3 files changed, 221 insertions, 0 deletions
diff --git a/src/buildtool/storage/TARGETS b/src/buildtool/storage/TARGETS
index a3e06628..38180055 100644
--- a/src/buildtool/storage/TARGETS
+++ b/src/buildtool/storage/TARGETS
@@ -81,4 +81,12 @@
     , "storage"
     ]
   }
+, "file_chunker":
+  { "type": ["@", "rules", "CC", "library"]
+  , "name": ["file_chunker"]
+  , "hdrs": ["file_chunker.hpp"]
+  , "srcs": ["file_chunker.cpp"]
+  , "stage": ["src", "buildtool", "storage"]
+  , "private-deps": [["@", "gsl", "", "gsl"]]
+  }
 }
diff --git a/src/buildtool/storage/file_chunker.cpp b/src/buildtool/storage/file_chunker.cpp
new file mode 100644
index 00000000..af318501
--- /dev/null
+++ b/src/buildtool/storage/file_chunker.cpp
@@ -0,0 +1,115 @@
+// Copyright 2023 Huawei Cloud Computing Technology Co., Ltd.
+//
+// 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
+//
+//     http://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 "src/buildtool/storage/file_chunker.hpp"
+
+#include <array>
+#include <random>
+
+#include "gsl/gsl"
+
+namespace {
+
+// Mask values taken from algorithm 2 of the paper
+// https://ieeexplore.ieee.org/document/9055082.
+constexpr std::uint64_t kMaskS{0x0000d9f003530000ULL};  // 15 '1' bits
+constexpr std::uint64_t kMaskL{0x0000d90003530000ULL};  // 11 '1' bits
+
+// Predefined array of 256 random 64-bit integers, needs to be initialized.
+constexpr std::uint32_t kRandomTableSize{256};
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+std::array<std::uint64_t, kRandomTableSize> gear_table{};
+
+}  // namespace
+
+auto FileChunker::Initialize(std::uint32_t seed) noexcept -> void {
+    std::mt19937_64 gen64(seed);
+    for (auto& item : gear_table) {
+        item = gen64();
+    }
+}
+
+auto FileChunker::IsOpen() const noexcept -> bool {
+    return stream_.is_open();
+}
+
+auto FileChunker::Finished() const noexcept -> bool {
+    return stream_.eof() && pos_ == size_;
+}
+
+auto FileChunker::NextChunk() noexcept -> std::optional<std::string> {
+    // Handle failed past read attempts from the stream.
+    if (not stream_.good() and not stream_.eof()) {
+        return std::nullopt;
+    }
+
+    // Ensure that at least max_chunk_size bytes are in the buffer, except if
+    // end-of-file is reached.
+    auto remaining = size_ - pos_;
+    if (remaining < max_chunk_size_ and not stream_.eof()) {
+        // Move the remaining bytes of the buffer to the front.
+        buffer_.copy(&buffer_[0], remaining, pos_);
+        auto ssize = static_cast<std::streamsize>(buffer_.size() - remaining);
+        // Fill the buffer with stream content.
+        stream_.read(&buffer_[remaining], ssize);
+        if (not stream_.good() and not stream_.eof()) {
+            return std::nullopt;
+        }
+        size_ = static_cast<std::size_t>(stream_.gcount()) + remaining;
+        pos_ = 0;
+    }
+
+    // Handle finished chunking.
+    if (pos_ == size_) {
+        return std::nullopt;
+    }
+
+    auto off = NextChunkBoundary();
+    auto chunk = buffer_.substr(pos_, off);
+    pos_ += off;
+    return chunk;
+}
+
+// Implementation of the FastCDC data deduplication algorithm described in
+// algorithm 2 of the paper https://ieeexplore.ieee.org/document/9055082.
+auto FileChunker::NextChunkBoundary() noexcept -> std::size_t {
+    auto n = size_ - pos_;
+    auto fp = 0ULL;
+    auto i = min_chunk_size_;
+    auto normal_size = average_chunk_size_;
+    if (n <= min_chunk_size_) {
+        return n;
+    }
+    if (n >= max_chunk_size_) {
+        n = max_chunk_size_;
+    }
+    else if (n <= normal_size) {
+        normal_size = n;
+    }
+    for (; i < normal_size; i++) {
+        fp = (fp << 1U) +
+             gsl::at(gear_table, static_cast<uint8_t>(buffer_[pos_ + i]));
+        if ((fp & kMaskS) == 0) {
+            return i;  // if the masked bits are all '0'
+        }
+    }
+    for (; i < n; i++) {
+        fp = (fp << 1U) +
+             gsl::at(gear_table, static_cast<uint8_t>(buffer_[pos_ + i]));
+        if ((fp & kMaskL) == 0) {
+            return i;  // if the masked bits are all '0'
+        }
+    }
+    return i;
+}
diff --git a/src/buildtool/storage/file_chunker.hpp b/src/buildtool/storage/file_chunker.hpp
new file mode 100644
index 00000000..c4611c48
--- /dev/null
+++ b/src/buildtool/storage/file_chunker.hpp
@@ -0,0 +1,98 @@
+// Copyright 2023 Huawei Cloud Computing Technology Co., Ltd.
+//
+// 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
+//
+//     http://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.
+
+#ifndef INCLUDED_SRC_BUILDTOOL_STORAGE_FILE_CHUNKER_HPP
+#define INCLUDED_SRC_BUILDTOOL_STORAGE_FILE_CHUNKER_HPP
+
+#include <cstddef>
+#include <cstdint>
+#include <filesystem>
+#include <fstream>
+#include <optional>
+#include <string>
+
+/// @brief This class provides content-defined chunking for a file stream. It
+/// allows to split a file stream into variable-sized chunks based on its data
+/// content. In contrast to fixed-sized chunking, which splits a data stream
+/// into chunks of fixed size, it is not prone to the data-shifting problem. In
+/// order to assemble the resulting file, the delivered chunks have to be
+/// concatenated in order.
+///
+/// A read buffer is used to progressively process the file content instead of
+/// reading the entire file content in memory.
+class FileChunker {
+    static constexpr std::uint32_t kDefaultChunkSize{1024 * 8};  // 8 KB
+    static constexpr std::uint32_t kDefaultSeed{0};
+
+  public:
+    /// @brief Create an instance of the file chunker for a given file.
+    /// @param path                 The path to the file to be splitted.
+    /// @param average_chunk_size   Targeted average chunk size in bytes
+    ///                             (default: 8 KB).
+    explicit FileChunker(std::filesystem::path const& path,
+                         std::uint32_t average_chunk_size = kDefaultChunkSize)
+        // According to section 4.1 of the paper
+        // https://ieeexplore.ieee.org/document/9055082, maximum and minimum
+        // chunk sizes are configured to the 8x and the 1/4x of the average
+        // chunk size.
+        : min_chunk_size_(average_chunk_size >> 2U),
+          average_chunk_size_(average_chunk_size),
+          max_chunk_size_(average_chunk_size << 3U),
+          stream_{path, std::ios::in | std::ios::binary} {
+        // The buffer size needs to be at least max_chunk_size_ large, otherwise
+        // max_chunk_size_ is not fully exhausted and the buffer size determines
+        // the maximum chunk size.
+        buffer_.resize(max_chunk_size_ << 4U);
+    }
+
+    FileChunker() noexcept = delete;
+    ~FileChunker() noexcept = default;
+    FileChunker(FileChunker const& other) noexcept = delete;
+    FileChunker(FileChunker&& other) noexcept = delete;
+    auto operator=(FileChunker const& other) noexcept = delete;
+    auto operator=(FileChunker&& other) noexcept = delete;
+
+    /// @brief Check if the underlying file is open.
+    /// @return True if the file was opened successfully, false otherwise.
+    [[nodiscard]] auto IsOpen() const noexcept -> bool;
+
+    /// @brief Check if chunking of the file stream was done successfully.
+    /// @return True if chunking was successful, false otherwise.
+    [[nodiscard]] auto Finished() const noexcept -> bool;
+
+    /// @brief Fetch the next chunk from the file stream.
+    /// @return The next chunk of the file stream.
+    [[nodiscard]] auto NextChunk() noexcept -> std::optional<std::string>;
+
+    /// @brief Initialize random number table used by the chunking algorithm.
+    /// @param seed Some random seed.
+    static auto Initialize(std::uint32_t seed = kDefaultSeed) noexcept -> void;
+
+  private:
+    // Different chunk size parameters, defined in number of bytes.
+    const std::uint32_t min_chunk_size_{};
+    const std::uint32_t average_chunk_size_{};
+    const std::uint32_t max_chunk_size_{};
+    std::ifstream stream_{};  // File stream to be splitted.
+    std::string buffer_{};    // Buffer for the file content.
+    std::size_t size_{0};     // Current size of the buffer.
+    std::size_t pos_{0};      // Current read position within the buffer.
+
+    /// @brief Find the next chunk boundary from the current read position
+    /// within the buffer.
+    /// @return The position of the next chunk boundary.
+    [[nodiscard]] auto NextChunkBoundary() noexcept -> std::size_t;
+};
+
+#endif  // INCLUDED_SRC_BUILDTOOL_STORAGE_FILE_CHUNKER_HPP