feature/featuretags: make QR codes modular (#18358)

QR codes are used by `tailscale up --qr` to provide an easy way to
open a web-page without transcribing a difficult URI. However, there’s
no need for this feature if the client will never be called
interactively. So this PR adds the `ts_omit_qrcodes` build tag.

Updates #18182

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

cmd/tailscale/cli/up.go

@@ -94,8 +94,10 @@ func newUpFlagSet(goos string, upArgs *upArgsT, cmd string) *flag.FlagSet {
 
 	// When adding new flags, prefer to put them under "tailscale set" instead
 	// of here. Setting preferences via "tailscale up" is deprecated.
-	upf.BoolVar(&upArgs.qr, "qr", false, "show QR code for login URLs")
-	upf.StringVar(&upArgs.qrFormat, "qr-format", string(qrcodes.FormatAuto), fmt.Sprintf("QR code formatting (%s, %s, %s, %s)", qrcodes.FormatAuto, qrcodes.FormatASCII, qrcodes.FormatLarge, qrcodes.FormatSmall))
+	if buildfeatures.HasQRCodes {
+		upf.BoolVar(&upArgs.qr, "qr", false, "show QR code for login URLs")
+		upf.StringVar(&upArgs.qrFormat, "qr-format", string(qrcodes.FormatAuto), fmt.Sprintf("QR code formatting (%s, %s, %s, %s)", qrcodes.FormatAuto, qrcodes.FormatASCII, qrcodes.FormatLarge, qrcodes.FormatSmall))
+	}
 	upf.StringVar(&upArgs.authKeyOrFile, "auth-key", "", `node authorization key; if it begins with "file:", then it's a path to a file containing the authkey`)
 	upf.StringVar(&upArgs.clientID, "client-id", "", "Client ID used to generate authkeys via workload identity federation")
 	upf.StringVar(&upArgs.clientSecretOrFile, "client-secret", "", `Client Secret used to generate authkeys via OAuth; if it begins with "file:", then it's a path to a file containing the secret`)
@@ -720,9 +722,11 @@ func runUp(ctx context.Context, cmd string, args []string, upArgs upArgsT) (retE
 				if upArgs.json {
 					js := &upOutputJSON{AuthURL: authURL, BackendState: st.BackendState}
 
-					png, err := qrcodes.EncodePNG(authURL, 128)
-					if err == nil {
-						js.QR = "data:image/png;base64," + base64.StdEncoding.EncodeToString(png)
+					if buildfeatures.HasQRCodes {
+						png, err := qrcodes.EncodePNG(authURL, 128)
+						if err == nil {
+							js.QR = "data:image/png;base64," + base64.StdEncoding.EncodeToString(png)
+						}
 					}
 
 					data, err := json.MarshalIndent(js, "", "\t")
@@ -733,7 +737,7 @@ func runUp(ctx context.Context, cmd string, args []string, upArgs upArgsT) (retE
 					}
 				} else {
 					fmt.Fprintf(Stderr, "\nTo authenticate, visit:\n\n\t%s\n\n", authURL)
-					if upArgs.qr {
+					if upArgs.qr && buildfeatures.HasQRCodes {
 						_, err := qrcodes.Fprintln(Stderr, qrcodes.Format(upArgs.qrFormat), authURL)
 						if err != nil {
 							log.Print(err)

cmd/tailscale/deps_test.go

@@ -0,0 +1,22 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package main
+
+import (
+	"testing"
+
+	"tailscale.com/tstest/deptest"
+)
+
+func TestOmitQRCodes(t *testing.T) {
+	const msg = "unexpected with ts_omit_qrcodes"
+	deptest.DepChecker{
+		GOOS:   "linux",
+		GOARCH: "amd64",
+		Tags:   "ts_omit_qrcodes",
+		BadDeps: map[string]string{
+			"github.com/skip2/go-qrcode": msg,
+		},
+	}.Check(t)
+}

cmd/tailscaled/depaware-minbox.txt

@@ -33,9 +33,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         github.com/peterbourgon/ff/v3/ffcli                          from tailscale.com/cmd/tailscale/cli+
         github.com/peterbourgon/ff/v3/internal                       from github.com/peterbourgon/ff/v3
      💣 github.com/safchain/ethtool                                  from tailscale.com/net/netkernelconf
-        github.com/skip2/go-qrcode                                   from tailscale.com/util/qrcodes
-        github.com/skip2/go-qrcode/bitset                            from github.com/skip2/go-qrcode+
-        github.com/skip2/go-qrcode/reedsolomon                       from github.com/skip2/go-qrcode
      💣 github.com/tailscale/wireguard-go/conn                       from github.com/tailscale/wireguard-go/device+
      💣 github.com/tailscale/wireguard-go/device                     from tailscale.com/net/tstun+
         github.com/tailscale/wireguard-go/ipc                        from github.com/tailscale/wireguard-go/device
@@ -193,7 +190,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/osshare                                   from tailscale.com/cmd/tailscaled
         tailscale.com/util/osuser                                    from tailscale.com/ipn/ipnlocal+
         tailscale.com/util/prompt                                    from tailscale.com/cmd/tailscale/cli
-     💣 tailscale.com/util/qrcodes                                   from tailscale.com/cmd/tailscale/cli
+        tailscale.com/util/qrcodes                                   from tailscale.com/cmd/tailscale/cli
         tailscale.com/util/race                                      from tailscale.com/net/dns/resolver
         tailscale.com/util/racebuild                                 from tailscale.com/logpolicy
         tailscale.com/util/rands                                     from tailscale.com/ipn/ipnlocal+
@@ -274,9 +271,8 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         bufio                                                        from compress/flate+
         bytes                                                        from bufio+
         cmp                                                          from encoding/json+
-        compress/flate                                               from compress/gzip+
+        compress/flate                                               from compress/gzip
         compress/gzip                                                from net/http+
-        compress/zlib                                                from image/png
         container/list                                               from crypto/tls+
         context                                                      from crypto/tls+
         crypto                                                       from crypto/ecdh+
@@ -355,13 +351,9 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         flag                                                         from tailscale.com/cmd/tailscaled+
         fmt                                                          from compress/flate+
         hash                                                         from crypto+
-        hash/adler32                                                 from compress/zlib
         hash/crc32                                                   from compress/gzip+
         hash/maphash                                                 from go4.org/mem
         html                                                         from tailscale.com/ipn/ipnlocal+
-        image                                                        from github.com/skip2/go-qrcode+
-        image/color                                                  from github.com/skip2/go-qrcode+
-        image/png                                                    from github.com/skip2/go-qrcode
         internal/abi                                                 from hash/maphash+
         internal/asan                                                from internal/runtime/maps+
         internal/bisect                                              from internal/godebug
@@ -406,7 +398,6 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         internal/unsafeheader                                        from internal/reflectlite+
         io                                                           from bufio+
         io/fs                                                        from crypto/x509+
-        io/ioutil                                                    from github.com/skip2/go-qrcode
         iter                                                         from bytes+
         log                                                          from github.com/klauspost/compress/zstd+
         log/internal                                                 from log

feature/buildfeatures/feature_qrcodes_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_qrcodes
+
+package buildfeatures
+
+// HasQRCodes is whether the binary was built with support for modular feature "QR codes in tailscale CLI".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_qrcodes" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasQRCodes = false

feature/buildfeatures/feature_qrcodes_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_qrcodes
+
+package buildfeatures
+
+// HasQRCodes is whether the binary was built with support for modular feature "QR codes in tailscale CLI".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_qrcodes" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasQRCodes = true

feature/featuretags/featuretags.go

@@ -222,6 +222,7 @@ var Features = map[FeatureTag]FeatureMeta{
 		Desc: "Linux NetworkManager integration",
 		Deps: []FeatureTag{"dbus"},
 	},
+	"qrcodes":     {Sym: "QRCodes", Desc: "QR codes in tailscale CLI"},
 	"relayserver": {Sym: "RelayServer", Desc: "Relay server"},
 	"resolved": {
 		Sym:  "Resolved",

util/qrcodes/format.go

@@ -0,0 +1,22 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package qrcodes
+
+// Format selects the text representation used to print QR codes.
+type Format string
+
+const (
+	// FormatAuto will format QR codes to best fit the capabilities of the
+	// [io.Writer].
+	FormatAuto Format = "auto"
+
+	// FormatASCII will format QR codes with only ASCII characters.
+	FormatASCII Format = "ascii"
+
+	// FormatLarge will format QR codes with full block characters.
+	FormatLarge Format = "large"
+
+	// FormatSmall will format QR codes with full and half block characters.
+	FormatSmall Format = "small"
+)

util/qrcodes/qrcodes.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_qrcodes
+
 // Package qrcodes provides functions to render or format QR codes.
 package qrcodes
 
@@ -12,24 +14,6 @@ import (
 	qrcode "github.com/skip2/go-qrcode"
 )
 
-// Format selects the text representation used to print QR codes.
-type Format string
-
-const (
-	// FormatAuto will format QR codes to best fit the capabilities of the
-	// [io.Writer].
-	FormatAuto Format = "auto"
-
-	// FormatASCII will format QR codes with only ASCII characters.
-	FormatASCII Format = "ascii"
-
-	// FormatLarge will format QR codes with full block characters.
-	FormatLarge Format = "large"
-
-	// FormatSmall will format QR codes with full and half block characters.
-	FormatSmall Format = "small"
-)
-
 // Fprintln formats s according to [Format] and writes a QR code to w, along
 // with a newline. It returns the number of bytes written and any write error
 // encountered.

util/qrcodes/qrcodes_disabled.go

@@ -0,0 +1,16 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_qrcodes
+
+package qrcodes
+
+import "io"
+
+func Fprintln(w io.Writer, format Format, s string) (n int, err error) {
+	panic("omitted")
+}
+
+func EncodePNG(s string, size int) ([]byte, error) {
+	panic("omitted")
+}

util/qrcodes/qrcodes_linux.go

@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build linux
+//go:build linux && !ts_omit_qrcodes
 
 package qrcodes
 

util/qrcodes/qrcodes_notlinux.go

@@ -1,7 +1,7 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
-//go:build !linux
+//go:build !linux && !ts_omit_qrcodes
 
 package qrcodes