serialize.hh

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#ifndef SERIALIZE_HH
#define SERIALIZE_HH

#include "serialize_core.hh"
#include "SerializeBuffer.hh"
#include "XMLElement.hh"
#include "MemBuffer.hh"
#include "hash_map.hh"
#include "inline.hh"
#include "strCat.hh"
#include "unreachable.hh"
#include <zlib.h>
#include <string>
#include <typeindex>
#include <type_traits>
#include <vector>
#include <sstream>
#include <cassert>
#include <memory>

namespace openmsx {

class LastDeltaBlocks;
class DeltaBlock;

// TODO move somewhere in utils once we use this more often
struct HashPair {
        template<typename T1, typename T2>
        size_t operator()(const std::pair<T1, T2>& p) const {
                return 31 * std::hash<T1>()(p.first) +
                            std::hash<T2>()(p.second);
        }
};


template<typename T> struct SerializeClassVersion;

// In this section, the archive classes are defined.
//
// Archives can be categorized in two ways:
//   - backing stream they use
//   - input or output (each backing stream has exactly one input and one
//     output variant)
//
// ATM these backing streams implemented:
//   - Mem
//      Stores stream in memory. Is meant to be very compact and very fast.
//      It does not support versioning (it's not possible to load this stream
//      in a newer version of openMSX). It is also not platform independent
//      (e.g. integers are stored using native platform endianess).
//      The main use case for this archive format is regular in memory
//      snapshots, for example to support replay/rewind.
//   - XML
//      Stores the stream in a XML file. These files are meant to be portable
//      to different architectures (e.g. little/big endian, 32/64 bit system).
//      There is version information in the stream, so it should be possible
//      to load streams created with older openMSX versions a newer openMSX.
//      The XML files are meant to be human readable. Having editable XML files
//      is not a design goal (e.g. simply changing a value will probably work,
//      but swapping the position of two tag or adding or removing tags can
//      easily break the stream).
//   - Text
//      This stores to stream in a flat ascii file (one item per line). This
//      format is only written as a proof-of-concept to test the design. It's
//      not meant to be used in practice.
//
// Archive code is heavily templatized. It uses the CRTP (curiously recuring
// template pattern ; a base class templatized on it's derived class). To
// implement static polymorphism. This means there is practically no run-time
// overhead of using this mechansim compared to 6 seperatly handcoded functions
// (Mem/XML/Text x input/output).
// TODO At least in theory, still need to verify this in practice.
//      Though my experience is that gcc is generally very good in this.

template<typename Derived> class ArchiveBase
{
public:
        template<typename Base, typename T>
        void serializeBase(T& t)
        {
                const char* tag = BaseClassName<Base>::getName();
                self().serialize(tag, static_cast<Base&>(t));
        }

        template<typename Base, typename T>
        void serializeInlinedBase(T& t, unsigned version)
        {
                ::openmsx::serialize(self(), static_cast<Base&>(t), version);
        }

        // Each concrete archive class also has the following methods:
        // Because of the implementation with static polymorphism, this
        // interface is not explictly visible in the base class.
        //
        //
        // template<typename T> void serializeWithID(const char* tag, const T& t, ...)
        //
        //   This is _the_most_important_ method of the serialization
        //   framework. Depending on the concrete archive type (loader/saver)
        //   this method will load or save the given type 't'. In case of an XML
        //   archive the 'tag' parameter will be used as tagname.
        //
        //   At the end there are still a number of optional parameters (in the
        //   current implementation there can be between 0 and 3, but can be
        //   extened when needed). These are 'global' constructor parameters,
        //   constructor parameters that are not stored in the stream, but that
        //   are needed to reconstruct the object (for example can be references
        //   to structures that were already stored in the stream). So these
        //   parameters are only actually used while loading.
        //   TODO document this in more detail in some section where the
        //        (polymorphic) constructors are also described.
        //
        //
        // void serialize_blob(const char* tag, const void* data, size_t len,
        //                     bool diff = true)
        //
        //   Serialize the given data as a binary blob.
        //   This cannot be part of the serialize() method above because we
        //   cannot know whether a byte-array should be serialized as a blob
        //   or as a collection of bytes (IOW we cannot decide it based on the
        //   type).
        //
        //
        // template<typename T> void serialize(const char* tag, const T& t)
        //
        //   This is much like the serializeWithID() method above, but it doesn't
        //   store an ID with this element. This means that it's not possible,
        //   later on in the stream, to refer to this element. For many elements
        //   you know this will not happen. This method results in a slightly
        //   more compact stream.
        //
        //   Note that for primitive types we already don't store an ID, because
        //   pointers to primitive types are not supported (at least not ATM).
        //
        //
        // template<typename T, typename ...Args>
        // void serialize(const char* tag, const T& t, Args&& ...args)
        //
        //   Optionally serialize() accepts more than one tag-variable pair.
        //   This does conceptually the same as repeated calls to serialize()
        //   with each time a single pair, but it might be more efficient. E.g.
        //   the MemOutputArchive implementation is more efficient when called
        //   with multiple simple types.
        //
        // template<typename T> void serializePointerID(const char* tag, const T& t)
        //
        //   Serialize a pointer by storing the ID of the object it points to.
        //   This only works if the object was already serialized. The only
        //   reason to use this method instead of the more general serialize()
        //   method is that this one does not instantiate the object
        //   construction code. (So in some cases you can avoid having to
        //   provide specializations of SerializeConstructorArgs.)
        //
        //
        // template<typename T> void serializePolymorphic(const char* tag, const T& t)
        //
        //   Serialize a value-type whose concrete type is not yet known at
        //   compile-time (polymorphic pointers are already handled by the
        //   generic serialize() method).
        //
        //   The difference between pointer and value-types is that for
        //   pointers, the de-serialize code also needs to construct the
        //   object, while for value-types, the object (with the correct
        //   concrete type) is already constructed, it only needs to be
        //   initialized.
        //
        //
        // bool versionAtLeast(unsigned actual, unsigned required) const
        // bool versionBelow  (unsigned actual, unsigned required) const
        //
        //   Checks whether the actual version is respective 'bigger or equal'
        //   or 'strictly lower' than the required version. So in fact these are
        //   equivalent to respectively:
        //       return actual >= required;
        //       return actual <  required;
        //   Note that these two methods are the exact opposite of each other.
        //   Though for memory-archives and output-archives we know that the
        //   actual version is always equal to the latest class version and the
        //   required version can never be bigger than this latest version, so
        //   in these cases the methods can be optimized to respectively:
        //       return true;
        //       return false;
        //   By using these methods instead of direct comparisons, the compiler
        //   is able to perform more dead-code-elimination.

/*internal*/
        // These must be public for technical reasons, but they should only
        // be used by the serialization framework.

        bool needVersion() const { return true; }

        bool isReverseSnapshot() const { return false; }

        bool translateEnumToString() const { return false; }

        template<typename T> void attribute(const char* name, T& t)
        {
                self().serialize(name, t);
        }
        void attribute(const char* name, const char* value);

        bool canHaveOptionalAttributes() const { return false; }

        bool hasAttribute(const char* /*name*/)
        {
                UNREACHABLE; return false;
        }

        bool findAttribute(const char* /*name*/, unsigned& /*value*/)
        {
                UNREACHABLE; return false;
        }

        bool canCountChildren() const { return false; }

        int countChildren() const
        {
                UNREACHABLE; return 0;
        }

        void beginTag(const char* /*tag*/)
        {
                // nothing
        }
        void endTag(const char* /*tag*/)
        {
                // nothing
        }

        // These (internal) methods should be implemented in the concrete
        // archive classes.
        //
        // template<typename T> void save(const T& t)
        //
        //   Should only be implemented for OuputArchives. Is called to
        //   store primitive types in the stream. In the end all structures
        //   are broken down to primitive types, so all data that ends up
        //   in the stream passes via this method (ok, depending on how
        //   attribute() and serialize_blob() is implemented, that data may
        //   not pass via save()).
        //
        //   Often this method will be overloaded to handle certain types in a
        //   specific way.
        //
        //
        // template<typename T> void load(T& t)
        //
        //   Should only be implemented for InputArchives. This is similar (but
        //   opposite) to the save() method above. Loading of primitive types
        //   is done via this method.

        // void beginSection()
        // void endSection()
        // void skipSection(bool skip)
        //   The methods beginSection() and endSection() can only be used in
        //   output archives. These mark the location of a section that can
        //   later be skipped during loading.
        //   The method skipSection() can only be used in input archives. It
        //   optionally skips a section that was marked during saving.
        //   For every beginSection() call in the output, there must be a
        //   corresponding skipSection() call in the input (even if you don't
        //   actually want to skip the section).

protected:
        inline Derived& self()
        {
                return static_cast<Derived&>(*this);
        }
};

// The part of OutputArchiveBase that doesn't depend on the template parameter
class OutputArchiveBase2
{
public:
        inline bool isLoader() const { return false; }
        inline bool versionAtLeast(unsigned /*actual*/, unsigned /*required*/) const
        {
                return true;
        }
        inline bool versionBelow(unsigned /*actual*/, unsigned /*required*/) const
        {
                return false;
        }

        void skipSection(bool /*skip*/)
        {
                UNREACHABLE;
        }

/*internal*/
        #ifdef linux
        // This routine is not portable, for example it breaks in
        // windows (mingw) because there the location of the stack
        // is _below_ the heap.
        // But this is anyway only used to check assertions. So for now
        // only do that in linux.
        static NEVER_INLINE bool addressOnStack(const void* p)
        {
                // This is not portable, it assumes:
                //  - stack grows downwards
                //  - heap is at lower address than stack
                // Also in c++ comparison between pointers is only defined when
                // the two pointers point to objects in the same array.
                int dummy;
                return &dummy < p;
        }
        #endif

        // Generate a new ID for the given pointer and store this association
        // for later (see getId()).
        template<typename T> unsigned generateId(const T* p)
        {
                // For composed structures, for example
                //   struct A { ... };
                //   struct B { A a; ... };
                // The pointer to the outer and inner structure can be the
                // same while we still want a different ID to refer to these
                // two. That's why we use a std::pair<void*, type_index> as key
                // in the map.
                // For polymorphic types you do sometimes use a base pointer
                // to refer to a subtype. So there we only use the pointer
                // value as key in the map.
                if constexpr (std::is_polymorphic_v<T>) {
                        return generateID1(p);
                } else {
                        return generateID2(p, typeid(T));
                }
        }

        template<typename T> unsigned getId(const T* p)
        {
                if constexpr (std::is_polymorphic_v<T>) {
                        return getID1(p);
                } else {
                        return getID2(p, typeid(T));
                }
        }

protected:
        OutputArchiveBase2() = default;

private:
        unsigned generateID1(const void* p);
        unsigned generateID2(const void* p, const std::type_info& typeInfo);
        unsigned getID1(const void* p);
        unsigned getID2(const void* p, const std::type_info& typeInfo);

        hash_map<std::pair<const void*, std::type_index>, unsigned, HashPair> idMap;
        hash_map<const void*, unsigned> polyIdMap;
        unsigned lastId = 0;
};

template<typename Derived>
class OutputArchiveBase : public ArchiveBase<Derived>, public OutputArchiveBase2
{
public:
        template<typename Base, typename T>
        void serializeInlinedBase(T& t, unsigned version)
        {
                // same implementation as base class, but with extra check
                static_assert(SerializeClassVersion<Base>::value ==
                              SerializeClassVersion<T   >::value,
                              "base and derived must have same version when "
                              "using serializeInlinedBase()");
                ArchiveBase<Derived>::template serializeInlinedBase<Base>(t, version);
        }
        // Main saver method. Heavy lifting is done in the Saver class.
        // The 'global constructor arguments' parameters are ignored because
        // the saver archives also completely ignore those extra parameters.
        // But we need to provide them because the same (templatized) code path
        // is used both for saving and loading.
        template<typename T, typename... Args>
        void serializeWithID(const char* tag, const T& t, Args... /*globalConstrArgs*/)
        {
                this->self().beginTag(tag);
                Saver<T> saver;
                saver(this->self(), t, true);
                this->self().endTag(tag);
        }

        // Default implementation is to base64-encode the blob and serialize
        // the resulting string. But memory archives will memcpy the blob.
        void serialize_blob(const char* tag, const void* data, size_t len,
                            bool diff = true);

        template<typename T> void serialize(const char* tag, const T& t)
        {
                this->self().beginTag(tag);
                Saver<T> saver;
                saver(this->self(), t, false);
                this->self().endTag(tag);
        }
        template<typename T> void serializePointerID(const char* tag, const T& t)
        {
                this->self().beginTag(tag);
                IDSaver<T> saver;
                saver(this->self(), t);
                this->self().endTag(tag);
        }
        template<typename T> void serializePolymorphic(const char* tag, const T& t)
        {
                static_assert(std::is_polymorphic_v<T>,
                              "must be a polymorphic type");
                PolymorphicSaverRegistry<Derived>::save(tag, this->self(), t);
        }
        template<typename T> void serializeOnlyOnce(const char* tag, const T& t)
        {
                if (!getId(&t)) {
                        serializeWithID(tag, t);
                }
        }

        // You shouldn't use this, it only exists for backwards compatibility
        void serializeChar(const char* tag, char c)
        {
                this->self().beginTag(tag);
                this->self().saveChar(c);
                this->self().endTag(tag);
        }

protected:
        OutputArchiveBase() = default;
};


// Part of InputArchiveBase that doesn't depend on the template parameter
class InputArchiveBase2
{
public:
        inline bool isLoader() const { return true; }

        void beginSection()
        {
                UNREACHABLE;
        }
        void endSection()
        {
                UNREACHABLE;
        }

/*internal*/
        void* getPointer(unsigned id);
        void addPointer(unsigned id, const void* p);
        unsigned getId(const void* p) const;

        template<typename T> void resetSharedPtr(std::shared_ptr<T>& s, T* r)
        {
                if (!r) {
                        s.reset();
                        return;
                }
                auto it = sharedPtrMap.find(r);
                if (it == end(sharedPtrMap)) {
                        s.reset(r);
                        sharedPtrMap.emplace_noDuplicateCheck(r, s);
                } else {
                        s = std::static_pointer_cast<T>(it->second);
                }
        }

protected:
        InputArchiveBase2() = default;

private:
        hash_map<unsigned, void*> idMap;
        hash_map<void*, std::shared_ptr<void>> sharedPtrMap;
};

template<typename Derived>
class InputArchiveBase : public ArchiveBase<Derived>, public InputArchiveBase2
{
public:
        template<typename T, typename... Args>
        void serializeWithID(const char* tag, T& t, Args... args)
        {
                doSerialize(tag, t, std::tuple<Args...>(args...));
        }
        void serialize_blob(const char* tag, void* data, size_t len,
                            bool diff = true);

        template<typename T>
        void serialize(const char* tag, T& t)
        {
                this->self().beginTag(tag);
                using TNC = std::remove_const_t<T>;
                auto& tnc = const_cast<TNC&>(t);
                Loader<TNC> loader;
                loader(this->self(), tnc, std::tuple<>(), -1); // don't load id
                this->self().endTag(tag);
        }
        template<typename T> void serializePointerID(const char* tag, const T& t)
        {
                this->self().beginTag(tag);
                using TNC = std::remove_const_t<T>;
                auto& tnc = const_cast<TNC&>(t);
                IDLoader<TNC> loader;
                loader(this->self(), tnc);
                this->self().endTag(tag);
        }
        template<typename T> void serializePolymorphic(const char* tag, T& t)
        {
                static_assert(std::is_polymorphic_v<T>,
                              "must be a polymorphic type");
                PolymorphicInitializerRegistry<Derived>::init(tag, this->self(), &t);
        }
        template<typename T> void serializeOnlyOnce(const char* tag, const T& t)
        {
                if (!getId(&t)) {
                        serializeWithID(tag, t);
                }
        }

        // You shouldn't use this, it only exists for backwards compatibility
        void serializeChar(const char* tag, char& c)
        {
                this->self().beginTag(tag);
                this->self().loadChar(c);
                this->self().endTag(tag);
        }

/*internal*/
        // Actual loader method. Heavy lifting is done in the Loader class.
        template<typename T, typename TUPLE>
        void doSerialize(const char* tag, T& t, TUPLE args, int id = 0)
        {
                this->self().beginTag(tag);
                using TNC = std::remove_const_t<T>;
                auto& tnc = const_cast<TNC&>(t);
                Loader<TNC> loader;
                loader(this->self(), tnc, args, id);
                this->self().endTag(tag);
        }

protected:
        InputArchiveBase() = default;
};


// Enumerate all types which can be serialized using a simple memcpy. This
// trait can be used by MemOutputArchive to apply certain optimizations.
template<typename T> struct SerializeAsMemcpy : std::false_type {};
template<> struct SerializeAsMemcpy<         bool     > : std::true_type {};
template<> struct SerializeAsMemcpy<         char     > : std::true_type {};
template<> struct SerializeAsMemcpy<  signed char     > : std::true_type {};
template<> struct SerializeAsMemcpy<unsigned char     > : std::true_type {};
template<> struct SerializeAsMemcpy<         short    > : std::true_type {};
template<> struct SerializeAsMemcpy<unsigned short    > : std::true_type {};
template<> struct SerializeAsMemcpy<         int      > : std::true_type {};
template<> struct SerializeAsMemcpy<unsigned int      > : std::true_type {};
template<> struct SerializeAsMemcpy<         long     > : std::true_type {};
template<> struct SerializeAsMemcpy<unsigned long     > : std::true_type {};
template<> struct SerializeAsMemcpy<         long long> : std::true_type {};
template<> struct SerializeAsMemcpy<unsigned long long> : std::true_type {};
template<> struct SerializeAsMemcpy<         float    > : std::true_type {};
template<> struct SerializeAsMemcpy<         double   > : std::true_type {};
template<> struct SerializeAsMemcpy<    long double   > : std::true_type {};
template<typename T, size_t N> struct SerializeAsMemcpy<T[N]> : SerializeAsMemcpy<T> {};

class MemOutputArchive final : public OutputArchiveBase<MemOutputArchive>
{
public:
        MemOutputArchive(LastDeltaBlocks& lastDeltaBlocks_,
                         std::vector<std::shared_ptr<DeltaBlock>>& deltaBlocks_,
                         bool reverseSnapshot_)
                : lastDeltaBlocks(lastDeltaBlocks_)
                , deltaBlocks(deltaBlocks_)
                , reverseSnapshot(reverseSnapshot_)
        {
        }

        ~MemOutputArchive()
        {
                assert(openSections.empty());
        }

        bool needVersion() const { return false; }
        bool isReverseSnapshot() const { return reverseSnapshot; }

        template <typename T> void save(const T& t)
        {
                put(&t, sizeof(t));
        }
        inline void saveChar(char c)
        {
                save(c);
        }
        void save(const std::string& s);
        void serialize_blob(const char* tag, const void* data, size_t len,
                            bool diff = true);

        using OutputArchiveBase<MemOutputArchive>::serialize;
        template<typename T, typename ...Args>
        ALWAYS_INLINE void serialize(const char* tag, const T& t, Args&& ...args)
        {
                // - Walk over all elements. Process non-memcpy-able elements at
                //   once. Collect memcpy-able elements in a tuple. At the end
                //   process the collected tuple with a single call.
                // - Only do this when there are at least two pairs (it is
                //   correct for a single pair, but it's less tuned for that
                //   case).
                serialize_group(std::tuple<>(), tag, t, std::forward<Args>(args)...);
        }
        template<typename T, size_t N>
        ALWAYS_INLINE void serialize(const char* /*tag*/, const T(&t)[N],
                std::enable_if_t<SerializeAsMemcpy<T>::value>* = nullptr)
        {
                buffer.insert(&t[0], N * sizeof(T));
        }

        void beginSection()
        {
                size_t skip = 0; // filled in later
                save(skip);
                size_t beginPos = buffer.getPosition();
                openSections.push_back(beginPos);
        }
        void endSection()
        {
                assert(!openSections.empty());
                size_t endPos   = buffer.getPosition();
                size_t beginPos = openSections.back();
                openSections.pop_back();
                size_t skip = endPos - beginPos;
                buffer.insertAt(beginPos - sizeof(skip),
                                &skip, sizeof(skip));
        }

        MemBuffer<uint8_t> releaseBuffer(size_t& size);

private:
        void put(const void* data, size_t len)
        {
                if (len) {
                        buffer.insert(data, len);
                }
        }

        ALWAYS_INLINE void serialize_group(const std::tuple<>& /*tuple*/)
        {
                // done categorizing, there were no memcpy-able elements
        }
        template<typename ...Args>
        ALWAYS_INLINE void serialize_group(const std::tuple<Args...>& tuple)
        {
                // done categorizing, process all memcpy-able elements
                buffer.insert_tuple_ptr(tuple);
        }
        template<typename TUPLE, typename T, typename ...Args>
        ALWAYS_INLINE void serialize_group(const TUPLE& tuple, const char* tag, const T& t, Args&& ...args)
        {
                // categorize one element
                if constexpr (SerializeAsMemcpy<T>::value) {
                        // add to the group and continue categorizing
                        (void)tag;
                        serialize_group(std::tuple_cat(tuple, std::tuple(&t)), std::forward<Args>(args)...);
                } else {
                        serialize(tag, t);      // process single (ungroupable) element
                        serialize_group(tuple, std::forward<Args>(args)...); // continue categorizing
                }
        }

private:
        OutputBuffer buffer;
        std::vector<size_t> openSections;
        LastDeltaBlocks& lastDeltaBlocks;
        std::vector<std::shared_ptr<DeltaBlock>>& deltaBlocks;
        const bool reverseSnapshot;
};

class MemInputArchive final : public InputArchiveBase<MemInputArchive>
{
public:
        MemInputArchive(const uint8_t* data, size_t size,
                        const std::vector<std::shared_ptr<DeltaBlock>>& deltaBlocks_)
                : buffer(data, size)
                , deltaBlocks(deltaBlocks_)
        {
        }

        bool needVersion() const { return false; }
        inline bool versionAtLeast(unsigned /*actual*/, unsigned /*required*/) const
        {
                return true;
        }
        inline bool versionBelow(unsigned /*actual*/, unsigned /*required*/) const
        {
                return false;
        }

        template<typename T> void load(T& t)
        {
                get(&t, sizeof(t));
        }
        inline void loadChar(char& c)
        {
                load(c);
        }
        void load(std::string& s);
        std::string_view loadStr();
        void serialize_blob(const char* tag, void* data, size_t len,
                            bool diff = true);

        using InputArchiveBase<MemInputArchive>::serialize;
        template<typename T, typename ...Args>
        ALWAYS_INLINE void serialize(const char* tag, T& t, Args&& ...args)
        {
                // see comments in MemOutputArchive
                serialize_group(std::tuple<>(), tag, t, std::forward<Args>(args)...);
        }

        template<typename T, size_t N>
        ALWAYS_INLINE void serialize(const char* /*tag*/, T(&t)[N],
                std::enable_if_t<SerializeAsMemcpy<T>::value>* = nullptr)
        {
                buffer.read(&t[0], N * sizeof(T));
        }

        void skipSection(bool skip)
        {
                size_t num;
                load(num);
                if (skip) {
                        buffer.skip(num);
                }
        }

private:
        void get(void* data, size_t len)
        {
                if (len) {
                        buffer.read(data, len);
                }
        }

        // See comments in MemOutputArchive
        template<typename TUPLE>
        ALWAYS_INLINE void serialize_group(const TUPLE& tuple)
        {
                auto read = [&](auto* p) { buffer.read(p, sizeof(*p)); };
                std::apply([&](auto&&... args) { (read(args), ...); }, tuple);
        }
        template<typename TUPLE, typename T, typename ...Args>
        ALWAYS_INLINE void serialize_group(const TUPLE& tuple, const char* tag, T& t, Args&& ...args)
        {
                if constexpr (SerializeAsMemcpy<T>::value) {
                        (void)tag;
                        serialize_group(std::tuple_cat(tuple, std::tuple(&t)), std::forward<Args>(args)...);
                } else {
                        serialize(tag, t);
                        serialize_group(tuple, std::forward<Args>(args)...);
                }
        }

private:
        InputBuffer buffer;
        const std::vector<std::shared_ptr<DeltaBlock>>& deltaBlocks;
};


class XmlOutputArchive final : public OutputArchiveBase<XmlOutputArchive>
{
public:
        explicit XmlOutputArchive(const std::string& filename);
        void close();
        ~XmlOutputArchive();

        template <typename T> void saveImpl(const T& t)
        {
                // TODO make sure floating point is printed with enough digits
                //      maybe print as hex?
                save(strCat(t));
        }
        template <typename T> void save(const T& t)
        {
                saveImpl(t);
        }
        void saveChar(char c);
        void save(const std::string& str);
        void save(bool b);
        void save(unsigned char b);
        void save(signed char c);
        void save(char c);
        void save(int i);                  // these 3 are not strictly needed
        void save(unsigned u);             // but having them non-inline
        void save(unsigned long long ull); // saves quite a bit of code

        void beginSection() { /*nothing*/ }
        void endSection()   { /*nothing*/ }

        // workaround(?) for visual studio 2015:
        //   put the default here instead of in the base class
        using OutputArchiveBase<XmlOutputArchive>::serialize;
        template<typename T, typename ...Args>
        ALWAYS_INLINE void serialize(const char* tag, const T& t, Args&& ...args)
        {
                // by default just repeatedly call the single-pair serialize() variant
                this->self().serialize(tag, t);
                this->self().serialize(std::forward<Args>(args)...);
        }

//internal:
        inline bool translateEnumToString() const { return true; }
        inline bool canHaveOptionalAttributes() const { return true; }
        inline bool canCountChildren() const { return true; }

        void beginTag(const char* tag);
        void endTag(const char* tag);

        template<typename T> void attributeImpl(const char* name, const T& t)
        {
                attribute(name, strCat(t));
        }
        template<typename T> void attribute(const char* name, const T& t)
        {
                attributeImpl(name, t);
        }
        void attribute(const char* name, const std::string& str);
        void attribute(const char* name, int i);
        void attribute(const char* name, unsigned u);

private:
        gzFile file;
        XMLElement root;
        std::vector<XMLElement*> current;
};

class XmlInputArchive final : public InputArchiveBase<XmlInputArchive>
{
public:
        explicit XmlInputArchive(const std::string& filename);

        inline bool versionAtLeast(unsigned actual, unsigned required) const
        {
                return actual >= required;
        }
        inline bool versionBelow(unsigned actual, unsigned required) const
        {
                return actual < required;
        }

        template<typename T> void load(T& t)
        {
                std::string str;
                load(str);
                std::istringstream is(str);
                is >> t;
        }
        void loadChar(char& c);
        void load(bool& b);
        void load(unsigned char& b);
        void load(signed char& c);
        void load(char& c);
        void load(int& i);                  // these 3 are not strictly needed
        void load(unsigned& u);             // but having them non-inline
        void load(unsigned long long& ull); // saves quite a bit of code
        void load(std::string& t);
        std::string_view loadStr();

        void skipSection(bool /*skip*/) { /*nothing*/ }

        // workaround(?) for visual studio 2015:
        //   put the default here instead of in the base class
        using InputArchiveBase<XmlInputArchive>::serialize;
        template<typename T, typename ...Args>
        ALWAYS_INLINE void serialize(const char* tag, T& t, Args&& ...args)
        {
                // by default just repeatedly call the single-pair serialize() variant
                this->self().serialize(tag, t);
                this->self().serialize(std::forward<Args>(args)...);
        }

//internal:
        inline bool translateEnumToString() const { return true; }
        inline bool canHaveOptionalAttributes() const { return true; }
        inline bool canCountChildren() const { return true; }

        void beginTag(const char* tag);
        void endTag(const char* tag);

        template<typename T> void attributeImpl(const char* name, T& t)
        {
                std::string str;
                attribute(name, str);
                std::istringstream is(str);
                is >> t;
        }
        template<typename T> void attribute(const char* name, T& t)
        {
                attributeImpl(name, t);
        }
        void attribute(const char* name, std::string& t);
        void attribute(const char* name, int& i);
        void attribute(const char* name, unsigned& u);

        bool hasAttribute(const char* name);
        bool findAttribute(const char* name, unsigned& value);
        int countChildren() const;

private:
        XMLElement rootElem;
        std::vector<std::pair<const XMLElement*, size_t>> elems;
};

#define INSTANTIATE_SERIALIZE_METHODS(CLASS) \
template void CLASS::serialize(MemInputArchive&,   unsigned); \
template void CLASS::serialize(MemOutputArchive&,  unsigned); \
template void CLASS::serialize(XmlInputArchive&,   unsigned); \
template void CLASS::serialize(XmlOutputArchive&,  unsigned);

} // namespace openmsx

#endif