Host header is ignored when using proxyRequest()

[afonsosantos]

Environment

• Node version: v20.15.1
• H3: v1.12.0

Reproduction

• Initialize a new Nuxt 3 app
• Add the following to nuxt.config.ts:

runtimeConfig: {
    public: {
      backend: {
        url: "http://localhost:8000",
        host_header: "dev.localhost:8000",
      },
    },
  },

• Create an API route: server/api/[...].ts
• Use the following snippet:

import { joinURL } from "ufo";

export default defineEventHandler(async (event) => {
  const {
    public: { backend },
  } = useRuntimeConfig(event);

  const path: string = event.path.replace(/^\/api\//, "");
  const target: string = joinURL(backend.url, path);

  console.info(
    `Proxying request: (frontend) ${event.method} ${event.path} -> (backend) ${target}`,
  );

  return await proxyRequest(event, target, {
    headers: { "Host": backend.host_header },
  });
});

• Use the newly created API route, like GET localhost:3000/api/users/, and observe that in the receiving end (backend) the Host header is not replaced by the correct value.

Describe the bug

When using the proxyRequest function in the latest Nuxt JS version, the Host header is ignored. From looking into the Github issues, a similar problem was found, as seen here: #709 (in this case, the Accept header is ignored), introduced by this PR: #646.

In the case of my project, we use the Host header to change the tenant domain on the backend side (one subdomain per tenant).

A culript piece of code was found here:

h3/src/utils/proxy.ts

Lines 25 to 33 in 17fc905

	const ignoredHeaders = new Set([
	"transfer-encoding",
	"connection",
	"keep-alive",
	"upgrade",
	"expect",
	"host",
	"accept",
	]);

where the Host header and others are explicitly being ignored.

If a fix is necessary, I can provide a PR with the code fix.

Additional context

No response

Logs

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