valtown.ts

// MasterHttpRelay exit node for val.town
// Deploy as HTTP endpoint in val.town and set PSK to a strong secret.

const PSK = "CHANGE_ME_TO_A_STRONG_SECRET";

const STRIP_HEADERS = new Set([
  "host",
  "connection",
  "content-length",
  "transfer-encoding",
  "proxy-connection",
  "proxy-authorization",
  "x-forwarded-for",
  "x-forwarded-host",
  "x-forwarded-proto",
  "x-forwarded-port",
  "x-real-ip",
  "forwarded",
  "via",
]);

function decodeBase64ToBytes(input: string): Uint8Array {
  const bin = atob(input);
  const out = new Uint8Array(bin.length);
  for (let i = 0; i < bin.length; i++) out[i] = bin.charCodeAt(i);
  return out;
}

function encodeBytesToBase64(bytes: Uint8Array): string {
  let bin = "";
  for (let i = 0; i < bytes.length; i++) bin += String.fromCharCode(bytes[i]);
  return btoa(bin);
}

function sanitizeHeaders(h: unknown): Record<string, string> {
  const out: Record<string, string> = {};
  if (!h || typeof h !== "object") return out;
  for (const [k, v] of Object.entries(h as Record<string, unknown>)) {
    if (!k) continue;
    if (STRIP_HEADERS.has(k.toLowerCase())) continue;
    out[k] = String(v ?? "");
  }
  return out;
}

export default async function(req: Request): Promise<Response> {
  try {
    if (req.method !== "POST") {
      return Response.json({ e: "method_not_allowed" }, { status: 405 });
    }

    const body = await req.json();
    if (!body || typeof body !== "object") {
      return Response.json({ e: "bad_json" }, { status: 400 });
    }

    const k = String((body as any).k ?? "");
    const u = String((body as any).u ?? "");
    const m = String((body as any).m ?? "GET").toUpperCase();
    const h = sanitizeHeaders((body as any).h);
    const b64 = (body as any).b;

    if (k !== PSK) return Response.json({ e: "unauthorized" }, { status: 401 });
    if (!/^https?:\/\//i.test(u)) return Response.json({ e: "bad url" }, { status: 400 });

    let payload: Uint8Array | undefined;
    if (typeof b64 === "string" && b64.length > 0) payload = decodeBase64ToBytes(b64);

    const resp = await fetch(u, {
      method: m,
      headers: h,
      body: payload,
      redirect: "manual",
    });

    const data = new Uint8Array(await resp.arrayBuffer());
    const respHeaders: Record<string, string> = {};
    resp.headers.forEach((value, key) => {
      respHeaders[key] = value;
    });

    return Response.json({
      s: resp.status,
      h: respHeaders,
      b: encodeBytesToBase64(data),
    });
  } catch (err) {
    const message = err instanceof Error ? err.message : String(err);
    return Response.json({ e: message }, { status: 500 });
  }
}