operations.hpp

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#pragma once
 
/// @file userver/dump/operations.hpp
/// @brief Binary dump Reader and Writer interfaces
 
#include <stdexcept>
#include <string>
#include <string_view>
#include <type_traits>
 
#include <userver/dump/fwd.hpp>
#include <userver/dump/meta.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace dump {
 
/// Indicates a failure reading or writing a dump. No further operations
/// should be performed with a failed dump.
class Error final : public std::runtime_error {
public:
    explicit Error(std::string message) : std::runtime_error(std::move(message)) {}
};
 
/// A general interface for binary data output
class Writer {
public:
    virtual ~Writer() = default;
 
    /// @brief Writes binary data
    /// @details Calls ADL-found `Write(writer, data)`
    /// @throws `Error` and any user-thrown `std::exception`
    template <typename T>
    void Write(const T& data);
 
    /// @brief Must be called once all data has been written
    /// @warning This method must not be called from within `Write`/`Read`
    /// @throws `Error` on write operation failure
    virtual void Finish() = 0;
 
protected:
    /// @brief Writes binary data
    /// @details Unlike `Write`, doesn't write the size of `data`
    /// @throws `Error` on write operation failure
    virtual void WriteRaw(std::string_view data) = 0;
 
    friend void WriteStringViewUnsafe(Writer& writer, std::string_view value);
};
 
/// A general interface for binary data input
class Reader {
public:
    virtual ~Reader() = default;
 
    /// @brief Reads binary data
    /// @details Calls ADL-found `Read(reader, To<T>)`
    /// @throws `Error` and any user-thrown `std::exception`
    template <typename T>
    T Read();
 
    /// @brief Must be called once all data has been read
    /// @warning This method must not be called from within `Write`/`Read`
    /// @throws `Error` on read operation failure or if there is leftover data
    virtual void Finish() = 0;
 
protected:
    /// @brief Reads binary data
    /// @note Invalidates the memory returned by the previous call of `ReadRaw`
    /// @note Normally, exactly `max_size` bytes is returned. On end-of-file,
    /// the amount of bytes returned can be less than `max_size`.
    /// @throws `Error` on read operation failure
    virtual std::string_view ReadRaw(std::size_t max_size) = 0;
 
    /// @brief Moves the internal cursor back by `size` bytes
    /// so that the next call to @ref ReadRaw returns the same data again
    /// @note If there has been no previous call to @ref ReadRaw,
    /// or `size` is greater than the number of bytes returned from that call,
    /// the behavior is undefined.
    virtual void BackUp(std::size_t size);
 
    friend std::string_view ReadUnsafeAtMost(Reader& reader, std::size_t size);
    friend void BackUpReadUnsafe(Reader& reader, std::size_t size);
};
 
namespace impl {
 
template <typename T>
void CallWrite(Writer& writer, const T& data) {
    Write(writer, data);
}
 
template <typename T>
// NOLINTNEXTLINE(readability-const-return-type)
T CallRead(Reader& reader, To<T> to) {
    return Read(reader, to);
}
 
}  // namespace impl
 
template <typename T>
void Writer::Write(const T& data) {
    if constexpr (kIsWritable<T>) {
        impl::CallWrite(*this, data);
    } else if constexpr (std::is_aggregate_v<T>) {
        static_assert(
            !sizeof(T),
            "Serialization is not implemented for this type. You "
            "either forgot to specialize IsDumpedAggregate for your type "
            "(see <userver/dump/aggregates.hpp>)"
            "or you've got a non-standard data type and need to implement "
            "`void Write(dump::Writer& writer, const T& data);` and put it "
            "in the namespace of `T` or in `dump`."
        );
    } else {
        static_assert(
            !sizeof(T),
            "You either forgot to `#include <userver/dump/common_containers.hpp>`, "
            "or you've got a non-standard data type and need to implement "
            "`void Write(dump::Writer& writer, const T& data);` and put it "
            "in the namespace of `T` or in `dump`."
        );
    }
}
 
template <typename T>
// NOLINTNEXTLINE(readability-const-return-type)
T Reader::Read() {
    if constexpr (kIsReadable<T>) {
        return impl::CallRead(*this, To<T>{});
    } else if constexpr (std::is_aggregate_v<T>) {
        static_assert(
            !sizeof(T),
            "Serialization is not implemented for this type. You "
            "either forgot to specialize IsDumpedAggregate for your type"
            "(see <userver/dump/aggregates.hpp>) "
            "or you've got a non-standard data type and need to implement "
            "`T Read(dump::Reader& reader, dump::To<T>);` and put it "
            "in the namespace of `T` or in `dump`."
        );
    } else {
        static_assert(
            !sizeof(T),
            "You either forgot to `#include <userver/dump/common_containers.hpp>`, "
            "or you've got a non-standard data type and need to implement"
            "`T Read(dump::Reader& reader, dump::To<T>);` and put it "
            "in the namespace of `T` or in `dump`."
        );
        return T{};
    }
}
 
}  // namespace dump
 
USERVER_NAMESPACE_END