Refactor IdleTracker to handle StateIdle transitions

* Remove stutter naming for package and types
* Stop treating StateIdle the same as StateClosed, rather transitions to
  StateIdle will keep API timeout window open
* Remove redundate code

Fixes #7826

Signed-off-by: Jhon Honce <jhonce@redhat.com>

pkg/api/server/idle/tracker.go

@@ -0,0 +1,96 @@
+package idle
+
+import (
+	"net"
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/sirupsen/logrus"
+)
+
+// Tracker holds the state for the server's idle tracking
+type Tracker struct {
+	// Duration is the API idle window
+	Duration time.Duration
+	hijacked int                   // count of active connections managed by handlers
+	managed  map[net.Conn]struct{} // set of active connections managed by http package
+	mux      sync.Mutex            // protect managed map
+	timer    *time.Timer
+	total    int // total number of connections made to this server instance
+}
+
+// NewTracker creates and initializes a new Tracker object
+// For best behavior, duration should be 2x http idle connection timeout
+func NewTracker(idle time.Duration) *Tracker {
+	return &Tracker{
+		managed:  make(map[net.Conn]struct{}),
+		Duration: idle,
+		timer:    time.NewTimer(idle),
+	}
+}
+
+// ConnState is called on HTTP connection state changes.
+// - Once StateHijacked, StateClose is _NOT_ called on that connection
+// - There are two "idle" timeouts, the http idle connection (not to be confused with the TCP/IP idle socket timeout)
+//   and the API idle window.  The caller should set the http idle timeout to 2x the time provided to NewTacker() which
+//   is the API idle window.
+func (t *Tracker) ConnState(conn net.Conn, state http.ConnState) {
+	t.mux.Lock()
+	defer t.mux.Unlock()
+
+	logrus.Debugf("IdleTracker %p:%v %dm+%dh/%dt connection(s)", conn, state, len(t.managed), t.hijacked, t.TotalConnections())
+	switch state {
+	case http.StateNew, http.StateActive:
+		// stop the API timer when the server transitions any connection to an "active" state
+		t.managed[conn] = struct{}{}
+		t.timer.Stop()
+		t.total++
+	case http.StateHijacked:
+		// hijacked connections should call Close() when finished.
+		// Note: If a handler hijack's a connection and then doesn't Close() it,
+		//       the API timer will not fire and the server will _NOT_ timeout.
+		delete(t.managed, conn)
+		t.hijacked++
+	case http.StateIdle:
+		// When any connection goes into the http idle state, we know:
+		// - we have an active connection
+		// - the API timer should not be counting down (See case StateNew/StateActive)
+		break
+	case http.StateClosed:
+		oldActive := t.ActiveConnections()
+
+		// Either the server or a hijacking handler has closed the http connection to a client
+		if _, found := t.managed[conn]; found {
+			delete(t.managed, conn)
+		} else {
+			t.hijacked-- // guarded by t.mux above
+		}
+
+		// Transitioned from any "active" connection to no connections
+		if oldActive > 0 && t.ActiveConnections() == 0 {
+			t.timer.Stop()            // See library source for Reset() issues and why they are not fixed
+			t.timer.Reset(t.Duration) // Restart the API window timer
+		}
+	}
+}
+
+// Close is used to update Tracker that a StateHijacked connection has been closed by handler (StateClosed)
+func (t *Tracker) Close() {
+	t.ConnState(nil, http.StateClosed)
+}
+
+// ActiveConnections returns the number of current managed or StateHijacked connections
+func (t *Tracker) ActiveConnections() int {
+	return len(t.managed) + t.hijacked
+}
+
+// TotalConnections returns total number of connections made to this instance of the service
+func (t *Tracker) TotalConnections() int {
+	return t.total
+}
+
+// Done is called when idle timer has expired
+func (t *Tracker) Done() <-chan time.Time {
+	return t.timer.C
+}