String and Filter validator.

src/Validators/FilterValidator.php

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+<?php
+
+namespace Web3\Validators;
+
+use Web3\Validators\IValidator;
+use Web3\Validators\QuantityValidator;
+use Web3\Validators\TagValidator;
+use Web3\Validators\HexValidator;
+use Web3\Validators\AddressValidator;
+
+class FilterValidator
+{
+    /**
+     * validate
+     *
+     * @param array $value
+     * @return bool
+     */
+    public static function validate($value)
+    {
+        if (!is_array($value)) {
+            return false;
+        }
+        if (
+            isset($value['fromBlock']) &&
+            QuantityValidator::validate($value['fromBlock']) === false &&
+            TagValidator::validate($value['fromBlock']) === false
+            ) {
+            return false;
+        }
+        if (
+            isset($value['toBlock']) &&
+            QuantityValidator::validate($value['toBlock']) === false &&
+            TagValidator::validate($value['toBlock']) === false
+            ) {
+            return false;
+        }
+        if (isset($value['address']) && AddressValidator::validate($value['address']) === false) {
+             return false;
+        }
+        if (isset($value['topics']) && is_array($value['topics'])) {
+            foreach ($value['topics'] as $topic) {
+                if (is_array($topic)) {
+                    foreach ($topic as $v) {
+                        if (isset($v) && HexValidator::validate($v) === false) {
+                            return false;
+                        }
+                    }
+                } else {
+                    if (isset($topic) && HexValidator::validate($topic) === false) {
+                        return false;
+                    }
+                }
+            }
+        }
+        return true;
+    }
+}

src/Validators/StringValidator.php

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+<?php
+
+namespace Web3\Validators;
+
+use Web3\Validators\IValidator;
+
+class StringValidator
+{
+    /**
+     * validate
+     *
+     * @param string $value
+     * @return bool
+     */
+    public static function validate($value)
+    {
+        return is_string($value);
+    }
+}