# USB Service Development

## When to Use

In Host mode, you can obtain the list of connected USB devices, enable or disable the devices, manage device access permissions, and perform data transfer or control transfer.

## APIs

The USB service provides the following functions: query of USB device list, bulk data transfer, control transfer, and access permission management.

The following table lists the USB APIs currently available. For details, see the [API Reference](../reference/apis/js-apis-usb.md).

**Table  1**  Open USB APIs

| API                                                          | Description                                                  |
| ------------------------------------------------------------ | ------------------------------------------------------------ |
| hasRight(deviceName: string): boolean                        | Checks whether the user, for example, the application or system, has the device access permissions. The value **true** is returned if the user has the device access permissions; the value **false** is returned otherwise. |
| requestRight(deviceName: string): Promise\<boolean>          | Requests the temporary permission for a given application to access the USB device. |
| removeRight(deviceName: string): boolean                     | Removes the permission for a given application to access the USB device. |
| connectDevice(device: USBDevice): Readonly\<USBDevicePipe>   | Connects to the USB device based on the device information returned by `getDevices()`. |
| getDevices(): Array<Readonly\<USBDevice>>                    | Obtains the USB device list.                                 |
| setConfiguration(pipe: USBDevicePipe, config: USBConfig): number | Sets the USB device configuration.                           |
| setInterface(pipe: USBDevicePipe, iface: USBInterface): number | Sets a USB interface.                                        |
| claimInterface(pipe: USBDevicePipe, iface: USBInterface, force?: boolean): number | Claims a USB interface.                                       |
| bulkTransfer(pipe: USBDevicePipe, endpoint: USBEndpoint, buffer: Uint8Array, timeout?: number): Promise\<number> | Performs bulk transfer.                                      |
| closePipe(pipe: USBDevicePipe): number                       | Closes a USB device pipe.                                    |
| releaseInterface(pipe: USBDevicePipe, iface: USBInterface): number | Releases a USB interface.                                    |
| getFileDescriptor(pipe: USBDevicePipe): number               | Obtains the file descriptor.                                 |
| getRawDescriptor(pipe: USBDevicePipe): Uint8Array            | Obtains the raw USB descriptor.                              |
| controlTransfer(pipe: USBDevicePipe, contrlparam: USBControlParams, timeout?: number): Promise\<number> | Performs control transfer.                                   |

## How to Develop

You can set a USB device as the USB host to connect to other USB devices for data transfer. The development procedure is as follows:

1.  Obtain the USB device list.

    ```js
    // Import the USB API package.
    import usb from '@ohos.usb';
    // Obtain the USB device list.
    let deviceList = usb.getDevices();
    /*
    Example deviceList structure
    [
      {
        name: "1-1",
        serial: "",
        manufacturerName: "",
        productName: "",
        version: "",
        vendorId: 7531,
        productId: 2,
        clazz: 9,
        subclass: 0,
        protocol: 1,
        devAddress: 1,
        busNum: 1,
        configs: [
          {
            id: 1,
            attributes: 224,
            isRemoteWakeup: true,
            isSelfPowered: true,
            maxPower: 0,
            name: "1-1",
            interfaces: [
              {
                id: 0,
                protocol: 0,
                clazz: 9,
                subclass: 0,
                alternateSetting: 0,
                name: "1-1",
                endpoints: [
                  {
                    address: 129,
                    attributes: 3,
                    interval: 12,
                    maxPacketSize: 4,
                    direction: 128,
                    number: 1,
                    type: 3,
                    interfaceId: 0,
                 }
               ]
             }
           ]
         }
       ]
     }
   ]
    */
    ```

2.  Obtain the device operation permissions.

    ```js
    let deviceName = deviceList[0].name;
    // Request the permissions to operate a specified device.
    usb.requestRight(deviceName).then(hasRight => {
      console.info("usb device request right result: " + hasRight);
    }).catch(error => {
      console.info("usb device request right failed : " + error);
    });
    ```

3.  Open the device.

    ```js
    // Open the device, and obtain the USB device pipe for data transfer.
    let pipe = usb.connectDevice(deviceList[0]);
    /*
    Claim the corresponding interface from deviceList.
    interface1 must be one present in the device configuration.
    */
    usb.claimInterface(pipe, interface1, true);
    ```

4.  Perform data transfer.

    ```js
    /*
    Read data. Select the corresponding RX endpoint from deviceList for data transfer.
    (endpoint.direction == 0x80); dataUint8Array indicates the data to read. The data type is Uint8Array.
    */
    
    usb.bulkTransfer(pipe, inEndpoint, dataUint8Array, 15000).then(dataLength => {
    if (dataLength >= 0) {
      console.info("usb readData result Length : " + dataLength);
      let resultStr = this.ab2str(dataUint8Array); // Convert uint8 data into a string.
      console.info("usb readData buffer : " + resultStr);
    } else {
      console.info("usb readData failed : " + dataLength);
    }
    }).catch(error => {
    console.info("usb readData error : " + JSON.stringify(error));
    });
    // Send data. Select the corresponding TX endpoint from deviceList for data transfer. (endpoint.direction == 0)
    usb.bulkTransfer(pipe, endpoint, dataUint8Array, 15000).then(dataLength => {
      if (dataLength >= 0) {
        console.info("usb writeData result write length : " + dataLength);
      } else {
        console.info("writeData failed");
      }
    }).catch(error => {
      console.info("usb writeData error : " + JSON.stringify(error));
    });
    ```

5.  Release the USB interface, and close the USB device.

    ```js
    usb.releaseInterface(pipe, interface);
    usb.closePipe(pipe);
    ```