add method_not_allowed_fallback to router

axum/src/routing/mod.rs

@@ -342,6 +342,16 @@ where
         .fallback_endpoint(Endpoint::Route(route))
     }
 
+    pub fn method_not_allowed_fallback<H, T>(self, handler: H) -> Self
+    where
+        H: Handler<T, S>,
+        T: 'static
+    {
+        self.tap_inner_mut(|this| {
+            this.path_router.method_not_allowed_fallback(handler.clone())
+        })
+    }
+
     fn fallback_endpoint(self, endpoint: Endpoint<S>) -> Self {
         self.tap_inner_mut(|this| {
             this.fallback_router.set_fallback(endpoint);

axum/src/routing/path_router.rs

@@ -1,4 +1,4 @@
-use crate::extract::{nested_path::SetNestedPath, Request};
+use crate::{extract::{nested_path::SetNestedPath, Request}, handler::Handler};
 use axum_core::response::IntoResponse;
 use matchit::MatchError;
 use std::{borrow::Cow, collections::HashMap, convert::Infallible, fmt, sync::Arc};
@@ -79,6 +79,18 @@ where
         Ok(())
     }
 
+    pub(super) fn method_not_allowed_fallback<H, T>(&mut self, handler: H)
+    where
+        H: Handler<T, S>,
+        T: 'static
+    {
+        for (_, endpoint) in self.routes.iter_mut() {
+            if let Endpoint::MethodRouter(rt) = endpoint {
+                *rt = rt.clone().fallback(handler.clone());
+            }
+        }
+    }
+
     pub(super) fn route_service<T>(
         &mut self,
         path: &str,