You’re defining a handler for actions that map to REST over http. POST and GET generally refer to update and query over an entity. There’s absolutely no reason you can’t just define a handler for generic versions of these CRUD operations that can be used in both contexts. The way I generally do this is by introducing the concept of a ‘route’ to the real-time transport, and mapping those back to the same CRUD handlers.
You have a session, you can impose the same ACL, etc.
+---------------------------------+
| |
| BROWSER |
| |
+--+--^-------------------+---^---+
| | | |
| | | |
+--v--+---+ +--v---+---+
| | | |
| HTTP | | SOCKET.IO|
+--+---^--+ +--+---^---+
| | | |
+--v---+------------------v---+---+
| |
| ROUTING/PUBSUB |
+-+--^-------+--^-------+--^------+
| | | | | |
+-v--+--+ +-v--+--+ +-v--+-+
| | | | | |
| USERS | | ITEMS | |ETC |
+-------+ +-------+ +------+
ENTITY CRUD HANDLERS