common: new json_util.h

With code to help factor out reading typed fields from JSON

src/common/json_util.h

@@ -0,0 +1,53 @@
+// Copyright (c) 2016, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once 
+
+#define GET_FIELD_FROM_JSON_RETURN_ON_ERROR(json, name, type, jtype, mandatory) \
+  type field_##name; \
+  bool field_##name##_found = false; \
+  (void)field_##name##_found; \
+  do if (json.HasMember(#name)) \
+  { \
+    if (json[#name].Is##jtype()) \
+    { \
+      field_##name = json[#name].Get##jtype(); \
+      field_##name##_found = true; \
+    } \
+    else \
+    { \
+      LOG_ERROR("Field " << #name << " found in JSON, but not " << #jtype); \
+      return false; \
+    } \
+  } \
+  else if (mandatory) \
+  { \
+    LOG_ERROR("Field " << #name << " not found in JSON"); \
+    return false; \
+  } while(0)
+