URL pathname assignment fails for custom scheme (opaque path), causing RPC path to be lost

[dmitriyzhirma]

Summary
When using a custom scheme base URL like ⁠orpc:/ in the client, RPC requests lose their path and are sent with ⁠u: "/", leading to 404 responses (“No procedure matched”). This is due to mutating ⁠url.pathname after constructing ⁠new URL(baseUrl), which is a no-op for URLs with an opaque path per the WHATWG URL spec.

This regression appears to have been introduced by a change similar to “feat(client): support search query in base url,” where safe string concatenation was replaced with ⁠url.pathname = ....

Affected packages/areas

1. Client-side URL building in Standard RPC link codec (e.g., StandardRPCLinkCodec.encode)

2. Custom scheme base URL (e.g., ⁠orpc:/), especially without authority (no host)

Expected behavior

Given:

• baseUrl = ⁠orpc:/

• path = ⁠["hello"]

The encoded request should produce:

• URL href = ⁠orpc:/hello

• URL pathname = ⁠/hello

• Serialized message field u = ⁠/hello
• Server should match the procedure and not respond 404.

Actual behavior

• URL href remains ⁠orpc:/

• URL pathname stays ⁠/

• Serialized message field u = ⁠/

• Server responds with 404 “No procedure matched”

Why this happens
Per WHATWG URL Standard, pathname setter is ignored if the URL has an opaque path:
“If this’s URL has an opaque path, then return.”
Custom schemes without authority commonly produce opaque paths (e.g., ⁠orpc:/, ⁠data:, ⁠mailto:). Therefore, doing:

const url = new URL('orpc:/');

url.pathname = '/hello';

does not change the resulting href/pathname in some environments.
This explains why the RPC path vanishes when using ⁠orpc:/ as base.

Environment

• Client: @orpc/client, @orpc/client/websocket
• Transport: WebSocket / standard peer

• Standard libs: @orpc/standard-server, @orpc/standard-server-peer
• Base URL: ⁠orpc:/ (no authority)
• Path: e.g., ⁠["hello"] → expected URL: ⁠orpc:/hello

[dosubot]

Hi @dmitriyzhirma! I'm Dosu and I’m helping the orpc team.

This happens because assigning to url.pathname is ignored for custom scheme URLs with opaque paths (like orpc:/) per the WHATWG URL spec, so the RPC path gets lost and requests end up with /, causing 404s on the server. The regression was introduced when the code switched from safe string concatenation to direct pathname assignment in StandardRPCLinkCodec.encode—which works for HTTP(S) URLs but not for custom schemes without authority source.

To fix this, avoid mutating url.pathname for custom schemes. Instead, build the URL by concatenating the base and path manually, for example:

const baseUrl = "orpc:/";
const path = "/hello";
const url = baseUrl.replace(/\/$/, "") + path; // yields "orpc:/hello"

This ensures the RPC path is preserved and encoded correctly, regardless of scheme or environment. This pattern is the recommended workaround for opaque-path URLs in JavaScript/TypeScript frameworks source.

To reply, just mention @dosu.

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[dinwwwh]

Can you give me a real case example - or minimal repro for this (just curious)

[dmitriyzhirma]

on server side:

import { os } from "@orpc/server";

import { RPCHandler } from "@orpc/server/websocket";

const router = os.router({
  hello: os.handler(() => "Hello world!"),
});

const handler = new RPCHandler(router);

Deno.serve({ port: 8080 }, (req) => {
  if (req.headers.get("upgrade") !== "websocket") {
    return new Response(null, { status: 501 });
  }

  const { socket, response } = Deno.upgradeWebSocket(req);

  handler.upgrade(socket, {
    context: {},
  });

  return response;
});

on client side:

import { RPCLink } from "@orpc/client/websocket";
import { createORPCClient } from "@orpc/client";

const websocket = new WebSocket("ws://localhost:8080/");
const link = new RPCLink({ websocket });
const orpc = createORPCClient(link);

await orpc.hello();

[dinwwwh]

@dmitriyzhirma I just tried your snippet, and everything works fine for me. How can I reproduce your error?

[dinwwwh]

Can you tell me which runtime ignores the pathname? I tested it in Hono, Bun, Node, and Chrome, and everything worked fine.

const url = new URL('orpc:/');

url.pathname = '/hello';
console.log(url) // orpc:/hello

[dmitriyzhirma]

I checked in Chromium version 125, not Google Chrome. Hmm, it works in Google Chrome. After update Chromium to latest version its work correct