1 files changed, 68 insertions, 0 deletions
diff --git a/third_party/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc b/third_party/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc
new file mode 100644
index 0000000000..5dc76966d2
--- /dev/null
+++ b/third_party/abseil-cpp/absl/strings/internal/cord_rep_btree_reader.cc
@@ -0,0 +1,68 @@
+// Copyright 2021 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/cord_rep_btree_reader.h"
+
+#include <cassert>
+
+#include "absl/base/config.h"
+#include "absl/strings/internal/cord_internal.h"
+#include "absl/strings/internal/cord_rep_btree.h"
+#include "absl/strings/internal/cord_rep_btree_navigator.h"
+#include "absl/strings/internal/cord_rep_flat.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+
+absl::string_view CordRepBtreeReader::Read(size_t n, size_t chunk_size,
+                                           CordRep*& tree) {
+  assert(chunk_size <= navigator_.Current()->length);
+
+  // If chunk_size is non-zero, we need to start inside last returned edge.
+  // Else we start reading at the next data edge of the tree.
+  CordRep* edge = chunk_size ? navigator_.Current() : navigator_.Next();
+  const size_t offset = chunk_size ? edge->length - chunk_size : 0;
+
+  // Read the sub tree and verify we got what we wanted.
+  ReadResult result = navigator_.Read(offset, n);
+  tree = result.tree;
+
+  // If the data returned in `tree` was covered entirely by `chunk_size`, i.e.,
+  // read from the 'previous' edge, we did not consume any additional data, and
+  // can directly return the substring into the current data edge as the next
+  // chunk. We can easily establish from the above code that `navigator_.Next()`
+  // has not been called as that requires `chunk_size` to be zero.
+  if (n < chunk_size) return CordRepBtree::EdgeData(edge).substr(result.n);
+
+  // The amount of data taken from the last edge is `chunk_size` and `result.n`
+  // contains the offset into the current edge trailing the read data (which can
+  // be 0). As the call to `navigator_.Read()` could have consumed all remaining
+  // data, calling `navigator_.Current()` is not safe before checking if we
+  // already consumed all remaining data.
+  const size_t consumed_by_read = n - chunk_size - result.n;
+  if (consumed_by_read >= remaining_) {
+    remaining_ = 0;
+    return {};
+  }
+
+  // We did not read all data, return remaining data from current edge.
+  edge = navigator_.Current();
+  remaining_ -= consumed_by_read + edge->length;
+  return CordRepBtree::EdgeData(edge).substr(result.n);
+}
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl