# IClientPublishOptions

**Kind:** Interface

**Source:** [`packages/microservices/external/mqtt-options.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/microservices/external/mqtt-options.interface.ts#L151)

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

`IClientPublishOptions` defines MQTT-specific options applied when publishing a message from a microservice client. It controls the delivery quality of service, whether the broker retains the message, and whether the message is marked as a duplicate delivery.

## Properties

| Property | Type |
|---|---|
| `qos` | `QoS` |
| `retain` | `boolean` |
| `dup` | `boolean` |

## Diagram

```mermaid
graph LR
  Client[MQTT Client] -->|publish topic + payload| Options[IClientPublishOptions]
  Options --> QoS[qos: QoS]
  Options --> Retain[retain: boolean]
  Options --> Duplicate[dup: boolean]
  Options --> Broker[MQTT Broker]
```

## Usage

```ts
import { IClientPublishOptions } from '@nestjs/microservices';

const publishOptions: IClientPublishOptions = {
  qos: 1,
  retain: true,
  dup: false,
};

client.publish(
  'devices/thermostat/status',
  JSON.stringify({ temperature: 21.5 }),
  publishOptions,
);
```

## AI Coding Instructions

- Set `qos` according to delivery requirements: `0` for best-effort, `1` for at-least-once delivery, and `2` for exactly-once delivery.
- Use `retain: true` only for topics where new subscribers should receive the latest published state.
- Keep `dup` as `false` for normal publishes; set it only when explicitly retransmitting a previously sent MQTT message.
- Pass these options to the underlying MQTT client's publish operation when implementing custom transport or client behavior.