make tmpfiles actually temporary and random

we can't use ioutil.TempFile because we need to set a prefix, many
language tools expect a certain prefix.

also, this probably means multiuser support!

go/linguaevalia/linguaevalia.go

// try it with `curl -i localhost:8000/run --data-binary @hello-world.go`
import (
	"crypto/rand"
	"fmt"
	"html/template"
	"io/ioutil"
	"log"
	"math/big"
	"net/http"
	"os"
	"os/exec"
	"path"
)
type Language interface {
func writeCode(code string, extension string) (*os.File, error) {
	// create tmp file
	f, err := os.Create(fmt.Sprintf("/tmp/linguaevalia-%s.%s", extension, extension)) // FIXME: actually create a tmpfile
	f, err := tempFile("/tmp", "linguaevalia", extension)
	if err != nil {
		return f, err
	}
	return f, nil
}
func tempFile(dir, prefix, suffix string) (*os.File, error) {
	rnd, _ := rand.Int(rand.Reader, big.NewInt(999999))
	f, err := os.Create(path.Join(dir, fmt.Sprintf("%s%d.%s", prefix, rnd, suffix)))
	return f, err
}
func Eval(lang Language, code string) ([]byte, error) {
	// write code to temp file
	f, err := writeCode(code, lang.Extension())