Validate RPC protocol frames with Schema

ts/EFFECT_NATIVE_REWRITE_AUDIT.md

@@ -1124,7 +1124,8 @@ Notes:
 - Remaining:
   - `ts/packages/flow/src/gateway/rpc-protocol.ts` remains a Fastify socket
     compatibility bridge, not a direct replacement target for Effect RPC
-    server layers yet.
+    server layers yet. Local parser validation and collection cleanup inside
+    that bridge remain valid migration targets.
 - Verification:
   - `bun run --cwd ts/packages/flow build`
   - `bun run --cwd ts/packages/client build`
@@ -2073,6 +2074,31 @@ Notes:
   - `cd ts && bun run lint`
   - `git diff --check`
 
+### 2026-06-04: Gateway RPC Protocol Decode Slice
+
+- Status: migrated and package-verified.
+- Completed:
+  - `ts/packages/flow/src/gateway/rpc-protocol.ts` no longer casts
+    `parser.decode(data)` to `ReadonlyArray<RpcMessage.FromClientEncoded>`.
+  - The socket protocol now validates parser output through a local Schema for
+    client-to-server `Request`, `Ack`, `Interrupt`, `Ping`, and `Eof`
+    envelopes before calling the server protocol write hook.
+  - Invalid client frames and parser failures now map to a tagged
+    `RpcProtocolDecodeError` and are written back as encoded RPC defects.
+  - The existing server-response defect encoding no longer uses a non-null
+    assertion on `parser.encode`.
+  - `ts/packages/flow/src/__tests__/gateway-rpc-protocol.test.ts` covers valid
+    request header prepending, control-frame forwarding, and rejection of
+    server response envelopes received from a client socket.
+- Verification:
+  - `cd ts/packages/flow && bunx --bun vitest run src/__tests__/gateway-rpc-protocol.test.ts`
+  - `cd ts/packages/flow && bunx --bun vitest run`
+  - `cd ts && bun run check:tsgo`
+  - `cd ts && bun run build`
+  - `cd ts && bun run test`
+  - `cd ts && bun run lint`
+  - `git diff --check`
+
 ## Subagent Findings To Preserve
 
 - MCP/workbench:
@@ -2160,9 +2186,11 @@ Notes:
     injected pubsub backends are not closed by the manager, one-shot producers
     are acquire/use/release bracketed, and serialization failures are typed
     Effect errors.
-  - Do not make `gateway/rpc-protocol.ts` the next cleanup target: it is a
+  - `gateway/rpc-protocol.ts` remains a Fastify socket compatibility bridge
-    Fastify socket compatibility bridge while the public Effect RPC server
+    while the public Effect RPC server layers require SocketServer or Effect
-    layers require SocketServer or Effect HTTP routing.
+    HTTP routing. The parser decode assertion is complete through Schema
+    validation; future local cleanups should focus on its connection
+    collections rather than replacing the whole bridge.
   - WebSocket adapter host fallbacks now use `Result.try` and tagged adapter
     errors while preserving sync exports.
 - RAG/providers/storage:
@@ -2470,9 +2498,10 @@ Do not flag these as rewrite blockers without additional proof:
   `start()` now initializes scoped Effect consumers and returns after startup,
   while `stop()` closes the native consumer scope.
 - `ts/packages/flow/src/gateway/rpc-protocol.ts` is a Fastify socket
-  compatibility bridge. Do not flag its internal connection maps/sets as a
+  compatibility bridge. Do not treat it as a wholesale server-layer replacement
-  standalone replacement target until the gateway is ready to move onto Effect
+  target until the gateway is ready to move onto Effect SocketServer or Effect
-  SocketServer or Effect HTTP routing.
+  HTTP routing; local parser validation and Effect collection cleanup inside
+  that bridge are still valid.
 
 ## Acceptance For Final Loop Completion
 

ts/packages/flow/src/__tests__/gateway-rpc-protocol.test.ts

@@ -0,0 +1,148 @@
+import { Effect, Queue } from "effect";
+import * as O from "effect/Option";
+import * as RpcMessage from "effect/unstable/rpc/RpcMessage";
+import * as RpcSerialization from "effect/unstable/rpc/RpcSerialization";
+import * as Socket from "effect/unstable/socket/Socket";
+import { describe, expect, it } from "vitest";
+import { makeSocketRpcProtocol } from "../gateway/rpc-protocol.js";
+
+interface ReceivedMessage {
+  readonly clientId: number;
+  readonly message: RpcMessage.FromClientEncoded;
+}
+
+interface ProtocolRunResult {
+  readonly messages: ReadonlyArray<ReceivedMessage>;
+  readonly writes: ReadonlyArray<string | Uint8Array | CloseEvent>;
+}
+
+const jsonFrame = (value: unknown): string => `${JSON.stringify(value)}\n`;
+
+const optionToArray = <A>(value: O.Option<A>): Array<A> =>
+  O.match(value, {
+    onNone: () => [],
+    onSome: (item) => [item],
+  });
+
+const runProtocolFrames = (
+  frames: ReadonlyArray<string | Uint8Array>,
+  headers?: ReadonlyArray<[string, string]>,
+): Promise<ProtocolRunResult> =>
+  Effect.runPromise(
+    Effect.scoped(
+      Effect.gen(function* () {
+        const received = yield* Queue.unbounded<ReceivedMessage>();
+        const writes: Array<string | Uint8Array | CloseEvent> = [];
+        const { onSocket, protocol } = yield* makeSocketRpcProtocol;
+
+        yield* protocol.run((clientId, message) =>
+          Queue.offer(received, { clientId, message }).pipe(Effect.asVoid)
+        ).pipe(Effect.forkScoped);
+        yield* Effect.yieldNow;
+
+        const socket = Socket.make({
+          writer: Effect.succeed((chunk) =>
+            Effect.sync(() => {
+              writes.push(chunk);
+            })
+          ),
+          runRaw: (handler) =>
+            Effect.forEach(frames, (frame) =>
+              Effect.suspend(() => {
+                const result = handler(frame);
+                return result === undefined ? Effect.void : result;
+              }), { discard: true }),
+        });
+
+        yield* onSocket(socket, headers);
+        yield* Effect.yieldNow;
+
+        const first = yield* Queue.poll(received);
+        const second = yield* Queue.poll(received);
+        const third = yield* Queue.poll(received);
+
+        return {
+          messages: [
+            ...optionToArray(first),
+            ...optionToArray(second),
+            ...optionToArray(third),
+          ],
+          writes,
+        };
+      }).pipe(
+        Effect.provideService(RpcSerialization.RpcSerialization, RpcSerialization.ndjson),
+      ),
+    ),
+  );
+
+describe("gateway RPC socket protocol", () => {
+  it("validates client request frames and prepends websocket headers", async () => {
+    const result = await runProtocolFrames([
+      jsonFrame({
+        _tag: "Request",
+        id: "1",
+        tag: "Dispatch",
+        payload: {
+          scope: "global",
+          service: "config",
+          request: {},
+        },
+        headers: [["rpc", "client"]],
+      }),
+    ], [["socket", "header"]]);
+
+    expect(result.writes).toEqual([]);
+    expect(result.messages).toHaveLength(1);
+
+    const received = result.messages[0];
+    expect(received).toBeDefined();
+    if (received === undefined) return;
+
+    expect(received.clientId).toBe(0);
+    expect(received.message._tag).toBe("Request");
+    if (received.message._tag !== "Request") return;
+
+    expect(received.message.id).toBe("1");
+    expect(received.message.tag).toBe("Dispatch");
+    expect(received.message.headers).toEqual([
+      ["socket", "header"],
+      ["rpc", "client"],
+    ]);
+  });
+
+  it("validates client control frames without mutating them", async () => {
+    const result = await runProtocolFrames([
+      jsonFrame({
+        _tag: "Ping",
+      }),
+      jsonFrame({
+        _tag: "Ack",
+        requestId: "1",
+      }),
+    ]);
+
+    expect(result.writes).toEqual([]);
+    expect(result.messages.map(({ message }) => message._tag)).toEqual(["Ping", "Ack"]);
+    expect(result.messages[1]?.message).toEqual({
+      _tag: "Ack",
+      requestId: "1",
+    });
+  });
+
+  it("rejects server response envelopes received from the socket", async () => {
+    const result = await runProtocolFrames([
+      jsonFrame({
+        _tag: "Exit",
+        requestId: "1",
+        exit: {
+          _tag: "Success",
+          value: { ok: true },
+        },
+      }),
+    ]);
+
+    expect(result.messages).toEqual([]);
+    expect(result.writes).toHaveLength(1);
+    expect(String(result.writes[0])).toContain("\"_tag\":\"Defect\"");
+  });
+});

ts/packages/flow/src/gateway/rpc-protocol.ts

@@ -1,9 +1,41 @@
 import { Effect, Queue, Scope } from "effect";
+import * as S from "effect/Schema";
 import * as RpcMessage from "effect/unstable/rpc/RpcMessage";
 import * as RpcSerialization from "effect/unstable/rpc/RpcSerialization";
 import * as RpcServer from "effect/unstable/rpc/RpcServer";
 import * as Socket from "effect/unstable/socket/Socket";
 
+export class RpcProtocolDecodeError extends S.TaggedErrorClass<RpcProtocolDecodeError>()(
+  "RpcProtocolDecodeError",
+  {
+    message: S.String,
+    cause: S.Unknown,
+  },
+) {}
+
+const HeaderSchema = S.mutable(S.Tuple([S.String, S.String]));
+const FromClientEncodedSchema = S.Union([
+  S.TaggedStruct("Request", {
+    id: S.String,
+    tag: S.String,
+    payload: S.Unknown,
+    headers: S.Array(HeaderSchema),
+    traceId: S.optionalKey(S.String),
+    spanId: S.optionalKey(S.String),
+    sampled: S.optionalKey(S.Boolean),
+  }),
+  S.TaggedStruct("Ack", {
+    requestId: S.String,
+  }),
+  S.TaggedStruct("Interrupt", {
+    requestId: S.String,
+  }),
+  S.TaggedStruct("Ping", {}),
+  S.TaggedStruct("Eof", {}),
+]).pipe(S.toTaggedUnion("_tag"));
+const FromClientEncodedMessagesSchema = S.Array(FromClientEncodedSchema);
+const decodeFromClientMessages = S.decodeUnknownEffect(FromClientEncodedMessagesSchema);
+
 export const makeSocketRpcProtocol = Effect.gen(function* () {
   const serialization = yield* RpcSerialization.RpcSerialization;
   const disconnects = yield* Queue.make<number>();
@@ -34,18 +66,17 @@ export const makeSocketRpcProtocol = Effect.gen(function* () {
     });
 
     const writeRaw = yield* socket.writer;
-    const encodeDefect = (cause: unknown) =>
+    const writeDefect = (cause: unknown) =>
-      Effect.sync(() => parser.encode(RpcMessage.ResponseDefectEncoded(cause))!);
+      Effect.sync(() => parser.encode(RpcMessage.ResponseDefectEncoded(cause))).pipe(
+        Effect.flatMap((encoded) => encoded === undefined ? Effect.void : writeRaw(encoded)),
+      );
     const write = (response: RpcMessage.FromServerEncoded) =>
       Effect.sync(() => parser.encode(response)).pipe(
         Effect.flatMap((encoded) =>
           encoded === undefined ? Effect.void : Effect.orDie(writeRaw(encoded)),
         ),
         Effect.catchDefect((cause: unknown) =>
-          encodeDefect(cause).pipe(
+          writeDefect(cause).pipe(Effect.orDie),
-            Effect.flatMap((encoded) => Effect.orDie(writeRaw(encoded))),
-            Effect.orDie,
-          ),
         ),
       );
 
@@ -53,7 +84,24 @@ export const makeSocketRpcProtocol = Effect.gen(function* () {
     clientIds.add(clientId);
 
     yield* socket.runRaw((data) =>
-      Effect.sync(() => parser.decode(data) as ReadonlyArray<RpcMessage.FromClientEncoded>).pipe(
+      Effect.try({
+        try: () => parser.decode(data),
+        catch: (cause) =>
+          RpcProtocolDecodeError.make({
+            message: "Failed to decode RPC socket frame",
+            cause,
+          }),
+      }).pipe(
+        Effect.flatMap((raw) =>
+          decodeFromClientMessages(raw).pipe(
+            Effect.mapError((cause) =>
+              RpcProtocolDecodeError.make({
+                message: "RPC socket frame did not contain valid client messages",
+                cause,
+              })
+            ),
+          )
+        ),
         Effect.flatMap((decoded) =>
           Effect.forEach(decoded, (message) => {
             if (message._tag === "Request" && headers !== undefined) {
@@ -65,11 +113,8 @@ export const makeSocketRpcProtocol = Effect.gen(function* () {
             return writeRequest(clientId, message);
           }, { discard: true }),
         ),
-        Effect.catchDefect((cause: unknown) =>
+        Effect.catch((cause) => writeDefect(cause)),
-          encodeDefect(cause).pipe(
+        Effect.catchDefect((cause: unknown) => writeDefect(cause)),
-            Effect.flatMap((encoded) => writeRaw(encoded)),
-          ),
-        ),
       )
     ).pipe(
       Effect.catchReason("SocketError", "SocketCloseError", () => Effect.void),