invalid memory address or nil pointer dereference on QueryRow - go

Question

I'm new to go and trying to create a signin function, When trying to query row from the database I get this error: runtime error: invalid memory address or nil pointer dere
ference
The crash caused by this line:
result := db.QueryRow("SELECT password FROM users WHERE email=$1", credentials.Email)
This is the code:
type Credentials struct {
Email string `json:"email", db:"email"`
Password string `json:"password", db:"password"`
}
func SignIn(w http.ResponseWriter, r *http.Request) {
credentials := &Credentials{}
err := json.NewDecoder(r.Body).Decode(credentials)
if err != nil {
// If there is something wrong with the request body, return a 400 status
w.WriteHeader(http.StatusBadRequest)
return
}
psqlInfo := fmt.Sprintf("host=%s port=%d user=%s "+"dbname=%s sslmode=disable", dbInfo.Host, dbInfo.Port, dbInfo.User, dbInfo.DBname)
db, err := sql.Open("postgres", psqlInfo)
println(credentials.Email)
result := db.QueryRow("SELECT password FROM users WHERE email=$1", credentials.Email)
defer db.Close()
if err != nil {
//If there is an issue with the database, return a 500 error.
w.WriteHeader(http.StatusInternalServerError)
return
}
//We create another instance of 'Credentials' t store the credentials we get from the database
storedCreds := &Credentials{}
// Store the obtained password in `storedCreds`
err = result.Scan(&storedCreds.Password)
if err != nil {
// If an entry with the email does not exist, send an "Unauthorized"(401) status
if err == sql.ErrNoRows {
w.WriteHeader(http.StatusUnauthorized)
return
}
//If the error is of any other type, send a 500 status
w.WriteHeader(http.StatusInternalServerError)
return
}
if credentials.Password != storedCreds.Password {
//The two passwords does not match, return a 401 status
w.WriteHeader(http.StatusUnauthorized)
}
}
I checked and credentials.Email is not null and I can't understand what causes this error.

Answer 1

db, err := sql.Open("postgres", psqlInfo)
// ...
result := db.QueryRow(...)
db is probably nil because the sql.Open failed.
You're not checking err != nil like you should always do when a function returns an error type.