security: Add v2::Validator implementation

Based on the code originally written by Qiuhan Ding

Change-Id: Ib66e24f49d0b6fb2ae21ea1fca7b9ec62ecb753a
Refs: #3289, #1872
diff --git a/src/security/v2/validation-policy.hpp b/src/security/v2/validation-policy.hpp
new file mode 100644
index 0000000..7d85803
--- /dev/null
+++ b/src/security/v2/validation-policy.hpp
@@ -0,0 +1,110 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2017 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_SECURITY_V2_VALIDATION_POLICY_HPP
+#define NDN_SECURITY_V2_VALIDATION_POLICY_HPP
+
+#include "validation-state.hpp"
+#include "certificate-request.hpp"
+#include "../../data.hpp"
+#include "../../interest.hpp"
+
+namespace ndn {
+namespace security {
+namespace v2 {
+
+/**
+ * @brief Abstraction that implements validation policy for Data and Interest packets
+ */
+class ValidationPolicy : noncopyable
+{
+public:
+  using ValidationContinuation = std::function<void(const shared_ptr<CertificateRequest>& certRequest,
+                                                    const shared_ptr<ValidationState>& state)>;
+
+  virtual
+  ~ValidationPolicy() = default;
+
+  /**
+   * @brief Check @p data against the policy
+   *
+   * Depending on implementation of the policy, this check can be done synchronously or
+   * asynchronously.
+   *
+   * Semantics of checkPolicy has changed from v1::Validator
+   * - If packet violates policy, the policy should call `state->fail` with appropriate error
+   *   code and error description.
+   * - If packet conforms to the policy and no further key retrievals are necessary,
+   *   the policy should call continueValidation(state, nullptr)
+   * - If packet conforms to the policy and a key needs to be fetched, the policy should call
+   *   continueValidation(state, <appropriate-key-request-instance>)
+   */
+  virtual void
+  checkPolicy(const Data& data, const shared_ptr<ValidationState>& state,
+              const ValidationContinuation& continueValidation) = 0;
+
+  /**
+   * @brief Check @p interest against the policy
+   *
+   * Depending on implementation of the policy, this check can be done synchronously or
+   * asynchronously.
+   *
+   * Semantics of checkPolicy has changed from v1::Validator
+   * - If packet violates policy, the policy should call `state->fail` with appropriate error
+   *   code and error description.
+   * - If packet conforms to the policy and no further key retrievals are necessary,
+   *   the policy should call continueValidation(state, nullptr)
+   * - If packet conforms to the policy and a key needs to be fetched, the policy should call
+   *   continueValidation(state, <appropriate-key-request-instance>)
+   */
+  virtual void
+  checkPolicy(const Interest& interest, const shared_ptr<ValidationState>& state,
+              const ValidationContinuation& continueValidation) = 0;
+
+  /**
+   * @brief Check @p certificate against the policy
+   *
+   * Unless overridden by the policy, this check defaults to `checkPolicy(const Data&, ...)`.
+   *
+   * Depending on implementation of the policy, this check can be done synchronously or
+   * asynchronously.
+   *
+   * Semantics of checkPolicy has changed from v1::Validator
+   * - If packet violates policy, the policy should call `state->fail` with appropriate error
+   *   code and error description.
+   * - If packet conforms to the policy and no further key retrievals are necessary,
+   *   the policy should call continueValidation(state, nullptr)
+   * - If packet conforms to the policy and a key needs to be fetched, the policy should call
+   *   continueValidation(state, <appropriate-key-request-instance>)
+   */
+  virtual void
+  checkPolicy(const Certificate& certificate, const shared_ptr<ValidationState>& state,
+              const ValidationContinuation& continueValidation)
+  {
+    checkPolicy(static_cast<const Data&>(certificate), state, continueValidation);
+  }
+};
+
+} // namespace v2
+} // namespace security
+} // namespace ndn
+
+#endif // NDN_SECURITY_V2_VALIDATION_POLICY_HPP