> ## Documentation Index
> Fetch the complete documentation index at: https://dragonwingdocs-staging.qualcomm.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Session Interface

**Header:** `session/1.0/inc/ISession.h`

## Structures

### `com::quic::sensinghub::session::V1_0::ISession`

ISession is transport-neutral, OS-agnostic, extensible interface for communicating to Sensing Hub.

#### Functions

##### `open`

Open the session and establish a connection to Sensing Hub.

Initiates the client session created using getSession(). Sets up and establishes communication channel between the client and the Sensing Hub framework.

This should be called exactly once per ISession instance before any other operations such as setCallBacks() or sendRequest().

```cpp theme={null}
int open()=0
```

**Returns**

0 Success (session is now open and ready for use).
-1 Failure (session remains closed).

##### `close`

Closes the session for this instance and release associated resources.

Terminates the communication channel between the client and the Sensing Hub framework and frees any resources held by this session.

After close() is called:
No further requests should be sent using this ISession instance.
Registered callbacks will no longer receive events.
The client is expected to call close() once it is done with the session to avoid leaks and dangling resources.

```cpp theme={null}
void close()=0
```

##### `setCallBacks`

Set the callbacks for specified sensor SUID.

Client needs to call only once per given suid.

Associates response, error, and event callbacks with the given SUID for this session. These callbacks are invoked for messages received from Sensing Hub that correspond to the specified SUID.

```cpp theme={null}
int setCallBacks(suid suid, respCallBack respCB, errorCallBack errorCB, eventCallBack eventCB)=0
```

**Parameters**

<ParamField path="suid" type="suid">
  Unique SUID of the sensor for which callbacks are set.
</ParamField>

<ParamField path="respCB" type="respCallBack">
  respCallBack pointer (may be nullptr).
</ParamField>

<ParamField path="errorCB" type="errorCallBack">
  errorCallBack pointer (may be nullptr)
</ParamField>

<ParamField path="eventCB" type="eventCallBack">
  eventCallBack pointer (may be nullptr).
</ParamField>

**Returns**

0 Success.
-1 Failure, if all callback functions are nullptr for an unregistered SUID.

##### `sendRequest`

Send an asynchronous request for a given sensor.

Sends a protocol-buffer-encoded request message to the Sensing Hub for the specified SUID.

```cpp theme={null}
int sendRequest(suid suid, std::string message)=0
```

**Parameters**

<ParamField path="suid" type="suid">
  Unique SUID of the target sensor.
</ParamField>

<ParamField path="message" type="std::string">
  Proto encoded request message, formulated with client API for the given sensor.
</ParamField>

**Returns**

0 Success
-1 Failure
Session is not open or already closed.
Encoded message size exceeds the allowed limit.
Underlying transport/channel error while sending.

##### `~ISession`

Destructor for ISession.

Clients are expected to delete the ISession instance once the use case is complete to avoid memory leaks.

```cpp theme={null}
 ~ISession()
```

#### Enumerations

##### `error`

Error codes, if any, from ISession.

###### Values

| Name           | Value | Description |
| -------------- | ----- | ----------- |
| `RESET`        |       |             |
| `SERVICE_DOWN` |       |             |

#### Type Aliases

##### `respCallBack`

This callback is invoked when a response is received for the registered sensor SUID.

```cpp theme={null}
using respCallBack = std::function< void(const uint32_t respValue, uint64_t clientConnectID)>
```

##### `errorCallBack`

This callback is invoked when an error occurs in Sensing Hub.

```cpp theme={null}
using errorCallBack = std::function< void(error errorValue)>
```

##### `eventCallBack`

This callback is invoked when an event is received for the registered sensor SUID.

```cpp theme={null}
using eventCallBack = std::function< void(const uint8_t *sensorData, size_t sensorDataSize, uint64_t sensorDataTimeStamp)>
```