Speak protocol 3.0 and fall back to 2.0 only when that is the reflector's maximum.

A reflector that has moved to 3.0 will not accept a station that always announces 2.0, and a 2.x reflector still needs one explicit plaintext session.

Co-authored-by: Cursor <cursoragent@cursor.com>

station/protocol_select_test.go

@@ -0,0 +1,140 @@
+package station_test
+
+import (
+	"context"
+	"net"
+	"os"
+	"testing"
+	"time"
+
+	"gitea.neitzel.de/konrad/funknetz/station"
+)
+
+func TestVersionErrorFallsBackWhenTheMaximumIs2(t *testing.T) {
+	for _, msg := range []string{
+		"Unsupported protocol version 3.0. May be at most 2.0.",
+		"Unsupported protocol version 3.0. May be at most 2.5.",
+	} {
+		t.Run(msg, func(t *testing.T) {
+			refl := newReflector(t)
+			path := writeConfigFile(t, configJSON(t, "127.0.0.1", refl.port, "DL1ABC", "key", 20))
+			clock := newFakeClock()
+			st, err := station.New(station.Options{ConfigPath: path, Clock: clock})
+			if err != nil {
+				t.Fatal(err)
+			}
+			ctx, cancel := context.WithCancel(t.Context())
+			defer cancel()
+			go func() { _ = st.Run(ctx) }()
+			refl.accept(t)
+			typ, body := refl.readFrame(t)
+			if typ != 5 || !versionIs(body, 3, 0) {
+				t.Fatalf("type %d body %v", typ, body)
+			}
+			refl.writeFrame(t, 13, appendStr(nil, msg))
+			refl.accept(t)
+			typ, body = refl.readFrame(t)
+			if typ != 5 || !versionIs(body, 2, 0) {
+				t.Fatalf("fallback type %d body %v", typ, body)
+			}
+		})
+	}
+}
+
+func TestVersionErrorBelow2Stops(t *testing.T) {
+	for _, msg := range []string{
+		"Unsupported protocol version 3.0. May be at most 1.9.",
+		"Unsupported protocol version 3.0. May be at most 0.6.",
+	} {
+		t.Run(msg, func(t *testing.T) {
+			refl := newReflector(t)
+			path := writeConfigFile(t, configJSON(t, "127.0.0.1", refl.port, "DL1ABC", "key", 20))
+			clock := newFakeClock()
+			st, err := station.New(station.Options{ConfigPath: path, Clock: clock})
+			if err != nil {
+				t.Fatal(err)
+			}
+			ctx, cancel := context.WithCancel(t.Context())
+			defer cancel()
+			go func() { _ = st.Run(ctx) }()
+			refl.accept(t)
+			refl.readFrame(t)
+			refl.writeFrame(t, 13, appendStr(nil, msg))
+			got, err := st.Wait(ctx, func(s station.State) bool { return s.Detail == msg })
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got.Connection != "Disconnected" || got.Protocol != "" {
+				t.Fatalf("State = %+v", got)
+			}
+			clock.Advance(2 * time.Second)
+			refl.ln.(*net.TCPListener).SetDeadline(time.Now().Add(150 * time.Millisecond))
+			if conn, err := refl.ln.Accept(); err == nil {
+				conn.Close()
+				t.Fatal("retried")
+			}
+		})
+	}
+}
+
+func TestDowngradeOtherThan2Stops(t *testing.T) {
+	for _, tc := range []struct {
+		major, minor uint16
+		want         string
+	}{
+		{1, 0, "Unsupported protocol version 1.0"},
+		{4, 2, "Unsupported protocol version 4.2"},
+	} {
+		t.Run(tc.want, func(t *testing.T) {
+			refl := newReflector(t)
+			path := writeConfigFile(t, configJSON(t, "127.0.0.1", refl.port, "DL1ABC", "key", 20))
+			clock := newFakeClock()
+			st, err := station.New(station.Options{ConfigPath: path, Clock: clock})
+			if err != nil {
+				t.Fatal(err)
+			}
+			ctx, cancel := context.WithCancel(t.Context())
+			defer cancel()
+			go func() { _ = st.Run(ctx) }()
+			refl.accept(t)
+			refl.readFrame(t)
+			refl.writeFrame(t, 6, versionWire(tc.major, tc.minor))
+			got, err := st.Wait(ctx, func(s station.State) bool { return s.Detail == tc.want })
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got.Protocol != "" || got.Connection != "Disconnected" {
+				t.Fatalf("State = %+v", got)
+			}
+			clock.Advance(2 * time.Second)
+			refl.ln.(*net.TCPListener).SetDeadline(time.Now().Add(150 * time.Millisecond))
+			if conn, err := refl.ln.Accept(); err == nil {
+				conn.Close()
+				t.Fatal("retried")
+			}
+		})
+	}
+}
+
+func TestDowngradeDoesNotCreateTheCertificateDirectory(t *testing.T) {
+	refl := newReflector(t)
+	dir := t.TempDir()
+	path := dir + "/funknetz.json"
+	body := configWithDir(t, "127.0.0.1", refl.port, "DL1ABC", "key", 20, "./funknetz", "")
+	if err := os.WriteFile(path, []byte(body), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	clock := newFakeClock()
+	st, err := station.New(station.Options{ConfigPath: path, Clock: clock})
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithCancel(t.Context())
+	defer cancel()
+	go func() { _ = st.Run(ctx) }()
+	refl.accept(t)
+	declineTo2(t, refl)
+	if _, err := os.Stat(dir + "/funknetz"); err == nil {
+		t.Fatal("created the certificate directory on a 2.0 fallback")
+	}
+}