Report ssh command failures to the surface (#1959)

Report ssh command failures to the surface (#1959)

The ssh debug commands told the user when something went wrong but
never told the surface that ran them, so `ssh host cmd` always exited 0
and a few failures were not reported at all. A failed command now
returns its error, a failure the user has already heard about is a
commands.Failure, and the ssh exec path exits 1 for either. The command
bodies also lose their ssh prefixes and the duplication they carried
over from ssh.go; both goldens pin that nothing else changed.

- Dispatch returns the callback's error, or shlex's; the ssh session
  logs it at debug, and not at all for a Failure the user already saw
- commands.Fail writes a message and returns it as a Failure in one step;
  an unknown command, `help` for a command that is not there, a failed
  reload and an unbalanced quote are failures
- ssh exec exit-status is 1 for a command, flag or failure error, 0
  otherwise; the e2e golden records the exit status for every case
- Clone rebinds help to the copy, so an ssh session's help lists logout
  and `help logout` and `logout -h` answer; sshd.LogoutCommand is the
  session's logout, exported for tests
- "did not understand" names the first word only, the one looked up;
  DispatchArgs takes just the tokens
- log-format writes its refusal to the user, as log-level does
- print-relays emits the relay error as a string and omits the key when
  there is none, where it printed {} or "Error":null
- list-hostmap and list-lighthouse-addrmap -json return the encode
  error; print-cert reports a certificate that will not marshal
- a flags type that is not the one registered is an internal error, not
  a silent success
- command functions and flag types are <name>Command and <name>Flags;
  parseVpnAddr and listHostMapFlagSet replace the repeated parse block
  and flag set; close-tunnel sends through sendCloseTunnel

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

commands_test.go

@@ -0,0 +1,67 @@
+package nebula
+
+import (
+	"bytes"
+	"io"
+	"net/netip"
+	"testing"
+
+	"github.com/slackhq/nebula/commands"
+	"github.com/slackhq/nebula/logging"
+	"github.com/slackhq/nebula/test"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestLogFormatRefusalIsShown: a format the logger does not know is reported to the user
+// as a failure, rather than returned bare, which over ssh was silence.
+func TestLogFormatRefusalIsShown(t *testing.T) {
+	l := logging.NewLogger(io.Discard)
+	out := &bytes.Buffer{}
+	w := commands.NewStringWriter(out)
+
+	var f *commands.Failure
+	require.ErrorAs(t, logFormatCommand(l, nil, []string{"bogus"}, w), &f)
+	assert.Equal(t, "Unable to set log format: unknown log format `bogus`. possible formats: [text json]\n", out.String())
+
+	out.Reset()
+	require.NoError(t, logFormatCommand(l, nil, []string{"JSON"}, w))
+	assert.Equal(t, "Log format is: json\n", out.String())
+}
+
+// TestPrintRelaysReportsErrorsAsText: the Error field was an error value, which encodes
+// as {} and lost the message. It is the message now, and absent when there is none.
+func TestPrintRelaysReportsErrorsAsText(t *testing.T) {
+	l := test.NewLogger()
+	hm := newHostMap(l)
+	relay := netip.MustParseAddr("10.0.0.1")
+	peer := netip.MustParseAddr("10.0.0.2")
+
+	// A relay host that is in Relays but not in Hosts, so its hostinfo cannot be found.
+	hm.Relays[1] = &HostInfo{vpnAddrs: []netip.Addr{relay}}
+	ifce := &Interface{hostMap: hm}
+
+	out := &bytes.Buffer{}
+	require.NoError(t, printRelaysCommand(ifce, &printTunnelFlags{}, nil, commands.NewStringWriter(out)))
+	assert.JSONEq(t, `{"Relays":[{"NebulaAddr":"10.0.0.1","RelayForAddrs":[{"Error":"could not find hostinfo","Type":"","State":"","PeerAddr":"","LocalIndex":0,"RemoteIndex":0,"RelayedThrough":null}]}]}`, out.String())
+
+	// The same relay host, found, relaying for a peer whose index matches: no Error key.
+	hi := hm.Relays[1]
+	r := &Relay{Type: ForwardingType, State: Established, PeerAddr: peer, LocalIndex: 1, RemoteIndex: 2}
+	hi.relayState = RelayState{
+		relayForByAddr: map[netip.Addr]*Relay{peer: r},
+		relayForByIdx:  map[uint32]*Relay{r.LocalIndex: r},
+	}
+	hm.Hosts[relay] = hi
+
+	out.Reset()
+	require.NoError(t, printRelaysCommand(ifce, &printTunnelFlags{}, nil, commands.NewStringWriter(out)))
+	assert.JSONEq(t, `{"Relays":[{"NebulaAddr":"10.0.0.1","RelayForAddrs":[{"Type":"forwarding","State":"established","PeerAddr":"10.0.0.2","LocalIndex":1,"RemoteIndex":2,"RelayedThrough":null}]}]}`, out.String())
+
+	// And an index mismatch names it.
+	hm.Relays[7] = hi
+	delete(hm.Relays, 1)
+	out.Reset()
+	require.NoError(t, printRelaysCommand(ifce, &printTunnelFlags{}, nil, commands.NewStringWriter(out)))
+	assert.Contains(t, out.String(), `"Error":"hostmap LocalIndex '7' does not match RelayState LocalIndex"`)
+}