Generic query protocol

The Query protocol is defined here:

• https://github.com/input-output-hk/marlowe-cardano/blob/main/marlowe-protocols/src/Language/Network/Protocol/Query/Types.hs

The Query protocol allows clients to send queries to a server. It is parameterized by the type of query that the server supports.

Protocol states

Protocol state	Agency	Parameter	Description
1. Req	Client		The client is preparing a request to send.
2. Res a	Server		The server handling a request from the client.
		a	The type of the response.
3. Done	Nobody		The terminal state.

Query Protocol messages

Message	Begin state	End state	Parameter	Description
1. Request req	Req	Res a		Sends a request to the server.
			ctx	An optional Open Telemetry span context originating from the sender from which child spans on the server should descend.
			req	A request tree with a result of type a.
2. Respond a	Res a	Req		Sends a response to the client.
			a	The response type.
3. Done	Req	Done		Terminates the session.
			ctx	An optional Open Telemetry span context originating from the sender from which child spans on the server should descend.

Request trees

The RequestTree structure allows multiple requests of a given request type to be sent in parallel, and combines the associated response types for those requests. For a request type req, the following request tree types are supported:

Request	Parameter	Result	Description
Leaf req		a	A single request at the leaf of the tree with result type a.
	req		A request with result type a.
Bin tree1 tree2		(a, b)	Two request sub-trees with a combined result type (a, b).
	tree1		A request tree with result type a.
	tree2		A request tree with result type b.