RPC supports middleware responses

[yusukebe]

What is the feature you are proposing?

Currently, the RPC mode does not support middleware response. The client can't handle the response from the middleware:

I'm not 100% sure, but perhaps we can implement it by modifying types.ts:

diff --git a/src/types.ts b/src/types.ts
index 3c7a53d..5e93fc1 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -190,13 +190,22 @@ export interface HandlerInterface<
     I3 extends Input = I & I2,
     E2 extends Env = E,
     E3 extends Env = E,
-    E4 extends Env = IntersectNonAnyTypes<[E, E2, E3]>
+    E4 extends Env = IntersectNonAnyTypes<[E, E2, E3]>,
+    // Response from Middleware
+    RM1 extends HandlerResponse<any> = any,
+    RM2 extends HandlerResponse<any> = any
   >(
     path: P,
-    ...handlers: [H<E2, MergedPath, I>, H<E3, MergedPath, I2>, H<E4, MergedPath, I3, R>]
+    ...handlers: [H<E2, MergedPath, I, RM1>, H<E3, MergedPath, I2, RM2>, H<E4, MergedPath, I3, R>]
   ): Hono<
     IntersectNonAnyTypes<[E, E2, E3, E4]>,
-    S & ToSchema<M, MergePath<BasePath, P>, I3, MergeTypedResponse<R>>,
+    S &
+      ToSchema<
+        M,
+        MergePath<BasePath, P>,
+        I3,
+        MergeTypedResponse<R> | MergeTypedResponse<RM1> | MergeTypedResponse<RM2>
+      >,
     BasePath
   >

It will be worth implementing, though the code will be very long.

[yusukebe]

Hey @kosei28 What do you think about it?

[kosei28]

This is exactly what I wanted!

However, merging this may cause type errors in many projects currently using Hono's RPC, so I think this should be considered carefully.

[yusukebe]

@kosei28 Thanks for the comment!

However, merging this may cause type errors in many projects currently using Hono's RPC, so I think this should be considered carefully.

Exactly. We don't have to hurry!