withEndpoint

function withEndpoint(endpoint: string): ClientOption;

The default is an empty string, so execution requires an explicit endpoint. Its pathname is kept as a directory; its query and hash are discarded. For WebSocket operations, an http: base becomes ws: and https: becomes wss:.

A missing, relative, or invalid endpoint, or an illegal request path, fails with REQ_BUILD_FAILED during building, before any interceptor or transport runs, even when an interceptor would short-circuit. HTTP, SSE, and WebSocket share this rule. The resolved request must keep the base origin and stay under its directory; C0 control characters (including tab, CR, and LF), backslashes, ?, #, and directory escapes in a path are rejected. Scheme-like and protocol-relative forms are rejected even with leading spaces; a plain inner space is allowed and sent as %20. An interceptor's final req.endpoint is checked against its final req.baseEndpoint with the same rule, but it may deliberately replace the base with another valid absolute URL. Deterministic URL errors are never retried.