chore: initial project import

backend/fleet/src/Fleet.Rpc/RpcRouter.cs

@@ -0,0 +1,115 @@
+using System.Text.Json;
+using System.Text.Json.Serialization.Metadata;
+using Fleet.Core;
+
+namespace Fleet.Rpc;
+
+/// <summary>方法路由，与传输方式无关。<typeparamref name="TContext"/> 由传输层提供（例如调用方节点）。</summary>
+public sealed class RpcRouter<TContext>
+{
+    private delegate ValueTask<Result<JsonElement?>> Route(TContext context, JsonElement? parameters, CancellationToken ct);
+
+    private static readonly JsonElement s_emptyObject = JsonDocument.Parse("{}").RootElement.Clone();
+
+    private readonly Dictionary<string, Route> _routes = new(StringComparer.Ordinal);
+    private readonly Action<string, Exception>? _onUnhandled;
+
+    public RpcRouter(Action<string, Exception>? onUnhandled = null)
+    {
+        _onUnhandled = onUnhandled;
+    }
+
+    public bool Has(string method) => _routes.ContainsKey(method);
+
+    public IReadOnlyCollection<string> Methods => _routes.Keys;
+
+    public RpcRouter<TContext> On<TParams, TResult>(
+        string method,
+        JsonTypeInfo<TParams> paramsInfo,
+        JsonTypeInfo<TResult> resultInfo,
+        Func<TContext, TParams, CancellationToken, ValueTask<Result<TResult>>> handler)
+    {
+        _routes[method] = async (context, raw, ct) =>
+        {
+            if (!TryDeserialize(raw, paramsInfo, out TParams? p))
+            {
+                return Result<JsonElement?>.Fail(FleetErrors.InvalidParams, "params could not be parsed");
+            }
+
+            Result<TResult> r = await handler(context, p, ct);
+            return r.TryGet(out TResult? value, out FleetError? error)
+                ? Result<JsonElement?>.Ok(JsonSerializer.SerializeToElement(value, resultInfo))
+                : Result<JsonElement?>.Fail(error);
+        };
+        return this;
+    }
+
+    public RpcRouter<TContext> OnNotify<TParams>(
+        string method,
+        JsonTypeInfo<TParams> paramsInfo,
+        Func<TContext, TParams, CancellationToken, ValueTask> handler)
+    {
+        _routes[method] = async (context, raw, ct) =>
+        {
+            if (!TryDeserialize(raw, paramsInfo, out TParams? p))
+            {
+                return Result<JsonElement?>.Fail(FleetErrors.InvalidParams, "params could not be parsed");
+            }
+
+            await handler(context, p, ct);
+            return Result<JsonElement?>.Ok(null);
+        };
+        return this;
+    }
+
+    /// <summary>
+    /// 处理一条请求或通知。请求返回响应；通知返回 null（失败时只丢弃）。
+    /// 处理函数里的异常属于程序缺陷：在这个边界捕获，回复 internal 错误，并交给 <c>onUnhandled</c> 记录。
+    /// </summary>
+    public async ValueTask<RpcMessage?> DispatchAsync(TContext context, RpcMessage message, CancellationToken ct)
+    {
+        string method = message.Method ?? "";
+        if (!_routes.TryGetValue(method, out Route? route))
+        {
+            return message.Id is null ? null : RpcMessage.Failure(message.Id, new FleetError(FleetErrors.Unsupported, $"unknown method {method}"));
+        }
+
+        Result<JsonElement?> result;
+        try
+        {
+            result = await route(context, message.Params, ct);
+        }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch (Exception ex)
+        {
+            _onUnhandled?.Invoke(method, ex);
+            result = Result<JsonElement?>.Fail(FleetErrors.Internal, "internal error");
+        }
+
+        if (message.Id is null)
+        {
+            return null;
+        }
+
+        return result.TryGet(out JsonElement? value, out FleetError? error)
+            ? new RpcMessage { Id = message.Id, Result = value ?? s_emptyObject }
+            : RpcMessage.Failure(message.Id, error);
+    }
+
+    private static bool TryDeserialize<T>(JsonElement? raw, JsonTypeInfo<T> info, [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] out T? value)
+    {
+        value = default;
+        try
+        {
+            value = raw is null ? JsonSerializer.Deserialize("{}", info) : raw.Value.Deserialize(info);
+            return value is not null;
+        }
+        catch (JsonException)
+        {
+            return false;
+        }
+    }
+}