# JsonSocket

**Kind:** Class

**Source:** [`packages/microservices/helpers/json-socket.ts`](https://github.com/nestjs/nest/blob/master/packages/microservices/helpers/json-socket.ts#L13)

**Part of:** [Microservices](subsystem-packages-microservices)

`JsonSocket` wraps a TCP socket with length-prefixed JSON message framing for the microservices transport layer. It serializes outgoing payloads in `handleSend()` and incrementally buffers, reconstructs, and parses incoming TCP chunks in `handleData()` before delivering complete messages to registered listeners.

**Extends:** `TcpSocket`

## Methods

| Method | Signature | Returns |
|---|---|---|
| `handleSend` | `handleSend(message: any, callback: (err?: any) => void)` | `void` |
| `handleData` | `handleData(dataRaw: Buffer | string)` | `void` |

## Diagram

```mermaid
graph LR
  A[Application message] --> B[JsonSocket.handleSend]
  B --> C[Serialize JSON and add length prefix]
  C --> D[TCP socket]

  D --> E[Incoming TCP chunks]
  E --> F[JsonSocket.handleData]
  F --> G[Buffer and resolve frame length]
  G --> H[Parse complete JSON message]
  H --> I[Message listener]
```

## AI Coding Instructions

- Preserve the length-prefixed framing format when changing `handleSend()` or `handleData()`; TCP data may arrive split across multiple chunks or contain multiple messages in one chunk.
- Use `handleSend()` for outgoing serialization rather than writing raw JSON directly to the underlying socket.
- Keep buffering logic resilient to partial payloads and reset parser state only after a complete frame has been processed.
- Treat malformed frame lengths and invalid JSON as transport-level errors; avoid silently emitting incomplete or corrupted messages.
- Prefer the inherited `send()`, `onMessage()`, `connect()`, and `close()` APIs at integration points instead of calling the internal handlers directly.