NGSIv2 rendering improvements (simplification, unification and performance)

CHANGES_NEXT_RELEASE

@@ -1,5 +1,7 @@
 - Fix: GET /v2/subscriptions and GET /v2/subscriptions/{id} crashes for permanent subscriptions created before version 1.13.0 (#3256)
 - Hardening: Mongo driver now compiled using --use-sasl-client --ssl to enable proper DB authentication mechanisms
 - Fix: correct error payload using errorCode (previously orionError was used) in POST /v1/queryContext and POST /v1/updateContext in some cases
+- Fix: bug in metadata compound value rendering in NGSIv2 (sometimes "toplevel" key was wrongly inserted in the resulting JSON object)
 - Hardening: modification of the URL parsing mechanism, making it more efficient, and the source code easier to follow (#3109, step 1)
+- Hardening: refactor NGSIv2 rendering code (throughput increase up to 33%/365% in entities/subscriptions rendering intensive scenarios) (#1298)
 - Fix: Missing or empty metadata values were not allowed in NGSIv2 create/update operations (#3121)

src/lib/apiTypesV2/Attribute.cpp

@@ -29,6 +29,7 @@
 #include "common/errorMessages.h"
 #include "common/RenderFormat.h"
 #include "common/string.h"
+#include "common/JsonHelper.h"
 #include "ngsi10/QueryContextResponse.h"
 #include "apiTypesV2/Attribute.h"
 
@@ -48,8 +49,7 @@ std::string Attribute::render
   HttpStatusCode*     scP,                 // out parameter (pass-through)
   bool                keyValues,           // in parameter
   const std::string&  metadataList,        // in parameter
-  RequestType         requestType,         // in parameter
-  bool                comma                // in parameter
+  RequestType         requestType          // in parameter
 )
 {
   RenderFormat  renderFormat = (keyValues == true)? NGSI_V2_KEYVALUES : NGSI_V2_NORMALIZED;
@@ -76,18 +76,16 @@ std::string Attribute::render
         stringSplit(metadataList, ',', metadataFilter);
       }
 
-      out = "{";
-
-      // First parameter (isLastElement) is 'true' as it is the last and only element
-      out += pcontextAttribute->toJson(true, renderFormat, metadataFilter, requestType);
-
-      out += "}";
-    }
-
-
-    if (comma)
-    {
-      out += ",";
+      if (renderFormat == NGSI_V2_KEYVALUES)
+      {
+        JsonHelper jh;
+        jh.addRaw(pcontextAttribute->name, pcontextAttribute->toJsonValue());
+        out = jh.str();
+      }
+      else  // NGSI_V2_NORMALIZED
+      {
+        out = pcontextAttribute->toJson(metadataFilter);
+      }
     }
 
     return out;

src/lib/apiTypesV2/Attribute.h

@@ -61,8 +61,7 @@ class Attribute
                       HttpStatusCode*     scP,
                       bool                keyValues,
                       const std::string&  metadataList,
-                      RequestType         requestType,
-                      bool                comma = false);
+                      RequestType         requestType);
   void         fill(QueryContextResponse* qcrsP, std::string attrName);
 };