chore(deps)!: upgrade to tower 0.5

this commit updates our tower dependency from 0.4 to 0.5.

note that this commit does not affect the `tower-service` and
`tower-layer` crates, reëxported by `tower` itself. the `Service<T>`
trait and the closely related `Layer<S>` trait have not been changed.

the `tower` crate's utilities have changed in various ways, some of
particular note for the linkerd2 proxy. see these items, excerpted from
the tower changelog:

- **retry**: **Breaking Change** `retry::Policy::retry` now accepts `&mut Req` and `&mut Res` instead of the previous mutable versions. This
  increases the flexibility of the retry policy. To update, update your method signature to include `mut` for both parameters. ([tower-rs/tower#584])
- **retry**: **Breaking Change** Change Policy to accept &mut self ([tower-rs/tower#681])
- **retry**: **Breaking Change** `Budget` is now a trait. This allows end-users to implement their own budget and bucket implementations. ([tower-rs/tower#703])
- **util**: **Breaking Change** `Either::A` and `Either::B` have been renamed `Either::Left` and `Either::Right`, respectively. ([tower-rs/tower#637])
- **util**: **Breaking Change** `Either` now requires its two services to have the same error type. ([tower-rs/tower#637])
- **util**: **Breaking Change** `Either` no longer implemenmts `Future`. ([tower-rs/tower#637])
- **buffer**: **Breaking Change** `Buffer<S, Request>` is now generic over `Buffer<Request, S::Future>.` ([tower-rs/tower#654])

see:

* <tower-rs/tower#584>
* <tower-rs/tower#681>
* <tower-rs/tower#703>
* <tower-rs/tower#637>
* <tower-rs/tower#654>

the `Either` trait bounds are particularly impactful for us. because
this runs counter to how we treat errors (skewing towards boxed errors,
in general), we temporarily vendor a version of `Either` from the 0.4
release, whose variants have been renamed to match the 0.5 interface.

updating to box the inner `A` and `B` services' errors, so we satiate
the new `A::Error = B::Error` bounds, can be addressed as a follow-on.
that's intentionally left as a separate change, due to the net size of
our patchset between this branch and #3504.

* <tower-rs/tower@v0.4.x...master>
* <https://github.com/tower-rs/tower/blob/master/tower/CHANGELOG.md>

this work is based upon #3504. for more information, see:

* linkerd/linkerd2#8733
* #3504

Signed-off-by: katelyn martin <kate@buoyant.io>
X-Ref: tower-rs/tower#815
X-Ref: tower-rs/tower#817
X-Ref: tower-rs/tower#818
X-Ref: tower-rs/tower#819

Author: cratelyn

Cargo.lock

@@ -991,7 +991,7 @@ dependencies = [
  "pin-project",
  "tokio",
  "tokio-test",
- "tower 0.4.13",
+ "tower 0.5.2",
 ]
 
 [[package]]
@@ -1410,7 +1410,7 @@ dependencies = [
  "tokio",
  "tokio-stream",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1433,7 +1433,7 @@ dependencies = [
  "serde_json",
  "thiserror 2.0.12",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1502,7 +1502,7 @@ dependencies = [
  "tokio",
  "tokio-stream",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1523,7 +1523,7 @@ dependencies = [
  "tokio",
  "tokio-test",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
  "tracing",
 ]
@@ -1562,7 +1562,7 @@ dependencies = [
  "tokio",
  "tokio-test",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1598,7 +1598,7 @@ dependencies = [
  "tokio-rustls",
  "tokio-stream",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
  "tracing-subscriber",
 ]
@@ -1646,7 +1646,7 @@ dependencies = [
  "tokio-rustls",
  "tokio-test",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
  "tracing",
 ]
@@ -1675,7 +1675,7 @@ dependencies = [
  "tokio-stream",
  "tokio-test",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
  "tracing-subscriber",
 ]
@@ -1852,7 +1852,7 @@ dependencies = [
  "http",
  "linkerd-stack",
  "pin-project",
- "tower 0.4.13",
+ "tower 0.5.2",
 ]
 
 [[package]]
@@ -1871,7 +1871,7 @@ dependencies = [
  "parking_lot",
  "pin-project",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1881,7 +1881,7 @@ version = "0.1.0"
 dependencies = [
  "http",
  "linkerd-stack",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1912,7 +1912,7 @@ dependencies = [
  "http-body",
  "linkerd-stack",
  "pin-project",
- "tower 0.4.13",
+ "tower 0.5.2",
 ]
 
 [[package]]
@@ -1936,7 +1936,7 @@ dependencies = [
  "pin-project",
  "thiserror 2.0.12",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -1990,7 +1990,7 @@ dependencies = [
  "pin-project",
  "thiserror 2.0.12",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
  "try-lock",
 ]
@@ -2026,7 +2026,7 @@ dependencies = [
  "linkerd-tracing",
  "parking_lot",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2230,7 +2230,7 @@ dependencies = [
  "rand 0.9.0",
  "tokio",
  "tokio-test",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
  "tracing",
 ]
@@ -2254,7 +2254,7 @@ dependencies = [
  "pin-project",
  "prost 0.13.5",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2272,7 +2272,7 @@ dependencies = [
  "linkerd-stack",
  "rand 0.9.0",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2337,7 +2337,7 @@ version = "0.1.0"
 dependencies = [
  "futures",
  "linkerd-error",
- "tower 0.4.13",
+ "tower 0.5.2",
 ]
 
 [[package]]
@@ -2352,7 +2352,7 @@ dependencies = [
  "linkerd-stack",
  "tokio",
  "tokio-stream",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2395,7 +2395,7 @@ dependencies = [
  "thiserror 2.0.12",
  "tokio",
  "tokio-test",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
  "tracing",
  "try-lock",
@@ -2430,7 +2430,7 @@ dependencies = [
  "linkerd-proxy-core",
  "pin-project",
  "thiserror 2.0.12",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2469,7 +2469,7 @@ dependencies = [
  "tokio",
  "tokio-test",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
  "x509-parser",
 ]
@@ -2501,7 +2501,7 @@ dependencies = [
  "thiserror 2.0.12",
  "tokio",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2517,7 +2517,7 @@ dependencies = [
  "pin-project",
  "rand 0.9.0",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
 ]
 
 [[package]]
@@ -2548,7 +2548,7 @@ dependencies = [
  "tokio",
  "tokio-stream",
  "tokio-test",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
  "tracing",
 ]
@@ -2560,7 +2560,7 @@ dependencies = [
  "futures",
  "linkerd-error",
  "linkerd-stack",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2602,7 +2602,7 @@ dependencies = [
  "tokio",
  "tokio-stream",
  "tonic",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2627,7 +2627,7 @@ dependencies = [
  "tokio",
  "tokio-test",
  "tokio-util",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
  "tracing",
 ]
@@ -2640,7 +2640,7 @@ dependencies = [
  "parking_lot",
  "tokio",
  "tokio-test",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tower-test",
 ]
 
@@ -2651,7 +2651,7 @@ dependencies = [
  "futures",
  "linkerd-error",
  "linkerd-stack",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -2672,7 +2672,7 @@ dependencies = [
  "pin-project",
  "thiserror 2.0.12",
  "tokio",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
  "untrusted",
 ]
@@ -2738,7 +2738,7 @@ dependencies = [
  "linkerd-stack",
  "rand 0.8.5",
  "thiserror 1.0.69",
- "tower 0.4.13",
+ "tower 0.5.2",
  "tracing",
 ]
 
@@ -4216,10 +4216,14 @@ checksum = "d039ad9159c98b70ecfd540b2573b97f7f52c3e8d9f8ad57a24b916a536975f9"
 dependencies = [
  "futures-core",
  "futures-util",
+ "indexmap 2.8.0",
  "pin-project-lite",
  "sync_wrapper",
+ "tokio",
+ "tokio-util",
  "tower-layer",
  "tower-service",
+ "tracing",
 ]
 
 [[package]]

Cargo.toml

@@ -115,7 +115,7 @@ tokio-rustls = { version = "0.26", default-features = false, features = [
 ] }
 tonic = { version = "0.12", default-features = false }
 tonic-build = { version = "0.12", default-features = false }
-tower = { version = "0.4", default-features = false }
+tower = { version = "0.5", default-features = false }
 tower-service = { version = "0.3" }
 tower-test = { version = "0.4" }
 

linkerd/app/gateway/src/server.rs

@@ -64,10 +64,10 @@ impl Gateway {
                             SessionProtocol::Http1 => http::Variant::Http1,
                             SessionProtocol::Http2 => http::Variant::H2,
                         };
-                        return Ok(svc::Either::A(Http { parent, version }));
+                        return Ok(svc::Either::Left(Http { parent, version }));
                     }
 
-                    Ok(svc::Either::B(Opaq(parent)))
+                    Ok(svc::Either::Right(Opaq(parent)))
                 },
                 opaq,
             )

linkerd/app/inbound/src/accept.rs

@@ -53,12 +53,12 @@ impl<N> Inbound<N> {
                     move |t: T| -> Result<_, Error> {
                         let addr: OrigDstAddr = t.param();
                         if addr.port() == proxy_port {
-                            return Ok(svc::Either::B(t));
+                            return Ok(svc::Either::Right(t));
                         }
 
                         let policy = policies.get_policy(addr);
                         tracing::debug!(policy = ?&*policy.borrow(), "Accepted");
-                        Ok(svc::Either::A(Accept {
+                        Ok(svc::Either::Left(Accept {
                             client_addr: t.param(),
                             orig_dst_addr: addr,
                             policy,