Add header validator

src/Appwrite/Functions/Validator/Header.php

@@ -0,0 +1,80 @@
+<?php
+
+namespace Appwrite\Functions\Validator;
+
+use Utopia\Validator;
+
+/**
+ * Header.
+ *
+ * Validates user provided headers
+ */
+class Header extends Validator
+{
+    protected bool $allowEmpty;
+
+    public function __construct(bool $allowEmpty = false)
+    {
+        $this->allowEmpty = $allowEmpty;
+    }
+
+    /**
+     * Get Description.
+     *
+     * Returns validator description
+     *
+     * @return string
+     */
+    public function getDescription(): string
+    {
+        return 'Header must be a string and not start with x-appwrite- prefix.';
+    }
+
+    /**
+     * Is valid.
+     *
+     * @param mixed $value
+     *
+     * @return bool
+     */
+    public function isValid($value): bool
+    {
+        if (!\is_string($value)) {
+            return false;
+        }
+
+        if (\strlen($value) > 256) {
+            return false;
+        }
+
+        if (0 === strpos($value, 'x-appwrite-')) {
+            return false;
+        }
+
+        return true;
+    }
+
+    /**
+     * Is array
+     *
+     * Function will return true if object is array.
+     *
+     * @return bool
+     */
+    public function isArray(): bool
+    {
+        return true;
+    }
+
+    /**
+     * Get Type
+     *
+     * Returns validator type.
+     *
+     * @return string
+     */
+    public function getType(): string
+    {
+        return self::TYPE_ARRAY;
+    }
+}