# SignalR Communication

The transport layer for AyCode real-time communication. Source: `AyCode.Services/SignalRs/` (client), `AyCode.Services.Server/SignalRs/` (server).

> For the change-tracked collection built on top of this transport, see [`SIGNALR_DATASOURCE.md`](SIGNALR_DATASOURCE.md).

## Design Overview

All communication flows through a **single hub method** with **tag-based dispatch**:

```
Client ──OnReceiveMessage(tag, bytes, requestId)──► Server
Client ◄──OnReceiveMessage(tag, bytes, requestId)── Server
```

`OnReceiveMessage` is the only transport channel — all calls go through it. The `tag` (int) determines **which server method to invoke**. The `DynamicMethodRegistry` maps the tag to a concrete `[SignalR(tag)]`-annotated method at runtime. Projects call any endpoint by specifying the tag; the server dispatches accordingly.

```
Client side:                          Server side:
─────────────────────                 ─────────────────────
AcSignalRClientBase                   AcWebSignalRHubBase<TTags, TLogger>
  ├─ HubConnection (WebSocket)          ├─ Hub<IAcSignalRHubItemServer>
  ├─ AcBinaryHubProtocol                ├─ DynamicMethodRegistry
  ├─ Pending request tracking           ├─ Parameter deserialization
  └─ Response callbacks                 └─ Broadcast to other clients
```

## Tag System

### Tag Definition

AyCode.Core defines only the base class and built-in infrastructure tags:

```csharp
public class AcSignalRTags
{
    public const int None = 0;
    public const int PingTag = 90001;
    public const int EchoTag = 90002;
}
```

**Consuming projects** define their own tags by inheriting `AcSignalRTags`:

```csharp
public abstract class MyProjectTags : AcSignalRTags
{
    public const int GetOrders = 100;
    public const int GetOrderById = 101;
    public const int SaveOrder = 102;
    // ... project-specific tags
}
```

Tags are plain `int` constants. The project decides the numbering. Tags must be unique across all registered services within a hub.

### Tag Attributes

Three attribute levels:

```csharp
// Base: maps an integer tag to a method
[Tag(42)]

// Server method: tag + optional broadcast behavior
[SignalR(messageTag: 100, sendToOtherClientTag: 100, sendToOtherClientType: SendToClientType.Others)]
// messageTag:              incoming tag this method handles
// sendToOtherClientTag:    tag used when broadcasting result to other clients (can differ from messageTag)
// sendToOtherClientType:   who receives the broadcast

// Client receive: marks method for server→client dispatch
[SignalRSendToClient(100)]
```

**SendToClientType:** `None` (no broadcast), `Others` (all except caller), `Caller` (response only), `All` (everyone).

### How Projects Use Tags

Projects call the SignalR transport directly — not only through DataSource:

```csharp
// Direct call: project code calls any endpoint by tag
var orders = await signalRClient.PostAsync<List<Order>>(MyTags.GetOrders, companyId);
var order = await signalRClient.GetByIdAsync<Order>(MyTags.GetOrderById, orderId);
await signalRClient.PostDataAsync(MyTags.SaveOrder, order);

// Async callback (non-blocking)
await signalRClient.PostDataAsync(MyTags.SaveOrder, order, async response => { ... });

// Fire-and-forget
await signalRClient.PostDataAsync(MyTags.SaveOrder, order, response => { ... });
```

The `AcSignalRClientBase` CRUD helpers (`PostAsync`, `GetByIdAsync`, `GetAllAsync`, `PostDataAsync`) are all generic transport methods that work with any tag — they are not tied to DataSource.

## Dynamic Method Dispatch

See also: [`AyCode.Models.Server/DynamicMethods/README.md`](../AyCode.Models.Server/DynamicMethods/README.md)

### Server-Side Lookup

```
1. OnReceiveMessage(tag=100, bytes, requestId)

2. DynamicMethodRegistry.GetMethodByMessageTag(100)
   ├─ Check static ConcurrentDictionary<int, (Type, AcMethodInfoModel)?> cache
   ├─ Hit? → find instance of cached Type from registered instances
   ├─ Miss? → scan all registered instances' methods for [SignalR(100)]
   │          cache the result (including negative = null)
   └─ Return (instance, methodInfoModel) or null

3. AcMethodInfoModel contains:
   ├─ MethodInfo (the method to invoke)
   ├─ SignalRAttribute (tag, sendToOtherClientTag, sendToOtherClientType)
   └─ ParamInfos[] (ParameterInfo for deserialization)
```

The `DynamicMethodRegistry` uses a static `ConcurrentDictionary` for the global tag→method cache. Note: `AcDynamicMethodCallModel` uses a `FrozenDictionary` per-type cache internally, but the registry's own lookup path does direct method scanning with `ConcurrentDictionary` caching.

### Registration

The hub registers service instances during initialization:

```csharp
DynamicMethodRegistry.Register(myService);    // scans [SignalR(tag)] methods lazily
DynamicMethodRegistry.Register(anotherService);
```

Reflection runs lazily per tag on first request, then results are cached statically.

## Wire Protocol

### AcBinaryHubProtocol

Custom `IHubProtocol` (name: `"acbinary"`), replaces default JSON. Frame format:

```
[4 bytes: payload length, little-endian] [1 byte: message type] [payload...]
```

Message types: Invocation(1), StreamItem(2), Completion(3), Ping(6), Close(7), Ack(8), Sequence(9).

Arguments serialized individually with VarUInt length prefix. Direct write to `IBufferWriter` via `BufferWriterBinaryOutput`.

### Response Message

`SignalResponseDataMessage` carries:

| Field | Type | Purpose |
|-------|------|---------|
| `MessageTag` | int | Tag identifying the operation |
| `Status` | SignalResponseStatus | Success/Error |
| `ResponseData` | byte[] | Binary-serialized payload (or GZip+JSON fallback) |
| `DataSerializerType` | AcSerializerType | Binary or Json |

**Binary mode** (default): `AcBinarySerializer.ToBinary(data)` → raw bytes.
**JSON fallback**: `ToJson(data)` → `GzipHelper.Compress(json)` → bytes.

## Request/Response Flow

### Client → Server

```
1. PostAsync<T>(tag, postData) or PostDataAsync(tag, data, callback)
2. CreatePostMessage(postData):
   ├─ Primitives/strings/enums/value types → IdMessage (JSON array of serialized values)
   └─ Complex objects → SignalPostJsonDataMessage<T>     ⚠️ tech debt: JSON-in-Binary
3. SerializeToBinary(message)                            wraps in Binary envelope
4. HubConnection.SendAsync("OnReceiveMessage", tag, bytes, requestId)
5. AcBinaryHubProtocol frames it on the wire
```

### Server Processing

```
6. OnReceiveMessage(tag, bytes, requestId)
7. DynamicMethodRegistry.GetMethodByMessageTag(tag)      ← ConcurrentDictionary lookup
8. DeserializeParameters(bytes):
   ├─ DeserializeFromBinary<SignalPostJsonMessage>()     ← unwrap Binary envelope
   ├─ IdMessage format? → parse each Ids[i] as JSON per parameter type
   └─ Complex object? → json.JsonTo(paramType)           ⚠️ tech debt: JSON parse
9. MethodInfo.InvokeMethod(instance, params)              ← unwraps Task/ValueTask
10. CreateResponseMessage(tag, Success, result)           ← pure Binary serialization
11. ResponseToCaller(tag, message, requestId)
12. If SendToOtherClientType != None:
    └─ SendMessageToOthers(sendToOtherClientTag, result) ← uses sendToOtherClientTag, not messageTag
```

### Server → Client

```
13. Client.OnReceiveMessage(tag, bytes, requestId)
14. Has matching requestId in pending ConcurrentDictionary?
    ├─ YES (response to own request):
    │   15. DeserializeFromBinary<SignalResponseDataMessage>(bytes)
    │   16. Route based on pending request type:
    │       ├─ null (sync wait) → set ResponseByRequestId, WaitToAsync completes
    │       ├─ Action<SignalResponseDataMessage> → invoke directly
    │       └─ Func<SignalResponseDataMessage, Task> → invoke and await
    │   17. GetResponseData<T>():
    │       ├─ Binary: ResponseData.BinaryTo<T>()
    │       └─ JSON: GzipDecompress → AcJsonDeserializer.Deserialize<T>()
    │
    └─ NO (broadcast from another client's action):
        18. abstract MessageReceived(tag, bytes).Forget()
            └─ Consuming project overrides to handle server push
```

**Broadcast receive:** When the server broadcasts to `Others`/`All`, receiving clients have no matching `requestId`. The message falls through to `MessageReceived(int messageTag, byte[] messageBytes)` — an abstract method the consuming project overrides to handle unsolicited server pushes (e.g., refresh UI, update local state).

**Request model pooling:** `SignalRRequestModel` instances are managed via `SignalRRequestModelPool` (ObjectPool<T> + IResettable) to avoid allocations per request.

### Response Patterns

| Pattern | Method | Blocking |
|---------|--------|----------|
| Sync wait | `PostAsync<T>(tag, data)` | Yes, polls up to `TransportSendTimeout` (60s) |
| Async callback | `PostDataAsync(tag, data, async msg => {...})` | No, `Func<SignalResponseDataMessage, Task>` |
| Fire-and-forget | `PostDataAsync(tag, data, msg => {...})` | No, `Action<SignalResponseDataMessage>` |

## Session Management

`AcSessionService<TSessionItem, TSessionItemId>` tracks connected clients:

```csharp
ConcurrentDictionary<TSessionItemId, TSessionItem> Sessions
```

`IAcSessionItem<TSessionItemId>` requires `SessionId` property. Used for targeting messages to specific users/connections.

## Broadcast Service

`AcSignalRSendToClientService<THub, TTags, TLogger>` provides server-push methods:

| Method | Target |
|--------|--------|
| `SendMessageToAllClients` | All connected |
| `SendMessageToConnection(connectionId)` | Single connection |
| `SendMessageToUser(userId)` | User (all connections) |
| `SendMessageToUsers(userIds)` | Multiple users |

All messages wrapped in `SignalResponseDataMessage` → binary serialized → `OnReceiveMessage`.

## Connection Lifecycle

**Client configuration:**
- Transport: WebSockets only (`SkipNegotiation = true`)
- Buffer: 30MB transport + 30MB application
- Reconnection: `WithAutomaticReconnect()` + `WithStatefulReconnect()`
- Keepalive: 60s interval, 180s server timeout

**Hub events:**
- `OnConnectedAsync()` — log connection
- `OnDisconnectedAsync(exception)` — log disconnection, cleanup session

## Diagnostics

Enable with `AcSignalRClientBase.EnableBinaryDiagnostics = true` or `AcWebSignalRHubBase.EnableBinaryDiagnostics = true`.

Logs: hex dump (500 byte sample), header parsing (version, marker), property count + names via VarUInt reading.

`SignalResponseDataMessage.DiagnosticLogger` — per-response logging: target type info, property list, inheritance chain, hex dump.

## Known Technical Debt

**JSON-in-Binary request parameters:** Client→server requests currently wrap parameters in JSON inside the binary envelope (`SignalPostJsonDataMessage`). This adds an unnecessary serialization round-trip. Responses are already pure binary. Do NOT attempt to fix as a side effect — requires coordinated changes across all consuming projects.

## Key Source Files

| Component | Path |
|-----------|------|
| Hub base | `AyCode.Services.Server/SignalRs/AcWebSignalRHubBase.cs` |
| Client base | `AyCode.Services/SignalRs/AcSignalRClientBase.cs` |
| Binary protocol | `AyCode.Services/SignalRs/AcBinaryHubProtocol.cs` |
| Message types | `AyCode.Services/SignalRs/IAcSignalRHubClient.cs` |
| Serialization | `AyCode.Services/SignalRs/SignalRSerializationHelper.cs` |
| Tag attributes | `AyCode.Services/SignalRs/SignalMessageTagAttribute.cs` |
| Base tags | `AyCode.Services/SignalRs/AcSignalRTags.cs` |
| Session service | `AyCode.Services.Server/SignalRs/AcSessionService.cs` |
| Broadcast service | `AyCode.Services.Server/SignalRs/AcSignalRSendToClientService.cs` |
| Dynamic dispatch | `AyCode.Models.Server/DynamicMethods/AcDynamicMethodRegistry.cs` |