// CPU-only allocation lab; exposes pprof only on loopback.
package main

import (
	"bytes"
	"flag"
	"fmt"
	"hash/crc32"
	"log"
	"net/http"
	"net/http/pprof"
	"runtime"
	"sync"
	"time"
)

func main() {
	addr := flag.Int("port", 19066, "loopback port")
	flag.Parse()
	// A lab-only sampling rate so that one request produces a readable profile.
	runtime.MemProfileRate = 4096
	payload := bytes.Repeat([]byte("a"), 4096)
	pool := sync.Pool{New: func() any { return new(bytes.Buffer) }}
	mux := http.NewServeMux()
	mux.HandleFunc("GET /debug/pprof/heap", pprof.Handler("heap").ServeHTTP)
	mux.HandleFunc("GET /debug/pprof/profile", pprof.Profile)
	mux.HandleFunc("GET /frames/{mode}", func(w http.ResponseWriter, r *http.Request) {
		mode := r.PathValue("mode")
		if mode != "fresh" && mode != "pool" {
			http.Error(w, "fresh or pool", 400)
			return
		}
		var sum uint32
		for i := 0; i < 4096; i++ {
			if r.Context().Err() != nil {
				return
			}
			var b *bytes.Buffer
			if mode == "pool" {
				b = pool.Get().(*bytes.Buffer)
				b.Reset()
			} else {
				b = new(bytes.Buffer)
			}
			b.WriteString("data: ")
			b.Write(payload)
			sum += crc32.ChecksumIEEE(b.Bytes())
			if mode == "pool" {
				pool.Put(b)
			}
		}
		fmt.Fprintln(w, sum)
	})
	log.Fatal((&http.Server{Addr: fmt.Sprintf("127.0.0.1:%d", *addr), Handler: mux, ReadHeaderTimeout: 3 * time.Second}).ListenAndServe())
}