fix: Save and close taking time when Flex or Icom is not connected

internal/cat/flex.go

@@ -4,6 +4,7 @@ package cat
 
 import (
 	"bufio"
+	"context"
 	"encoding/binary"
 	"fmt"
 	"math"
@@ -25,9 +26,10 @@ type Flex struct {
 	host string
 	port int
 
-	mu        sync.Mutex
-	conn      net.Conn
-	wmu       sync.Mutex // serialises writes to conn
+	mu         sync.Mutex
+	conn       net.Conn
+	dialCancel context.CancelFunc // cancels an in-flight Connect dial (Interrupt/Stop); nil when not dialing
+	wmu        sync.Mutex         // serialises writes to conn
 	seq       int
 	handle    string
 	model     string
@@ -171,7 +173,19 @@ func (f *Flex) Connect() error {
 	if host == "" {
 		return fmt.Errorf("flex: no radio IP configured")
 	}
-	conn, err := net.DialTimeout("tcp", net.JoinHostPort(host, strconv.Itoa(port)), 5*time.Second)
+	// Cancellable dial: Interrupt() (called by Stop/Start) aborts it at once so a
+	// dead radio's 5 s dial timeout doesn't make Stop / Settings "Save & Close"
+	// wait several seconds for the poll goroutine to give up.
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	f.mu.Lock()
+	f.dialCancel = cancel
+	f.mu.Unlock()
+	var d net.Dialer
+	conn, err := d.DialContext(ctx, "tcp", net.JoinHostPort(host, strconv.Itoa(port)))
+	cancel()
+	f.mu.Lock()
+	f.dialCancel = nil
+	f.mu.Unlock()
 	if err != nil {
 		return fmt.Errorf("flex: connect %s:%d: %w", host, port, err)
 	}
@@ -224,6 +238,23 @@ func (f *Flex) Disconnect() {
 	}
 }
 
+// Interrupt aborts an in-flight Connect dial so Stop()/Start() (Settings
+// "Save & Close", CAT backend switch) don't block on a dead radio's 5 s dial
+// timeout. Satisfies the Manager's optional interruptible interface. Safe to call
+// anytime and from another goroutine; a no-op when not dialing.
+func (f *Flex) Interrupt() {
+	f.mu.Lock()
+	cancel := f.dialCancel
+	c := f.conn
+	f.mu.Unlock()
+	if cancel != nil {
+		cancel()
+	}
+	if c != nil {
+		_ = c.Close() // unblock the reader if we're already past the dial
+	}
+}
+
 // send writes a sequenced command (C<seq>|<cmd>) to the radio and returns the
 // sequence number (so the caller can match the R<seq> response, e.g. to learn a
 // new spot's index). Returns 0 when not connected. Best effort.