SVSimServer/SVSim.EmulatedEntrypoint/Middlewares/ShadowverseTranslationMiddleware.cs

using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using MessagePack;
using MessagePack.Resolvers;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.Extensions.Primitives;
using Newtonsoft.Json.Linq;
using SVSim.Database.Models;
using SVSim.EmulatedEntrypoint.Constants;
using SVSim.EmulatedEntrypoint.Extensions;
using SVSim.EmulatedEntrypoint.Models.Dtos;
using SVSim.EmulatedEntrypoint.Models.Dtos.Internal;
using SVSim.EmulatedEntrypoint.Security;
using SVSim.EmulatedEntrypoint.Services;

namespace SVSim.EmulatedEntrypoint.Middlewares;

/// <summary>
/// Translates incoming requests and outgoing responses from the Shadowverse client into the messagepack format.
/// </summary>
public class ShadowverseTranslationMiddleware : IMiddleware
{
    private readonly IActionDescriptorCollectionProvider _actionDescriptorCollectionProvider;
    private readonly ShadowverseSessionService _sessionService;

    // Serialization policy MUST match what AddJsonOptions configured on the controllers, or the
    // model binder won't find the snake_case keys we write into the synthetic request body and
    // every request 400s with empty ModelState. WhenWritingNull is irrelevant for request
    // serialization but kept here for symmetry.
    private static readonly JsonSerializerOptions ControllerJsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower,
        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
    };

    public ShadowverseTranslationMiddleware(IActionDescriptorCollectionProvider actionDescriptorCollectionProvider, ShadowverseSessionService sessionService)
    {
        _actionDescriptorCollectionProvider = actionDescriptorCollectionProvider;
        _sessionService = sessionService;
    }

    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        bool isUnity = context.Request.Headers.UserAgent.Any(agent => agent?.Contains("UnityPlayer") ?? false);
        string path = context.Request.Path;
        ActionDescriptor? endpointDescriptor =
            _actionDescriptorCollectionProvider.ActionDescriptors.Items.FirstOrDefault(ad =>
                $"/{ad.AttributeRouteInfo.Template}".Equals(path, StringComparison.InvariantCultureIgnoreCase));
        if (!isUnity || endpointDescriptor == null)
        {
            await next.Invoke(context);
            return;
        }
        
        // Replace response body stream to re-access it.
        using MemoryStream tempResponseBody = new MemoryStream();
        Stream originalResponsebody = context.Response.Body;
        context.Response.Body = tempResponseBody;
        
        // Pull out the request bytes into a stream
        using MemoryStream requestBytesStream = new MemoryStream();
        await context.Request.Body.CopyToAsync(requestBytesStream);
        byte[] requestBytes = requestBytesStream.ToArray();
        
        // Get encryption values for this request
        string sid = context.Request.Headers[NetworkConstants.SessionIdHeaderName];
        string udid = _sessionService.GetUdidFromSessionId(sid).GetValueOrDefault().ToString();
        
        // Decrypt incoming data.
        requestBytes = Encryption.Decrypt(requestBytes, udid);
        Type requestType = endpointDescriptor.Parameters.FirstOrDefault().ParameterType;
        object? data = MessagePackSerializer.Deserialize(requestType, requestBytes);
        // Re-serialize via System.Text.Json with the SAME options the controllers use, so the
        // model binder sees snake_case keys it can match. Using JsonConvert here writes the
        // CLR property names (PascalCase) and every property silently binds to default → 400.
        string json = JsonSerializer.Serialize(data, requestType, ControllerJsonOptions);
        StringContent newStream = new StringContent(json, Encoding.UTF8, "application/json");
        context.Request.Body = newStream.ReadAsStream();
        context.Request.Headers.ContentType = new StringValues("application/json");
        
        await next.Invoke(context);

        Viewer? viewer = context.GetViewer();

        // Read the controller's JSON response body. System.Text.Json was configured with
        // SnakeCaseLower + WhenWritingNull, so the JSON keys are already in the wire shape and
        // null/optional properties have been omitted. Parse to a JToken tree to preserve that
        // "absent vs null" information — going back through a typed DTO via JsonConvert would
        // re-introduce nulls for missing properties and they'd reach the client as msgpack Nil.
        using MemoryStream responseBytesStream = new MemoryStream();
        context.Response.Body.Seek(0, SeekOrigin.Begin);
        await context.Response.Body.CopyToAsync(responseBytesStream);
        string responseJson = Encoding.UTF8.GetString(responseBytesStream.ToArray());
        object? responseData = string.IsNullOrEmpty(responseJson)
            ? null
            : ConvertJsonTreeToPlainObject(JToken.Parse(responseJson));

        // Wrap the response in a datawrapper
        DataWrapper wrappedResponseData = new DataWrapper
        {
            Data = responseData,
            DataHeaders = new DataHeaders
            {
                Servertime = DateTimeOffset.UtcNow.ToUnixTimeSeconds(),
                // SID intentionally empty. See docs/api-spec/common/envelope.md §"SID
                // rotation" — the client's SessionId is a hash-on-read property, so echoing
                // the request's SID poisons its backing field and the next request hashes
                // the hash, missing our SID→UDID dict and crashing decryption. To rotate
                // sessions in the future, use the "stable-prefix + counter" pattern from
                // that doc (Option B), and pre-hash the rotated value to index the map by
                // what the client will actually send back on the next request.
                Sid = "",
                // TODO error handling
                ResultCode = 1,
                // Anonymous endpoints (e.g. /check/special_title with [AllowAnonymous]) reach this
                // middleware without an authenticated viewer — the auth handler either declined or
                // failed to find a Steam-linked viewer. The wire still needs short_udid / viewer_id
                // populated (prod sends real numbers for the title check too, but 0 / 0 satisfies
                // the client's BaseTask.Parse which only reads result_code + servertime here).
                ShortUdid = viewer?.ShortUdid ?? 0,
                ViewerId = viewer?.Id ?? 0
            }
        };

        // Convert the response into a messagepack, encrypt it. ContractlessStandardResolver
        // walks the DataWrapper's typed properties (DataHeaders) AND the boxed object/list/
        // primitive tree under Data — emitting only the keys present in the dictionary.
        var msgPackOptions = MessagePackSerializerOptions.Standard
            .WithResolver(ContractlessStandardResolver.Instance);
        byte[] packedData = MessagePackSerializer.Serialize(wrappedResponseData, msgPackOptions);
        packedData = Encryption.Encrypt(packedData, udid);
        await originalResponsebody.WriteAsync(Encoding.UTF8.GetBytes(Convert.ToBase64String(packedData)));
        context.Response.Body = originalResponsebody;
    }

    /// <summary>
    /// Walks a parsed JSON tree into the plain CLR shape MessagePack-CSharp's contractless
    /// resolver understands: objects → <c>Dictionary&lt;string, object?&gt;</c>, arrays →
    /// <c>List&lt;object?&gt;</c>, scalars unboxed to their nearest primitive. Crucially, JSON
    /// objects that lacked a key DON'T get one in the dictionary — preserving "absent" as a
    /// distinct state from "null" all the way to the msgpack writer.
    /// </summary>
    internal static object? ConvertJsonTreeToPlainObject(JToken? token)
    {
        if (token is null || token.Type == JTokenType.Null) return null;
        return token.Type switch
        {
            JTokenType.Object => token.Children<JProperty>()
                .ToDictionary(p => p.Name, p => ConvertJsonTreeToPlainObject(p.Value)),
            JTokenType.Array => token.Children().Select(ConvertJsonTreeToPlainObject).ToList(),
            JTokenType.Integer => token.Value<long>(),
            JTokenType.Float => token.Value<double>(),
            JTokenType.String => token.Value<string>(),
            JTokenType.Boolean => token.Value<bool>(),
            JTokenType.Date => token.Value<DateTime>(),
            JTokenType.Bytes => token.Value<byte[]>(),
            _ => token.ToString()
        };
    }
}