From 921d77062ebfb4b4d26629278abea7ea55cfc942 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Sun, 7 Sep 2025 20:25:54 -0700
Subject: [PATCH] cmd/omitsize: add tool to dump build sizes

Updates #12614

Change-Id: I8f85d7275bc8eecedbabe6631b50e1cf70791d2d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 cmd/omitsize/omitsize.go | 124 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 124 insertions(+)
 create mode 100644 cmd/omitsize/omitsize.go

diff --git a/cmd/omitsize/omitsize.go b/cmd/omitsize/omitsize.go
new file mode 100644
index 000000000..d8e1a6540
--- /dev/null
+++ b/cmd/omitsize/omitsize.go
@@ -0,0 +1,124 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// The omitsize tool prints out how large the Tailscale binaries are with
+// different build tags.
+package main
+
+import (
+	"crypto/sha256"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"slices"
+	"strconv"
+	"strings"
+
+	"tailscale.com/util/must"
+)
+
+var (
+	cacheDir = flag.String("cachedir", "", "if non-empty, use this directory to store cached size results to speed up subsequent runs. The tool does not consider the git status when deciding whether to use the cache. It's on you to nuke it between runs if the tree changed.")
+	features = flag.String("features", "", "comma-separated list of features to consider, with or without the ts_omit_ prefix (default: all detected in build_dist.sh)")
+)
+
+func main() {
+	flag.Parse()
+
+	var all []string
+	if *features == "" {
+		sh := must.Get(os.ReadFile("build_dist.sh"))
+		omitRx := regexp.MustCompile(`\b(ts_omit_\w+)\b`)
+		all = omitRx.FindAllString(string(sh), -1)
+	} else {
+		for v := range strings.SplitSeq(*features, ",") {
+			if !strings.HasPrefix(v, "ts_omit_") {
+				v = "ts_omit_" + v
+			}
+			all = append(all, v)
+		}
+	}
+
+	slices.Sort(all)
+	all = slices.Compact(all)
+
+	baseD := measure("tailscaled")
+	baseC := measure("tailscale")
+	baseBoth := measure("tailscaled", "ts_include_cli")
+
+	fmt.Printf("(a) starting with everything and removing a feature...\n\n")
+
+	fmt.Printf("%9s %9s %9s\n", "tailscaled", "tailscale", "combined (linux/amd64)")
+	fmt.Printf("%9d %9d %9d\n", baseD, baseC, baseBoth)
+
+	minD := measure("tailscaled", all...)
+	minC := measure("tailscale", all...)
+	minBoth := measure("tailscaled", append(slices.Clone(all), "ts_include_cli")...)
+	fmt.Printf("-%8d -%8d -%8d omit-all\n", baseD-minD, baseC-minC, baseBoth-minBoth)
+
+	for _, t := range all {
+		sizeD := measure("tailscaled", t)
+		sizeC := measure("tailscale", t)
+		sizeBoth := measure("tailscaled", append([]string{t}, "ts_include_cli")...)
+		saveD := max(baseD-sizeD, 0)
+		saveC := max(baseC-sizeC, 0)
+		saveBoth := max(baseBoth-sizeBoth, 0)
+		fmt.Printf("-%8d -%8d -%8d %s\n", saveD, saveC, saveBoth, t)
+	}
+
+	fmt.Printf("\n(b) or, starting at minimal and adding one feature back...\n")
+	fmt.Printf("%9s %9s %9s\n", "tailscaled", "tailscale", "combined (linux/amd64)")
+	fmt.Printf("%9d %9d %9d omitting everything\n", minD, minC, minBoth)
+	for _, t := range all {
+		tags := allExcept(all, t)
+		sizeD := measure("tailscaled", tags...)
+		sizeC := measure("tailscale", tags...)
+		sizeBoth := measure("tailscaled", append(tags, "ts_include_cli")...)
+		fmt.Printf("+%8d +%8d +%8d .. add %s\n", max(sizeD-minD, 0), max(sizeC-minC, 0), max(sizeBoth-minBoth, 0), strings.TrimPrefix(t, "ts_omit_"))
+	}
+
+}
+
+func allExcept(all []string, omit string) []string {
+	return slices.DeleteFunc(slices.Clone(all), func(s string) bool { return s == omit })
+}
+
+func measure(bin string, tags ...string) int64 {
+	tags = slices.Clone(tags)
+	slices.Sort(tags)
+	tags = slices.Compact(tags)
+	comma := strings.Join(tags, ",")
+
+	var cacheFile string
+	if *cacheDir != "" {
+		cacheFile = filepath.Join(*cacheDir, fmt.Sprintf("%02x", sha256.Sum256(fmt.Appendf(nil, "%s-%s.size", bin, comma))))
+		if v, err := os.ReadFile(cacheFile); err == nil {
+			if size, err := strconv.ParseInt(strings.TrimSpace(string(v)), 10, 64); err == nil {
+				return size
+			}
+		}
+	}
+
+	cmd := exec.Command("go", "build", "-tags", strings.Join(tags, ","), "-o", "tmpbin", "./cmd/"+bin)
+	log.Printf("# Measuring %v", cmd.Args)
+	cmd.Env = append(os.Environ(), "CGO_ENABLED=0", "GOOS=linux", "GOARCH=amd64")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Fatalf("error measuring %q: %v, %s\n", bin, err, out)
+	}
+	fi, err := os.Stat("tmpbin")
+	if err != nil {
+		log.Fatal(err)
+	}
+	n := fi.Size()
+	if cacheFile != "" {
+		if err := os.WriteFile(cacheFile, fmt.Appendf(nil, "%d", n), 0644); err != nil {
+			log.Fatalf("error writing size to cache: %v\n", err)
+		}
+	}
+	return n
+}