Golang中的重构功能

I'm trying to refactor my code but I am stuck.

I want to clean this HandleExportDevicesAsCsv function. So, decided to code from where I start my comment to the end of the comment. Then I refactored and moved that block of code to another function.

Can anyone guide me on returning the value from ExportDevicesAsCsv so that I can pass it to c.Data(http.StatusOK, "text/csv", b.Bytes())

this function working correctly

func HandleExportDevicesAsCsv(c *gin.Context) {

    deviceIDs := c.Request.FormValue("deviceIDs")
    var data []byte
    token := c.Request.Header.Get("Authorization")
    data = services.ExportDevicesData(token, deviceIDs)  

    //===================================================================
    //I want to refactor this code from here 
    //====================================================================
    type DR []models.DeviceResponse
    var deviceResponse DR
    json.Unmarshal([]byte(data), &deviceResponse)
    b := &bytes.Buffer{}
    w := csv.NewWriter(b)
    if err := w.Write([]string{"Name", "Id", "Createdon","Lastupdated", "qrcode", "mac", "state", "kind"});
    err != nil {
        log.Fatalln("error writing record to csv:", err)
    }

    for _, device := range deviceResponse {
        var record []string
        record = append(record, device.Name)
        record = append(record, device.ID)
        record = append(record, device.Createdon)
        record = append(record, device.Lastupdated)
        record = append(record, device.Qrcode)
        record = append(record, device.State)
        record = append(record, device.Kind)

        if err := w.Write(record); err != nil {
            log.Fatalln("error writing record to csv:", err)
        }

    }

    w.Flush()
    if err := w.Error(); 
       err != nil {
        log.Fatal(err)
    }

      //===================================================================
     // to here end of refactor code
    //====================================================================

    c.Header("Content-type", "application/octet-stream")
    c.Header("Content-Disposition", "attachment; filename=devices.csv")    
    c.Data(http.StatusOK, "text/csv", b.Bytes())

}

when I refactor function this is not working.

func HandleExportDevicesAsCsv(c *gin.Context) {

    METHOD_NAME := "HandleExportDevicesAsCsv() - "
    mlog.Debug("%s request = %v", METHOD_NAME, c.Request)
    deviceIDs := c.Request.FormValue("deviceIDs")
    mlog.Debug("%s deviceIDs = %s", METHOD_NAME, deviceIDs)
    var data []byte
    token := c.Request.Header.Get("Authorization")     
    data = services.ExportDevicesData(token, deviceIDs)      
    cdata := services.ExportDevicesAsCsv(data)
    ccdata := cdata.Bytes()  
    mlog.Debug("%s response = %s", METHOD_NAME, string(data))
    c.Header("Content-type", "application/octet-stream")
    c.Header("Content-Disposition", "attachment; filename=devices.csv")
    //c.Data(http.StatusOK, "application/octet-stream", data) // text/csv
    // c.Header("Content-Description", "File Transfer")
    // c.Header("Content-Disposition", "attachment; filename=devices.csv")
    c.Data(http.StatusOK, "text/csv", ccdata)
    // c.Header("Content-Type", "text/csv")
    // c.Writer.Write(b.Bytes())
    // c.Writer.Flush()
}

Here I refactor and put that code in another function and call in HandleExportDevicesAsCsv

func ExportDevicesAsCsv(data []byte) *bytes.Buffer {
        //METHOD_NAME := "ExportDevicesAsCsv() - "
        //var Handlersdata handlers.data
        //var csvVal []byte
        //var devices []interface{}
        //var nextPageToken string
        //for len(nextPageToken) > 0 {
        type DR []models.DeviceResponse
        var deviceResponse DR
        json.Unmarshal([]byte(data), &deviceResponse)
        b := &bytes.Buffer{}
        w := csv.NewWriter(b)
        if err := w.Write([]string{"Name", "Id", "Createdon",
    "Lastupdated", "qrcode", "mac", "state", "kind"}); err != nil {
            log.Fatalln("error writing record to csv:", err)
        }
        for _, device := range deviceResponse {
            var record []string
            record = append(record, device.Name)
            record = append(record, device.ID)
            record = append(record, device.Createdon)
            record = append(record, device.Lastupdated)
            record = append(record, device.Qrcode)
            record = append(record, device.State)
            record = append(record, device.Kind)
            if err := w.Write(record); err != nil {
                log.Fatalln("error writing record to csv:", err)
            }
        }
        w.Flush()
        if err := w.Error(); err != nil {
            log.Fatal(err)
        }
        // c.Header("Content-Description", "File Transfer")
        // c.Header("Content-Disposition", "attachment; filename=devices.csv")
        // c.Data(http.StatusOK, "text/csv", b.Bytes())
        return b
    }