refactor: Tweak asLegacyMiddleware and docs

Author: rekmarks

packages/json-rpc-engine/README.md

@@ -81,7 +81,13 @@ await server.handle(notification);
 
 ### Legacy compatibility
 
-Use the `asLegacyMiddleware` function to use a `JsonRpcEngineV2` or V2 middleware as middleware in a legacy `JsonRpcEngine`:
+Use the `asLegacyMiddleware` function to use a `JsonRpcEngineV2` or V2 middleware as middleware in a legacy `JsonRpcEngine`.
+
+#### Context propagation
+
+In keeping with the conventions of the legacy engine, non-JSON-RPC string properties of the `context` will be
+copied over to the request once the V2 engine is done with the request. _Note that **only `string` keys** of
+the `context` will be copied over._
 
 #### Converting a V2 engine
 
@@ -105,8 +111,6 @@ legacyEngine.push(asLegacyMiddleware(v2Engine));
 
 #### Converting V2 middleware
 
-You can also directly convert one or more V2 middlewares without creating an engine:
-
 ```ts
 import {
   asLegacyMiddleware,
@@ -131,10 +135,6 @@ const legacyEngine2 = new JsonRpcEngine();
 legacyEngine2.push(asLegacyMiddleware(middleware1, middleware2));
 ```
 
-In keeping with the conventions of the legacy engine, non-JSON-RPC string properties of the `context` will be
-copied over to the request once the V2 engine is done with the request. _Note that **only `string` keys** of
-the `context` will be copied over._
-
 ### Middleware
 
 Middleware functions can be sync or async.

packages/json-rpc-engine/src/README.md

@@ -26,6 +26,12 @@ engine.push(function (req, res, next, end) {
 Use the `asV2Middleware` function to use a `JsonRpcEngine` or legacy middleware as middleware in a
 `JsonRpcEngineV2`:
 
+#### Context propagation
+
+Non-JSON-RPC string properties on the request object will be copied over to the V2 engine's `context` object
+once the legacy engine is done with the request, _unless_ they already exist on the `context`, in which case
+they will be ignored.
+
 #### Converting a legacy engine
 
 ```ts
@@ -67,12 +73,6 @@ const v2Engine2 = JsonRpcEngineV2.create({
 });
 ```
 
-#### Context propagation
-
-Non-JSON-RPC string properties on the request object will be copied over to the V2 engine's `context` object
-once the legacy engine is done with the request, _unless_ they already exist on the `context`, in which case
-they will be ignored.
-
 ### Middleware
 
 Requests are handled asynchronously, stepping down the stack until complete.

packages/json-rpc-engine/src/asV2Middleware.ts

@@ -22,7 +22,7 @@ import {
   unserializeError,
 } from './v2/compatibility-utils';
 import type {
-  // JsonRpcEngineV2 is used in docs.
+  // Used in docs.
   // eslint-disable-next-line @typescript-eslint/no-unused-vars
   JsonRpcEngineV2,
   JsonRpcMiddleware,
@@ -67,8 +67,7 @@ export function asV2Middleware<
   engineOrMiddleware: JsonRpcEngine | LegacyMiddleware<JsonRpcParams, Json>,
   ...rest: LegacyMiddleware<JsonRpcParams, Json>[]
 ): JsonRpcMiddleware<Request> {
-  // Determine the legacy middleware function from input(s)
-  const middleware =
+  const legacyMiddleware =
     typeof engineOrMiddleware === 'function'
       ? mergeMiddleware([engineOrMiddleware, ...rest])
       : engineOrMiddleware.asMiddleware();
@@ -98,7 +97,7 @@ export function asV2Middleware<
       const legacyNext = ((cb: JsonRpcEngineEndCallback) =>
         cb(end)) as JsonRpcEngineNextCallback;
 
-      middleware(req, res, legacyNext, end);
+      legacyMiddleware(req, res, legacyNext, end);
     });
     propagateToContext(req, context);
 

packages/json-rpc-engine/src/v2/asLegacyMiddleware.ts

@@ -6,12 +6,8 @@ import {
   makeContext,
   propagateToRequest,
 } from './compatibility-utils';
-import type {
-  JsonRpcEngineV2,
-  JsonRpcMiddleware as V2Middleware,
-  ResultConstraint,
-} from './JsonRpcEngineV2';
-import { JsonRpcEngineV2 as EngineV2 } from './JsonRpcEngineV2';
+import type { JsonRpcMiddleware, ResultConstraint } from './JsonRpcEngineV2';
+import { JsonRpcEngineV2 } from './JsonRpcEngineV2';
 import { createAsyncMiddleware } from '..';
 import type { JsonRpcMiddleware as LegacyMiddleware } from '..';
 
@@ -38,7 +34,7 @@ export function asLegacyMiddleware<
   Params extends JsonRpcParams,
   Request extends JsonRpcRequest<Params>,
 >(
-  ...middleware: V2Middleware<Request, ResultConstraint<Request>>[]
+  ...middleware: JsonRpcMiddleware<Request, ResultConstraint<Request>>[]
 ): LegacyMiddleware<Params, ResultConstraint<Request>>;
 
 /**
@@ -54,23 +50,22 @@ export function asLegacyMiddleware<
 >(
   engineOrMiddleware:
     | JsonRpcEngineV2<Request>
-    | V2Middleware<Request, ResultConstraint<Request>>,
-  ...rest: V2Middleware<Request, ResultConstraint<Request>>[]
+    | JsonRpcMiddleware<Request, ResultConstraint<Request>>,
+  ...rest: JsonRpcMiddleware<Request, ResultConstraint<Request>>[]
 ): LegacyMiddleware<Params, ResultConstraint<Request>> {
-  // Determine the V2 middleware function from input(s)
-  const middleware =
+  const JsonRpcMiddleware =
     typeof engineOrMiddleware === 'function'
-      ? // eslint-disable-next-line @typescript-eslint/no-explicit-any
-        EngineV2.create<any>({
+      ? JsonRpcEngineV2.create({
           middleware: [engineOrMiddleware, ...rest],
         }).asMiddleware()
       : engineOrMiddleware.asMiddleware();
+
   return createAsyncMiddleware(async (req, res, next) => {
     const request = fromLegacyRequest(req as Request);
     const context = makeContext(req);
     let modifiedRequest: Request | undefined;
 
-    const result = await middleware({
+    const result = await JsonRpcMiddleware({
       request,
       context,
       next: (finalRequest) => {