fix(client-ip): Fall back to peer IP instead of returning 500

src/api/client_ip.rs

@@ -0,0 +1,135 @@
+use std::{
+	convert::Infallible,
+	net::{IpAddr, Ipv4Addr, SocketAddr},
+};
+
+use axum::extract::{ConnectInfo, FromRequestParts};
+use axum_client_ip::ClientIp as SourcedClientIp;
+use conduwuit::debug_warn;
+use http::request::Parts;
+
+const UNKNOWN_IP: IpAddr = IpAddr::V4(Ipv4Addr::UNSPECIFIED);
+
+/// [`ClientIp`] extractor that falls back to the connection peer address
+/// instead of rejecting the request when `request_ip_source` can't be resolved.
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct ClientIp(pub IpAddr);
+
+impl<S> FromRequestParts<S> for ClientIp
+where
+	S: Sync,
+{
+	type Rejection = Infallible;
+
+	async fn from_request_parts(parts: &mut Parts, state: &S) -> Result<Self, Self::Rejection> {
+		let ip = match SourcedClientIp::from_request_parts(parts, state).await {
+			| Ok(SourcedClientIp(ip)) => ip,
+			| Err(rejection) => {
+				debug_warn!(
+					%rejection,
+					"Could not resolve client IP from request_ip_source; using peer address"
+				);
+				parts
+					.extensions
+					.get::<ConnectInfo<SocketAddr>>()
+					.map_or(UNKNOWN_IP, |ConnectInfo(addr)| addr.ip())
+			},
+		};
+
+		Ok(Self(ip))
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use std::net::Ipv6Addr;
+
+	use axum_client_ip::ClientIpSource;
+
+	use super::*;
+
+	const PEER: SocketAddr = SocketAddr::new(IpAddr::V4(Ipv4Addr::new(198, 51, 100, 7)), 8448);
+	const PEER_V6: SocketAddr =
+		SocketAddr::new(IpAddr::V6(Ipv6Addr::new(0x2001, 0xDB8, 0, 0, 0, 0, 0, 1)), 8448);
+
+	fn parts(
+		source: Option<ClientIpSource>,
+		peer: Option<SocketAddr>,
+		headers: &[(&str, &str)],
+	) -> Parts {
+		let mut builder = http::Request::builder();
+		for (name, value) in headers {
+			builder = builder.header(*name, *value);
+		}
+
+		let (mut parts, ()) = builder.body(()).unwrap().into_parts();
+		if let Some(source) = source {
+			parts.extensions.insert(source);
+		}
+		if let Some(peer) = peer {
+			parts.extensions.insert(ConnectInfo(peer));
+		}
+
+		parts
+	}
+
+	async fn extract(mut parts: Parts) -> IpAddr {
+		let ClientIp(ip) = ClientIp::from_request_parts(&mut parts, &()).await.unwrap();
+		ip
+	}
+
+	#[tokio::test]
+	async fn resolves_from_configured_source() {
+		let parts =
+			parts(Some(ClientIpSource::XRealIp), Some(PEER), &[("x-real-ip", "203.0.113.5")]);
+
+		assert_eq!(extract(parts).await, IpAddr::V4(Ipv4Addr::new(203, 0, 113, 5)));
+	}
+
+	#[tokio::test]
+	async fn resolves_ipv6_from_configured_source() {
+		let parts =
+			parts(Some(ClientIpSource::XRealIp), Some(PEER), &[("x-real-ip", "2001:db8::2")]);
+
+		assert_eq!(
+			extract(parts).await,
+			IpAddr::V6(Ipv6Addr::new(0x2001, 0xDB8, 0, 0, 0, 0, 0, 2))
+		);
+	}
+
+	#[tokio::test]
+	async fn falls_back_to_peer_when_header_missing() {
+		let parts = parts(Some(ClientIpSource::XRealIp), Some(PEER), &[]);
+
+		assert_eq!(extract(parts).await, PEER.ip());
+	}
+
+	#[tokio::test]
+	async fn falls_back_to_ipv6_peer_when_header_missing() {
+		let parts = parts(Some(ClientIpSource::XRealIp), Some(PEER_V6), &[]);
+
+		assert_eq!(extract(parts).await, PEER_V6.ip());
+	}
+
+	#[tokio::test]
+	async fn falls_back_to_peer_when_header_unparsable() {
+		let parts =
+			parts(Some(ClientIpSource::XRealIp), Some(PEER), &[("x-real-ip", "not-an-ip")]);
+
+		assert_eq!(extract(parts).await, PEER.ip());
+	}
+
+	#[tokio::test]
+	async fn falls_back_to_peer_when_source_unset() {
+		let parts = parts(None, Some(PEER), &[("x-real-ip", "203.0.113.5")]);
+
+		assert_eq!(extract(parts).await, PEER.ip());
+	}
+
+	#[tokio::test]
+	async fn falls_back_to_unspecified_without_peer() {
+		let parts = parts(Some(ClientIpSource::XRealIp), None, &[]);
+
+		assert_eq!(extract(parts).await, UNKNOWN_IP);
+	}
+}