# USB Service Development ## When to Use In Host mode, you can obtain the list of connected devices, enable or disable the devices, manage device access permissions, and perform data transfer or control transfer. ## APIs The OpenHarmony 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_. **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.
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
function 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 a host to connect to a device for data transfer. The development procedure is as follows: 1. Obtain the USB device list. ``` // Import the USB API package. import usb from '@ohos.usb'; // Obtain the USB device list. var 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. ``` var 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. ``` // Open the device, and obtain the USB device pipe for data transfer. var pipe = usb.connectDevice(deviceList[0]); /* Claim the corresponding interface from deviceList. interface must be one present in the device configuration. */ usb.claimInterface(pipe , interface, true); ``` 4. Perform data transfer. ``` /* 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); var 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. ``` usb.releaseInterface(pipe, interface); usb.closePipe(pipe); ```