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main_linux.go
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main_linux.go
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// Binary bat is a battery management utility for Linux laptops.
package main
import (
"bytes"
_ "embed"
"errors"
"fmt"
"io"
"io/fs"
"os"
"os/exec"
"path"
"path/filepath"
"runtime/debug"
"strconv"
"strings"
"syscall"
"text/template"
"golang.org/x/sys/unix"
)
const (
device = "/sys/class/power_supply/BAT?"
threshold = "charge_control_end_threshold"
services = "/etc/systemd/system/"
)
var events = [...]string{
"hibernate",
"hybrid-sleep",
"multi-user",
"suspend",
"suspend-then-hibernate",
}
var build, tag string
var (
//go:embed bat.service
unit string
//go:embed help.txt
help string
//go:embed version.fmt
version string
)
func exists(battery, variable string) bool {
_, err := os.Stat(filepath.Join(battery, variable))
if err != nil && errors.Is(err, fs.ErrNotExist) {
return false
}
return true
}
func must[T any](v T, err error) T {
if err != nil {
panic(err)
}
return v
}
func read(battery, variable string) (string, error) {
f, err := os.Open(filepath.Join(battery, variable))
if err != nil {
return "", err
}
defer f.Close()
buf := make([]byte, 32)
n, err := f.Read(buf)
if err != nil && err != io.EOF {
return "", err
}
return string(buf[:n-1]), nil
}
type options struct{ debug, help, version bool }
func main() {
var opts options
for _, arg := range os.Args {
switch arg {
case "-d", "--debug":
opts.debug = true
case "-h", "--help":
opts.help = true
case "-v", "--version":
opts.version = true
}
}
if len(os.Args) == 1 {
fmt.Fprint(os.Stderr, help)
os.Exit(2)
}
if opts.help {
fmt.Print(help)
return
}
if opts.version {
fmt.Printf(version, tag)
return
}
defer func() {
if err := recover(); err != nil {
if opts.debug {
fmt.Fprintf(os.Stderr, "%s\n\n%s", err, string(debug.Stack()))
} else {
fmt.Println("A fatal error occurred. Please rerun the command with the `--debug` flag enabled\nand file an issue with the resulting output at the following address\nhttps://github.com/tshakalekholoane/bat/issues/new.")
}
}
}()
batteries := must(filepath.Glob(device))
if len(batteries) == 0 {
fmt.Fprintln(os.Stderr, "This program is most likely not compatible with your system. See\nhttps://github.com/tshakalekholoane/bat#disclaimer for details.")
os.Exit(1)
}
// Default to using the first.
bat := batteries[0]
switch variable := os.Args[1]; variable {
case "capacity", "status":
fmt.Println(must(read(bat, variable)))
case "health":
// Some devices use charge_* and others energy_* so probe both. The
// health is computed as v / w where v is the eroded capacity and w
// is the capacity when the battery was new.
var enoent bool
x, y := "charge_full", "charge_full_design"
_, err := os.Stat(filepath.Join(bat, x))
if err != nil {
if !errors.Is(err, fs.ErrNotExist) {
panic(err)
}
enoent = true
}
_, err = os.Stat(filepath.Join(bat, y))
if err != nil {
if !errors.Is(err, fs.ErrNotExist) {
panic(err)
}
enoent = true
}
if enoent {
x, y = "energy_full", "energy_full_design"
}
v := must(strconv.Atoi(must(read(bat, x))))
w := must(strconv.Atoi(must(read(bat, y))))
fmt.Println(v * 100 / w)
case "persist":
if !exists(bat, threshold) {
fmt.Fprintf(os.Stderr, "Charging threshold setting not found.\n")
os.Exit(1)
}
// systemd 244-rc1 is the earliest version to allow restarts for
// oneshot services.
out := must(exec.Command("systemctl", "--version").CombinedOutput())
var rev int
_ = must(fmt.Sscanf(string(out), "systemd %d", &rev))
if rev < 244 {
fmt.Fprintln(os.Stderr, "Requires systemd version 243-rc1 or later.")
os.Exit(1)
}
curr := must(strconv.Atoi(must(read(bat, threshold))))
sh, err := exec.LookPath("sh")
if err != nil {
if errors.Is(err, exec.ErrNotFound) {
fmt.Fprintln(os.Stderr, "Could not find 'sh' on your system.")
os.Exit(1)
}
panic(err)
}
p := path.Join(bat, threshold)
tmpl := template.Must(template.New("unit").Parse(unit))
for _, event := range events {
name := services + "bat-" + event + ".service"
f, err := os.Create(name)
if err != nil {
if errors.Is(err, syscall.EACCES) {
fmt.Fprintln(os.Stderr, "Permission denied. Try running this command using sudo.")
os.Exit(1)
}
panic(err)
}
defer f.Close()
svc := struct {
Event, Path, Shell string
Threshold int
}{event, p, sh, curr}
if err := tmpl.Execute(f, svc); err != nil {
panic(err)
}
if err := exec.Command("systemctl", "enable", name).Run(); err != nil {
panic(err)
}
}
fmt.Println("Persistence of the current charging threshold enabled.")
case "threshold":
if !exists(bat, threshold) {
fmt.Fprintf(os.Stderr, "Charging threshold setting not found.\n")
os.Exit(1)
}
if len(os.Args) == 2 || len(os.Args) == 3 && opts.debug {
// Get.
fmt.Println(must(read(bat, threshold)))
} else {
// Set.
// The earliest version of the Linux kernel to expose the battery
// charging threshold is 5.4.
var utsname unix.Utsname
if err := unix.Uname(&utsname); err != nil {
panic(err)
}
var maj, min int
_ = must(fmt.Sscanf(string(utsname.Release[:]), "%d.%d", &maj, &min))
if maj <= 5 && (maj != 5 || min < 4) {
fmt.Fprintf(os.Stderr, "Requires Linux kernel version 5.4 or later.")
os.Exit(1)
}
a := os.Args[2]
i, err := strconv.Atoi(a)
if err != nil {
if errors.Is(err, strconv.ErrSyntax) {
fmt.Fprintln(os.Stderr, "Argument should be an integer.")
os.Exit(1)
}
panic(err)
}
if i < 1 || i > 100 {
fmt.Fprintln(os.Stderr, "Threshold value should be between 1 and 100.")
os.Exit(1)
}
if err := os.WriteFile(filepath.Join(bat, threshold), []byte(a), 0o644); err != nil {
if errors.Is(err, syscall.EACCES) {
fmt.Fprintln(os.Stderr, "Permission denied. Try running this command using sudo.")
os.Exit(1)
}
panic(err)
}
fmt.Println("Charging threshold set.\nRun `sudo bat persist` to persist the setting between restarts.")
}
case "reset":
for _, event := range events {
name := services + "bat-" + event + ".service"
buf := new(bytes.Buffer)
cmd := exec.Command("systemctl", "disable", name)
cmd.Stderr = buf
if err := cmd.Run(); err != nil {
switch message := buf.String(); {
case strings.Contains(message, "does not exist"):
continue
case strings.Contains(message, "Access denied"):
fmt.Fprintln(os.Stderr, "Permission denied. Try running this command using sudo.")
os.Exit(1)
default:
panic(err)
}
}
if err := os.Remove(name); err != nil && !errors.Is(err, syscall.ENOENT) {
if errors.Is(err, syscall.EACCES) {
fmt.Fprintln(os.Stderr, "Permission denied. Try running this command using sudo.")
os.Exit(1)
}
panic(err)
}
}
fmt.Println("Charging threshold persistence reset.")
default:
fmt.Fprintf(os.Stderr, "There is no %s command. Run `bat --help` to see a list of available commands.\n", variable)
os.Exit(1)
}
}