SwapMeta.h

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/*
 * Copyright (C) 1996-2023 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */
 
#ifndef SQUID_SRC_STORE_SWAPMETA_H
#define SQUID_SRC_STORE_SWAPMETA_H
 
#include "defines.h"
 
#include <limits>
 
// store swap metadata interfaces shared by input and output code
 
namespace Store {
 
 
enum SwapMetaType {
    STORE_META_VOID = 0,
 
    STORE_META_KEY_MD5 = 3,
 
    STORE_META_URL = 4,
 
    STORE_META_STD = 5,
 
    STORE_META_VARY_HEADERS = 8,
 
    STORE_META_STD_LFS = 9,
 
    // TODO: Document this type after we start using it; see UnpackHitSwapMeta()
    STORE_META_OBJSIZE = 10
};
 
using RawSwapMetaType = char;
 
using RawSwapMetaLength = int;
 
const size_t SwapMetaFieldValueLengthMax = 64*1024;
 
static_assert(SwapMetaFieldValueLengthMax >= MAX_URL, "MAX_URL will fit in a swap meta field");
static_assert(SwapMetaFieldValueLengthMax <= uint64_t(std::numeric_limits<RawSwapMetaLength>::max()), "any swap metadata value size can be stored as RawSwapMetaLength");
 
const char SwapMetaMagic = 0x03;
 
using RawSwapMetaPrefixLength = int;
 
const auto SwapMetaPrefixSize = sizeof(SwapMetaMagic) + sizeof(RawSwapMetaPrefixLength);
 
const RawSwapMetaType RawSwapMetaTypeBottom = 0;
 
inline constexpr RawSwapMetaType
RawSwapMetaTypeTop()
{
    // This "constant" switch forces developers to update this function when
    // they add SwapMetaType values [-Wswitch]. It is better than an end_ enum
    // marker because it does not force us to add that marker to every switch
    // statement, with an assert(false) or similar "unreachable code" handler.
    // Optimizing compilers optimize this statement away into a constant.
    // The non-constant variable is needed for older compilers.
 
    // always use the last/maximum enum value here
    auto top = STORE_META_OBJSIZE;
    switch (top) {
    case STORE_META_VOID:
    case STORE_META_KEY_MD5:
    case STORE_META_URL:
    case STORE_META_STD:
    case STORE_META_VARY_HEADERS:
    case STORE_META_STD_LFS:
    case STORE_META_OBJSIZE:
        break;
    }
    return top;
}
 
inline constexpr bool
DeprecatedSwapMetaType(const RawSwapMetaType type)
{
    enum class DeprecatedMetas {
        STORE_META_KEY_URL = 1,
        STORE_META_KEY_SHA = 2,
        STORE_META_HITMETERING = 6,
        STORE_META_VALID = 7
    };
    return
        type == static_cast<RawSwapMetaType>(DeprecatedMetas::STORE_META_KEY_URL) ||
        type == static_cast<RawSwapMetaType>(DeprecatedMetas::STORE_META_KEY_SHA) ||
        type == static_cast<RawSwapMetaType>(DeprecatedMetas::STORE_META_HITMETERING) ||
        type == static_cast<RawSwapMetaType>(DeprecatedMetas::STORE_META_VALID);
}
 
inline constexpr bool
ReservedSwapMetaType(const RawSwapMetaType type)
{
    enum class ReservedMetas {
        STORE_META_STOREURL = 11,
        STORE_META_VARY_ID = 12
    };
    return
        type == static_cast<RawSwapMetaType>(ReservedMetas::STORE_META_STOREURL) ||
        type == static_cast<RawSwapMetaType>(ReservedMetas::STORE_META_VARY_ID);
}
 
inline constexpr bool
HonoredSwapMetaType(const RawSwapMetaType type)
{
    switch (type) {
    case STORE_META_VOID:
        return false;
 
    case STORE_META_KEY_MD5:
    case STORE_META_URL:
    case STORE_META_STD:
    case STORE_META_VARY_HEADERS:
    case STORE_META_STD_LFS:
    case STORE_META_OBJSIZE:
        return true;
 
    default:
        return false;
    }
}
 
inline constexpr bool
IgnoredSwapMetaType(const RawSwapMetaType type)
{
    return DeprecatedSwapMetaType(type) || ReservedSwapMetaType(type);
}
 
const auto STORE_HDR_METASIZE =
    4*sizeof(time_t) + sizeof(uint64_t) + 2*sizeof(uint16_t);
 
const auto STORE_HDR_METASIZE_OLD =
    4*sizeof(time_t) + sizeof(size_t) + 2*sizeof(uint16_t);
 
void CheckSwapMetaSerialization(RawSwapMetaType, RawSwapMetaLength, const void *);
 
} // namespace Store
 
#endif /* SQUID_SRC_STORE_SWAPMETA_H */