nautechsystems/nautilus_trader · error · Error::Io(std::io::Error)

URL missing host

Error message

URL missing host

What it means

This error means the parsed URL had no host component (e.g. `wss:///path` or `tcp://:8080`). The library cannot establish a socket connection without knowing which host to connect to, so `parse_socket_url` rejects the URL with `ErrorKind::InvalidInput` before any network I/O is attempted.

Source

Thrown at crates/network/src/socket/client.rs:291

    /// Accepts either:
    /// - Raw socket address: "host:port" → returns ("host:port", "scheme://host:port")
    /// - Full URL: "scheme://host:port/path" → returns ("host:port", original URL)
    ///
    /// # Errors
    ///
    /// Returns an error if the URL is invalid or missing required components.
    fn parse_socket_url(url: &str, mode: Mode) -> Result<(String, String), Error> {
        if url.contains("://") {
            // URL with scheme (e.g., "wss://host:port/path")
            let parsed = url.parse::<http::Uri>().map_err(|e| {
                Error::Io(std::io::Error::new(
                    std::io::ErrorKind::InvalidInput,
                    format!("Invalid URL: {e}"),
                ))
            })?;

            let host = parsed.host().ok_or_else(|| {
                Error::Io(std::io::Error::new(
                    std::io::ErrorKind::InvalidInput,
                    "URL missing host",
                ))
            })?;

            let port = parsed
                .port_u16()
                .unwrap_or_else(|| match parsed.scheme_str() {
                    Some("wss" | "https") => 443,
                    Some("ws" | "http") => 80,
                    _ => match mode {
                        Mode::Tls => 443,
                        Mode::Plain => 80,
                    },
                });

            Ok((format!("{host}:{port}"), url.to_string()))
        } else {

View on GitHub (pinned to 18893faf8b)

Solutions

1. Print/inspect the URL string just before the call and confirm it contains a host (e.g. `tcp://127.0.0.1:8080`).
2. If the host comes from config/env, add validation that it is non-empty before constructing the URL.
3. If a default host is expected, supply one explicitly instead of relying on omission.

Example fix

// before
let url = format!("tcp://:{}", port); // missing host
// after
let url = format!("tcp://127.0.0.1:{}", port);

fn validate_socket_url(url: &str) -> Result<(), String> {
    match url::Url::parse(url) {
        Ok(parsed) if parsed.host_str().is_some() => Ok(()),
        Ok(_) => Err(format!("URL missing host: {url}")),
        Err(e) => Err(format!("invalid URL: {e}")),
    }
}

fn has_host(url: &url::Url) -> bool {
    url.host_str().map(|h| !h.is_empty()).unwrap_or(false)
}

match parse_socket_url(&raw) {
    Ok(parsed) => /* proceed */,
    Err(e) if e.to_string().contains("URL missing host") => {
        eprintln!("bad endpoint config: {raw:?}");
        return;
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Calling a socket client constructor/connect function with a URL string that parses as a valid URL but has an empty or absent host, such as `tcp://:9000`, `wss:///ws`, or a URL built by string concatenation where the host variable was empty.

Common situations: Config files or environment variables where the host part was omitted, URL templates like `{}://{}:{}` filled with an empty host value, or code that strips the host when adding a path or defaulting schemes.

Understand the failure class

Background: "Invalid URL" / "URL cannot be empty": fix the malformed or missing URL behind request-construction failures — this error's family across 50 libraries.

Related errors

• rate limiter decision lock poisoned
• Invalid `ConnectionMode` value: {value}
• Binance Futures data teardown failed: {}
• Binance Spot data teardown failed: {}
• Failed to connect after {max_attempts} attempts

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/57e4484cba2dbb74. Report an issue: GitHub.