Feature | RegisterCustomSchemeHandler won't let do fetch and XMLHttpRequest requests

[AnnaSasDev]

Impact

Medium

Problem / Motivation

Custom schemes exist; CORS/fetch/XHR compatibility needs explicit end-to-end assertions for headers and origin policy interaction.

Current behavior

Relevant primitives exist in the files listed above, but this backlog item does not have a complete, explicit InfiniFrame contract with dedicated coverage.

Expected behavior

Add integration tests for scheme URLs with fragments, fetch/XHR, and CORS headers; adjust scheme response metadata and origin policy handling as needed.

Proposed solution

Implement this incrementally:

1. Define/adjust the managed public API in InfiniFrame.Shared.
2. Wire implementation in InfiniFrame and InfiniFrame.Native where required.
3. Add focused tests (tests/InfiniFrameTests*) and docs updates (docs/docs/guides/*, docs/docs/migration/*).

Alternatives considered

• Keep as unsupported and document migration limitation.
• Provide a workaround-only approach without first-class API.

Use case

Applications migrating from Photino expect this behavior and currently need custom handling for "RegisterCustomSchemeHandler won't let do fetch and XMLHttpRequest requests".

Example implementation (current API)

using System.Text;

builder.RegisterCustomSchemeHandler("app", (_, _, url, out string? contentType) => {
    contentType = "application/json";
    var json = "{\"ok\":true,\"source\":\"app-scheme\"}";
    return new MemoryStream(Encoding.UTF8.GetBytes(json));
});

const response = await fetch("app://host/data.json");
const data = await response.json();
console.log(data.ok);

Technical proposal

Scope implementation to: core managed runtime (src/InfiniFrame/*, src/InfiniFrame.Shared/*, src/InfiniFrame.Js/*). Keep behavior deterministic across Windows/Linux/macOS and document platform-specific limitations explicitly.

Additional context

Photino reference: tryphotino/photino.NET#232

Checklist

• I searched existing issues
• This is not a support question