Function build_provider_url

crates/openshell-router/src/backend.rs:764–809

Build the upstream URL for a provider route. `stream_response` selects between the unary and streaming Vertex AI Anthropic endpoint suffixes. Pass the same value used for the enclosing [`prepare_backend_request`] call. See that function's documentation for the full caller table. Behavior matrix (`request_path_override`, `model_in_path`): - `(Some(suffix), true)`: `{endpoint}/{model_id}{suffix}`

(
    route: &ResolvedRoute,
    model_id: &str,
    protocol_path: &str,
    stream_response: bool,
)

///   Model embedded before protocol path.
/// - `(None, false)`: delegates to `build_backend_url` (default, with /v1 dedup).
fn build_provider_url(
    route: &ResolvedRoute,
    model_id: &str,
    protocol_path: &str,
    stream_response: bool,
) -> String {
    let base = route.endpoint.trim_end_matches('/');
    match (&route.request_path_override, route.model_in_path) {
        // Vertex AI publisher endpoint: model in URL path with suffix
        // e.g. .../publishers/anthropic/models/claude-3-5-sonnet@20241022:rawPredict
        (Some(suffix), true) => {
            // suffix is appended directly after model_id (e.g. ":rawPredict").
            // It must not start with '/' — use the (Some, false) arm for path overrides.
            debug_assert!(
                !suffix.starts_with('/'),
                "suffix in model_in_path branch must not start with '/'; got: {suffix:?}"
            );
            let suffix = if stream_response
                && suffix == ":rawPredict"
                && is_vertex_anthropic_rawpredict_route(route)
            {
                ":streamRawPredict"
            } else {
                suffix.as_str()
            };
            format!("{base}/{model_id}{suffix}")
        }
        // Explicit path override, model NOT in URL.
        // Normalize: ensure override_path begins with '/' so the concatenation
        // never produces a broken URL like `https://host.compath`.
        (Some(override_path), false) => {
            if override_path.starts_with('/') || override_path.is_empty() {
                format!("{base}{override_path}")
            } else {
                format!("{base}/{override_path}")
            }
        }
        // Model in path, no override — append model then protocol-derived path
        (None, true) => {
            let path = protocol_path.trim_start_matches('/');
            format!("{base}/{model_id}/{path}")
        }
        // Default: existing behavior (includes /v1 deduplication)
        (None, false) => build_backend_url(&route.endpoint, protocol_path),
    }
}

fn build_backend_url(endpoint: &str, path: &str) -> String {
    let base = endpoint.trim_end_matches('/');