1 files changed, 34 insertions, 21 deletions

diff --git a/src/protocol.rs b/src/protocol.rs
index 3a24195..d6fce5f 100644
--- a/src/protocol.rs
+++ b/src/protocol.rs
@@ -36,6 +36,15 @@ pub const LINK_DEBOUNCE_MISSES: u32 = 2;
 /// How long to wait for a link response after sending the query.
 const LINK_RESPONSE_TIMEOUT: Duration = Duration::from_millis(400);
 
+/// Input report id the dongle answers with when the headset is linked.
+const LINK_RESPONSE_REPORT: u8 = 0x3c;
+/// Selector byte we query with; the response echoes it back.
+const LINK_SELECTOR: u8 = 0x01;
+/// Command prefix at the start of the query payload.
+const CMD_PREFIX: [u8; 2] = [0x09, 0x22];
+/// Link query frame size: report id + 60-byte payload.
+const LINK_QUERY_LEN: usize = 61;
+
 /// Headset link state as seen through the dongle.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum LinkState {
@@ -52,20 +61,20 @@ pub enum Transition {
     ToDisconnected { initial: bool },
 }
 
-/// Builds the 61-byte link query output report (report id `0x3a` + payload).
-pub fn link_query_frame() -> Vec<u8> {
-    let mut frame = vec![0u8; 61];
+/// Builds the link query output report (report id `0x3a` + payload).
+pub fn link_query_frame() -> [u8; LINK_QUERY_LEN] {
+    let mut frame = [0u8; LINK_QUERY_LEN];
     frame[0] = reports::OUT_60_C;
-    frame[1] = 0x09;
-    frame[2] = 0x22;
-    frame[3] = 0x01;
+    frame[1] = CMD_PREFIX[0];
+    frame[2] = CMD_PREFIX[1];
+    frame[3] = LINK_SELECTOR;
     frame
 }
 
 /// True if `data` is a link-status response report (`0x3c` echoing the
 /// query selector).
 pub fn is_link_response(data: &[u8]) -> bool {
-    data.len() >= 2 && data[0] == 0x3c && data[1] == 0x01
+    data.len() >= 2 && data[0] == LINK_RESPONSE_REPORT && data[1] == LINK_SELECTOR
 }
 
 /// Queries the dongle once for the headset link state. Returns
@@ -116,25 +125,29 @@ impl StateTracker {
             if self.state == Some(LinkState::Connected) {
                 return None;
             }
-            let initial = self.state.is_none();
-            self.state = Some(LinkState::Connected);
-            if initial && !self.fire_initial {
-                None
-            } else {
-                Some(Transition::ToConnected { initial })
-            }
+            self.settle(LinkState::Connected)
         } else {
             self.misses += 1;
             if self.misses < LINK_DEBOUNCE_MISSES || self.state == Some(LinkState::Disconnected) {
                 return None;
             }
-            let initial = self.state.is_none();
-            self.state = Some(LinkState::Disconnected);
-            if initial && !self.fire_initial {
-                None
-            } else {
-                Some(Transition::ToDisconnected { initial })
-            }
+            self.settle(LinkState::Disconnected)
+        }
+    }
+
+    /// Pin the state, producing the transition unless it is the first
+    /// determination and initial hooks are suppressed.
+    fn settle(&mut self, state: LinkState) -> Option<Transition> {
+        let initial = self.state.is_none();
+        self.state = Some(state);
+        let transition = match state {
+            LinkState::Connected => Transition::ToConnected { initial },
+            LinkState::Disconnected => Transition::ToDisconnected { initial },
+        };
+        if initial && !self.fire_initial {
+            None
+        } else {
+            Some(transition)
         }
     }
 }