error management when parsing multiple floats

Question

I am writing a handler to render a GIF of a Lorentz attractor. I need to parse floating point numbers from the some querystrings attached to the GIF path. If any of them are bad, I need to log an error.

func lorenzHandler(w http.ResponseWriter, r *http.Request) {
    var e error
    rho := atof(r.FormValue("r"), &e)
    sigma := atof(r.FormValue("s"), &e)
    b := atof(r.FormValue("b"), &e)
    if e != nil {
        log.Printf("bad parameters: r=%s; s=%s; b=%s;\n", r.FormValue("r"), r.FormValue("s"), r.FormValue("b"))
    } else {
        // draw lorenz GIF with parameters rho, sigma and b
        // but until then...
        log.Println("yay!", rho, sigma, b)
    }
}


func atof(s string, e *error) float32 {
    if *e == nil {
        var x float64
        x, *e = strconv.ParseFloat(s, 32)
        return float32(x)
    }
    return 0
}

Is passing around an error, then cleaning it up, correct?

Answer 1

I miss the reason you are working with a pointer of an error and passing it in different functions.

Why not doing in the simple way?

func lorenzHandler(w http.ResponseWriter, r *http.Request) {
    rho, e1 := strconv.ParseFloat(r.FormValue("r"), 32)
    sigma, e2 := strconv.ParseFloat(r.FormValue("s"), 32)
    b, e3 := strconv.ParseFloat(r.FormValue("b"), 32)
    if e1 != nil || e2 != nil || e3 != nil {
        log.Printf("bad parameters: r=%s; s=%s; b=%s;\n", r.FormValue("r"), r.FormValue("s"), r.FormValue("b"))
        w.WriteHeader(http.StatusBadRequest)
        return
    }

    // draw lorenz GIF with parameters rho, sigma and b
    // but until then...
    log.Println("yay!", rho, sigma, b)
}

If the problem is about performance, and you want to stop after the first error, without waiting all three executions, you can do

func lorenzHandler(w http.ResponseWriter, r *http.Request) {
    rho, err := strconv.ParseFloat(r.FormValue("r"), 32)
    if err != nil {
        log.Printf("bad parameters: r=%s\n", r.FormValue("r"))
        w.WriteHeader(http.StatusBadRequest)
        return
    }

    sigma, err := strconv.ParseFloat(r.FormValue("s"), 32)
    if err != nil {
        log.Printf("bad parameters: s=%s\n", r.FormValue("s"))
        w.WriteHeader(http.StatusBadRequest)
        return
    }

    b, err := strconv.ParseFloat(r.FormValue("b"), 32)
    if err != nil {
        log.Printf("bad parameters: b=%s\n", r.FormValue("b"))
        w.WriteHeader(http.StatusBadRequest)
        return
    }

    // draw lorenz GIF with parameters rho, sigma and b
    // but until then...
    log.Println("yay!", rho, sigma, b)
}