diff --git a/crates/tor-proto/src/circuit/reactor.rs b/crates/tor-proto/src/circuit/reactor.rs
index 3d923a93b..3525cc818 100644
--- a/crates/tor-proto/src/circuit/reactor.rs
+++ b/crates/tor-proto/src/circuit/reactor.rs
@@ -35,6 +35,8 @@ use std::pin::Pin;
 use tor_cell::chancell::msg::{AnyChanMsg, Relay};
 use tor_cell::relaycell::msg::{AnyRelayMsg, End, Sendme};
 use tor_cell::relaycell::{AnyRelayCell, RelayCmd, StreamId, UnparsedRelayCell};
+#[cfg(feature = "hs-service")]
+use crate::stream::IncomingStreamRequest;
 
 use futures::channel::{mpsc, oneshot};
 use futures::Stream;
@@ -537,6 +539,35 @@ pub struct Reactor {
     channel_id: CircId,
     /// A handler for a meta cell, together with a result channel to notify on completion.
     meta_handler: Option<Box<dyn MetaCellHandler>>,
+    /// A handler for incoming stream requests.
+    #[cfg(feature = "hs-service")]
+    incoming_stream_req_handler: Option<IncomingStreamRequestHandler>,
+}
+
+/// Information about an incoming stream request.
+#[cfg(feature = "hs-service")]
+#[derive(Debug)]
+pub(super) struct IncomingStreamRequestContext {
+    /// The [`IncomingStreamRequest`].
+    pub(super) req: IncomingStreamRequest,
+    /// The ID of the stream being requested.
+    pub(super) stream_id: StreamId,
+    /// The [`HopNum`].
+    pub(super) hop_num: HopNum,
+    /// A channel for receiving messages from this stream.
+    pub(super) receiver: mpsc::Receiver<UnparsedRelayCell>,
+    /// A channel for sending messages to be sent on this stream.
+    pub(super) msg_tx: mpsc::Sender<AnyRelayMsg>,
+}
+
+/// Data required for handling an incoming stream request.
+#[cfg(feature = "hs-service")]
+#[derive(Debug)]
+struct IncomingStreamRequestHandler {
+    /// A sender for sharing information about an incoming stream request.
+    incoming_sender: mpsc::Sender<IncomingStreamRequestContext>,
+    /// A [`AnyCmdChecker`] for validating incoming stream requests.
+    cmd_checker: AnyCmdChecker,
 }
 
 impl Reactor {
@@ -573,6 +604,8 @@ impl Reactor {
             channel_id,
             crypto_out,
             meta_handler: None,
+            #[cfg(feature = "hs-service")]
+            incoming_stream_req_handler: None,
             mutable: mutable.clone(),
         };
 
@@ -1247,6 +1280,22 @@ impl Reactor {
         }
     }
 
+    /// Try to install a given cell handler on this circuit.
+    #[cfg(feature = "hs-service")]
+    fn set_incoming_stream_req_handler(
+        &mut self,
+        handler: IncomingStreamRequestHandler,
+    ) -> Result<()> {
+        if self.incoming_stream_req_handler.is_none() {
+            self.incoming_stream_req_handler = Some(handler);
+            Ok(())
+        } else {
+            Err(Error::from(internal!(
+                "Tried to install a BEGIN cell handler before the old one was gone."
+            )))
+        }
+    }
+
     /// Handle a CtrlMsg other than Create and Shutdown.
     fn handle_control(&mut self, cx: &mut Context<'_>, msg: CtrlMsg) -> Result<()> {
         trace!("{}: reactor received {:?}", self.unique_id, msg);