feat(kv-ir): Add StringBlob for compact storage of multiple strings in a contiguous byte buffer. (#1544)

Co-authored-by: Devin Gibson <[email protected]>

Author: LinZhihao-723

components/core/CMakeLists.txt

@@ -484,6 +484,7 @@ set(SOURCE_FILES_unitTest
         src/clp/ffi/encoding_methods.cpp
         src/clp/ffi/encoding_methods.hpp
         src/clp/ffi/encoding_methods.inc
+        src/clp/ffi/test/test_StringBlob.cpp
         src/clp/ffi/ir_stream/byteswap.hpp
         src/clp/ffi/ir_stream/Deserializer.hpp
         src/clp/ffi/ir_stream/decoding_methods.cpp
@@ -535,6 +536,7 @@ set(SOURCE_FILES_unitTest
         src/clp/ffi/search/Subquery.hpp
         src/clp/ffi/search/WildcardToken.cpp
         src/clp/ffi/search/WildcardToken.hpp
+        src/clp/ffi/StringBlob.hpp
         src/clp/ffi/utils.cpp
         src/clp/ffi/utils.hpp
         src/clp/ffi/Value.hpp

components/core/src/clp/ffi/StringBlob.hpp

@@ -0,0 +1,66 @@
+#ifndef CLP_FFI_STRINGBLOB_HPP
+#define CLP_FFI_STRINGBLOB_HPP
+
+#include <cstddef>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include "../ErrorCode.hpp"
+#include "../ReaderInterface.hpp"
+
+namespace clp::ffi {
+// Stores a list of strings as an indexable blob.
+class StringBlob {
+public:
+    // Constructors
+    StringBlob() = default;
+
+    // Methods
+    [[nodiscard]] auto get_num_strings() const -> size_t { return m_offsets.size() - 1; }
+
+    /**
+     * @param index
+     * @return A view of the string at the given `index` in the blob.
+     * @return std::nullopt if `index` is out of bounds.
+     */
+    [[nodiscard]] auto get_string(size_t index) const -> std::optional<std::string_view> {
+        if (index >= get_num_strings()) {
+            return std::nullopt;
+        }
+        size_t const start_offset{m_offsets[index]};
+        size_t const end_offset{m_offsets[index + 1]};
+        return std::string_view{m_data}.substr(start_offset, end_offset - start_offset);
+    }
+
+    /**
+     * Reads a string of the given `length` from the `reader` and appends it to the blob.
+     * @param reader
+     * @param length The exact length of the string to read.
+     * @return std::nullopt on success.
+     * @return Forwards `ReaderInterface::try_read_exact_length`'s error code on failure.
+     */
+    [[nodiscard]] auto read_from(ReaderInterface& reader, size_t length)
+            -> std::optional<ErrorCode> {
+        auto const start_offset{m_data.size()};
+        auto const end_offset{start_offset + length};
+        m_data.resize(static_cast<std::string::size_type>(end_offset));
+        // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+        if (auto const err{reader.try_read_exact_length(m_data.data() + start_offset, length)};
+            ErrorCode::ErrorCode_Success != err)
+        {
+            m_data.resize(start_offset);
+            return err;
+        }
+        m_offsets.emplace_back(end_offset);
+        return std::nullopt;
+    }
+
+private:
+    std::string m_data;
+    std::vector<size_t> m_offsets{0};
+};
+}  // namespace clp::ffi
+
+#endif  // CLP_FFI_STRINGBLOB_HPP

components/core/src/clp/ffi/test/test_StringBlob.cpp

@@ -0,0 +1,45 @@
+#include <cstddef>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include <catch2/catch_test_macros.hpp>
+
+#include "../../BufferReader.hpp"
+#include "../../ErrorCode.hpp"
+#include "../StringBlob.hpp"
+
+TEST_CASE("StringBlob basic functionality", "[StringBlob]") {
+    clp::ffi::StringBlob string_blob;
+
+    std::vector<std::string> const test_strings{
+            "Hello, World!",
+            "This is a test string.",
+            "StringBlob is working correctly.",
+    };
+
+    std::string buffer;
+    for (auto const& str : test_strings) {
+        buffer += str;
+    }
+    clp::BufferReader reader{buffer.data(), buffer.size()};
+
+    size_t expected_num_strings{0};
+    for (auto const& expected_str : test_strings) {
+        REQUIRE((expected_num_strings == string_blob.get_num_strings()));
+
+        auto const result{string_blob.read_from(reader, expected_str.size())};
+        REQUIRE_FALSE(result.has_value());
+        ++expected_num_strings;
+        REQUIRE((expected_num_strings == string_blob.get_num_strings()));
+        auto const optional_retrieved_str{string_blob.get_string(expected_num_strings - 1)};
+        REQUIRE((optional_retrieved_str.has_value()));
+        // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
+        REQUIRE((optional_retrieved_str.value() == expected_str));
+    }
+
+    auto const read_from_eof{string_blob.read_from(reader, 1)};
+    REQUIRE(read_from_eof.has_value());
+    // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
+    REQUIRE((clp::ErrorCode::ErrorCode_EndOfFile == read_from_eof.value()));
+}