ice: Fix USE-CANDIDATE in controlled agent (#647)

A controlled agent should reply to USE-CANDIDATE binding requests, also
when the candidate pair state isn't already Succeeded. In this case the
candidate pair should be nominated immediately if the ping succeeds.

Ported from pion/ice@e0db6d2.

ice/src/agent/agent_selector.rs

@@ -488,6 +488,12 @@ impl ControlledSelector for AgentInternal {
                 p.state
                     .store(CandidatePairState::Succeeded as u8, Ordering::SeqCst);
                 log::trace!("Found valid candidate pair: {}", p);
+
+                if p.nominate_on_binding_success.load(Ordering::SeqCst)
+                    && self.agent_conn.get_selected_pair().is_none()
+                {
+                    self.set_selected_pair(Some(Arc::clone(&p))).await;
+                }
             } else {
                 // This shouldn't happen
                 log::error!("Success response from invalid candidate pair");
@@ -524,7 +530,6 @@ impl ControlledSelector for AgentInternal {
                     if self.agent_conn.get_selected_pair().is_none() {
                         self.set_selected_pair(Some(Arc::clone(&p))).await;
                     }
-                    self.send_binding_success(m, local, remote).await;
                 } else {
                     // If the received Binding request triggered a new check to be
                     // enqueued in the triggered-check queue (Section 7.3.1.4), once the
@@ -534,12 +539,12 @@ impl ControlledSelector for AgentInternal {
                     // MUST remove the candidate pair from the valid list, set the
                     // candidate pair state to Failed, and set the checklist state to
                     // Failed.
-                    self.ping_candidate(local, remote).await;
+                    p.nominate_on_binding_success.store(true, Ordering::SeqCst);
                 }
-            } else {
-                self.send_binding_success(m, local, remote).await;
-                self.ping_candidate(local, remote).await;
             }
+
+            self.send_binding_success(m, local, remote).await;
+            self.ping_candidate(local, remote).await;
         }
     }
 }

ice/src/candidate/mod.rs

@@ -234,6 +234,7 @@ pub struct CandidatePair {
     pub(crate) binding_request_count: AtomicU16,
     pub(crate) state: AtomicU8, // convert it to CandidatePairState,
     pub(crate) nominated: AtomicBool,
+    pub(crate) nominate_on_binding_success: AtomicBool,
 }
 
 impl Default for CandidatePair {
@@ -245,6 +246,7 @@ impl Default for CandidatePair {
             state: AtomicU8::new(CandidatePairState::Waiting as u8),
             binding_request_count: AtomicU16::new(0),
             nominated: AtomicBool::new(false),
+            nominate_on_binding_success: AtomicBool::new(false),
         }
     }
 }
@@ -297,6 +299,7 @@ impl CandidatePair {
             state: AtomicU8::new(CandidatePairState::Waiting as u8),
             binding_request_count: AtomicU16::new(0),
             nominated: AtomicBool::new(false),
+            nominate_on_binding_success: AtomicBool::new(false),
         }
     }