Add post validation

public/post/index.php

@@ -101,6 +101,9 @@ function do_post() {
 		$body = sanitize_post_body($body);
 		$error_body = validate_post_body($body);
 	}
+	if (!$error_body && $thread_id !== NULL && !(ENABLE_IMAGE && $has_file)) {
+		$error_body = validate_post_body_with_anchor($body);
+	}
 
 	$errors = array_merge($error_title, $error_body);
 	if ($errors) { return on_error(400, $errors); }

validate.php

@@ -64,6 +64,13 @@ function validate_post_body($s) {
 	return [];
 }
 
+function validate_post_body_with_anchor($s) {
+	// アンカーのみ(返信時のデフォルト)は不許可
+	$s = preg_replace('/^>>[0-9]+/', '', $s);
+	if (mbtrim($s) === '') { return ['アンカー「>>○○」1つだけの返信は不可。']; }
+	return [];
+}
+
 function sanitize_post_body($s) {
 	return sanitize_multiline($s);
 }