HTTP Headers baseline

Using the HttpWebRequest functionality in system.http and using the HTTP headers to upload the GPS position data is a pretty simple and low code approach. For this initial version I’m uploading the

  • Device Mac Address
  • 2D vs 3D fix
  • Latitude
  • Longitude
  • Horizontal dilution of position (HDoP)
  • Altitude
  • Speed
  • Heading

The server responds with

  • Minimum time between position reports

This approach does have some disadvantages

Adding system.http increases the size of the download to by roughly 40K which on the Netduino Plus could be a problem. The HTTP requests and responses can also be a bit chunky. The HttpWebRequest.GetResponse call is synchronous which could cause some issues with the processing of the GPS NMEA data stream (particularly when there are connectivity problems).

I’ll be looking at solutions to these issues in future posts

Client application

using (HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(CloudServerUrl))
{
request.Method = "POST";
request.Headers.Add("x-DeviceMacAddress", DeviceMacAddress());
request.Headers.Add("x-3DFix", Gps.Fix3D.ToString());
request.Headers.Add("x-GPSTime", DateTime.Now.ToString("yyyy MM dd hh:mm:ss"));
request.Headers.Add("x-Latitude", Gps.Latitude.ToString("F5"));
request.Headers.Add("x-Longitude", Gps.Longitude.ToString("F5"));
request.Headers.Add("x-HDoP", Gps.HDoP.ToString("F2"));
request.Headers.Add("x-Altitude", Gps.Altitude.ToString("F1"));
request.Headers.Add("x-Speed", Gps.Kmh.ToString("F0"));
request.Headers.Add("x-Heading", Gps.TrackAngle.ToString("F0"));
request.ContentLength = 0;


using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
Debug.Print(" HTTP Status:" + response.StatusDescription);

if (response.StatusCode == HttpStatusCode.OK)
{
if (response.Headers["x-UpdateIntervalSecs"] != null)
{
positionUpdateIntervalMinimum = new TimeSpan(0, 0, int.Parse(response.Headers["x-UpdateIntervalSecs"].ToString()));
}
}
}

On the server side

protected void Page_Load(object sender, EventArgs e)
{
if (this.Request.Headers["x-DeviceMacAddress"] == null)
{
return;
}
string deviceMacAddress = this.Request.Headers["x-DeviceMacAddress"];


if (this.Request.Headers["x-GPSTime"] == null)
{
return;
}
DateTime gpsTime = DateTime.ParseExact(this.Request.Headers["x-GPSTime"], "yyyy MM dd hh:mm:ss", CultureInfo.InvariantCulture);

if (this.Request.Headers["x-3DFix"] == null)
{
return;
}
bool is3DFix = bool.Parse(this.Request.Headers["x-3DFix"]);

if (this.Request.Headers["x-Latitude"] == null)
{
return;
}
Double latitude = Double.Parse(this.Request.Headers["x-Latitude"]);

if (this.Request.Headers["x-Longitude"] == null)
{
return;
}
Double longitude = Double.Parse(this.Request.Headers["x-Longitude"]);

if (this.Request.Headers["x-HDoP"] == null)
{
return;
}
Double hDoP = Double.Parse(this.Request.Headers["x-HDoP"]);

if (this.Request.Headers["x-Altitude"] == null)
{
return;
}
Double altitude = Double.Parse(this.Request.Headers["x-Altitude"]);

if (this.Request.Headers["x-Speed"] == null)
{
return;
}
int speed = int.Parse(this.Request.Headers["x-Speed"]);

if (this.Request.Headers["x-Heading"] == null)
{
return;
}
int heading = int.Parse(this.Request.Headers["x-Heading"]);

this.Response.Headers.Add("x-UpdateIntervalSecs", "30") ;
}

Source for HTTP Headers Client V1, and HTTP Headers ServiceV1

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