Channel: Make mutable() and engage_padding_activities infallible

As per
  https://gitlab.torproject.org/tpo/core/arti/-/merge_requests/657#note_2826151

This gets rid of quite some Bug error paths.

crates/tor-chanmgr/src/builder.rs

@@ -2,7 +2,6 @@
 
 use std::io;
 use std::net::SocketAddr;
-use std::result::Result as StdResult;
 use std::sync::{Arc, Mutex};
 
 use crate::{event::ChanMgrEventSender, Error};
@@ -255,8 +254,8 @@ impl crate::mgr::AbstractChannel for tor_proto::channel::Channel {
     fn reparameterize(&mut self, updates: Arc<ChannelsParamsUpdates>) -> tor_proto::Result<()> {
         self.reparameterize(updates)
     }
-    fn engage_padding_activities(&self) -> StdResult<(), tor_error::Bug> {
-        self.engage_padding_activities()
+    fn engage_padding_activities(&self) {
+        self.engage_padding_activities();
     }
 }
 

crates/tor-chanmgr/src/mgr.rs

@@ -54,7 +54,7 @@ pub(crate) trait AbstractChannel: Clone {
     /// Idempotent.
     ///
     /// There is no way to undo the effect of this call.
-    fn engage_padding_activities(&self) -> StdResult<(), tor_error::Bug>;
+    fn engage_padding_activities(&self);
 }
 
 /// Trait to describe how channels are created.
@@ -148,7 +148,7 @@ impl<CF: ChannelFactory> AbstractChanMgr<CF> {
 
         match usage {
             CU::Dir | CU::UselessCircuit => {}
-            CU::Exit => chan.0.engage_padding_activities()?,
+            CU::Exit => chan.0.engage_padding_activities(),
         }
 
         Ok(chan)
@@ -393,9 +393,7 @@ mod test {
             self.last_params = Some((*updates).clone());
             Ok(())
         }
-        fn engage_padding_activities(&self) -> StdResult<(), tor_error::Bug> {
-            Ok(())
-        }
+        fn engage_padding_activities(&self) {}
     }
 
     impl FakeChannel {

crates/tor-chanmgr/src/mgr/map.rs

@@ -583,9 +583,7 @@ mod test {
             self.params_update = Some(update);
             Ok(())
         }
-        fn engage_padding_activities(&self) -> StdResult<(), tor_error::Bug> {
-            Ok(())
-        }
+        fn engage_padding_activities(&self) {}
     }
     fn ch(ident: &'static str) -> ChannelState<FakeChannel> {
         let channel = FakeChannel {

crates/tor-chanmgr/src/mgr/map/padding_test.rs

@@ -278,7 +278,7 @@ async fn padding_control_through_layers() {
     c.expect_0();
 
     eprintln!("### Exit ###");
-    c.channel.engage_padding_activities().unwrap();
+    c.channel.engage_padding_activities();
     c.expect_1(Expected {
         enabled: Some(true), // we now turn on our padding sender
         timing: None,        // with default parameters

crates/tor-proto/src/channel.rs

@@ -412,18 +412,18 @@ impl Channel {
     }
 
     /// Acquire the lock on `mutable` (and handle any poison error)
-    fn mutable(&self) -> StdResult<MutexGuard<MutableDetails>, tor_error::Bug> {
+    fn mutable(&self) -> MutexGuard<MutableDetails> {
         self.details
             .mutable
             .lock()
-            .map_err(|_| internal!("channel details poisoned"))
+            .expect("channel details poisoned")
     }
 
     /// Specify that this channel should do activities related to channel padding
     ///
     /// See [`AbstractChannel::set_channel_padding_relevant`]
-    pub fn engage_padding_activities(&self) -> StdResult<(), tor_error::Bug> {
-        let mut mutable = self.mutable()?;
+    pub fn engage_padding_activities(&self) {
+        let mut mutable = self.mutable();
 
         match &mutable.padding {
             PCS::UsageDoesNotImplyPadding {
@@ -442,7 +442,7 @@ impl Channel {
 
                 match self.send_control(CtrlMsg::ConfigUpdate(Arc::new(params))) {
                     Ok(()) => {}
-                    Err(ChannelClosed) => return Ok(()),
+                    Err(ChannelClosed) => return,
                 }
 
                 mutable.padding = PCS::PaddingConfigured;
@@ -454,7 +454,6 @@ impl Channel {
         }
 
         drop(mutable); // release the lock now: lock span covers the send, ensuring ordering
-        Ok(())
     }
 
     /// Reparameterise (update parameters; reconfigure)