chore: add vpn-daemon run subcommand for windows (#15526)

`coder vpn-daemon run` will instantiate a RPC connection with the
specified pipe handles and communicate with the (yet to be implemented)
parent process.

The tests don't ensure that the tunnel is actually usable yet as the
tunnel functionality isn't implemented, but it does make sure that the
tunnel tries to read from the RPC pipe.

Closes #14735

cli/root.go

@@ -125,6 +125,7 @@ func (r *RootCmd) CoreSubcommands() []*serpent.Command {
 		r.expCmd(),
 		r.gitssh(),
 		r.support(),
+		r.vpnDaemon(),
 		r.vscodeSSH(),
 		r.workspaceAgent(),
 	}

cli/vpndaemon.go

@@ -0,0 +1,21 @@
+package cli
+
+import (
+	"github.com/coder/serpent"
+)
+
+func (r *RootCmd) vpnDaemon() *serpent.Command {
+	cmd := &serpent.Command{
+		Use:    "vpn-daemon [subcommand]",
+		Short:  "VPN daemon commands used by Coder Desktop.",
+		Hidden: true,
+		Handler: func(inv *serpent.Invocation) error {
+			return inv.Command.HelpHandler(inv)
+		},
+		Children: []*serpent.Command{
+			r.vpnDaemonRun(),
+		},
+	}
+
+	return cmd
+}

cli/vpndaemon_other.go

@@ -0,0 +1,24 @@
+//go:build !windows
+
+package cli
+
+import (
+	"golang.org/x/xerrors"
+
+	"github.com/coder/serpent"
+)
+
+func (*RootCmd) vpnDaemonRun() *serpent.Command {
+	cmd := &serpent.Command{
+		Use:   "run",
+		Short: "Run the VPN daemon on Windows.",
+		Middleware: serpent.Chain(
+			serpent.RequireNArgs(0),
+		),
+		Handler: func(_ *serpent.Invocation) error {
+			return xerrors.New("vpn-daemon subcommand is not supported on this platform")
+		},
+	}
+
+	return cmd
+}

cli/vpndaemon_windows.go

@@ -0,0 +1,75 @@
+//go:build windows
+
+package cli
+
+import (
+	"golang.org/x/xerrors"
+
+	"cdr.dev/slog"
+	"cdr.dev/slog/sloggers/sloghuman"
+	"github.com/coder/coder/v2/vpn"
+	"github.com/coder/serpent"
+)
+
+func (r *RootCmd) vpnDaemonRun() *serpent.Command {
+	var (
+		rpcReadHandleInt  int64
+		rpcWriteHandleInt int64
+	)
+
+	cmd := &serpent.Command{
+		Use:   "run",
+		Short: "Run the VPN daemon on Windows.",
+		Middleware: serpent.Chain(
+			serpent.RequireNArgs(0),
+		),
+		Options: serpent.OptionSet{
+			{
+				Flag:        "rpc-read-handle",
+				Env:         "CODER_VPN_DAEMON_RPC_READ_HANDLE",
+				Description: "The handle for the pipe to read from the RPC connection.",
+				Value:       serpent.Int64Of(&rpcReadHandleInt),
+				Required:    true,
+			},
+			{
+				Flag:        "rpc-write-handle",
+				Env:         "CODER_VPN_DAEMON_RPC_WRITE_HANDLE",
+				Description: "The handle for the pipe to write to the RPC connection.",
+				Value:       serpent.Int64Of(&rpcWriteHandleInt),
+				Required:    true,
+			},
+		},
+		Handler: func(inv *serpent.Invocation) error {
+			ctx := inv.Context()
+			logger := inv.Logger.AppendSinks(sloghuman.Sink(inv.Stderr)).Leveled(slog.LevelDebug)
+
+			if rpcReadHandleInt < 0 || rpcWriteHandleInt < 0 {
+				return xerrors.Errorf("rpc-read-handle (%v) and rpc-write-handle (%v) must be positive", rpcReadHandleInt, rpcWriteHandleInt)
+			}
+			if rpcReadHandleInt == rpcWriteHandleInt {
+				return xerrors.Errorf("rpc-read-handle (%v) and rpc-write-handle (%v) must be different", rpcReadHandleInt, rpcWriteHandleInt)
+			}
+
+			// We don't need to worry about duplicating the handles on Windows,
+			// which is different from Unix.
+			logger.Info(ctx, "opening bidirectional RPC pipe", slog.F("rpc_read_handle", rpcReadHandleInt), slog.F("rpc_write_handle", rpcWriteHandleInt))
+			pipe, err := vpn.NewBidirectionalPipe(uintptr(rpcReadHandleInt), uintptr(rpcWriteHandleInt))
+			if err != nil {
+				return xerrors.Errorf("create bidirectional RPC pipe: %w", err)
+			}
+			defer pipe.Close()
+
+			logger.Info(ctx, "starting tunnel")
+			tunnel, err := vpn.NewTunnel(ctx, logger, pipe)
+			if err != nil {
+				return xerrors.Errorf("create new tunnel for client: %w", err)
+			}
+			defer tunnel.Close()
+
+			<-ctx.Done()
+			return nil
+		},
+	}
+
+	return cmd
+}

cli/vpndaemon_windows_test.go

@@ -0,0 +1,93 @@
+//go:build windows
+
+package cli_test
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/cli/clitest"
+	"github.com/coder/coder/v2/testutil"
+)
+
+func TestVPNDaemonRun(t *testing.T) {
+	t.Parallel()
+
+	t.Run("InvalidFlags", func(t *testing.T) {
+		t.Parallel()
+
+		cases := []struct {
+			Name          string
+			Args          []string
+			ErrorContains string
+		}{
+			{
+				Name:          "NoReadHandle",
+				Args:          []string{"--rpc-write-handle", "10"},
+				ErrorContains: "rpc-read-handle",
+			},
+			{
+				Name:          "NoWriteHandle",
+				Args:          []string{"--rpc-read-handle", "10"},
+				ErrorContains: "rpc-write-handle",
+			},
+			{
+				Name:          "NegativeReadHandle",
+				Args:          []string{"--rpc-read-handle", "-1", "--rpc-write-handle", "10"},
+				ErrorContains: "rpc-read-handle",
+			},
+			{
+				Name:          "NegativeWriteHandle",
+				Args:          []string{"--rpc-read-handle", "10", "--rpc-write-handle", "-1"},
+				ErrorContains: "rpc-write-handle",
+			},
+			{
+				Name:          "SameHandles",
+				Args:          []string{"--rpc-read-handle", "10", "--rpc-write-handle", "10"},
+				ErrorContains: "rpc-read-handle",
+			},
+		}
+
+		for _, c := range cases {
+			c := c
+			t.Run(c.Name, func(t *testing.T) {
+				t.Parallel()
+				ctx := testutil.Context(t, testutil.WaitLong)
+				inv, _ := clitest.New(t, append([]string{"vpn-daemon", "run"}, c.Args...)...)
+				err := inv.WithContext(ctx).Run()
+				require.ErrorContains(t, err, c.ErrorContains)
+			})
+		}
+	})
+
+	t.Run("StartsTunnel", func(t *testing.T) {
+		t.Parallel()
+
+		r1, w1, err := os.Pipe()
+		require.NoError(t, err)
+		defer r1.Close()
+		defer w1.Close()
+		r2, w2, err := os.Pipe()
+		require.NoError(t, err)
+		defer r2.Close()
+		defer w2.Close()
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+		inv, _ := clitest.New(t, "vpn-daemon", "run", "--rpc-read-handle", fmt.Sprint(r1.Fd()), "--rpc-write-handle", fmt.Sprint(w2.Fd()))
+		waiter := clitest.StartWithWaiter(t, inv.WithContext(ctx))
+
+		// Send garbage which should cause the handshake to fail and the daemon
+		// to exit.
+		_, err = w1.Write([]byte("garbage"))
+		require.NoError(t, err)
+		waiter.Cancel()
+		err = waiter.Wait()
+		require.ErrorContains(t, err, "handshake failed")
+	})
+
+	// TODO: once the VPN tunnel functionality is implemented, add tests that
+	// actually try to instantiate a tunnel to a workspace
+}