Add an auto-measure toggle with a cable length range, and console keys through the harness

harness/main.go

@@ -20,6 +20,8 @@ import (
 	"strings"
 	"syscall"
 	"time"
+
+	"golang.org/x/sys/unix"
 )
 
 var errInterrupted = errors.New("interrupted")
@@ -43,18 +45,40 @@ func main() {
 		os.Exit(1)
 	}
 
+	restoreTerm := rawKeys()
+
 	var err error
 	if *fuzzN > 0 {
 		err = fuzz(*fuzzN, *runFor, flag.Args())
 	} else {
 		err = run(*runFor, *at, os.Stdout, flag.Args())
 	}
+	restoreTerm()
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
 }
 
+// Console keys reach cabletest as they are pressed, the same as at the
+// appliance; isig stays on so ^C still stops the run through the relay.
+func rawKeys() func() {
+	fd := int(os.Stdin.Fd())
+	orig, err := unix.IoctlGetTermios(fd, unix.TCGETS)
+	if err != nil {
+		return func() {}
+	}
+	saved := *orig
+	raw := *orig
+	raw.Lflag &^= unix.ICANON | unix.ECHO
+	raw.Cc[unix.VMIN] = 1
+	raw.Cc[unix.VTIME] = 0
+	if unix.IoctlSetTermios(fd, unix.TCSETS, &raw) != nil {
+		return func() {}
+	}
+	return func() { unix.IoctlSetTermios(fd, unix.TCSETS, &saved) }
+}
+
 func fuzz(n int, runFor time.Duration, args []string) error {
 	failed := 0
 	for i := 1; i <= n; i++ {
@@ -133,6 +157,13 @@ func run(runFor time.Duration, at string, out io.Writer, args []string) error {
 	// killed when go run dies, and an orphan holding the wire poisons every
 	// measurement after it.
 	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	// The child's own process group makes the tty off limits to it (reading
+	// from the background raises SIGTTIN), so the harness reads and forwards.
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return err
+	}
+	go io.Copy(stdin, os.Stdin)
 	if err := cmd.Start(); err != nil {
 		return err
 	}