OpsLog/internal/rotator/dcu1/session_test.go

package dcu1

import (
	"net"
	"strconv"
	"strings"
	"sync"
	"testing"
	"time"
)

// fakeRT21 is a controller that accepts ONE session at a time and counts how
// many it was asked for, which is the thing under test.
type fakeRT21 struct {
	ln net.Listener

	mu       sync.Mutex
	sessions int
	cmds     []string
}

func newFakeRT21(t *testing.T) *fakeRT21 {
	t.Helper()
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}
	f := &fakeRT21{ln: ln}
	go f.serve()
	t.Cleanup(func() { _ = ln.Close() })
	return f
}

func (f *fakeRT21) serve() {
	for {
		conn, err := f.ln.Accept()
		if err != nil {
			return
		}
		f.mu.Lock()
		f.sessions++
		f.mu.Unlock()
		// Served one at a time, on purpose: a second caller waits in the accept
		// queue rather than being talked to, which is how these modules behave.
		f.handle(conn)
	}
}

func (f *fakeRT21) handle(conn net.Conn) {
	defer conn.Close()
	buf := make([]byte, 64)
	for {
		_ = conn.SetReadDeadline(time.Now().Add(2 * time.Second))
		n, err := conn.Read(buf)
		if n > 0 {
			for _, cmd := range strings.Split(string(buf[:n]), ";") {
				if cmd = strings.TrimSpace(cmd); cmd == "" {
					continue
				}
				f.mu.Lock()
				f.cmds = append(f.cmds, cmd)
				f.mu.Unlock()
				if cmd == "AI1" {
					_, _ = conn.Write([]byte(";123"))
				}
			}
		}
		if err != nil {
			return
		}
	}
}

func (f *fakeRT21) port() int {
	return f.ln.Addr().(*net.TCPAddr).Port
}

func (f *fakeRT21) seen() (int, []string) {
	f.mu.Lock()
	defer f.mu.Unlock()
	return f.sessions, append([]string(nil), f.cmds...)
}

// One session for the whole conversation.
//
// It used to be one per command: the heading is polled twice a second while the
// antenna turns and GoTo sends two commands (AP1 then AM1), each with its own
// connect and close. An RT-21's Ethernet option — like most embedded serial
// servers — commonly accepts a single session and needs a moment to release it,
// so the churn alone looked like a controller ignoring half of what it was told.
func TestOneSessionServesEveryCommand(t *testing.T) {
	f := newFakeRT21(t)
	c := New("127.0.0.1", f.port())
	defer c.Close()

	if az, _, err := c.Heading(); err != nil || az != 123 {
		t.Fatalf("Heading() = %d, %v; want 123", az, err)
	}
	if err := c.GoTo(240); err != nil {
		t.Fatalf("GoTo: %v", err)
	}
	if az, _, err := c.Heading(); err != nil || az != 123 {
		t.Fatalf("second Heading() = %d, %v", az, err)
	}

	sessions, cmds := f.seen()
	if sessions != 1 {
		t.Errorf("the controller was asked for %d sessions; four commands must share one", sessions)
	}
	want := []string{"AI1", "AP1240", "AM1", "AI1"}
	if strings.Join(cmds, ",") != strings.Join(want, ",") {
		t.Errorf("commands %v, want %v", cmds, want)
	}
}

// A session the controller has dropped is redialled, and the command that found
// it dead is retried rather than reported as a failure — a kept socket's first
// write succeeds long after the far end has gone.
func TestADroppedSessionIsRedialled(t *testing.T) {
	f := newFakeRT21(t)
	c := New("127.0.0.1", f.port())
	defer c.Close()

	if _, _, err := c.Heading(); err != nil {
		t.Fatalf("first Heading: %v", err)
	}
	// The controller power-cycles: close our end the way a dropped session
	// leaves it, then ask again.
	c.mu.Lock()
	if c.conn != nil {
		_ = c.conn.Close() // closed underneath, but still held — a half-dead socket
	}
	c.mu.Unlock()

	if az, _, err := c.Heading(); err != nil || az != 123 {
		t.Fatalf("Heading after the session dropped = %d, %v; want 123", az, err)
	}
	if sessions, _ := f.seen(); sessions != 2 {
		t.Errorf("%d sessions; the dropped one should have been redialled exactly once", sessions)
	}
}

// Nothing is kept open for a controller that is not there, and the error names
// the address so it can be checked.
func TestADeadControllerReportsWhereItLooked(t *testing.T) {
	// Port 1 on loopback: nothing listens, and the refusal is immediate.
	c := New("127.0.0.1", 1)
	defer c.Close()
	_, _, err := c.Heading()
	if err == nil {
		t.Fatal("no error from a controller that is not there")
	}
	if !strings.Contains(err.Error(), "127.0.0.1:"+strconv.Itoa(1)) {
		t.Errorf("error %q does not name the address it tried", err)
	}
	c.mu.Lock()
	held := c.conn != nil
	c.mu.Unlock()
	if held {
		t.Error("a failed dial left a connection behind")
	}
}