Add optional context for certificate errors.

net/cert/internal/cert_error_params.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_CERT_INTERNAL_CERT_ERROR_PARAMS_H_
+#define NET_CERT_INTERNAL_CERT_ERROR_PARAMS_H_
+
+#include <memory>
+#include <string>
+
+#include "base/macros.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+namespace der {
+class Input;
+}
+
+// CertErrorParams is a base class for describing extra parameters attached to
+// a CertErrorNode.
+//
+// An example use for parameters is to identify the OID for an unconsumed
+// critical extension. This parameter could then be pretty printed when
+// diagnosing the error.
+class NET_EXPORT CertErrorParams {
+ public:
+  CertErrorParams();
+  virtual ~CertErrorParams();
+
+  // Creates a representation of this parameter as a string, which may be
+  // used for pretty printing the error.
+  virtual std::string ToDebugString() const = 0;
+
+  // TODO(crbug.com/634443): Add methods to access the underlying
+  // structure, should they be needed for non-pretty-printing use cases.
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CertErrorParams);
+};
+
+// TODO(crbug.com/634443): Should the underlying parameter classes be exposed
+// so error consumers can access their data directly? (Without having to go
+// through the generic virtuals).
+
+// Creates a parameter object that holds a copy of |der1|, and names it |name1|
+// in debug string outputs.
+NET_EXPORT std::unique_ptr<CertErrorParams> CreateCertErrorParams1Der(
+    const char* name1,
+    const der::Input& der1);
+
+// Same as CreateCertErrorParams1Der() but has a second DER blob.
+NET_EXPORT std::unique_ptr<CertErrorParams> CreateCertErrorParams2Der(
+    const char* name1,
+    const der::Input& der1,
+    const char* name2,
+    const der::Input& der2);
+
+// Creates a parameter object that holds a single size_t value. |name| is used
+// when pretty-printing the parameters.
+NET_EXPORT std::unique_ptr<CertErrorParams> CreateCertErrorParamsSizeT(
+    const char* name,
+    size_t value);
+
+}  // namespace net
+
+#endif  // NET_CERT_INTERNAL_CERT_ERROR_PARAMS_H_