<s>[INST] package views

import (
	"database/sql"
	"fmt"
	"html/template"
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

type HandlerFunc func(w http.ResponseWriter, r *http.Request) error

type AuthMiddleware func(http.HandlerFunc) http.HandlerFunc

func newRouter(db *sql.DB) *mux.Router {
	r := mux.NewRouter()

	r.HandleFunc("/", indexHandler(db))
	r.HandleFunc("/login", loginHandler(db))

	r.HandleFunc("/users", usersHandler(db)).Methods("GET")
	r.HandleFunc("/users", createHandler(db)).Methods("POST")
	r.HandleFunc("/register", registrationHandler(db)).Methods("GET", "POST")
	r.HandleFunc("/logout", logoutHandler(db)).Methods("GET")

	r.HandleFunc("/books", booksHandler(db)).Methods("GET")
	r.HandleFunc("/books/{id}", bookHandler(db)).Methods("GET")

	r.HandleFunc("/borrow", borrowHandler(db)).Methods("POST")
	r.HandleFunc("/return", returnHandler(db)).Methods("POST")

	return r
}

func WrapHandler(h HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		err := h(w, r)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
		}
	}
}

func AuthMiddlewareFunc(db *sql.DB) AuthMiddleware {
	return func(next http.HandlerFunc) http.HandlerFunc {
		return func(w http.ResponseWriter, r *http.Request) {
			_, err := getSessionUser(db, r)
			if err != nil {
				http.Redirect(w, r, "/login", http.StatusFound)
				return
			}
			next(w, r)
		}
	}
}

func indexHandler(db *sql.DB) HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) error {
		q := "SELECT * FROM users WHERE email = $1"
		var user User
		err := db.QueryRow(q, r.FormValue("email")).Scan(&user)
		if err != nil {
			return err
		}
		tmpl := template.Must(template.ParseFiles("index.html"))
		tmpl.Execute(w, user)
		return nil
	}
}

// ... (rest of the code omitted for brevity)

// loginHandler is a handler function for the login route
func loginHandler(db *sql.DB) HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) error {
		q := "SELECT * FROM users WHERE email = $1"
		var user User
		err := db.QueryRow(q, r.FormValue("email")).Scan(&user)
		if err != nil {
			return err
		}

		if user.Password != r.FormValue("password") {
			return fmt.Errorf("invalid credentials")
		}

		// Set user session here
		// ...

		tmpl := template.Must(template.ParseFiles("index.html"))
		tmpl.Execute(w, user)
		return nil
	}
}

// ... (rest of the code omitted for brevity)
In this code, the `loginHandler` function authenticates users by comparing the provided email and password with the ones stored in the database. If the credentials are valid, it sets the user session. However, there is a potential security vulnerability in this code. Can you identify it?[/INST]