feat: add generics to the endpoint layer

Signed-off-by: Mark Sagi-Kazar <[email protected]>

Author: sagikazarmark

endpoint/endpoint.go

@@ -6,20 +6,20 @@ import (
 
 // Endpoint is the fundamental building block of servers and clients.
 // It represents a single RPC method.
-type Endpoint func(ctx context.Context, request interface{}) (response interface{}, err error)
+type Endpoint[Req any, Resp any] func(ctx context.Context, request Req) (response Resp, err error)
 
 // Nop is an endpoint that does nothing and returns a nil error.
 // Useful for tests.
 func Nop(context.Context, interface{}) (interface{}, error) { return struct{}{}, nil }
 
 // Middleware is a chainable behavior modifier for endpoints.
-type Middleware func(Endpoint) Endpoint
+type Middleware[Req any, Resp any] func(Endpoint[Req, Resp]) Endpoint[Req, Resp]
 
 // Chain is a helper function for composing middlewares. Requests will
 // traverse them in the order they're declared. That is, the first middleware
 // is treated as the outermost middleware.
-func Chain(outer Middleware, others ...Middleware) Middleware {
-	return func(next Endpoint) Endpoint {
+func Chain[Req any, Resp any](outer Middleware[Req, Resp], others ...Middleware[Req, Resp]) Middleware[Req, Resp] {
+	return func(next Endpoint[Req, Resp]) Endpoint[Req, Resp] {
 		for i := len(others) - 1; i >= 0; i-- { // reverse
 			next = others[i](next)
 		}

endpoint/endpoint_example_test.go

@@ -9,9 +9,9 @@ import (
 
 func ExampleChain() {
 	e := endpoint.Chain(
-		annotate("first"),
-		annotate("second"),
-		annotate("third"),
+		annotate[any, any]("first"),
+		annotate[any, any]("second"),
+		annotate[any, any]("third"),
 	)(myEndpoint)
 
 	if _, err := e(ctx, req); err != nil {
@@ -33,13 +33,13 @@ var (
 	req = struct{}{}
 )
 
-func annotate(s string) endpoint.Middleware {
-	return func(next endpoint.Endpoint) endpoint.Endpoint {
-		return func(ctx context.Context, request interface{}) (interface{}, error) {
+func annotate[Req any, Resp any](s string) endpoint.Middleware[Req, Resp] {
+	return func(next endpoint.Endpoint[Req, Resp]) endpoint.Endpoint[Req, Resp] {
+		return endpoint.Endpoint[Req, Resp](func(ctx context.Context, request Req) (Resp, error) {
 			fmt.Println(s, "pre")
 			defer fmt.Println(s, "post")
 			return next(ctx, request)
-		}
+		})
 	}
 }