Function copy_printer_interface_deviceid

backend/usb-darwin.c:1552–1598

}

static CFStringRef copy_printer_interface_deviceid(printer_interface_t printer, UInt8 alternateSetting)
{
	// I have tried to make this function as neat as I can, but the possibility of needing to resend
	// a request to get the entire string makes it hideous...
	//
	// We package the job of sending a request up into the block (^sendRequest), which takes the size
	// it should allocate for the message buffer. It frees the current buffer if one is set and
	// allocates one of the specified size, then performs the request. We can then easily retry by
	// calling the block again if we fail to get the whole string the first time around.

	#define kUSBPrintClassGetDeviceID           0
	#define kDefaultNoDataTimeout               5000L
	#define pack_device_id_wIndex(intf, alt)  ((UInt16)((((UInt16)(intf)) << 8) | ((UInt8)(alt))))

	if (printer == NULL)
			return NULL;


	IOReturn err        = kIOReturnError;
	UInt8    configurationIndex	= 0;
	UInt8    interfaceNumber	= 0;
	size_t   bufferLength		= 256;
	CFStringRef ret             = NULL;

	if ((*printer)->GetConfigurationValue( printer, &configurationIndex) == kIOReturnSuccess &&
			(*printer)->GetInterfaceNumber( printer, &interfaceNumber) == kIOReturnSuccess)
	{
		__block IOUSBDevRequestTO	request;
		IOReturn (^sendRequest)(size_t) = ^ (size_t size)
		{
			if (request.pData)
			{
				free(request.pData);
				request.wLength = 0;
				request.pData = NULL;
			}

			IOReturn berr = kIOReturnError;
			char *buffer = malloc(size);
			if (buffer == NULL)
				return kIOReturnNoMemory;

			request.wLength = HostToUSBWord(size);
			request.pData = buffer;
			berr = (*printer)->ControlRequestTO(printer, 0, &request);
			return berr;
		};

		/* This request takes the 0 based configuration index. IOKit returns a 1 based configuration index */
		configurationIndex -= 1;