Replace a terribly expensive json parsing with a peek for the value.

We should reduce the amount of callbacks from the core in the first place, so
that we don't have to deduplicate this much here, but this already helps a
lot.

Change-Id: Idf4a3681ac0f47536e00c1d97152f3f8bb99894b

desktop/source/lib/init.cxx

@@ -446,10 +446,26 @@ bool lcl_isViewCallbackType(const int type)
 
 int lcl_getViewId(const std::string& payload)
 {
-    boost::property_tree::ptree aTree;
-    std::stringstream aStream(payload);
-    boost::property_tree::read_json(aStream, aTree);
-    return aTree.get<int>("viewId");
+    // this is a cheap way how to get the viewId from a JSON message; proper
+    // parsing is terribly expensive, and we just need the viewId here
+    size_t viewIdPos = payload.find("viewId");
+    if (viewIdPos == std::string::npos)
+        return 0;
+
+    size_t numberPos = payload.find(":", viewIdPos + 6);
+    if (numberPos == std::string::npos)
+        return 0;
+
+    for (++numberPos; numberPos < payload.length(); ++numberPos)
+    {
+        if (payload[numberPos] == ',' || payload[numberPos] == '}' || (payload[numberPos] >= '0' && payload[numberPos] <= '9'))
+            break;
+    }
+
+    if (numberPos < payload.length() && payload[numberPos] >= '0' && payload[numberPos] <= '9')
+        return std::stoi(payload.substr(numberPos));
+
+    return 0;
 }
 
 }  // end anonymous namespace