Module network::protocols::rpc

Implementation of the unary RPC protocol as per DiemNet wire protocol v1.

Design:

The unary RPC protocol is implemented here as two independent async completion queues: InboundRpcs and OutboundRpcs.

The InboundRpcs queue is responsible for handling inbound rpc requests off-the-wire, forwarding the request to the application layer, waiting for the application layer’s response, and then enqueuing the rpc response to-be written over-the-wire.

Likewise, the OutboundRpcs queue is responsible for handling outbound rpc requests from the application layer, enqueuing the request for writing onto the wire, waiting for a corresponding rpc response, and then notifying the requestor of the arrived response message.

Both InboundRpcs and OutboundRpcs are owned and driven by the Peer actor. This has a few implications. First, it means that each connection has its own pair of local rpc completion queues; the queues are not shared across connections. Second, the queues don’t do any IO work. They’re purely driven by the owning Peer actor, who calls handle_ methods on new NetworkMessage arrivals and polls for completed rpc requests. The queues also do not write to the wire directly; instead, they’re given a reference to the Peer actor’s write queue, which they can enqueue a new outbound NetworkMessage onto.

Timeouts:

Both inbound and outbound requests have mandatory timeouts. The tasks in the async completion queues are each wrapped in a timeout future, which causes the task to complete with an error if the task isn’t fulfilled before the deadline.

Limits:

We limit the number of pending inbound and outbound RPC tasks to ensure that resource usage is bounded.

Modules

• error
  Rpc protocol errors

Structs

• InboundRpcRequest
  A wrapper struct for an inbound rpc request and its associated context.
• InboundRpcs
  InboundRpcs handles new inbound rpc requests off the wire, notifies the PeerManager of the new request, and stores the pending response on a queue. If the response eventually completes, InboundRpc records some metrics and enqueues the response message onto the outbound write queue.
• OutboundRpcRequest
  A wrapper struct for an outbound rpc request and its associated context.
• OutboundRpcs
  OutboundRpcs handles new outbound rpc requests made from the application layer.