src/Layers/trpc/createTRCPErrorMapper.ts

@@ -1,12 +1,7 @@
 import { Effect, type Cause } from "effect"
-import { ImportError } from "../../ImportError"
+import { importTRPCServer } from "./importTRPCServer"
 
 
-const importTRPCServer = Effect.tryPromise({
-    try: () => import("@trpc/server"),
-    catch: cause => new ImportError({ path: "@trpc/server", cause }),
-})
-
 export const createTRCPErrorMapper = importTRPCServer.pipe(Effect.map(({ TRPCError }) =>
     <A, E, R>(effect: Effect.Effect<A, E, R>) => Effect.sandbox(effect).pipe(
         Effect.catchTags({

src/Layers/trpc/importTRPCServer.ts

@@ -0,0 +1,8 @@
+import { Effect } from "effect"
+import { ImportError } from "../../ImportError"
+
+
+export const importTRPCServer = Effect.tryPromise({
+    try: () => import("@trpc/server"),
+    catch: cause => new ImportError({ path: "@trpc/server", cause }),
+})

src/Layers/trpc/index.ts

@@ -1,3 +1,4 @@
+export * from "./middlewares"
 export * as TRPCBuilder from "./TRPCBuilder"
 export * as TRPCContext from "./TRPCContext"
 export * as TRPCContextCreator from "./TRPCContextCreator"

src/Layers/trpc/middlewares.ts

@@ -0,0 +1,24 @@
+import { Effect, Match } from "effect"
+import type { TRPCContextTransaction } from "./TRPCContext"
+import { importTRPCServer } from "./importTRPCServer"
+
+
+export const ExpressOnly = importTRPCServer.pipe(Effect.map(({
+    experimental_standaloneMiddleware,
+    TRPCError,
+}) => experimental_standaloneMiddleware<{
+    ctx: { readonly transaction: TRPCContextTransaction }
+}>().create(opts =>
+    Match.value(opts.ctx.transaction).pipe(
+        Match.tag("Express", transaction =>
+            opts.next({ ctx: { transaction } })
+        ),
+
+        Match.orElse(() => {
+            throw new TRPCError({
+                code: "BAD_REQUEST",
+                message: "Only Express backend is supported by this procedure",
+            })
+        }),
+    )
+)))