fixup! Implement typed request data using generics

handler.go

@@ -3,6 +3,7 @@ package e5e
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 )
 
 // A Handler responds to a request.
@@ -39,12 +40,11 @@ func (h handlerFunc[T, TContext]) Handle(ctx context.Context, evt Request[T, TCo
 // invoked with a Request[T]) in such a way as to make it non-generic so that it can
 // be used in other non-generic code like [Mux].
 type handlerFactory interface {
-	// UnmarshalJob unmarshals the request to the internal state of the factory and returns any errors.
-	UnmarshalJob(payload []byte) error
-
-	// Execute the handler with the internal request state.
-	// Only called after UnmarshalJob.
-	Execute(ctx context.Context) (*Result, error)
+	// Execute the handler with payload, which should be a deserializable JSON object.
+	// Any errors that occur due to deserialization or otherwise are returned.
+	//
+	// It is safe to call this method from multiple goroutines if the underlying [Handler] is.
+	Execute(ctx context.Context, payload []byte) (*Result, error)
 }
 
 type typedHandlerFactory[T, TContext Data] struct {
@@ -56,6 +56,11 @@ func (t *typedHandlerFactory[T, TContext]) UnmarshalJob(data []byte) error {
 	return json.Unmarshal(data, &t.request)
 }
 
-func (t *typedHandlerFactory[T, TContext]) Execute(ctx context.Context) (*Result, error) {
+func (t *typedHandlerFactory[T, TContext]) Execute(ctx context.Context, payload []byte) (*Result, error) {
+	var request Request[T, TContext]
+	if err := json.Unmarshal(payload, &request); err != nil {
+		return nil, fmt.Errorf("unmarshaling JSON failed: %w", err)
+	}
+
 	return t.h.Handle(ctx, t.request)
 }

mux.go

@@ -175,11 +175,7 @@ func (m *Mux) execute(ctx context.Context, payload []byte) (string, error) {
 	}
 
 	factory := m.handlers[m.Options.Entrypoint]
-	if err := factory.UnmarshalJob(payload); err != nil {
-		return "", fmt.Errorf("unmarshalling request into request: %w", err)
-	}
-
-	res, err := factory.Execute(ctx)
+	res, err := factory.Execute(ctx, payload)
 	if err != nil {
 		return "", fmt.Errorf("handler execution: %w", err)
 	}