src/shared/constants/upstreamHeaders.ts

/**
 * User-supplied upstream extra headers: names we never forward (Host / hop-by-hop / framing).
 * Changing this list requires syncing: `sanitizeUpstreamHeadersMap` (models.ts), Zod
 * `upstreamHeaderNameSchema` / record refine (schemas.ts), and `upstream-headers-sanitize` tests.
 */
const FORBIDDEN = new Set(
  [
    "host",
    "connection",
    "content-length",
    "keep-alive",
    "proxy-connection",
    "transfer-encoding",
    "te",
    "trailer",
    "upgrade",
  ].map((s) => s.toLowerCase())
);

export function isForbiddenUpstreamHeaderName(name: string): boolean {
  return FORBIDDEN.has(String(name).trim().toLowerCase());
}

/**
 * Auth headers that must come from the connection's credentials, never from
 * operator-set per-provider custom headers. Kept here as the single source of
 * truth so the Zod `customHeadersSchema` (schemas.ts) and the executor's
 * apply-loop (open-sse/executors/default.ts) cannot drift apart.
 */
const FORBIDDEN_AUTH = new Set(
  ["authorization", "x-api-key", "x-goog-api-key", "api-key"].map((s) => s.toLowerCase())
);

/**
 * Forbidden for operator-supplied custom headers: the hop-by-hop/framing set
 * PLUS auth headers (owned by the credential layer). Use this in both the
 * validation schema and the executor so there is one canonical denylist.
 */
export function isForbiddenCustomHeaderName(name: string): boolean {
  const n = String(name).trim().toLowerCase();
  return isForbiddenUpstreamHeaderName(n) || FORBIDDEN_AUTH.has(n);
}