Read MXL flow labels from top-level metadata

MxlSdkFeed.cpp

@@ -59,44 +59,98 @@ namespace
         const char* json,
         const char* key)
     {
-        std::string searchKey = std::string("\"") + key + "\"";
-        const char* pos = std::strstr(json, searchKey.c_str());
-        if (!pos)
+        int depth = 0;
+
+        for (const char* p = json; *p != '\0'; ++p)
         {
-            return "";
-        }
-
-        pos += searchKey.size();
-
-        while (*pos == ' ' || *pos == '\t' || *pos == '\n' ||
-               *pos == '\r' || *pos == ':')
-        {
-            pos++;
-        }
-
-        if (*pos != '"')
-        {
-            return "";
-        }
-
-        ++pos;
-        const char* valueBegin = pos;
-        bool escaped = false;
-
-        while (*pos != '\0')
-        {
-            if (!escaped && *pos == '"')
+            if (*p == '"')
             {
-                return unescapeJsonString(valueBegin, pos);
+                const char* keyBegin = p + 1;
+                const char* keyEnd = keyBegin;
+                bool keyEscaped = false;
+
+                while (*keyEnd != '\0')
+                {
+                    if (!keyEscaped && *keyEnd == '"')
+                    {
+                        break;
+                    }
+
+                    keyEscaped = !keyEscaped && *keyEnd == '\\';
+                    if (*keyEnd != '\\')
+                    {
+                        keyEscaped = false;
+                    }
+
+                    ++keyEnd;
+                }
+
+                if (*keyEnd == '\0')
+                {
+                    return "";
+                }
+
+                const char* value = keyEnd + 1;
+                while (*value == ' ' || *value == '\t' ||
+                       *value == '\n' || *value == '\r')
+                {
+                    ++value;
+                }
+
+                if (depth == 1 &&
+                    *value == ':' &&
+                    unescapeJsonString(keyBegin, keyEnd) == key)
+                {
+                    ++value;
+                    while (*value == ' ' || *value == '\t' ||
+                           *value == '\n' || *value == '\r')
+                    {
+                        ++value;
+                    }
+
+                    if (*value != '"')
+                    {
+                        return "";
+                    }
+
+                    ++value;
+                    const char* valueBegin = value;
+                    bool valueEscaped = false;
+
+                    while (*value != '\0')
+                    {
+                        if (!valueEscaped && *value == '"')
+                        {
+                            return unescapeJsonString(
+                                valueBegin,
+                                value);
+                        }
+
+                        valueEscaped =
+                            !valueEscaped && *value == '\\';
+                        if (*value != '\\')
+                        {
+                            valueEscaped = false;
+                        }
+
+                        ++value;
+                    }
+
+                    return "";
+                }
+
+                p = keyEnd;
+                continue;
             }
 
-            escaped = !escaped && *pos == '\\';
-            if (*pos != '\\')
+            if (*p == '{' || *p == '[')
             {
-                escaped = false;
+                ++depth;
+            }
+            else if ((*p == '}' || *p == ']') && depth > 0)
+            {
+                --depth;
             }
-
-            ++pos;
         }
 
         return "";