fibsrv.go

// Fibsrv is an HTTP server that calculate Fibonacci numbers.
package main

import (
	"fmt"
	"log"
	"math/big"
	"net/http"
	"strconv"
)

func main() {
	http.HandleFunc("/", fibHandle)
	log.Fatal(http.ListenAndServe("localhost:8000", nil))
}

func fibHandle(w http.ResponseWriter, r *http.Request) {
	s := r.URL.Query().Get("fib")
	// s := strings.Split(r.URL.Path, "/")[1]
	n, err := strconv.ParseUint(s, 10, 64)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		fmt.Fprintf(w, "%q is not unsigned int", s)
		return
	}
	if n > 999999 {
		fmt.Fprint(w, "Whoa, who am I, a millionare?\n")
		return
	}
	res := fib(uint(n))
	fmt.Fprintf(w, "%d\n", res)
}

// fib calculates nth number from the Fibonacci sequence.
func fib(n uint) *big.Int {
	if n < 2 {
		return big.NewInt(int64(n))
	}
	a, b := big.NewInt(0), big.NewInt(1)
	for n--; n > 0; n-- {
		a.Add(a, b)
		a, b = b, a
	}
	return b
}