Generic DOM: Add DomBackend abstraction and JSON support

This change adds a `DomBackend` interface and a `DomBackendRegistry` for backend discovery (currently not hooked up to anything) alongside a JSON backend implementation.

The JSON backend comes with a small suite of unit and performance tests. The unit tests validate generic DOM conversion to and from serialized JSON and rapidjson::Document objects (the support for which lives in `JsonSerializationUtils.h`).

The performance tests show a throughput decrease compared to directly using the rapidjson serializer when mirroring our current pattern of copying strings from the serialized JSON representation, but with the coming in-memory store we have the opportunity to keep the buffer in memory and deserialize in-situ using rapidjson's API, which is consistently at least 100MiB/s faster on my machine (Ryzen Threadripper 3970X). The first parameter is the nested object complexity (N*N, objects with N keys comprised of arrays with N values) and the second parameter is the base size of the strings within each entry of this object.
```
----------------------------------------------------------------------------------------------------------------------
Benchmark                                                            Time             CPU   Iterations UserCounters...
----------------------------------------------------------------------------------------------------------------------
DomJsonBenchmark/DomDeserializeToDocumentInPlace/10/5            0.050 ms        0.050 ms        10000 bytes_per_second=355.816M/s
DomJsonBenchmark/DomDeserializeToDocumentInPlace/10/50           0.057 ms        0.057 ms        11200 bytes_per_second=386.064M/s
DomJsonBenchmark/DomDeserializeToDocumentInPlace/100/5            4.77 ms         4.88 ms          112 bytes_per_second=364.046M/s
DomJsonBenchmark/DomDeserializeToDocumentInPlace/100/500          11.6 ms         11.7 ms           64 bytes_per_second=554.518M/s
DomJsonBenchmark/DomDeserializeToDocumentWithCopies/10/5         0.084 ms        0.084 ms         7467 bytes_per_second=212.55M/s
DomJsonBenchmark/DomDeserializeToDocumentWithCopies/10/50        0.099 ms        0.100 ms         6400 bytes_per_second=220.608M/s
DomJsonBenchmark/DomDeserializeToDocumentWithCopies/100/5         8.22 ms         8.16 ms           90 bytes_per_second=217.847M/s
DomJsonBenchmark/DomDeserializeToDocumentWithCopies/100/500       23.2 ms         22.9 ms           30 bytes_per_second=283.56M/s
DomJsonBenchmark/JsonUtilsDeserializeToDocument/10/5             0.070 ms        0.070 ms        11200 bytes_per_second=255.049M/s
DomJsonBenchmark/JsonUtilsDeserializeToDocument/10/50            0.086 ms        0.087 ms         8960 bytes_per_second=253.258M/s
DomJsonBenchmark/JsonUtilsDeserializeToDocument/100/5             6.86 ms         6.84 ms          112 bytes_per_second=260.033M/s
DomJsonBenchmark/JsonUtilsDeserializeToDocument/100/500           22.8 ms         22.9 ms           32 bytes_per_second=283.158M/s
```

For `AZ::DOM::Document`, the current plan is to offer helper methods that can load from a file path or string using a given backend that can take advantage of in-place parsing by internally storing the serialized buffer.

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

Code/Framework/AzCore/AzCore/DOM/Backends/JSON/JsonBackend.cpp

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#include <AzCore/DOM/Backends/JSON/JsonBackend.h>
+
+#include <AzCore/DOM/DomBackendRegistry.h>
+
+namespace AZ::DOM
+{
+    Visitor::Result JsonBackend::ReadFromStringInPlace(AZStd::string& buffer, Visitor* visitor)
+    {
+        return Json::VisitSerializedJsonInPlace(buffer, visitor);
+    }
+
+    Visitor::Result JsonBackend::ReadFromString(AZStd::string_view buffer, Lifetime lifetime, Visitor* visitor)
+    {
+        return Json::VisitSerializedJson(buffer, lifetime, visitor);
+    }
+
+    AZStd::unique_ptr<Visitor> JsonBackend::CreateStreamWriter(AZ::IO::GenericStream* stream)
+    {
+        return Json::GetJsonStreamWriter(stream, Json::OutputFormatting::PrettyPrintedJson);
+    }
+
+    void JsonBackend::Register()
+    {
+        if (auto backendRegistry = BackendRegistry::Get())
+        {
+            backendRegistry->RegisterBackend<JsonBackend>(kName, {kExtension});
+        }
+    }
+}

Code/Framework/AzCore/AzCore/DOM/Backends/JSON/JsonBackend.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#pragma once
+
+#include <AzCore/DOM/DomBackend.h>
+#include <AzCore/DOM/Backends/JSON/JsonSerializationUtils.h>
+
+namespace AZ::DOM
+{
+    class JsonBackend final : public Backend
+    {
+    public:
+        Visitor::Result ReadFromStringInPlace(AZStd::string& buffer, Visitor* visitor) override;
+        Visitor::Result ReadFromString(AZStd::string_view buffer, Lifetime lifetime, Visitor* visitor) override;
+        AZStd::unique_ptr<Visitor> CreateStreamWriter(AZ::IO::GenericStream* stream) override;
+
+        static constexpr const char* kName = "JSON";
+        static constexpr const char* kExtension = ".json";
+        static void Register();
+    };
+} // namespace AZ::DOM

Code/Framework/AzCore/AzCore/DOM/Backends/JSON/JsonSerializationUtils.cpp

@@ -0,0 +1,675 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#include <AzCore/DOM/Backends/JSON/JsonSerializationUtils.h>
+
+#include <AzCore/IO/ByteContainerStream.h>
+#include <AzCore/IO/TextStreamWriters.h>
+#include <AzCore/JSON/filewritestream.h>
+#include <AzCore/JSON/memorystream.h>
+#include <AzCore/JSON/prettywriter.h>
+#include <AzCore/JSON/rapidjson.h>
+#include <AzCore/JSON/reader.h>
+#include <AzCore/JSON/writer.h>
+#include <AzCore/std/containers/queue.h>
+#include <AzCore/std/containers/stack.h>
+#include <AzCore/std/containers/variant.h>
+#include <AzCore/std/optional.h>
+
+namespace AZ::DOM::Json
+{
+    //
+    // class DocumentWriter
+    //
+    // Visitor that produces a rapidjson::Document
+    class DocumentWriter final : public Visitor
+    {
+    public:
+        VisitorFlags GetVisitorFlags() const override
+        {
+            return VisitorFlags::SupportsRawKeys | VisitorFlags::SupportsArrays | VisitorFlags::SupportsObjects;
+        }
+
+        Result Null() override
+        {
+            CurrentValue().SetNull();
+            return FinishWrite();
+        }
+
+        Result Bool(bool value) override
+        {
+            CurrentValue().SetBool(value);
+            return FinishWrite();
+        }
+
+        Result Int64(AZ::s64 value) override
+        {
+            CurrentValue().SetInt64(value);
+            return FinishWrite();
+        }
+
+        Result Uint64(AZ::u64 value) override
+        {
+            CurrentValue().SetUint64(value);
+            return FinishWrite();
+        }
+
+        Result Double(double value) override
+        {
+            CurrentValue().SetDouble(value);
+            return FinishWrite();
+        }
+
+        Result String(AZStd::string_view value, Lifetime lifetime) override
+        {
+            if (lifetime == Lifetime::Temporary)
+            {
+                CurrentValue().SetString(value.data(), static_cast<rapidjson::SizeType>(value.length()), m_result.GetAllocator());
+            }
+            else
+            {
+                CurrentValue().SetString(value.data(), static_cast<rapidjson::SizeType>(value.size()));
+            }
+            return FinishWrite();
+        }
+
+        Result StartObject() override
+        {
+            CurrentValue().SetObject();
+
+            const bool isObject = true;
+            m_entryStack.emplace_front(isObject, CurrentValue());
+            return VisitorSuccess();
+        }
+
+        Result EndObject(AZ::u64 attributeCount) override
+        {
+            if (m_entryStack.empty())
+            {
+                return VisitorFailure(VisitorErrorCode::InternalError, "EndObject called without a matching BeginObject call");
+            }
+
+            if (!m_entryStack.front().m_isObject)
+            {
+                return VisitorFailure(VisitorErrorCode::InternalError, "Expected EndArray and received EndObject instead");
+            }
+
+            if (m_entryStack.front().m_entryCount != attributeCount)
+            {
+                return FormatVisitorFailure(
+                    VisitorErrorCode::InternalError, "EndObject: Expected %lu attributes but received %lu attributes instead",
+                    attributeCount, m_entryStack.front().m_entryCount);
+            }
+
+            m_entryStack.pop_front();
+            return FinishWrite();
+        }
+
+        Result Key(AZ::Name key) override
+        {
+            return RawKey(key.GetStringView(), Lifetime::Persistent);
+        }
+
+        Result RawKey(AZStd::string_view key, Lifetime lifetime) override
+        {
+            AZ_Assert(!m_entryStack.empty(), "Attempmted to push a key with no object");
+            AZ_Assert(m_entryStack.front().m_isObject, "Attempted to push a key to an array");
+            if (lifetime == Lifetime::Persistent)
+            {
+                m_entryStack.front().m_key.SetString(key.data(), static_cast<rapidjson::SizeType>(key.size()));
+            }
+            else
+            {
+                m_entryStack.front().m_key.SetString(key.data(), static_cast<rapidjson::SizeType>(key.size()), m_result.GetAllocator());
+            }
+            return VisitorSuccess();
+        }
+
+        Result StartArray() override
+        {
+            CurrentValue().SetArray();
+
+            const bool isObject = false;
+            m_entryStack.emplace_front(isObject, CurrentValue());
+            return VisitorSuccess();
+        }
+
+        Result EndArray(AZ::u64 elementCount) override
+        {
+            if (m_entryStack.empty())
+            {
+                return VisitorFailure(VisitorErrorCode::InternalError, "EndArray called without a matching BeginArray call");
+            }
+
+            if (m_entryStack.front().m_isObject)
+            {
+                return VisitorFailure(VisitorErrorCode::InternalError, "Expected EndObject and received EndArray instead");
+            }
+
+            if (m_entryStack.front().m_entryCount != elementCount)
+            {
+                return FormatVisitorFailure(
+                    VisitorErrorCode::InternalError, "EndArray: Expected %lu elements but received %lu elements instead", elementCount,
+                    m_entryStack.front().m_entryCount);
+            }
+
+            m_entryStack.pop_front();
+            return FinishWrite();
+        }
+
+        rapidjson::Document&& TakeDocument()
+        {
+            return AZStd::move(m_result);
+        }
+
+    private:
+        Result FinishWrite()
+        {
+            if (m_entryStack.empty())
+            {
+                return VisitorSuccess();
+            }
+
+            // Retrieve the top value of the stack and replace it with a null value
+            rapidjson::Value value;
+            m_entryStack.front().m_value.Swap(value);
+            ++m_entryStack.front().m_entryCount;
+
+            if (m_entryStack.front().m_key.IsString())
+            {
+                m_entryStack.front().m_container.AddMember(m_entryStack.front().m_key.Move(), AZStd::move(value), m_result.GetAllocator());
+                m_entryStack.front().m_key.SetNull();
+            }
+            else
+            {
+                m_entryStack.front().m_container.PushBack(AZStd::move(value), m_result.GetAllocator());
+            }
+
+            return VisitorSuccess();
+        }
+
+        rapidjson::Value& CurrentValue()
+        {
+            if (m_entryStack.empty())
+            {
+                return m_result;
+            }
+            return m_entryStack.front().m_value;
+        }
+
+        struct ValueInfo
+        {
+            ValueInfo(bool isObject, rapidjson::Value& container)
+                : m_isObject(isObject)
+                , m_container(container)
+            {
+            }
+
+            bool m_isObject;
+            rapidjson::Value& m_container;
+            rapidjson::Value m_value;
+            AZ::u64 m_entryCount = 0;
+            rapidjson::Value m_key;
+        };
+
+        rapidjson::Document m_result;
+        AZStd::deque<ValueInfo> m_entryStack;
+        AZ::u64 m_entryCount = 0;
+    };
+
+    //
+    // class StreamWriter
+    //
+    // Visitor that writes to a rapidjson::Writer
+    template<class TWriter>
+    class StreamWriter : public Visitor
+    {
+    public:
+        StreamWriter(AZ::IO::GenericStream* stream)
+            : m_streamWriter(stream)
+            , m_writer(TWriter(m_streamWriter))
+        {
+        }
+
+        VisitorFlags GetVisitorFlags() const override
+        {
+            return VisitorFlags::SupportsRawKeys | VisitorFlags::SupportsArrays | VisitorFlags::SupportsObjects;
+        }
+
+        Result Null() override
+        {
+            return CheckWrite(m_writer.Null());
+        }
+
+        Result Bool(bool value) override
+        {
+            return CheckWrite(m_writer.Bool(value));
+        }
+
+        Result Int64(AZ::s64 value) override
+        {
+            return CheckWrite(m_writer.Int64(value));
+        }
+
+        Result Uint64(AZ::u64 value) override
+        {
+            return CheckWrite(m_writer.Uint64(value));
+        }
+
+        Result Double(double value) override
+        {
+            return CheckWrite(m_writer.Double(value));
+        }
+
+        Result String(AZStd::string_view value, Lifetime lifetime) override
+        {
+            const bool shouldCopy = lifetime == Lifetime::Temporary;
+            return CheckWrite(m_writer.String(value.data(), static_cast<rapidjson::SizeType>(value.size()), shouldCopy));
+        }
+
+        Result StartObject() override
+        {
+            return CheckWrite(m_writer.StartObject());
+        }
+
+        Result EndObject(AZ::u64 attributeCount) override
+        {
+            return CheckWrite(m_writer.EndObject(static_cast<rapidjson::SizeType>(attributeCount)));
+        }
+
+        Result Key(AZ::Name key) override
+        {
+            return RawKey(key.GetStringView(), Lifetime::Persistent);
+        }
+
+        Result RawKey(AZStd::string_view key, Lifetime lifetime) override
+        {
+            const bool shouldCopy = lifetime == Lifetime::Temporary;
+            return CheckWrite(m_writer.Key(key.data(), static_cast<rapidjson::SizeType>(key.size()), shouldCopy));
+        }
+
+        Result StartArray() override
+        {
+            return CheckWrite(m_writer.StartArray());
+        }
+
+        Result EndArray(AZ::u64 elementCount) override
+        {
+            return CheckWrite(m_writer.EndArray(static_cast<rapidjson::SizeType>(elementCount)));
+        }
+
+    private:
+        Result CheckWrite(bool writeSucceeded)
+        {
+            if (!writeSucceeded)
+            {
+                return VisitorFailure(VisitorErrorCode::InternalError, "Failed to write JSON");
+            }
+            return VisitorSuccess();
+        }
+
+        AZ::IO::RapidJSONStreamWriter m_streamWriter;
+        TWriter m_writer;
+    };
+
+    //
+    // struct JsonReadHandler
+    //
+    // Handler for a rapidjson::Reader that translates reads into an AZ::DOM::Visitor
+    struct JsonReadHandler : public rapidjson::BaseReaderHandler<rapidjson::UTF8<>, JsonReadHandler>
+    {
+    public:
+        JsonReadHandler(Visitor* visitor, Lifetime stringLifetime)
+            : m_visitor(visitor)
+            , m_stringLifetime(stringLifetime)
+            , m_outcome(AZ::Success())
+        {
+        }
+
+        bool Null()
+        {
+            return CheckResult(m_visitor->Null());
+        }
+
+        bool Bool(bool b)
+        {
+            return CheckResult(m_visitor->Bool(b));
+        }
+
+        bool Int(int i)
+        {
+            return CheckResult(m_visitor->Int64(static_cast<AZ::s64>(i)));
+        }
+
+        bool Uint(unsigned i)
+        {
+            return CheckResult(m_visitor->Uint64(static_cast<AZ::u64>(i)));
+        }
+
+        bool Int64(int64_t i)
+        {
+            return CheckResult(m_visitor->Int64(i));
+        }
+
+        bool Uint64(uint64_t i)
+        {
+            return CheckResult(m_visitor->Uint64(i));
+        }
+
+        bool Double(double d)
+        {
+            return CheckResult(m_visitor->Double(d));
+        }
+
+        bool RawNumber([[maybe_unused]] const Ch* str, [[maybe_unused]] rapidjson::SizeType length, [[maybe_unused]] bool copy)
+        {
+            AZ_Assert(false, "Raw numbers are unsupported");
+            return false;
+        }
+
+        bool String(const Ch* str, rapidjson::SizeType length, bool copy)
+        {
+            Lifetime lifetime = m_stringLifetime;
+            if (!copy)
+            {
+                lifetime = Lifetime::Temporary;
+            }
+            return CheckResult(m_visitor->String(AZStd::string_view(str, length), lifetime));
+        }
+
+        bool StartObject()
+        {
+            return CheckResult(m_visitor->StartObject());
+        }
+
+        bool Key(const Ch* str, rapidjson::SizeType length, [[maybe_unused]] bool copy)
+        {
+            AZStd::string_view key = AZStd::string_view(str, length);
+            if (!m_visitor->SupportsRawKeys())
+            {
+                m_visitor->Key(AZ::Name(key));
+            }
+            Lifetime lifetime = m_stringLifetime;
+            if (!copy)
+            {
+                lifetime = Lifetime::Temporary;
+            }
+            return CheckResult(m_visitor->RawKey(key, lifetime));
+        }
+
+        bool EndObject([[maybe_unused]] rapidjson::SizeType memberCount)
+        {
+            return CheckResult(m_visitor->EndObject(memberCount));
+        }
+
+        bool StartArray()
+        {
+            return CheckResult(m_visitor->StartArray());
+        }
+
+        bool EndArray([[maybe_unused]] rapidjson::SizeType elementCount)
+        {
+            return CheckResult(m_visitor->EndArray(elementCount));
+        }
+
+        Visitor::Result&& TakeOutcome()
+        {
+            return AZStd::move(m_outcome);
+        }
+
+    private:
+        bool CheckResult(Visitor::Result result)
+        {
+            if (!result.IsSuccess())
+            {
+                m_outcome = AZStd::move(result);
+                return false;
+            }
+            return true;
+        }
+
+        Visitor::Result m_outcome;
+        Visitor* m_visitor;
+        Lifetime m_stringLifetime;
+    };
+
+    //
+    // struct AzStringStream
+    //
+    // rapidjson stream wrapper for AZStd::string suitable for in-situ parsing
+    struct AzStringStream
+    {
+        using Ch = char;
+
+        AzStringStream(AZStd::string& buffer)
+        {
+            m_cursor = buffer.data();
+            m_begin = m_cursor;
+        }
+
+        char Peek() const
+        {
+            return *m_cursor;
+        }
+
+        char Take()
+        {
+            return *m_cursor++;
+        }
+
+        size_t Tell() const
+        {
+            return static_cast<size_t>(m_cursor - m_begin);
+        }
+
+        char* PutBegin()
+        {
+            m_write = m_cursor;
+            return m_cursor;
+        }
+
+        void Put(char c)
+        {
+            (*m_write++) = c;
+        }
+
+        void Flush()
+        {
+        }
+
+        size_t PutEnd(char* begin)
+        {
+            return m_write - begin;
+        }
+
+        const char* Peek4() const
+        {
+            AZ_Assert(false, "Not implemented, encoding is hard-coded to UTF-8");
+        }
+
+        char* m_cursor; //!< Current read position.
+        char* m_write; //!< Current write position.
+        const char* m_begin; //!< Head of string.
+    };
+
+    //
+    // Serialized JSON util functions
+    //
+    AZStd::unique_ptr<Visitor> GetJsonStreamWriter(AZ::IO::GenericStream* stream, OutputFormatting format)
+    {
+        if (format == OutputFormatting::MinifiedJson)
+        {
+            using WriterType = rapidjson::Writer<AZ::IO::RapidJSONStreamWriter>;
+            return AZStd::make_unique<StreamWriter<WriterType>>(stream);
+        }
+        else
+        {
+            using WriterType = rapidjson::PrettyWriter<AZ::IO::RapidJSONStreamWriter>;
+            return AZStd::make_unique<StreamWriter<WriterType>>(stream);
+        }
+    }
+
+    Visitor::Result VisitSerializedJson(AZStd::string_view buffer, Lifetime lifetime, Visitor* visitor)
+    {
+        rapidjson::Reader reader;
+        rapidjson::MemoryStream stream(buffer.data(), buffer.size());
+        JsonReadHandler handler(visitor, lifetime);
+
+        constexpr int flags = rapidjson::kParseCommentsFlag;
+        reader.Parse<flags>(stream, handler);
+        return handler.TakeOutcome();
+    }
+
+    Visitor::Result VisitSerializedJsonInPlace(AZStd::string& buffer, Visitor* visitor)
+    {
+        rapidjson::Reader reader;
+        AzStringStream stream(buffer);
+        JsonReadHandler handler(visitor, Lifetime::Persistent);
+
+        constexpr int flags = rapidjson::kParseCommentsFlag | rapidjson::kParseInsituFlag;
+        reader.Parse<flags>(stream, handler);
+        return handler.TakeOutcome();
+    }
+
+    //
+    // In-memory rapidjson util functions
+    //
+    AZ::Outcome<rapidjson::Document, AZStd::string> WriteToRapidJsonDocument(Backend::WriteCallback writeCallback)
+    {
+        DocumentWriter writer;
+        auto result = writeCallback(&writer);
+        if (!result.IsSuccess())
+        {
+            return AZ::Failure(result.TakeError().FormatVisitorErrorMessage());
+        }
+        return AZ::Success(writer.TakeDocument());
+    }
+
+    Visitor::Result VisitRapidJsonValue(const rapidjson::Value& value, Visitor* visitor, Lifetime lifetime)
+    {
+        enum class EndMarker
+        {
+            EndArray,
+            EndObject
+        };
+
+        // Processing stack consists of values comprised of one of a:
+        // - rapidjson::Value to process
+        // - EndMarker denoting the end of an array or object
+        // - string denoting a key at the beginning of a key/value pair
+        using Entry = AZStd::variant<const rapidjson::Value*, EndMarker, AZStd::string_view>;
+        AZStd::stack<Entry> entryStack;
+        AZStd::stack<u64> entryCountStack;
+        entryStack.push(&value);
+
+        while (!entryStack.empty())
+        {
+            const auto currentEntry = entryStack.top();
+            entryStack.pop();
+
+            if (AZStd::holds_alternative<EndMarker>(currentEntry))
+            {
+                EndMarker marker = AZStd::get<EndMarker>(currentEntry);
+                if (marker == EndMarker::EndArray)
+                {
+                    visitor->EndArray(entryCountStack.top());
+                }
+                else
+                {
+                    visitor->EndObject(entryCountStack.top());
+                }
+                entryCountStack.pop();
+                continue;
+            }
+
+            if (AZStd::holds_alternative<AZStd::string_view>(currentEntry))
+            {
+                AZStd::string_view key = AZStd::get<AZStd::string_view>(currentEntry);
+                if (visitor->SupportsRawKeys())
+                {
+                    visitor->RawKey(key, lifetime);
+                }
+                else
+                {
+                    visitor->Key(AZ::Name(key));
+                }
+                continue;
+            }
+
+            const rapidjson::Value& currentValue = *AZStd::get<const rapidjson::Value*>(currentEntry);
+            if (!entryCountStack.empty())
+            {
+                ++entryCountStack.top();
+            }
+
+            Visitor::Result result = AZ::Success();
+
+            switch (currentValue.GetType())
+            {
+            case rapidjson::kNullType:
+                result = visitor->Null();
+                break;
+            case rapidjson::kFalseType:
+                result = visitor->Bool(false);
+                break;
+            case rapidjson::kTrueType:
+                result = visitor->Bool(true);
+                break;
+            case rapidjson::kObjectType:
+                entryStack.push(EndMarker::EndObject);
+                entryCountStack.push(0);
+                result = visitor->StartObject();
+                for (auto it = currentValue.MemberEnd(); it != currentValue.MemberBegin(); --it)
+                {
+                    auto entry = (it - 1);
+                    const AZStd::string_view key(entry->name.GetString(), static_cast<size_t>(entry->name.GetStringLength()));
+                    entryStack.push(&entry->value);
+                    entryStack.push(key);
+                }
+                break;
+            case rapidjson::kArrayType:
+                entryStack.push(EndMarker::EndArray);
+                entryCountStack.push(0);
+                result = visitor->StartArray();
+                for (auto it = currentValue.End(); it != currentValue.Begin(); --it)
+                {
+                    auto entry = (it - 1);
+                    entryStack.push(entry);
+                }
+                break;
+            case rapidjson::kStringType:
+                result = visitor->String(
+                    AZStd::string_view(currentValue.GetString(), static_cast<size_t>(currentValue.GetStringLength())), lifetime);
+                break;
+            case rapidjson::kNumberType:
+                if (currentValue.IsFloat() || currentValue.IsDouble())
+                {
+                    result = visitor->Double(currentValue.GetDouble());
+                }
+                else if (currentValue.IsInt64() || currentValue.IsInt())
+                {
+                    result = visitor->Int64(currentValue.GetInt64());
+                }
+                else
+                {
+                    result = visitor->Uint64(currentValue.GetUint64());
+                }
+                break;
+            default:
+                return AZ::Failure(VisitorError(VisitorErrorCode::InvalidData, "Value with invalid type specified"));
+            }
+
+            if (!result.IsSuccess())
+            {
+                return result;
+            }
+        }
+
+        return AZ::Success();
+    }
+} // namespace AZ::DOM::Json

Code/Framework/AzCore/AzCore/DOM/Backends/JSON/JsonSerializationUtils.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#pragma once
+
+#include <AzCore/DOM/DomBackend.h>
+#include <AzCore/DOM/DomVisitor.h>
+#include <AzCore/IO/GenericStreams.h>
+#include <AzCore/IO/Path/Path.h>
+#include <AzCore/JSON/document.h>
+#include <AzCore/std/containers/vector.h>
+#include <AzCore/std/smart_ptr/unique_ptr.h>
+
+namespace AZ::DOM::Json
+{
+    //! Specifies how JSON should be formatted when serialized.
+    enum class OutputFormatting
+    {
+        MinifiedJson, //!< Formats JSON in compact minified form, focusing on minimizing output size.
+        PrettyPrintedJson, //!< Formats JSON in a pretty printed form, focusing on legibility to readers.
+    };
+
+    //! Creates a Visitor that will write serialized JSON to the specified stream.
+    //! \param stream The stream the visitor will write to.
+    //! \param format The format to write in.
+    //! \return A Visitor that will write to stream when visited.
+    AZStd::unique_ptr<Visitor> GetJsonStreamWriter(
+        AZ::IO::GenericStream* stream, OutputFormatting format = OutputFormatting::PrettyPrintedJson);
+    //! Reads serialized JSON from a string and applies it to a visitor.
+    //! \param buffer The UTF-8 serialized JSON to read.
+    //! \param lifetime Specifies the lifetime of the specified buffer. If the string specified by buffer might be deallocated,
+    //! ensure specify Lifetime::Temporary is specified.
+    //! \param visitor The visitor to visit with the JSON buffer's contents.
+    //! \return The aggregate result specifying whether the visitor operations were successful.
+    Visitor::Result VisitSerializedJson(AZStd::string_view buffer, Lifetime lifetime, Visitor* visitor);
+    //! Reads serialized JSON from a string in-place and applies it to a visitor.
+    //! \param buffer The UTF-8 serialized JSON to read. This buffer will be modified as part of the deserialization process to
+    //! apply null terminators.
+    //! \param visitor The visitor to visit with the JSON buffer's contents. The strings provided to the visitor will only
+    //! be valid for the lifetime of buffer.
+    //! \return The aggregate result specifying whether the visitor operations were successful.
+    Visitor::Result VisitSerializedJsonInPlace(AZStd::string& buffer, Visitor* visitor);
+
+    //! Takes a visitor specified by a callback and produces a rapidjson::Document.
+    //! \param writeCallback A callback specifying a visitor to accept to build the resulting document.
+    //! \return An outcome with either the rapidjson::Document or an error message.
+    AZ::Outcome<rapidjson::Document, AZStd::string> WriteToRapidJsonDocument(Backend::WriteCallback writeCallback);
+    //! Accepts a visitor with the contents of a rapidjson::Value.
+    //! \param value The rapidjson::Value to apply to visitor.
+    //! \param visitor The visitor to receive the contents of value.
+    //! \param lifetime The lifetime to specify for visiting strings. If the rapidjson::Value might be destroyed or changed
+    //! before the visitor is finished using these values, Lifetime::Temporary should be specified.
+    //! \return The aggregate result specifying whether the visitor operations were successful.
+    Visitor::Result VisitRapidJsonValue(const rapidjson::Value& value, Visitor* visitor, Lifetime lifetime);
+} // namespace AZ::DOM::Json

Code/Framework/AzCore/AzCore/DOM/DomBackend.cpp

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#include <AzCore/DOM/DomBackend.h>
+
+#include <AzCore/Utils/Utils.h>
+#include <AzCore/IO/ByteContainerStream.h>
+#include "DomBackend.h"
+
+namespace AZ::DOM
+{
+    Visitor::Result Backend::ReadFromPath(AZ::IO::PathView pathName, Visitor* visitor, size_t maxFileSize)
+    {
+        auto readResult = AZ::Utils::ReadFile(pathName.Native(), maxFileSize);
+        if (!readResult.IsSuccess())
+        {
+            return AZ::Failure(VisitorError(VisitorErrorCode::InternalError, readResult.TakeError()));
+        }
+
+        AZStd::string fileContents = readResult.TakeValue();
+        return ReadFromString(fileContents, Lifetime::Temporary, visitor);
+    }
+
+    Visitor::Result Backend::ReadFromStream(AZ::IO::GenericStream* stream, Visitor* visitor, size_t maxSize)
+    {
+        size_t length = stream->GetLength();
+        if (length > maxSize)
+        {
+            return AZ::Failure(VisitorError(VisitorErrorCode::InternalError, "Stream is too large."));
+        }
+        AZStd::string buffer;
+        buffer.resize(maxSize);
+        stream->Read(length, buffer.data());
+        return ReadFromString(buffer, Lifetime::Temporary, visitor);
+    }
+
+    Visitor::Result Backend::ReadFromStringInPlace(AZStd::string& buffer, Visitor* visitor)
+    {
+        return ReadFromString(buffer, Lifetime::Persistent, visitor);
+    }
+
+    Visitor::Result Backend::WriteToStream(AZ::IO::GenericStream* stream, WriteCallback callback)
+    {
+        AZStd::unique_ptr<Visitor> writer = CreateStreamWriter(stream);
+        return callback(writer.get());
+    }
+
+    Visitor::Result Backend::WriteToPath(AZ::IO::PathView pathName, WriteCallback callback)
+    {
+        AZStd::string buffer;
+        auto serializeResult = WriteToString(buffer, callback);
+        if (!serializeResult.IsSuccess())
+        {
+            return serializeResult;
+        }
+
+        auto writeResult = AZ::Utils::WriteFile(buffer, pathName.Native());
+        if (!writeResult.IsSuccess())
+        {
+            return AZ::Failure(VisitorError(VisitorErrorCode::InternalError, writeResult.TakeError()));
+        }
+
+        return AZ::Success();
+    }
+
+    Visitor::Result Backend::WriteToString(AZStd::string& buffer, WriteCallback callback)
+    {
+        AZ::IO::ByteContainerStream<AZStd::string> stream{&buffer};
+        AZStd::unique_ptr<Visitor> writer = CreateStreamWriter(&stream);
+        return callback(writer.get());
+    }
+}

Code/Framework/AzCore/AzCore/DOM/DomBackend.h

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#pragma once
+
+#include <AzCore/DOM/DomVisitor.h>
+#include <AzCore/IO/GenericStreams.h>
+#include <AzCore/IO/Path/Path.h>
+#include <AzCore/std/containers/vector.h>
+#include <AzCore/std/smart_ptr/unique_ptr.h>
+
+namespace AZ::DOM
+{
+    //! Backends are registered centrally and used to transition DOM formats to and from a textual format.
+    class Backend
+    {
+    public:
+        virtual ~Backend() = default;
+
+        //! Attempt to read this format from the given file into the target Visitor.
+        Visitor::Result ReadFromPath(
+            AZ::IO::PathView pathName, Visitor* visitor, size_t maxFileSize = AZStd::numeric_limits<size_t>::max());
+        //! Attempt to read this format from the given stream into the target Visitor.
+        //! The base implementation reads the stream into memory and calls ReadFromString.
+        virtual Visitor::Result ReadFromStream(
+            AZ::IO::GenericStream* stream, Visitor* visitor, size_t maxSize = AZStd::numeric_limits<size_t>::max());
+        //! Attempt to read this format from a mutable string into the target Visitor. This enables some backends to
+        //! parse without making additional string allocations.
+        //! This string may be modified and read in place without being copied, so when calling this please ensure that:
+        //! - The string won't be deallocated until the visitor no longer needs the values and
+        //! - The string is safe to modify in place.
+        //! The base implementation simply calls ReadFromString.
+        virtual Visitor::Result ReadFromStringInPlace(AZStd::string& buffer, Visitor* visitor);
+        //! Attempt to read this format from an immutable buffer in memory into the target Visitor.
+        virtual Visitor::Result ReadFromString(AZStd::string_view buffer, Lifetime lifetime, Visitor* visitor) = 0;
+
+        //! Acquire a visitor interface for writing to the target output file.
+        virtual AZStd::unique_ptr<Visitor> CreateStreamWriter(AZ::IO::GenericStream* stream) = 0;
+        //! A callback that accepts a Visitor, making DOM calls to inform the serializer, and returns an
+        //! aggregate error code to indicate whether or not the operation succeeded.
+        using WriteCallback = AZStd::function<Visitor::Result(Visitor*)>;
+        //! Attempt to write a value to a stream using a write callback.
+        Visitor::Result WriteToStream(AZ::IO::GenericStream* stream, WriteCallback callback);
+        //! Attempt to write a value to a file using a write callback.
+        Visitor::Result WriteToPath(AZ::IO::PathView pathName, WriteCallback callback);
+        //! Attempt to write a value to a string using a write callback.
+        Visitor::Result WriteToString(AZStd::string& buffer, WriteCallback callback);
+    };
+} // namespace AZ::DOM

Code/Framework/AzCore/AzCore/DOM/DomBackendRegistry.cpp

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#include <AzCore/DOM/DomBackendRegistry.h>
+
+#include <AzCore/Interface/Interface.h>
+
+namespace AZ::DOM
+{
+    BackendRegistry* BackendRegistry::s_instance = nullptr;
+
+    BackendRegistryInterface* BackendRegistry::Get()
+    {
+        return AZ::Interface<BackendRegistryInterface>::Get();
+    }
+
+    void BackendRegistry::Create()
+    {
+        AZ_Assert(!s_instance, "Attempted to register BackendRegistry when it's already registered");
+        s_instance = aznew BackendRegistry;
+        AZ::Interface<BackendRegistryInterface>::Register(s_instance);
+    }
+
+    void BackendRegistry::Destroy()
+    {
+        AZ_Assert(s_instance, "Attempted to unregister a non-existent BackendRegistry");
+        AZ::Interface<BackendRegistryInterface>::Unregister(s_instance);
+        delete s_instance;
+        s_instance = nullptr;
+    }
+
+    AZStd::unique_ptr<Backend> BackendRegistry::GetBackendByName(AZStd::string_view name)
+    {
+        auto backendIterator = m_nameToBackend.find(name);
+        if (backendIterator != m_nameToBackend.end())
+        {
+            return backendIterator->second();
+        }
+        return nullptr;
+    }
+
+    AZStd::unique_ptr<Backend> BackendRegistry::GetBackendForExtension(AZStd::string_view extension)
+    {
+        auto extensionIterator = m_extensionToName.find(extension);
+        if (extensionIterator != m_extensionToName.end())
+        {
+            return GetBackendByName(extensionIterator->second);
+        }
+        return nullptr;
+    }
+
+    void BackendRegistry::RegisterBackendInternal(
+        BackendRegistryInterface::BackendFactory factory, AZStd::string name, AZStd::vector<AZStd::string> extensions)
+    {
+        AZ_Assert(m_nameToBackend.find(name) == m_nameToBackend.end(), "DOM Backend %s already registered", name.c_str());
+        m_nameToBackend.insert({name, factory});
+        for (AZStd::string& extension : extensions)
+        {
+            AZ_Assert(m_extensionToName.find(extension) == m_extensionToName.end(), "DOM Extensions already registered", extension.c_str());
+            m_extensionToName.insert({AZStd::move(extension), name});
+        }
+    }
+}

Code/Framework/AzCore/AzCore/DOM/DomBackendRegistry.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#pragma once
+
+#include <AzCore/DOM/DomBackendRegistryInterface.h>
+#include <AzCore/std/containers/unordered_map.h>
+
+namespace AZ::DOM
+{
+    //! DOM backend registry implementation.
+    //! \see BackendRegistryInterface
+    class BackendRegistry final : public BackendRegistryInterface
+    {
+    public:
+        AZ_RTTI(BackendRegistry, "{95533861-6201-4E45-BD03-097A20850C48}", BackendRegistryInterface);
+        AZ_CLASS_ALLOCATOR(BackendRegistry, AZ::SystemAllocator, 0);
+
+        AZStd::unique_ptr<Backend> GetBackendByName(AZStd::string_view name) override;
+        AZStd::unique_ptr<Backend> GetBackendForExtension(AZStd::string_view extension) override;
+
+        //! Convenience method, gets the current instance of the BackendRegistry via AZ::Interface.
+        static BackendRegistryInterface* Get();
+        //! Creates a singleton BackendRegistry and registers it via AZ::Interface.
+        static void Create();
+        //! Destroys the singleton BackendRegistry created by Create and unregisters it from AZ::Interface.
+        static void Destroy();
+
+    protected:
+        void RegisterBackendInternal(BackendFactory factory, AZStd::string name, AZStd::vector<AZStd::string> extensions) override;
+
+    private:
+        using BackendFactory = AZStd::function<AZStd::unique_ptr<Backend>()>;
+        AZStd::unordered_map<AZStd::string, BackendFactory> m_nameToBackend;
+        AZStd::unordered_map<AZStd::string, AZStd::string> m_extensionToName;
+
+        static BackendRegistry* s_instance;
+    };
+} // namespace AZ::DOM

Code/Framework/AzCore/AzCore/DOM/DomBackendRegistryInterface.h

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) Contributors to the Open 3D Engine Project.
+ * For complete copyright and license terms please see the LICENSE at the root of this distribution.
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ *
+ */
+
+#pragma once
+
+#include <AzCore/DOM/DomBackend.h>
+
+namespace AZ::DOM
+{
+    //! Central interface for registering and looking up backend types by file extension.
+    class BackendRegistryInterface
+    {
+    public:
+        AZ_RTTI(BackendRegistryInterface, "{B72A88AC-DF15-4F92-9489-ABCDEA3D94E6}")
+        using BackendFactory = AZStd::function<AZStd::unique_ptr<Backend>()>;
+
+        virtual ~BackendRegistryInterface() = default;
+
+        //! Registers a factory for a given backend.
+        //! \param name A unique name to identify this backend.
+        //! \param extensions A set of file extensions this backend supports.
+        //! Extensions should by the entire file suffix including any dots (.), for example:
+        //! ".json" or ".tar.gz"
+        template<class TBackend>
+        void RegisterBackend(AZStd::string name, AZStd::vector<AZStd::string> extensions);
+
+        //! Looks up a DOM backend based on its name.
+        virtual AZStd::unique_ptr<Backend> GetBackendByName(AZStd::string_view name) = 0;
+
+        //! Looks up a DOM backend based on a file extension.
+        virtual AZStd::unique_ptr<Backend> GetBackendForExtension(AZStd::string_view extension) = 0;
+
+    protected:
+        //! Registers a factory for a given backend, called by RegisterBackend.
+        //! \param factory The factory function to create new backend instances.
+        //! \param name The unique name to identify this backend.
+        //! \param extensions A set of file extensions this backend supports.
+        //! \see RegisterBackend
+        virtual void RegisterBackendInternal(BackendFactory factory, AZStd::string name, AZStd::vector<AZStd::string> extensions) = 0;
+    };
+
+    template<class TBackend>
+    void BackendRegistryInterface::RegisterBackend(AZStd::string name, AZStd::vector<AZStd::string> extensions)
+    {
+        RegisterBackendInternal([](){
+            return AZStd::make_unique<TBackend>();
+        }, AZStd::move(name), AZStd::move(extensions));
+    }
+} // namespace AZ::DOM

Code/Framework/AzCore/AzCore/DOM/DomVisitor.h

@@ -17,7 +17,7 @@ namespace AZ::DOM
 {
     //
     // Lifetime enum
-    // 
+    //
     //! Specifies the period in which a reference value will still be alive and safe to read.
     enum class Lifetime
     {
@@ -30,7 +30,7 @@ namespace AZ::DOM
 
     //
     // VisitorErrorCode enum
-    // 
+    //
     //! Error code specifying the reason a Visitor operation failed.
     enum class VisitorErrorCode
     {
@@ -75,7 +75,7 @@ namespace AZ::DOM
     };
 
     //! A type alias for opaque DOM types that aren't meant to be serializable.
-    //! /see VisitorInterface::OpaqueValue
+    //! \see VisitorInterface::OpaqueValue
     using OpaqueType = AZStd::any;
 
     //
@@ -116,7 +116,7 @@ namespace AZ::DOM
     //!     - \ref Double: 64 bit double precision float
     //!     - \ref Null: sentinel "empty" type with no value representation
     //! - \ref String: UTF8 encoded string
-    //! - \ref Object: an ordered container of key/value pairs where keys are  AZ::Names and values may be any DOM type
+    //! - \ref Object: an ordered container of key/value pairs where keys are \ref AZ::Name and values may be any DOM type
     //!   (including Object)
     //! - \ref Array: an ordered container of values, in which values are any DOM value type (including Array)
     //! - \ref Node: a container
@@ -144,17 +144,17 @@ namespace AZ::DOM
         //! Raw (\see VisitorFlags::SupportsRawValues) and opaque values (\see VisitorFlags::SupportsOpaqueValues)
         //! are disallowed by default, as their handling is intended to be implementation-specific.
         virtual VisitorFlags GetVisitorFlags() const;
-        //! /see VisitorFlags::SupportsRawValues
+        //! \see VisitorFlags::SupportsRawValues
         bool SupportsRawValues() const;
-        //! /see VisitorFlags::SupportsRawKeys
+        //! \see VisitorFlags::SupportsRawKeys
         bool SupportsRawKeys() const;
-        //! /see VisitorFlags::SupportsObjects
+        //! \see VisitorFlags::SupportsObjects
         bool SupportsObjects() const;
-        //! /see VisitorFlags::SupportsArrays
+        //! \see VisitorFlags::SupportsArrays
         bool SupportsArrays() const;
-        //! /see VisitorFlags::SupportsNodes
+        //! \see VisitorFlags::SupportsNodes
         bool SupportsNodes() const;
-        //! /see VisitorFlags::SupportsOpaqueValues
+        //! \see VisitorFlags::SupportsOpaqueValues
         bool SupportsOpaqueValues() const;
 
         //! Operates on an empty null value.
@@ -231,6 +231,15 @@ namespace AZ::DOM
         static Result VisitorFailure(VisitorErrorCode code, AZStd::string additionalInfo);
         //! Helper method, constructs a failure \ref Result with the specified error.
         static Result VisitorFailure(VisitorError error);
+
+        //! Helper method, constructs a failure \ref Result with the specified code and supplemental info specified by a format string
+        //! and its arguments.
+        template<class... TArgs>
+        static Result FormatVisitorFailure(VisitorErrorCode code, TArgs... formatArgs)
+        {
+            return VisitorFailure(code, AZStd::string::format(formatArgs...));
+        }
+
         //! Helper method, constructs a success \ref Result.
         static Result VisitorSuccess();
     };

Code/Framework/AzCore/AzCore/azcore_files.cmake

@@ -125,8 +125,18 @@ set(FILES
     Debug/TraceMessagesDrillerBus.h
     Debug/TraceReflection.cpp
     Debug/TraceReflection.h
+    DOM/DomAdapter.h
+    DOM/DomBackend.cpp
+    DOM/DomBackend.h
+    DOM/DomBackendRegistry.cpp
+    DOM/DomBackendRegistry.h
+    DOM/DomBackendRegistryInterface.h
     DOM/DomVisitor.cpp
     DOM/DomVisitor.h
+    DOM/Backends/JSON/JsonBackend.cpp
+    DOM/Backends/JSON/JsonBackend.h
+    DOM/Backends/JSON/JsonSerializationUtils.cpp
+    DOM/Backends/JSON/JsonSerializationUtils.h
     Driller/DefaultStringPool.h
     Driller/Driller.cpp
     Driller/Driller.h