fetch() from localhost does not work

[chrisfarber]

Attempts to fetch() from localhost (when running inside Viceroy, with dynamic backends enabled in the application) result in errors.

For example, running this code:

fetch("http://localhost:4200/index.html");

Will result in these errors printed to the Viceroy console:

Error: hyper::Error(Connect, Custom { kind: InvalidData, error: CorruptMessage })
2023-06-07T20:15:10.852817Z ERROR request{id=0}: Hostcall yielded an error: error trying to connect: received corrupt message
Log: (new Error("NetworkError when attempting to fetch resource.", ""))

It appears as though it's attempting to negotiate SSL. Note that the following program does work:

/// <reference types="@fastly/js-compute" />

import { allowDynamicBackends } from "fastly:experimental";

allowDynamicBackends(true);

addEventListener("fetch", event => event.respondWith(fetch('http://innerastoundingmajesticlight.neverssl.com/online/')));

A Rust compute@edge app running in Viceroy can successfully uses localhost + an arbitrary port as a dynamic backend, suggesting this problem exists in our JS runtime.