OpenAPI Client throws "Invalid URL" error when using relative paths like "/api"

[SeraphimKaito]

Environment

• os: Darwin Kernel Version 25.0.0: Wed Sep 17 21:35:32 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T6020 arm64
• node: v24.2.0
• orpc: V1.10.2

Reproduction

client

import { createORPCClient } from '@orpc/client'
import { OpenAPILink } from '@orpc/openapi-client/fetch'
import { contract } from './contract'

const link = new OpenAPILink(contract, {
  url: '/api', 
})

export const client: JsonifiedClient<ContractRouterClient<typeof contract>> = createORPCClient(link)

vite config

export default defineConfig({
  plugins: [tailwindcss(), reactRouter(), tsconfigPaths()],
  server: {
    proxy: {
      "/api": {
        target: "http://localhost:3000",
        changeOrigin: true,
      },
    },
  },
});

• Frontend: Running on http://localhost:5173 (Vite dev server)
• Backend: Running on http://localhost:3000 (API server)

Describe the bug

When configuring OpenAPILink with a relative URL (e.g., /api), the client throws an error:

Current behavior:

The StandardOpenapiLinkCodec uses new URL(baseUrl) which requires an absolute URL. This fails when users provide relative paths.

Expected behavior:

The client should support relative URLs in browser environments, automatically resolving them against location.origin.

[dosubot]

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

This error happens because orpc's OpenAPILink and StandardOpenapiLinkCodec require the url option to be an absolute URL. Internally, they use new URL(baseUrl), which throws if you pass a relative path like /api—unlike native fetch(), which resolves relative URLs against window.location.origin in the browser. There’s no built-in logic to resolve relative URLs automatically in orpc as of v1.10.2, and all official examples and tests use absolute URLs (source, docs).

To work around this, you can use a "lazy URL" function that returns an absolute URL at runtime, for example:

const link = new OpenAPILink(contract, {
  url: () => `${window.location.origin}/api`,
})

This approach works in browser environments and keeps your code compatible with proxies like Vite’s dev server.

To reply, just mention @dosu.

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[dinwwwh]

This is expected limitation and will improve in future.

[dinwwwh]

This issue will be resolved in v2 through PR #1593.