http.go

package main

import (
	"net/http"
	//	"crypto/tls"
	//	"crypto/x509"
	"fmt"
	"io/ioutil"
	"net/url"
	"os"
	"runtime"
	"strconv"
	"strings"

	"crypto/hmac"
	"crypto/sha256"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

const cfile = "/home/lka/dg/skopos/cfile.pem"

var m []byte
var dflt_qry string

type ApiHandler struct{}

func (ApiHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var v string
	var a, u bool
	var data string
	var http_status int

	qry := r.URL.RawQuery
	if qry == "" {
		qry = dflt_qry
	}
	vals, _ := url.ParseQuery(qry) // map[string] []string ; NB: use vals.Get() to get the 1st value

	http_status = 200

	if v = vals.Get("busy"); v != "" {
		t := time.Now()
		c, _ := strconv.ParseUint(v, 10, 64)
		k := make([]byte, 32)
		mac := hmac.New(sha256.New, k)
		for i := 0; i < int(c); i++ {
			mac.Write(k)
			mac.Write(k)
			runtime.GC()
		}
		data += fmt.Sprintf("busy for %d us\n", time.Now().Sub(t)/1000)
	}

	if v = vals.Get("call"); v != "" {
		if !strings.ContainsRune(v, '/') {
			v = fmt.Sprintf("http://%s:8080/", v)
		}
		rsp, err := http.Get(v)
		if err != nil {
			data = "err: " + err.Error() + "\n"
			http_status = 400
		} else {
			var d []byte
			d, err = ioutil.ReadAll(rsp.Body) // TODO: err
			data += "call: " + string(d)
		}
	}

	if v = vals.Get("alloc"); v != "" {
		a = true
	}
	if vals.Get("use") != "" {
		u = true
	}

	if a {
		var sz uint64
		sz, _ = strconv.ParseUint(v, 10, 64)
		//@err
		m = nil
		runtime.GC()
		m = make([]byte, sz*4096)
		data += fmt.Sprintf("allocated memory %d bytes (%d pages)\n", len(m), len(m)/4096)
	}
	if u {
		var i int
		for i = 0; i < len(m); i += 4096 {
			m[i] = 1
		}
		data += fmt.Sprintf("accessed %d bytes (%d pages)\n", len(m), len(m)/4096)
	}

	w.Header().Add("Content-length", strconv.Itoa(len(data)))
	w.Header().Add("Content-type", "text/plain")
	w.WriteHeader(http_status)
	w.Write([]byte(data))
}

func main() {
	var s http.Server
	var err error
	s.Addr = ":8080"
	if addr := os.Getenv("HTTP_ADDR"); addr != "" {
		s.Addr = addr
	}

	// default query from command line
	if len(os.Args) > 1 {
		dflt_qry = os.Args[1]
	}

	/*
		// We could call ListenAndServeTLS without initializing the TLS config, but we
		// set it up explicitly here anyway, to allow adding things like client cert verify, etc. later
		var tlscfg tls.Config
		tlscfg.Certificates = make([]tls.Certificate, 1)
		tlscfg.Certificates[0], err = tls.LoadX509KeyPair(cfile,cfile)
		// @@ err
		// pre-init the leaf cert, too (so it isn't parsed every time when serving requests)
		tlscfg.Certificates[0].Leaf, err = x509.ParseCertificate(tlscfg.Certificates[0].Certificate[0])
		// @@ err
		s.TLSConfig = &tlscfg
	*/

	// Handler - default
	counter := prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "api_requests_total",
			Help: "A counter for requests to the wrapped handler.",
		},
		[]string{"code", "method"},
	)

	prometheus.MustRegister(counter)
	apiHandlerFn := promhttp.InstrumentHandlerCounter(counter, ApiHandler{})

	http.Handle("/metrics", promhttp.Handler())
	http.HandleFunc("/", apiHandlerFn)

	// err = s.ListenAndServeTLS("","")
	runtime.GC()
	err = s.ListenAndServe()
	fmt.Println(err)
}