Implement ConstConstraint

src/JsonSchema/ConstraintError.php

@@ -14,6 +14,7 @@ class ConstraintError extends Enum
     const DISALLOW = 'disallow';
     const DIVISIBLE_BY = 'divisibleBy';
     const ENUM = 'enum';
+    const CONSTANT = 'const';
     const EXCLUSIVE_MINIMUM = 'exclusiveMinimum';
     const EXCLUSIVE_MAXIMUM = 'exclusiveMaximum';
     const FORMAT_COLOR = 'colorFormat';
@@ -63,6 +64,7 @@ public function getMessage()
             self::DISALLOW => 'Disallowed value was matched',
             self::DIVISIBLE_BY => 'Is not divisible by %d',
             self::ENUM => 'Does not have a value in the enumeration %s',
+            self::CONSTANT => 'Does not have a value equal to %s',
             self::EXCLUSIVE_MINIMUM => 'Must have a minimum value greater than %d',
             self::EXCLUSIVE_MAXIMUM => 'Must have a maximum value less than %d',
             self::FORMAT_COLOR => 'Invalid color',

src/JsonSchema/Constraints/ConstConstraint.php

@@ -0,0 +1,54 @@
+<?php
+
+/*
+ * This file is part of the JsonSchema package.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace JsonSchema\Constraints;
+
+use JsonSchema\ConstraintError;
+use JsonSchema\Entity\JsonPointer;
+
+/**
+ * The ConstConstraint Constraints, validates an element against a constant value
+ *
+ * @author Martin Helmich <martin@helmich.me>
+ */
+class ConstConstraint extends Constraint
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function check(&$element, $schema = null, JsonPointer $path = null, $i = null)
+    {
+        // Only validate enum if the attribute exists
+        if ($element instanceof UndefinedConstraint && (!isset($schema->required) || !$schema->required)) {
+            return;
+        }
+        $const = $schema->const;
+
+        $type = gettype($element);
+        $constType = gettype($const);
+
+        if ($this->factory->getConfig(self::CHECK_MODE_TYPE_CAST) && $type == 'array' && $constType == 'object') {
+            if ((object) $element == $const) {
+                return;
+            }
+        }
+
+        if ($type === gettype($const)) {
+            if ($type == 'object') {
+                if ($element == $const) {
+                    return;
+                }
+            } elseif ($element === $const) {
+                return;
+            }
+        }
+
+        $this->addError(ConstraintError::CONSTANT(), $path, array('const' => $schema->const));
+    }
+}

src/JsonSchema/Constraints/Constraint.php

@@ -169,6 +169,22 @@ protected function checkEnum($value, $schema = null, JsonPointer $path = null, $
         $this->addErrors($validator->getErrors());
     }
 
+    /**
+     * Checks a const element
+     *
+     * @param mixed            $value
+     * @param mixed            $schema
+     * @param JsonPointer|null $path
+     * @param mixed            $i
+     */
+    protected function checkConst($value, $schema = null, JsonPointer $path = null, $i = null)
+    {
+        $validator = $this->factory->createInstanceFor('const');
+        $validator->check($value, $schema, $path, $i);
+
+        $this->addErrors($validator->getErrors());
+    }
+
     /**
      * Checks format of an element
      *

src/JsonSchema/Constraints/Factory.php

@@ -58,6 +58,7 @@ class Factory
         'string' => 'JsonSchema\Constraints\StringConstraint',
         'number' => 'JsonSchema\Constraints\NumberConstraint',
         'enum' => 'JsonSchema\Constraints\EnumConstraint',
+        'const' => 'JsonSchema\Constraints\ConstConstraint',
         'format' => 'JsonSchema\Constraints\FormatConstraint',
         'schema' => 'JsonSchema\Constraints\SchemaConstraint',
         'validator' => 'JsonSchema\Validator'

src/JsonSchema/Constraints/UndefinedConstraint.php

@@ -96,6 +96,11 @@ public function validateTypes(&$value, $schema = null, JsonPointer $path, $i = n
         if (isset($schema->enum)) {
             $this->checkEnum($value, $schema, $path, $i);
         }
+
+        // check const
+        if (isset($schema->const)) {
+            $this->checkConst($value, $schema, $path, $i);
+        }
     }
 
     /**