3 files changed, 30 insertions, 11 deletions
diff --git a/crates/tor-proto/src/stream/flow_ctrl/state.rs b/crates/tor-proto/src/stream/flow_ctrl/state.rs
index 41682fac2..ff51abeba 100644
--- a/crates/tor-proto/src/stream/flow_ctrl/state.rs
+++ b/crates/tor-proto/src/stream/flow_ctrl/state.rs
@@ -52,14 +52,14 @@ impl StreamFlowCtrl {
     #[cfg(feature = "flowctl-cc")]
     pub(crate) fn new_xon_xoff(
         params: Arc<FlowCtrlParameters>,
-        use_sidechannel_mitigations: bool,
+        with_sidechannel_mitigations: WithSidechannelMitigations,
         rate_limit_updater: watch::Sender<StreamRateLimit>,
         drain_rate_requester: NotifySender<DrainRateRequest>,
     ) -> Self {
         Self {
             inner: StreamFlowCtrlInner::XonXoff(XonXoffFlowCtrl::new(
                 params,
-                use_sidechannel_mitigations,
+                with_sidechannel_mitigations,
                 rate_limit_updater,
                 drain_rate_requester,
             )),
@@ -261,6 +261,19 @@ impl StreamRateLimit {
     }
 }
 
+/// Whether sidechannel mitigations are enabled or not for flow control.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub(crate) enum WithSidechannelMitigations {
+    /// Flow control sidechannel mitigations are *enabled*.
+    ///
+    /// Should be enabled for clients (including onion services).
+    Enabled,
+    /// Flow control sidechannel mitigations are *disabled*.
+    ///
+    /// Should be disabled for exits.
+    Disabled,
+}
+
 impl std::fmt::Display for StreamRateLimit {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "{} bytes/s", self.rate)
diff --git a/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/reader.rs b/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/reader.rs
index 2d02c0d18..182a0fef3 100644
--- a/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/reader.rs
+++ b/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/reader.rs
@@ -204,7 +204,9 @@ mod test {
     use std::sync::atomic::{AtomicU64, Ordering};
 
     use crate::stream::flow_ctrl::params::FlowCtrlParameters;
-    use crate::stream::flow_ctrl::state::{FlowCtrlHooks, StreamRateLimit};
+    use crate::stream::flow_ctrl::state::{
+        FlowCtrlHooks, StreamRateLimit, WithSidechannelMitigations,
+    };
     use crate::stream::flow_ctrl::xon_xoff::state::XonXoffFlowCtrl;
     use crate::util::notify::NotifySender;
 
@@ -345,7 +347,7 @@ mod test {
     /// 4. The flow control logic.
     #[allow(clippy::type_complexity)]
     fn init_flow_ctrl(
-        use_sidechannel_mitigations: bool,
+        with_sidechannel_mitigations: WithSidechannelMitigations,
     ) -> (
         WriterWithLength<Compat<DuplexStream>>,
         XonXoffReader<ReaderWithLength<Compat<DuplexStream>>, TestingDrainRateUpdates>,
@@ -365,7 +367,7 @@ mod test {
         // The flow control logic.
         let flow_ctrl = XonXoffFlowCtrl::new(
             Arc::new(params),
-            use_sidechannel_mitigations,
+            with_sidechannel_mitigations,
             rate_limit_tx,
             drain_rate_request_tx,
         );
@@ -443,7 +445,7 @@ mod test {
             // This is the stream queue for incoming data.
             // So the `reader` is the stream reader and the `writer` would be within the reactor.
             let (mut writer, mut reader, mut drain_rate_receiver, mut flow_ctrl) =
-                init_flow_ctrl(/* use_sidechannel_mitigations= */ true);
+                init_flow_ctrl(WithSidechannelMitigations::Enabled);
 
             // Data has arrived on the stream.
             // We always consider sending an XOFF when a stream has received data.
@@ -528,7 +530,7 @@ mod test {
             // This is the stream queue for incoming data.
             // So the `reader` is the stream reader and the `writer` would be within the reactor.
             let (mut writer, mut reader, mut drain_rate_receiver, mut flow_ctrl) =
-                init_flow_ctrl(/* use_sidechannel_mitigations= */ true);
+                init_flow_ctrl(WithSidechannelMitigations::Enabled);
 
             // Data has arrived on the stream.
             // We always consider sending an XOFF when a stream has received data.
diff --git a/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/state.rs b/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/state.rs
index 49795cc68..b2236edc1 100644
--- a/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/state.rs
+++ b/crates/tor-proto/src/stream/flow_ctrl/xon_xoff/state.rs
@@ -43,7 +43,9 @@ use tracing::trace;
 use super::reader::DrainRateRequest;
 
 use crate::stream::flow_ctrl::params::{CellCount, FlowCtrlParameters};
-use crate::stream::flow_ctrl::state::{FlowCtrlHooks, HalfStreamFlowCtrlHooks, StreamRateLimit};
+use crate::stream::flow_ctrl::state::{
+    FlowCtrlHooks, HalfStreamFlowCtrlHooks, StreamRateLimit, WithSidechannelMitigations,
+};
 use crate::util::notify::NotifySender;
 use crate::{Error, Result};
 
@@ -83,12 +85,14 @@ impl XonXoffFlowCtrl {
     /// Returns a new xon/xoff-based state.
     pub(crate) fn new(
         params: Arc<FlowCtrlParameters>,
-        use_sidechannel_mitigations: bool,
+        with_sidechannel_mitigations: WithSidechannelMitigations,
         rate_limit_updater: watch::Sender<StreamRateLimit>,
         drain_rate_requester: NotifySender<DrainRateRequest>,
     ) -> Self {
-        let sidechannel_mitigation =
-            use_sidechannel_mitigations.then_some(SidechannelMitigation::new());
+        let sidechannel_mitigation = match with_sidechannel_mitigations {
+            WithSidechannelMitigations::Enabled => Some(SidechannelMitigation::new()),
+            WithSidechannelMitigations::Disabled => None,
+        };
 
         // We use the same XOFF limit regardless of if we're a client or exit.
         // See https://gitlab.torproject.org/tpo/core/torspec/-/issues/371#note_3260658