Merge pull request #8949 from ProofOfKeags/fn/req

[MICRO]: fn: Add new Req type to abstract the pattern of remote processing.

fn/req.go

@@ -0,0 +1,52 @@
+package fn
+
+// Req is a type to encapsulate RPC-like calls wherein we send some data
+// structure as a request, as well as a channel to receive the response on where
+// the remote goroutine will send the result.
+//
+// NOTE: This construct should only be used for request/response patterns for
+// which there is only a single response for the request.
+type Req[Input any, Output any] struct {
+	// Request is the data we are sending to the remote goroutine for
+	// processing.
+	Request Input
+
+	// response is the channel on which we will receive the result of the
+	// remote computation.
+	response chan<- Output
+}
+
+// Dispatch is a convenience method that lifts a function that transforms the
+// Input to the Output type into a full request handling cycle.
+func (r *Req[Input, Output]) Dispatch(handler func(Input) Output) {
+	r.Resolve(handler(r.Request))
+}
+
+// Resolve is a function that is used to send a value of the Output type back
+// to the requesting thread.
+func (r *Req[Input, Output]) Resolve(output Output) {
+	select {
+	case r.response <- output:
+	default:
+		// We do nothing here because the only situation in which this
+		// case will fire is if the request handler attempts to resolve
+		// a request more than once which is explicitly forbidden.
+	}
+}
+
+// NewReq is the base constructor of the Req type. It returns both the packaged
+// Req object as well as the receive side of the response channel that we will
+// listen on for the response.
+func NewReq[Input, Output any](input Input) (
+	Req[Input, Output], <-chan Output) {
+
+	// Always buffer the response channel so that the goroutine doing the
+	// processing job does not block if the original requesting routine
+	// takes an unreasonably long time to read the response.
+	responseChan := make(chan Output, 1)
+
+	return Req[Input, Output]{
+		Request:  input,
+		response: responseChan,
+	}, responseChan
+}