From 17a3c89a6838e6aec3d4205b11e8a1904fb1afe3 Mon Sep 17 00:00:00 2001
From: David Pedersen <david.pdrsn@gmail.com>
Date: Fri, 3 Mar 2023 10:59:04 +0100
Subject: [PATCH] Fix routing issues when loading a `Router` via a dynamic
 library

---
 axum/CHANGELOG.md       |  1 +
 axum/src/routing/mod.rs | 35 ++++++++++++++++++++---------------
 2 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/axum/CHANGELOG.md b/axum/CHANGELOG.md
index 194c8b4d41b..521076bd8ca 100644
--- a/axum/CHANGELOG.md
+++ b/axum/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 # Unreleased
 
 - **fixed:** Add `#[must_use]` to `WebSocketUpgrade::on_upgrade` ([#1801])
+- **fixed:** Fix routing issues when loading a `Router` via a dynamic library
 
 [#1801]: https://github.com/tokio-rs/axum/pull/1801
 
diff --git a/axum/src/routing/mod.rs b/axum/src/routing/mod.rs
index e7b717ea41d..7f9af4540be 100644
--- a/axum/src/routing/mod.rs
+++ b/axum/src/routing/mod.rs
@@ -47,24 +47,12 @@ pub use self::method_routing::{
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub(crate) struct RouteId(u32);
 
-impl RouteId {
-    fn next() -> Self {
-        use std::sync::atomic::{AtomicU32, Ordering};
-        // `AtomicU64` isn't supported on all platforms
-        static ID: AtomicU32 = AtomicU32::new(0);
-        let id = ID.fetch_add(1, Ordering::Relaxed);
-        if id == u32::MAX {
-            panic!("Over `u32::MAX` routes created. If you need this, please file an issue.");
-        }
-        Self(id)
-    }
-}
-
 /// The router type for composing handlers and services.
 pub struct Router<S = (), B = Body> {
     routes: HashMap<RouteId, Endpoint<S, B>>,
     node: Arc<Node>,
     fallback: Fallback<S, B>,
+    prev_route_id: Option<RouteId>,
 }
 
 impl<S, B> Clone for Router<S, B> {
@@ -73,6 +61,7 @@ impl<S, B> Clone for Router<S, B> {
             routes: self.routes.clone(),
             node: Arc::clone(&self.node),
             fallback: self.fallback.clone(),
+            prev_route_id: self.prev_route_id,
         }
     }
 }
@@ -117,6 +106,7 @@ where
             routes: Default::default(),
             node: Default::default(),
             fallback: Fallback::Default(Route::new(NotFound)),
+            prev_route_id: Default::default(),
         }
     }
 
@@ -134,7 +124,7 @@ where
 
         validate_path(path);
 
-        let id = RouteId::next();
+        let id = self.next_route_id();
 
         let endpoint = if let Some((route_id, Endpoint::MethodRouter(prev_method_router))) = self
             .node
@@ -189,7 +179,7 @@ where
             panic!("Paths must start with a `/`");
         }
 
-        let id = RouteId::next();
+        let id = self.next_route_id();
         self.set_node(path, id);
         self.routes.insert(id, endpoint);
         self
@@ -286,6 +276,7 @@ where
             routes,
             node,
             fallback,
+            prev_route_id: _,
         } = other.into();
 
         for (id, route) in routes {
@@ -335,6 +326,7 @@ where
             routes,
             node: self.node,
             fallback,
+            prev_route_id: self.prev_route_id,
         }
     }
 
@@ -368,6 +360,7 @@ where
             routes,
             node: self.node,
             fallback: self.fallback,
+            prev_route_id: self.prev_route_id,
         }
     }
 
@@ -419,6 +412,7 @@ where
             routes,
             node: self.node,
             fallback,
+            prev_route_id: self.prev_route_id,
         }
     }
 
@@ -506,6 +500,17 @@ where
             Endpoint::NestedRouter(router) => router.call_with_state(req, state),
         }
     }
+
+    fn next_route_id(&mut self) -> RouteId {
+        let next_id = self.prev_route_id.map_or(RouteId(0), |RouteId(id)| {
+            let next = id
+                .checked_add(1)
+                .expect("Over `u32::MAX` routes created. If you need this, please file an issue.");
+            RouteId(next)
+        });
+        self.prev_route_id = Some(next_id);
+        next_id
+    }
 }
 
 impl<B> Router<(), B>