cmd/tailscale/cli: add whoami subcommand

Add a "tailscale whoami" subcommand that is equivalent to running
"tailscale whois $(tailscale ip -4)" but more ergonomic. It supports
the --json flag just like whois, and shares the WhoIsResponse
rendering code with whois.

Fixes #19907

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I8f33ba7a5608bab7dffa8213303beb5f345936d3

cmd/tailscale/cli/cli.go

@@ -299,6 +299,7 @@ change in the future.
 			exitNodeCmd(),
 			nilOrCall(maybeUpdateCmd),
 			whoisCmd,
+			whoamiCmd,
 			debugCmd(),
 			nilOrCall(maybeDriveCmd),
 			idTokenCmd,

cmd/tailscale/cli/whoami.go

@@ -0,0 +1,52 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package cli
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/peterbourgon/ff/v3/ffcli"
+)
+
+var whoamiCmd = &ffcli.Command{
+	Name:       "whoami",
+	ShortUsage: "tailscale whoami [--json]",
+	ShortHelp:  "Show the machine and user identity of the current machine",
+	LongHelp: strings.TrimSpace(`
+	'tailscale whoami' shows the machine and user identity of the current machine.
+	It is equivalent to running 'tailscale whois' against one of the current machine's own Tailscale IP addresses.
+	`),
+	Exec: runWhoami,
+	FlagSet: func() *flag.FlagSet {
+		fs := newFlagSet("whoami")
+		fs.BoolVar(&whoamiArgs.json, "json", false, "output in JSON format")
+		return fs
+	}(),
+}
+
+var whoamiArgs struct {
+	json bool // output in JSON format
+}
+
+func runWhoami(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		return errors.New("too many arguments, expected none")
+	}
+	st, err := localClient.StatusWithoutPeers(ctx)
+	if err != nil {
+		return err
+	}
+	if len(st.TailscaleIPs) == 0 {
+		return fmt.Errorf("no current Tailscale IP address; state: %v", st.BackendState)
+	}
+	who, err := localClient.WhoIsProto(ctx, "", st.TailscaleIPs[0].String())
+	if err != nil {
+		return err
+	}
+	return printWhoIs(who, whoamiArgs.json)
+}

cmd/tailscale/cli/whois.go

@@ -13,6 +13,7 @@ import (
 	"text/tabwriter"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
+	"tailscale.com/client/tailscale/apitype"
 )
 
 var whoisCmd = &ffcli.Command{
@@ -46,7 +47,13 @@ func runWhoIs(ctx context.Context, args []string) error {
 	if err != nil {
 		return err
 	}
-	if whoIsArgs.json {
+	return printWhoIs(who, whoIsArgs.json)
+}
+
+// printWhoIs prints the WhoIsResponse to Stdout, either as JSON (if asJSON is
+// true) or in a human-readable form.
+func printWhoIs(who *apitype.WhoIsResponse, asJSON bool) error {
+	if asJSON {
 		ec := json.NewEncoder(Stdout)
 		ec.SetIndent("", "  ")
 		ec.Encode(who)