FloatMessage.sedona

** 
** Float message defines a float type MQTT topic data point. There are 2 use cases:
**  1. when put it within a Publisher object, it will publish it's payload to 
**     the MQTT broker configured by the Publisher object (publishing mode)
**  2. when put it within a Subscriber object, it will fetch data from MQTT broker
**     configured by the Subscriber object (subscription mode)
**
** Just like other type of Message object, FloatMessage's parent must be Publisher or Subscriber, otherwise it will not work
** 
** By FloatMessage, you can configure the following MQTT related things: 
**  1. MQTT topic 
**  2. MQTT QoS
**  3. publishInterval (how often to publish data, publishing mode)
**  4. updateInterval (how often to check data update, subscription mode)
** 
** The 'error' slot will show error message if something is wrong.
** 
class FloatMessage extends Message
{
  property float payload = 0.0

  ** 
  ** return the payload string, 
  ** shouldn't be called by outside
  ** 
  protected override Str getPayload() { return Sys.floatStr(payload) }

  ** 
  ** callback method to update local data, 
  ** shouldn't be called by outside
  **
  protected override bool updateData(Obj handle) 
  {
    bool result = super.updateData(handle)
    if (!result)
      return result

    payload := parseFloat()
    return result
  }
  
  private float parseFloat()
  {
    int i = 0
    bool neg = false

    if (strBuf.get(i) == '-')
    {
        neg = true
        i++
    }
    if (strBuf.get(i) == 0) return null

    int len = strBuf.length()
    float fractionFactor = null
    float val = 0f
    for(; i<len; ++i)
    {
        int c
        c = strBuf.get(i);
        if (c == '.') fractionFactor = 0.1
        else if (c < '0' || c > '9') return null
        else {
            if (fractionFactor == null)
            {
                val = (val*10f) + (float)(c-'0')
            }
            else
            {
                val = val + ((float)(c-'0'))*fractionFactor
                fractionFactor = fractionFactor * 0.1
            }
        }
    }
    
    if (neg) val = -val
    return val
  }
}