1 files changed, 31 insertions, 0 deletions
diff --git a/src/google/protobuf/io/zero_copy_stream_impl_lite.cc b/src/google/protobuf/io/zero_copy_stream_impl_lite.cc
index 686e63f2..083beca4 100644
--- a/src/google/protobuf/io/zero_copy_stream_impl_lite.cc
+++ b/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() {}