Extend ODL RESTCONF to support X-Path expressions # Controller will determine if mounted NETCONF server supports X-Path expressions

1. 1. If so, controller will convert JSON to XML and make NETCONF request southbound with X-Path expressions
   2. If not, controller can:
      1. Retrieve entire subtree and perform filtering
      2. Other option is to decompose X-Path expressions and attempt to make an optimized series of calls to NETCONF client to minimize amount of data transferred between NETCONF server and controller

In RFC 8040 the depth and field query params are used to instruct a RESTCONF server to filter responses. This does nothing to limit the quantity of data served by a NETCONF server, and therefore provides limited performance optimization.

Ideally, RESTCONF would support full Xpath expressions. Short of that, passing the field parameter on to the NETCONF server is essential for some deployments. This feature would have the controller query the NETCONF server to discover if it supports Xpath - if yes, transform ‘field’ into an Xpath, if not, transform it into a subtree expression.