roverd tty alerts stuffs

pi/roverd/console_notifier.go

@@ -0,0 +1,67 @@
+package roverd
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"sync"
+	"time"
+)
+
+const roverConsolePath = "/dev/tty1"
+
+// ConsoleNotifier writes the small set of rover lifecycle events that must be
+// visible even when nobody is logged in. This intentionally targets tty1
+// directly instead of using wall: wall discovers recipients through utmp, so
+// it does not reliably reach a virtual console that is only showing a login
+// prompt.
+type ConsoleNotifier struct {
+	path   string
+	logger *log.Logger
+	mu     sync.Mutex
+}
+
+// NewConsoleNotifier returns the production notifier for the rover's primary
+// local virtual console. Keeping the path inside the notifier also gives tests
+// a way to substitute a regular temporary file without touching a real TTY.
+func NewConsoleNotifier(logger *log.Logger) *ConsoleNotifier {
+	return newConsoleNotifier(roverConsolePath, logger)
+}
+
+func newConsoleNotifier(path string, logger *log.Logger) *ConsoleNotifier {
+	return &ConsoleNotifier{path: path, logger: logger}
+}
+
+// Notify appends one self-contained alert to the console. Console output is a
+// diagnostic convenience rather than part of rover control, so an unavailable
+// tty is logged but never allowed to stop startup, reconnection, docking, or
+// reboot behavior.
+func (n *ConsoleNotifier) Notify(message string) {
+	if n == nil {
+		return
+	}
+
+	n.mu.Lock()
+	defer n.mu.Unlock()
+
+	console, err := os.OpenFile(n.path, os.O_WRONLY|os.O_APPEND, 0)
+	if err != nil {
+		n.logFailure("open", err)
+		return
+	}
+	defer console.Close()
+
+	// Leading and trailing CRLFs keep the alert separate from an agetty login
+	// prompt, while plain text avoids leaving an unknown terminal in a modified
+	// color or cursor state.
+	timestamp := time.Now().UTC().Format("2006-01-02 15:04:05 UTC")
+	if _, err := fmt.Fprintf(console, "\r\n*** rover alert - %s ***\r\n%s\r\n", timestamp, message); err != nil {
+		n.logFailure("write", err)
+	}
+}
+
+func (n *ConsoleNotifier) logFailure(operation string, err error) {
+	if n.logger != nil {
+		n.logger.Printf("console notification %s failed for %s: %v", operation, n.path, err)
+	}
+}