cmd/tailscale: clean up dns --help messages (#16306)

This patch contains the following cleanups:

1. Simplify `ffcli.Command` definitions;
2. Word-wrap help text, consistent with other commands;
3. `tailscale dns --help` usage makes subcommand usage more obvious;
4. `tailscale dns query --help` describes DNS record types.

Updates #cleanup

Signed-off-by: Simon Law <sfllaw@tailscale.com>

cmd/tailscale/cli/dns-query.go

@@ -9,12 +9,31 @@ import (
 	"fmt"
 	"net/netip"
 	"os"
+	"strings"
 	"text/tabwriter"
 
+	"github.com/peterbourgon/ff/v3/ffcli"
 	"golang.org/x/net/dns/dnsmessage"
 	"tailscale.com/types/dnstype"
 )
 
+var dnsQueryCmd = &ffcli.Command{
+	Name:       "query",
+	ShortUsage: "tailscale dns query <name> [a|aaaa|cname|mx|ns|opt|ptr|srv|txt]",
+	Exec:       runDNSQuery,
+	ShortHelp:  "Perform a DNS query",
+	LongHelp: strings.TrimSpace(`
+The 'tailscale dns query' subcommand performs a DNS query for the specified name
+using the internal DNS forwarder (100.100.100.100).
+
+By default, the DNS query will request an A record. Another DNS record type can
+be specified as the second parameter.
+
+The output also provides information about the resolver(s) used to resolve the
+query.
+`),
+}
+
 func runDNSQuery(ctx context.Context, args []string) error {
 	if len(args) < 1 {
 		return flag.ErrHelp

cmd/tailscale/cli/dns-status.go

@@ -5,15 +5,77 @@ package cli
 
 import (
 	"context"
+	"flag"
 	"fmt"
 	"maps"
 	"slices"
 	"strings"
 
+	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/ipn"
 	"tailscale.com/types/netmap"
 )
 
+var dnsStatusCmd = &ffcli.Command{
+	Name:       "status",
+	ShortUsage: "tailscale dns status [--all]",
+	Exec:       runDNSStatus,
+	ShortHelp:  "Print the current DNS status and configuration",
+	LongHelp: strings.TrimSpace(`
+The 'tailscale dns status' subcommand prints the current DNS status and
+configuration, including:
+
+- Whether the built-in DNS forwarder is enabled.
+
+- The MagicDNS configuration provided by the coordination server.
+
+- Details on which resolver(s) Tailscale believes the system is using by
+  default.
+
+The --all flag can be used to output advanced debugging information, including
+fallback resolvers, nameservers, certificate domains, extra records, and the
+exit node filtered set.
+
+=== Contents of the MagicDNS configuration ===
+
+The MagicDNS configuration is provided by the coordination server to the client
+and includes the following components:
+
+- MagicDNS enablement status: Indicates whether MagicDNS is enabled across the
+  entire tailnet.
+
+- MagicDNS Suffix: The DNS suffix used for devices within your tailnet.
+
+- DNS Name: The DNS name that other devices in the tailnet can use to reach this
+  device.
+
+- Resolvers: The preferred DNS resolver(s) to be used for resolving queries, in
+  order of preference. If no resolvers are listed here, the system defaults are
+  used.
+
+- Split DNS Routes: Custom DNS resolvers may be used to resolve hostnames in
+  specific domains, this is also known as a 'Split DNS' configuration. The
+  mapping of domains to their respective resolvers is provided here.
+
+- Certificate Domains: The DNS names for which the coordination server will
+  assist in provisioning TLS certificates.
+
+- Extra Records: Additional DNS records that the coordination server might
+  provide to the internal DNS resolver.
+
+- Exit Node Filtered Set: DNS suffixes that the node, when acting as an exit
+  node DNS proxy, will not answer.
+
+For more information about the DNS functionality built into Tailscale, refer to
+https://tailscale.com/kb/1054/dns.
+`),
+	FlagSet: (func() *flag.FlagSet {
+		fs := newFlagSet("status")
+		fs.BoolVar(&dnsStatusArgs.all, "all", false, "outputs advanced debugging information")
+		return fs
+	})(),
+}
+
 // dnsStatusArgs are the arguments for the "dns status" subcommand.
 var dnsStatusArgs struct {
 	all bool
@@ -208,35 +270,3 @@ func fetchNetMap() (netMap *netmap.NetworkMap, err error) {
 	}
 	return notify.NetMap, nil
 }
-
-func dnsStatusLongHelp() string {
-	return `The 'tailscale dns status' subcommand prints the current DNS status and configuration, including:
-	
-- Whether the built-in DNS forwarder is enabled.
-- The MagicDNS configuration provided by the coordination server.
-- Details on which resolver(s) Tailscale believes the system is using by default.
-
-The --all flag can be used to output advanced debugging information, including fallback resolvers, nameservers, certificate domains, extra records, and the exit node filtered set.
-
-=== Contents of the MagicDNS configuration ===
-
-The MagicDNS configuration is provided by the coordination server to the client and includes the following components:
-
-- MagicDNS enablement status: Indicates whether MagicDNS is enabled across the entire tailnet.
-
-- MagicDNS Suffix: The DNS suffix used for devices within your tailnet.
-
-- DNS Name: The DNS name that other devices in the tailnet can use to reach this device.
-
-- Resolvers: The preferred DNS resolver(s) to be used for resolving queries, in order of preference. If no resolvers are listed here, the system defaults are used.
-
-- Split DNS Routes: Custom DNS resolvers may be used to resolve hostnames in specific domains, this is also known as a 'Split DNS' configuration. The mapping of domains to their respective resolvers is provided here.
-
-- Certificate Domains: The DNS names for which the coordination server will assist in provisioning TLS certificates.
-
-- Extra Records: Additional DNS records that the coordination server might provide to the internal DNS resolver.
-
-- Exit Node Filtered Set: DNS suffixes that the node, when acting as an exit node DNS proxy, will not answer.
-
-For more information about the DNS functionality built into Tailscale, refer to https://tailscale.com/kb/1054/dns.`
-}

cmd/tailscale/cli/dns.go

@@ -4,46 +4,32 @@
 package cli
 
 import (
-	"flag"
+	"strings"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 )
 
 var dnsCmd = &ffcli.Command{
-	Name:       "dns",
-	ShortHelp:  "Diagnose the internal DNS forwarder",
-	LongHelp:   dnsCmdLongHelp(),
-	ShortUsage: "tailscale dns <subcommand> [flags]",
-	UsageFunc:  usageFuncNoDefaultValues,
+	Name:      "dns",
+	ShortHelp: "Diagnose the internal DNS forwarder",
+	LongHelp: strings.TrimSpace(`
+The 'tailscale dns' subcommand provides tools for diagnosing the internal DNS
+forwarder (100.100.100.100).
+
+For more information about the DNS functionality built into Tailscale, refer to
+https://tailscale.com/kb/1054/dns.
+`),
+	ShortUsage: strings.Join([]string{
+		dnsStatusCmd.ShortUsage,
+		dnsQueryCmd.ShortUsage,
+	}, "\n"),
+	UsageFunc: usageFuncNoDefaultValues,
 	Subcommands: []*ffcli.Command{
-		{
-			Name:       "status",
-			ShortUsage: "tailscale dns status [--all]",
-			Exec:       runDNSStatus,
-			ShortHelp:  "Print the current DNS status and configuration",
-			LongHelp:   dnsStatusLongHelp(),
-			FlagSet: (func() *flag.FlagSet {
-				fs := newFlagSet("status")
-				fs.BoolVar(&dnsStatusArgs.all, "all", false, "outputs advanced debugging information (fallback resolvers, nameservers, cert domains, extra records, and exit node filtered set)")
-				return fs
-			})(),
-		},
-		{
-			Name:       "query",
-			ShortUsage: "tailscale dns query <name> [a|aaaa|cname|mx|ns|opt|ptr|srv|txt]",
-			Exec:       runDNSQuery,
-			ShortHelp:  "Perform a DNS query",
-			LongHelp:   "The 'tailscale dns query' subcommand performs a DNS query for the specified name using the internal DNS forwarder (100.100.100.100).\n\nIt also provides information about the resolver(s) used to resolve the query.",
-		},
+		dnsStatusCmd,
+		dnsQueryCmd,
 
 		// TODO: implement `tailscale log` here
 
 		// The above work is tracked in https://github.com/tailscale/tailscale/issues/13326
 	},
 }
-
-func dnsCmdLongHelp() string {
-	return `The 'tailscale dns' subcommand provides tools for diagnosing the internal DNS forwarder (100.100.100.100).
-	
-For more information about the DNS functionality built into Tailscale, refer to https://tailscale.com/kb/1054/dns.`
-}