Integrating to legacy temperature monitoring device

Posted on Thursday, October 26, 2017 by Nicki

Below is sample code of a proxy ASP.Net page that queries a TempageR 4E realtime temperature monitor and exposes the temperature to PRTG in order to report and escalate out of range values.

public partial class FetchTemp : System.Web.UI.Page
        protected void Page_Load(object sender, EventArgs e)
            System.Net.Sockets.TcpClient client = new System.Net.Sockets.TcpClient(System.Configuration.ConfigurationManager.AppSettings["ip"], 80);
            NetworkStream ns = client.GetStream();
            byte[] request = System.Text.Encoding.ASCII.GetBytes("GET /getData.htm HTTP/1.1\r\n\r\n");

            ns.Write(request, 0, request.Length);

            byte[] resp = new byte[2048];
            int bytes = -1;

            StringBuilder sb = new StringBuilder(); 

            while (bytes != 0)
                bytes = ns.Read(resp, 0, resp.Length);
                sb.Append(System.Text.Encoding.ASCII.GetString(resp, 0, bytes));

            dynamic obj = JsonConvert.DeserializeObject(sb.ToString());
            Response.Write("[" + obj.sensor[0].tempc + "]");

It calls the getData.htm page, which exposes the device info, sensors and their values as a JSON object. This gets parsed, and the value of the first sensor is written to the Response in blockquotes. The PRTG HTTP Content sensor is configured with the URL of the page (FetchTemp.aspx).

The code uses a TcpClient instance to retrieve the data. The getData.htm page does not return HTTP response headers, which causes HttpWebRequest as well as the built-in PRTG HTTP XML/REST sensor to fail with "The underlying connection was closed unexpectedly", using TcpClient solves this issue.