proksi 0.9.0

A batteries-included reverse proxy with automatic HTTPS using Cloudflare Pingora and Let's Encrypt.
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//! The client of a request: the connection's address, or behind trusted proxies, the address
//! they forwarded (`X-Forwarded-For`)

use std::{net::IpAddr, sync::OnceLock};

use ipnet::IpNet;

/// Proxies (addresses or networks) whose `X-Forwarded-For` is trusted
#[derive(Debug, Default, Clone, PartialEq)]
pub struct TrustedProxies(Vec<IpNet>);

static TRUSTED: OnceLock<TrustedProxies> = OnceLock::new();

impl TrustedProxies {
    /// From addresses (`10.0.0.1`) and networks (`10.0.0.0/8`)
    pub fn parse(proxies: &[String]) -> Result<Self, String> {
        proxies
            .iter()
            .map(|proxy| {
                proxy
                    .parse::<IpNet>()
                    .or_else(|_| proxy.parse::<IpAddr>().map(IpNet::from))
                    .map_err(|_| {
                        format!(
                            "trusted_proxies: {proxy:?} is not an address or a network (10.0.0.0/8)"
                        )
                    })
            })
            .collect::<Result<Vec<_>, _>>()
            .map(Self)
    }

    fn trusts(&self, ip: &IpAddr) -> bool {
        self.0.iter().any(|network| network.contains(ip))
    }

    /// The client of a connection from `peer`: `peer` itself, unless it's a trusted proxy.
    /// Then, going from the right of `X-Forwarded-For` (the closest hop), the first address
    /// that isn't a trusted proxy. Addresses a client wrote itself (on the left) are never used
    /// when a trusted proxy appended one after them.
    pub fn client(&self, peer: IpAddr, forwarded_for: Option<&str>) -> IpAddr {
        if !self.trusts(&peer) {
            return peer;
        }
        let mut client = peer;
        for hop in forwarded_for.unwrap_or_default().rsplit(',') {
            let Some(ip) = parse_hop(hop.trim()) else {
                break;
            };
            client = ip;
            if !self.trusts(&ip) {
                break;
            }
        }
        client
    }
}

/// An address of `X-Forwarded-For`, with or without a port (`1.2.3.4:80`, `[2001:db8::1]:80`)
fn parse_hop(hop: &str) -> Option<IpAddr> {
    hop.parse::<IpAddr>()
        .ok()
        .or_else(|| hop.parse::<std::net::SocketAddr>().ok().map(|addr| addr.ip()))
}

/// The `X-Forwarded-*` headers of a request, as received
#[derive(Debug, Default, Clone, Copy)]
pub struct Incoming<'a> {
    pub forwarded_for: Option<&'a str>,
    pub proto: Option<&'a str>,
    pub host: Option<&'a str>,
}

/// The headers sent to upstreams about the client
#[derive(Debug, PartialEq)]
#[allow(clippy::struct_field_names)] // named after the headers
pub struct Forwarded {
    pub forwarded_for: String,
    pub proto: String,
    pub host: Option<String>,
    pub real_ip: String,
}

impl TrustedProxies {
    /// The headers for a request from `peer`, received over `proto` (`http`, `https`) for
    /// `host`. What a trusted proxy sent is kept (and `peer` appended to `X-Forwarded-For`);
    /// what anyone else sent is replaced, so clients can't forge them.
    pub fn forwarded(
        &self,
        peer: IpAddr,
        incoming: Incoming<'_>,
        proto: &str,
        host: Option<&str>,
    ) -> Forwarded {
        let trusted = self.trusts(&peer);
        let kept = |value: Option<&str>| {
            value
                .map(str::trim)
                .filter(|value| trusted && !value.is_empty())
                .map(ToString::to_string)
        };
        Forwarded {
            forwarded_for: match kept(incoming.forwarded_for) {
                Some(chain) => format!("{chain}, {peer}"),
                None => peer.to_string(),
            },
            proto: kept(incoming.proto).unwrap_or_else(|| proto.to_string()),
            host: kept(incoming.host).or_else(|| host.map(ToString::to_string)),
            real_ip: self.client(peer, incoming.forwarded_for).to_string(),
        }
    }
}

/// See [`TrustedProxies::forwarded`]
pub fn forwarded(
    peer: IpAddr,
    incoming: Incoming<'_>,
    proto: &str,
    host: Option<&str>,
) -> Forwarded {
    TRUSTED
        .get()
        .unwrap_or(&TrustedProxies(vec![]))
        .forwarded(peer, incoming, proto, host)
}

/// Sets the trusted proxies (once, when proksi starts)
pub fn init(proxies: TrustedProxies) {
    let _ = TRUSTED.set(proxies);
}

/// The client of a request, see [`TrustedProxies::client`]
pub fn client_ip(peer: IpAddr, forwarded_for: Option<&str>) -> IpAddr {
    match TRUSTED.get() {
        Some(trusted) => trusted.client(peer, forwarded_for),
        None => peer,
    }
}

#[cfg(test)]
mod tests {
    use std::net::IpAddr;

    use super::TrustedProxies;

    fn ip(value: &str) -> IpAddr {
        value.parse().unwrap()
    }

    fn trusted(proxies: &[&str]) -> TrustedProxies {
        TrustedProxies::parse(&proxies.iter().map(ToString::to_string).collect::<Vec<_>>())
            .unwrap()
    }

    #[test]
    fn test_parse() {
        assert!(TrustedProxies::parse(&["10.0.0.0/8".into(), "127.0.0.1".into(), "::1".into()]).is_ok());
        assert_eq!(
            TrustedProxies::parse(&["10.0.0".into()]),
            Err("trusted_proxies: \"10.0.0\" is not an address or a network (10.0.0.0/8)".to_string())
        );
    }

    #[test]
    fn test_untrusted_connections_are_the_client() {
        let proxies = trusted(&["10.0.0.0/8"]);

        // Whatever they send
        assert_eq!(proxies.client(ip("203.0.113.9"), Some("1.2.3.4")), ip("203.0.113.9"));
        assert_eq!(TrustedProxies::default().client(ip("10.0.0.1"), Some("1.2.3.4")), ip("10.0.0.1"));
    }

    #[test]
    fn test_behind_trusted_proxies() {
        let proxies = trusted(&["10.0.0.0/8", "192.168.1.1"]);

        assert_eq!(proxies.client(ip("10.0.0.1"), Some("203.0.113.9")), ip("203.0.113.9"));
        // A chain of trusted proxies
        assert_eq!(
            proxies.client(ip("10.0.0.1"), Some("203.0.113.9, 192.168.1.1, 10.1.1.1")),
            ip("203.0.113.9")
        );
        // An address the client wrote itself, on the left, isn't used
        assert_eq!(
            proxies.client(ip("10.0.0.1"), Some("1.2.3.4, 203.0.113.9")),
            ip("203.0.113.9")
        );
        // Several headers are joined with commas by the time they're read; IPv6, ports
        assert_eq!(proxies.client(ip("10.0.0.1"), Some(" 2001:db8::1 ")), ip("2001:db8::1"));
        assert_eq!(proxies.client(ip("10.0.0.1"), Some("203.0.113.9:4711")), ip("203.0.113.9"));
        assert_eq!(proxies.client(ip("10.0.0.1"), Some("[2001:db8::1]:4711")), ip("2001:db8::1"));
    }

    #[test]
    fn test_without_a_usable_header() {
        let proxies = trusted(&["10.0.0.0/8"]);

        // The proxy itself
        assert_eq!(proxies.client(ip("10.0.0.1"), None), ip("10.0.0.1"));
        assert_eq!(proxies.client(ip("10.0.0.1"), Some("")), ip("10.0.0.1"));
        // Only trusted proxies: the furthest one
        assert_eq!(proxies.client(ip("10.0.0.1"), Some("10.0.0.2, 10.0.0.3")), ip("10.0.0.2"));
        // Garbage stops the walk: the last address that was valid
        assert_eq!(proxies.client(ip("10.0.0.1"), Some("unknown, 10.0.0.2")), ip("10.0.0.2"));
    }

    #[test]
    fn test_forwarded_headers_from_clients_are_replaced() {
        let proxies = trusted(&["10.0.0.0/8"]);
        let incoming = super::Incoming {
            forwarded_for: Some("1.2.3.4"),
            proto: Some("https"),
            host: Some("forged.test"),
        };

        assert_eq!(
            proxies.forwarded(ip("203.0.113.9"), incoming, "http", Some("a.test")),
            super::Forwarded {
                forwarded_for: "203.0.113.9".to_string(),
                proto: "http".to_string(),
                host: Some("a.test".to_string()),
                real_ip: "203.0.113.9".to_string(),
            }
        );
    }

    #[test]
    fn test_forwarded_headers_from_trusted_proxies_are_kept() {
        let proxies = trusted(&["10.0.0.0/8"]);
        let incoming = super::Incoming {
            forwarded_for: Some("203.0.113.9, 10.0.0.2"),
            proto: Some("https"),
            host: Some("www.a.test"),
        };

        assert_eq!(
            proxies.forwarded(ip("10.0.0.1"), incoming, "http", Some("a.test")),
            super::Forwarded {
                forwarded_for: "203.0.113.9, 10.0.0.2, 10.0.0.1".to_string(),
                proto: "https".to_string(),
                host: Some("www.a.test".to_string()),
                real_ip: "203.0.113.9".to_string(),
            }
        );
        // Without headers: as for any client
        let forwarded =
            proxies.forwarded(ip("10.0.0.1"), super::Incoming::default(), "https", None);
        assert_eq!(forwarded.forwarded_for, "10.0.0.1");
        assert_eq!(forwarded.proto, "https");
        assert_eq!(forwarded.host, None);
    }
}