impl(GCS+gRPC): more efficient Cord construction (#12729)

Author: coryan

google/cloud/storage/internal/grpc/buffer_read_object_data.cc

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 #include "google/cloud/storage/internal/grpc/buffer_read_object_data.h"
+#include "google/cloud/storage/internal/grpc/make_cord.h"
 #include <algorithm>
 
 namespace google {
@@ -21,27 +22,26 @@ namespace storage_internal {
 
 std::size_t GrpcBufferReadObjectData::FillBuffer(char* buffer, std::size_t n) {
   std::size_t offset = 0;
-  for (auto v : spill_view_.Chunks()) {
+  for (auto v : contents_.Chunks()) {
     if (offset == n) break;
     auto const count = std::min(v.size(), n - offset);
     std::copy(v.data(), v.data() + count, buffer + offset);
     offset += count;
   }
-  spill_view_ = spill_view_.Subcord(offset, spill_view_.size() - offset);
+  contents_.RemovePrefix(offset);
   return offset;
 }
 
 std::size_t GrpcBufferReadObjectData::HandleResponse(char* buffer,
                                                      std::size_t n,
                                                      std::string contents) {
-  return HandleResponse(buffer, n, absl::Cord(std::move(contents)));
+  return HandleResponse(buffer, n, MakeCord(std::move(contents)));
 }
 
 std::size_t GrpcBufferReadObjectData::HandleResponse(char* buffer,
                                                      std::size_t n,
                                                      absl::Cord contents) {
   contents_ = std::move(contents);
-  spill_view_ = contents_;
   return FillBuffer(buffer, n);
 }
 

google/cloud/storage/internal/grpc/buffer_read_object_data.h

@@ -65,7 +65,6 @@ class GrpcBufferReadObjectData {
 
  private:
   absl::Cord contents_;
-  absl::Cord spill_view_;
 };
 
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END