33. Request dan formulir — Solusi PR

package main

import (
    "fmt"
    "net/http"
)

func handleGreet(w http.ResponseWriter, r *http.Request) {
    name := r.URL.Query().Get("name")
    if name == "" {
        http.Error(w, "Please give a name.", http.StatusBadRequest)
        return
    }

    w.Header().Set("Content-Type", "text/plain; charset=utf-8")
    fmt.Fprintf(w, "Good morning, %s.\n", name)
}

func main() {
    http.HandleFunc("GET /greet", handleGreet)

    fmt.Println("Server running at http://localhost:8080")
    fmt.Println("Press Ctrl+C to stop it.")

    err := http.ListenAndServe("localhost:8080", nil)
    if err != nil {
        fmt.Println("Server stopped:", err)
    }
}

package main

import (
    "fmt"
    "net/http"
    "strconv"
)

func handleDouble(w http.ResponseWriter, r *http.Request) {
    n, err := strconv.Atoi(r.PathValue("n"))
    if err != nil {
        http.Error(w, "The path must end in a whole number.", http.StatusBadRequest)
        return
    }
    if n < -1000000 || n > 1000000 {
        http.Error(w, "The number must be from -1000000 to 1000000.", http.StatusBadRequest)
        return
    }

    fmt.Fprintf(w, "%d doubled is %d\n", n, n*2)
}

func main() {
    http.HandleFunc("GET /double/{n}", handleDouble)

    fmt.Println("Server running at http://localhost:8080")
    fmt.Println("Press Ctrl+C to stop it.")

    err := http.ListenAndServe("localhost:8080", nil)
    if err != nil {
        fmt.Println("Server stopped:", err)
    }
}

package main

import (
    "fmt"
    "net/http"
    "strconv"
)

const formPage = `<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Rate this book</title>
</head>
<body>
<h1>Rate this book</h1>
<form action="/rating" method="post">
<p><label>Rating from 1 to 5: <input type="text" name="rating"></label></p>
<p><button type="submit">Send</button></p>
</form>
</body>
</html>
`

func handleForm(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    fmt.Fprint(w, formPage)
}

func handleRating(w http.ResponseWriter, r *http.Request) {
    rating, err := strconv.Atoi(r.FormValue("rating"))
    if err != nil {
        http.Error(w, "The rating must be a whole number.", http.StatusBadRequest)
        return
    }
    if rating < 1 || rating > 5 {
        http.Error(w, "The rating must be from 1 to 5.", http.StatusBadRequest)
        return
    }

    fmt.Println("Rating received:", rating)

    http.Redirect(w, r, "/thanks", http.StatusSeeOther)
}

func handleThanks(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Thank you for your rating.")
}

func main() {
    http.HandleFunc("GET /{$}", handleForm)
    http.HandleFunc("POST /rating", handleRating)
    http.HandleFunc("GET /thanks", handleThanks)

    fmt.Println("Server running at http://localhost:8080")
    fmt.Println("Press Ctrl+C to stop it.")

    err := http.ListenAndServe("localhost:8080", nil)
    if err != nil {
        fmt.Println("Server stopped:", err)
    }
}

package main

import (
    "errors"
    "fmt"
    "net/http"
    "strconv"
)

const formPage = `<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Calculator</title>
</head>
<body>
<h1>Calculator</h1>
<form action="/calc" method="get">
<p><label>a: <input type="text" name="a"></label></p>
<p><label>op:
<select name="op">
<option>add</option>
<option>sub</option>
<option>mul</option>
<option>div</option>
</select>
</label></p>
<p><label>b: <input type="text" name="b"></label></p>
<p><button type="submit">Calculate</button></p>
</form>
</body>
</html>
`

const limit = 1000000

// readNumber converts one form value, and checks its range.
func readNumber(label string, text string) (int, error) {
    n, err := strconv.Atoi(text)
    if err != nil {
        return 0, fmt.Errorf("%s must be a whole number", label)
    }
    if n < -limit || n > limit {
        return 0, fmt.Errorf("%s must be from %d to %d", label, -limit, limit)
    }
    return n, nil
}

// calculate returns the answer, or an error that is safe to show the visitor.
func calculate(a int, op string, b int) (int, error) {
    switch op {
    case "add":
        return a + b, nil
    case "sub":
        return a - b, nil
    case "mul":
        return a * b, nil
    case "div":
        if b == 0 {
            return 0, errors.New("cannot divide by zero")
        }
        return a / b, nil
    }
    return 0, errors.New("op must be add, sub, mul or div")
}

func handleForm(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    fmt.Fprint(w, formPage)
}

func handleCalc(w http.ResponseWriter, r *http.Request) {
    a, err := readNumber("a", r.FormValue("a"))
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    b, err := readNumber("b", r.FormValue("b"))
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    op := r.FormValue("op")
    answer, err := calculate(a, op, b)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }

    fmt.Fprintf(w, "%d %s %d = %d\n", a, op, b, answer)
}

func main() {
    http.HandleFunc("GET /{$}", handleForm)
    http.HandleFunc("GET /calc", handleCalc)

    fmt.Println("Server running at http://localhost:8080")
    fmt.Println("Press Ctrl+C to stop it.")

    err := http.ListenAndServe("localhost:8080", nil)
    if err != nil {
        fmt.Println("Server stopped:", err)
    }
}