How can i write a SPI read/write function to use with my BME680 sensor?

Hi, I want to use a BME680 sensor and the drivers provided by Bosch, but i have to write two read and write function prototypes to communicate via SPI with the sensor. I started writing a wrapper for this driver, but i'm doing something wrong with my communication functions.

This is the function pointer prototype 

 * Generic communication function pointer
 * @param[in] dev_id: Place holder to store the id of the device structure
 *                    Can be used to store the index of the Chip select or
 *                    I2C address of the device.
 * @param[in] reg_addr:	Used to select the register the where data needs to
 *                      be read from or written to.
 * @param[in/out] reg_data: Data array to read/write
 * @param[in] len: Length of the data array
 */
typedef int8_t (*bme680_com_fptr_t)(uint8_t dev_id, uint8_t reg_addr, uint8_t *data, uint16_t len);

The function that i wrote and does not communicate with the sensor:

static struct bme680_dev gBME680Struct = {};
static SPI_Handle gSpi;
static SPI_Transaction gSpiTransaction;
static uint8_t gRegAddr = 0;

int8_t userTransfer(uint8_t dev_id, uint8_t reg_addr, uint8_t *data,
                    uint16_t len)
{
    if (dev_id != gBME680Struct.dev_id)
    {
        return __LINE__;
    }

    gRegAddr = reg_addr;

    gSpiTransaction.txBuf = (void*) &gRegAddr;
    gSpiTransaction.rxBuf = (void*)data;
    gSpiTransaction.count = len;

    bool success = SPI_transfer(gSpi, &gSpiTransaction);

    if (!success)
    {
        return __LINE__;
    }

    return 0;
}

It is unclear to me what ought to be different between a write and a read function, as there is only one SPI_Transfer function. How do i send one byte and receive more? Or how do i send multiple bytes and receive no response? Would appreciate some clarifications on this issue. Thanks.