A year ago we installed ServersCheck Temperature & Sensor Gateway that measures temperature and relative humidity in our data center. The gateway itself is a convenient (approx. 10cm long) piece of HW that you can easily mount in some free spot in a rack.

It comes with a built-in web server where you can configure various settings and read current status of device, including internal temperature (inside sensors), external temperature and in our case humidity. After you login to ServerCheck web application you can check status in the data center:

Nice, but I would prefer if I could simply skip the user interaction with a GUI; why not run s simple command line tool/script that will display temperature and humidity in our data center. The bonus feature would be to allow us to simply select ServersCheck status from SQL*Plus.
In the first part of the article I’ll show you how I did it with a simple Google Go program.

Note that we’re currently using ServersCheck gateway with Hardware version: 4.0, Firmware version 2.11. This program might or might not work for you if you’re using something else.

Since ServersCheck gateway doesn’t ship with some documented API I had to do some research and finally found that sensor status data is served from simple xml page that is accessible from h t t p=//10.10.10.10/retcurvalue.xml (replace dummy IP with the IP that you assigned to your ServersCheck gateway).

<retcurvalue>
<ssvalue0>16.06</ssvalue0>
<ssvalue1>19.75</ssvalue1>
<ssvalue2>78.65</ssvalue2>
<ssvalue3>?</ssvalue3>
<ssvalue4>?</ssvalue4>
<ssvalue5>?</ssvalue5>
<ssvalue6>?</ssvalue6>
...
...
</retcurvalue>

So all that we need to do is to authenticate to ServersCheck internal webserver, parse xml and display temperature and humidity….something like this:

I thought it would be a good exercise to write this with a Google Go, so here it goes:

//
// vpctemp.go by alesk (excercise in golang)
//
package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"regexp"
	"strings"
	"time"
)

const (
	VERSION   = "0.10"
	LOCATION  = "DATACENTER1"
	STATUSURL = "http://10.10.10.1/retcurvalue.xml"
	USER      = "admin"
	PWD       = "r049D;FMNgGHHLFKRRJEJFDD"
	TIMEFORMAT = "2006-1-2 15:04:05"
)

type SensorStatus struct {
	temp1 string // <ssvalue0> internal temperature
	temp2 string // <ssvalue1> external sensor temperature
	hum1  string // <ssvalue2> relative humidity
}

var sensor SensorStatus

func main() {

	request, err := http.NewRequest("GET", STATUSURL, nil)
	// I'm using simple obfuscation function getFoo to prevent casual password 
	// leak - this is more than adequate approach in my case. You're free to
	// change the code to ask user for a password every time or do something more clever.
	request.SetBasicAuth(USER, getFoo(PWD))

	client := &http.Client{}
	response, err := client.Do(request)

	if err != nil {
		log.Fatal(err)
	}
	defer response.Body.Close()

	body, err := ioutil.ReadAll(response.Body)

	// uncomment the following line if you wish to print the content of complete xml 
	// fmt.Println(string(body))		// debugging

	// print values <ssvalue0,1,2> without tags
	// obviously I could use encoding/xml package in golang standard library but
	// rather than that took a shortcut with a simple regex string parsing.
	re := regexp.MustCompile("<[/]?ssvalue[0-9]>")
	i := 0
	for _, line := range strings.Split(string(body), "\n") {
		if i < 4 {
			//skip first line <retcurvalue>
			if i != 0 {
				switch i {
				case 1:
					sensor.temp1 = re.ReplaceAllString(line, "")
				case 2:
					sensor.temp2 = re.ReplaceAllString(line, "")
				case 3:
					sensor.hum1 = re.ReplaceAllString(line, "")
				}
			}
			i += 1
		} else {
			break
		}
	}
	timestamp := time.Now().Format(TIMEFORMAT)
	fmt.Printf("\nVPCtemp v%s        Location: %s\n", VERSION, LOCATION)
	fmt.Println("***********************************")
	fmt.Printf("Timestamp     : %s\n", timestamp)
	fmt.Printf("Temp. internal: %s\n", sensor.temp1)
	fmt.Printf("Temp. external: %s\n", sensor.temp2)
	fmt.Printf("Humidity      : %s\n", sensor.hum1)
}

func getFoo(foo string) string {
	bar := foo[22:24] + foo[16:19] + foo[10:11] + foo[3:4] + foo[12:13] + foo[4:6]
	return strings.Replace(bar, "V", "v", 1)
}

In the part 2 I’ll show you how little code was needed to script my “vpctemp” with PowerShell 3.0.