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package systemd
import (
"bufio"
"bytes"
"errors"
"fmt"
"os"
"os/exec"
"path/filepath"
"strconv"
"strings"
systemdDbus "github.com/coreos/go-systemd/v22/dbus"
dbus "github.com/godbus/dbus/v5"
"github.com/moby/sys/userns"
)
// newUserSystemdDbus creates a connection for systemd user-instance.
func newUserSystemdDbus() (*systemdDbus.Conn, error) {
addr, err := DetectUserDbusSessionBusAddress()
if err != nil {
return nil, err
}
uid, err := DetectUID()
if err != nil {
return nil, err
}
return systemdDbus.NewConnection(func() (*dbus.Conn, error) {
conn, err := dbus.Dial(addr)
if err != nil {
return nil, fmt.Errorf("error while dialing %q: %w", addr, err)
}
methods := []dbus.Auth{dbus.AuthExternal(strconv.Itoa(uid))}
err = conn.Auth(methods)
if err != nil {
conn.Close()
return nil, fmt.Errorf("error while authenticating connection (address=%q, UID=%d): %w", addr, uid, err)
}
if err = conn.Hello(); err != nil {
conn.Close()
return nil, fmt.Errorf("error while sending Hello message (address=%q, UID=%d): %w", addr, uid, err)
}
return conn, nil
})
}
// DetectUID detects UID from the OwnerUID field of `busctl --user status`
// if running in userNS. The value corresponds to sd_bus_creds_get_owner_uid(3) .
//
// Otherwise returns os.Getuid() .
func DetectUID() (int, error) {
if !userns.RunningInUserNS() {
return os.Getuid(), nil
}
b, err := exec.Command("busctl", "--user", "--no-pager", "status").CombinedOutput()
if err != nil {
return -1, fmt.Errorf("could not execute `busctl --user --no-pager status` (output: %q): %w", string(b), err)
}
scanner := bufio.NewScanner(bytes.NewReader(b))
for scanner.Scan() {
s := strings.TrimSpace(scanner.Text())
if uidStr, ok := strings.CutPrefix(s, "OwnerUID="); ok {
i, err := strconv.Atoi(uidStr)
if err != nil {
return -1, fmt.Errorf("could not detect the OwnerUID: %w", err)
}
return i, nil
}
}
if err := scanner.Err(); err != nil {
return -1, err
}
return -1, errors.New("could not detect the OwnerUID")
}
// DetectUserDbusSessionBusAddress returns $DBUS_SESSION_BUS_ADDRESS, if set.
// Otherwise it returns "unix:path=$XDG_RUNTIME_DIR/bus", if $XDG_RUNTIME_DIR/bus exists.
func DetectUserDbusSessionBusAddress() (string, error) {
if env := os.Getenv("DBUS_SESSION_BUS_ADDRESS"); env != "" {
return env, nil
}
if xdr := os.Getenv("XDG_RUNTIME_DIR"); xdr != "" {
busPath := filepath.Join(xdr, "bus")
if _, err := os.Stat(busPath); err == nil {
busAddress := "unix:path=" + dbus.EscapeBusAddressValue(busPath)
return busAddress, nil
}
}
return "", errors.New("could not detect DBUS_SESSION_BUS_ADDRESS from the environment; make sure you have installed the dbus-user-session or dbus-daemon package; note you may need to re-login")
}
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