Reduce binary size, Allow changing UID/GID

build.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -e
+
 userID=$(id -u)
 groupID=$(id -g)
 

docker/Dockerfile

@@ -1,9 +1,11 @@
-FROM golang:latest AS builder
+FROM golang:1.21-rc-alpine AS builder
 
 ARG UID=1000
 ARG GID=1000
 
-RUN addgroup --gid ${GID} bobthebuilder && adduser --gid ${GID} --uid ${UID} bobthebuilder
+RUN apk add upx shadow
+
+RUN groupadd --gid ${GID} bobthebuilder && useradd -m --gid ${GID} --uid ${UID} bobthebuilder
 
 RUN mkdir /build
 RUN chown -Rv bobthebuilder:bobthebuilder /build
@@ -14,7 +16,9 @@ RUN chown -Rv bobthebuilder:bobthebuilder /workspace
 USER bobthebuilder
 WORKDIR /workspace
 
-RUN [ "go", "build", "-o", "/build/docker_launcher", "." ]
+RUN [ "go", "build", "-ldflags", "-s -w", "-o", "/build/docker_launcher", "." ]
+
+RUN [ "upx", "/build/docker_launcher" ]
 
 FROM alpine:latest
 

main.go

@@ -5,7 +5,9 @@ import (
 	"flag"
 	"log"
 	"os"
+	"os/exec"
 	"regexp"
+	"strings"
 )
 
 type file struct {
@@ -18,9 +20,19 @@ type config struct {
 	VariableRegex  string
 	RegexGroup     int
 	ForceOverwrite bool
+
+	UpdateUID   bool
+	User        string
+	UIDVariable string
+
+	UpdateGID   bool
+	Group       string
+	GIDVariable string
 }
 
-var defaultVariableRegex = `\$\{([a-zA-Z0-9_-]+)\}`
+const defaultVariableRegex = `\$\{([a-zA-Z0-9_-]+)\}`
+const defaultUIDVariable = "UID"
+const defaultGIDVariable = "GID"
 
 func loadConfig(path string) (*config, error) {
 	raw, err := os.ReadFile(path)
@@ -121,11 +133,55 @@ func filterFiles(config config) error {
 	return nil
 }
 
+func updateUID(config config) error {
+	uidVariable := config.UIDVariable
+	if len(uidVariable) == 0 {
+		uidVariable = defaultUIDVariable
+	}
+
+	newUID := os.Getenv(uidVariable)
+	if len(newUID) == 0 {
+		log.Println("UID variable is not set. Not updating UID")
+		return nil
+	}
+
+	err := exec.Command("usermod", "-u", newUID, config.User).Run()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func updateGID(config config) error {
+	gidVariable := config.GIDVariable
+	if len(gidVariable) == 0 {
+		gidVariable = defaultGIDVariable
+	}
+
+	newGID := os.Getenv(gidVariable)
+	if len(newGID) == 0 {
+		log.Println("GID variable is not set. Not updating GID")
+		return nil
+	}
+
+	err := exec.Command("groupmod", "-g", newGID, config.Group).Run()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func main() {
 	configPath := flag.String("config", "config.json", "Path to config file")
 	force := flag.Bool("force", false, "Forcibly overwrite existing files (equivalent to setting forceOverwrite to true in the config)")
 	flag.Parse()
 
+	if flag.NArg() == 0 {
+		log.Fatal("Missing command")
+	}
+
 	config, err := loadConfig(*configPath)
 	if err != nil {
 		log.Fatalln("Failed to load config:", err)
@@ -137,4 +193,31 @@ func main() {
 	if err != nil {
 		log.Fatalln(err)
 	}
+
+	if config.UpdateUID {
+		log.Println("Updating UID")
+		err = updateUID(*config)
+		if err != nil {
+			log.Fatalln(err)
+		}
+	}
+
+	if config.UpdateGID {
+		log.Println("Updating GID")
+		err = updateGID(*config)
+		if err != nil {
+			log.Fatalln(err)
+		}
+	}
+
+	command := flag.Args()
+	log.Println(">", strings.Join(command, " "))
+	cmd := exec.Command(command[0], command[1:]...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	err = cmd.Run()
+	if err != nil {
+		log.Fatal("Error: ", err)
+	}
 }