
 inline ResultCallback1<R, A1>* NewCallback(R (*function)(A1)) {