src/tint/utils/bytes/reader.h

// Copyright 2023 The Dawn & Tint Authors
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#ifndef SRC_TINT_UTILS_BYTES_READER_H_
#define SRC_TINT_UTILS_BYTES_READER_H_

#include <bit>
#include <string>

#include "src/tint/utils/bytes/swap.h"
#include "src/tint/utils/result.h"

namespace tint::bytes {

/// A binary stream reader interface
class Reader {
  public:
    /// Destructor
    virtual ~Reader();

    /// Read reads bytes from the stream, blocking until there are @p count bytes available, or the
    /// end of the stream has been reached.
    /// @param out a pointer to the byte buffer that will be filled with the read data. Must be at
    /// least @p count size.
    /// @param count the number of bytes to read. Must be greater than 0.
    /// @returns the number of bytes read from the stream. If Read() returns less than @p count,
    /// then the end of the stream has been reached.
    virtual size_t Read(std::byte* out, size_t count) = 0;

    /// @returns true if the Reader has no more bytes to read.
    virtual bool IsEOF() const = 0;

    /// Reads an integer from the stream, performing byte swapping if the stream's endianness
    /// differs from the native endianness.
    /// If there are too few bytes remaining in the stream, then a failure is returned.
    /// @param endianness the encoded endianness of the integer
    /// @return the deserialized integer
    template <typename T>
    Result<T> Int(std::endian endianness = std::endian::little) {
        static_assert(std::is_integral_v<T>);
        T out = 0;
        if (size_t n = Read(reinterpret_cast<std::byte*>(&out), sizeof(T)); n != sizeof(T)) {
            return Failure{"EOF"};
        }
        if (std::endian::native != endianness) {
            out = Swap(out);
        }
        return out;
    }

    /// Reads a float from the stream.
    /// If there are too few bytes remaining in the stream, then a failure is returned.
    /// @return the deserialized floating point number
    template <typename T>
    Result<T> Float() {
        static_assert(std::is_floating_point_v<T>);
        T out = 0;
        if (size_t n = Read(reinterpret_cast<std::byte*>(&out), sizeof(T)); n != sizeof(T)) {
            return Failure{"EOF"};
        }
        return out;
    }

    /// Reads a boolean from the stream
    /// If there are too few bytes remaining in the stream, then a failure is returned.
    /// @returns true if the next byte is non-zero
    Result<bool> Bool() {
        std::byte b{0};
        if (size_t n = Read(&b, 1); n != 1) {
            return Failure{"EOF"};
        }
        return b != std::byte{0};
    }

    /// Reads a string of @p len bytes from the stream.
    /// If there are too few bytes remaining in the stream, then a failure is returned.
    /// @param len the length of the returned string in bytes
    /// @return the deserialized string
    Result<std::string> String(size_t len) {
        std::string out;
        out.resize(len);
        if (size_t n = Read(reinterpret_cast<std::byte*>(out.data()), sizeof(char) * len);
            n != len) {
            return Failure{"EOF"};
        }
        return out;
    }
};

}  // namespace tint::bytes

#endif  // SRC_TINT_UTILS_BYTES_READER_H_