Redirect and POST at the same time - php

Question

I have a form and I don't do client-side validation other than required attribute. I'm doing the validation on the server side.
lyrics/add.php
<form action="../scripts/lyrics/submit_lyrics.php" id="lyricsForm" method="post" autocomplete="off" enctype="multipart/form-data">
Form data is processed in a seperate php file. Retrieving and validating the form data in the following way:
scripts/lyrics/submit_lyrics.php
$form_data = new FormData(["artist", "album", "song", "year", "track_no", "lyrics"], "sssiis");
$form_data->validate();
What the validate method does is
public function validate() {
$valid = $this->check_form_data($fields);
$fields = implode(",", $fields);
if (!$valid) {
header("location: ".BASE."lyrics/add?status=error&problem=input&specifics=$fields");
exit;
}
}
check the form data and redirect the page (scripts/lyrics/submit_lyrics.php) to the form page (lyrics/add.php) with the information on validation (if it failed). Then I output an error message indicating that there's something wrong with the input using GET method.
I'm curious if I can do this using POST. I would need to modify this line
header("location: ".BASE."lyrics/add?status=error&problem=input&specifics=$fields");
make it redirect the page to BASE."lyrics/add" and also send the validation information using POST to that page. So I'd still be able output the validation error, but using POST instead of GET.
Is this possible?

Answer 1

No, this is not possible because you are rewriting the request. The browser will always send a "GET" request in response to a redirect request, unless it receives a 307 request in which it will repeat the request using the same method and parameters. See this related question on Programmers.
The workaround is to redirect to a new page with an embedded form that you generate, and have javascript POST that form for the user. It's an extra request but it's the only way to have the client make a second POST.

Answer 2

Using u_mulder's suggesion (storing values in a session), I've solved the problem in the following way:
scripts/lyrics/submit_lyrics.php
public function validate() {
$valid = $this->check_form_data($fields); // check if input fields are valid
$fields = implode(";", $fields); // invalid input fields
if (!$valid) { // not all fields are valid, so we return
session_start(); // start session
if (!isset($_SESSION["problem"])) { // making sure session variable doesn't exist
$_SESSION["problem"] = "input"; // error type: input, file_upload, db_insert, etc.
$_SESSION["specifics"] = $fields; // artist, album, etc. (for input)
}
header("location: ".BASE."lyrics/add?status=error"); // redirect to form page
exit;
}
}
lyrics/add.php
if (isset($_GET["status"])) {
$status = $_GET["status"];
switch ($status) {
case "error":
session_start();
if (isset($_SESSION["problem"])) {
$problem = $_SESSION["problem"];
$specifics = explode(";", $_SESSION["specifics"]);
$error_message = "There was an error.";
switch ($problem) {
case "input":
$error_message = "Invalid input on the following fields:";
break;
// other cases ...
}
session_destroy();
output("Error!", $error_message, $specifics);
} else {
// if the user reloads the page, session data is lost
// but we're still in the error page "lyrics/add?status=error" and have no error to show
// we either show an appropriate message or redirect to "lyrics/add"
session_destroy();
// output("Error!", "You're in the form validation error page, but there aren't any errors. Did you reload the page?");
// header("location: ".BASE."lyrics/add");
// exit;
}
break;
case "success":
// form submitted successfully
break;
}
} else {
// show form
}