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// 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
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