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spawn.go
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spawn.go
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package container_daemon
import (
"fmt"
"io"
"os"
"os/exec"
"syscall"
)
type Spawn struct {
PTY PTYOpener
Runner Runner
}
//go:generate counterfeiter -o fake_runner/fake_runner.go . Runner
type Runner interface {
Start(cmd *exec.Cmd) error
Wait(cmd *exec.Cmd) byte
}
//go:generate counterfeiter -o fake_ptyopener/fake_ptyopener.go . PTYOpener
type PTYOpener interface {
Open() (pty *os.File, tty *os.File, err error)
}
func (w *Spawn) Spawn(cmd *exec.Cmd, tty bool) ([]*os.File, error) {
if tty {
return w.spawnWithTty(cmd)
} else {
return w.spawnNoninteractive(cmd)
}
}
func (w *Spawn) spawnWithTty(cmd *exec.Cmd) ([]*os.File, error) {
pty, tty, err := w.PTY.Open()
if err != nil {
return nil, fmt.Errorf("container_daemon: open pipe: %s", err)
}
cmd.Stdin = tty
cmd.Stdout = tty
cmd.Stderr = tty
if cmd.SysProcAttr == nil {
cmd.SysProcAttr = &syscall.SysProcAttr{}
}
cmd.SysProcAttr.Setctty = true
cmd.SysProcAttr.Setsid = true
exitFd, err := wireExit(cmd, w.Runner)
if err != nil {
pty.Close()
tty.Close()
return nil, err
}
return []*os.File{pty, exitFd}, err
}
func (w *Spawn) spawnNoninteractive(cmd *exec.Cmd) ([]*os.File, error) {
var pipes [3]struct {
r *os.File
w *os.File
}
var err error
for i := 0; i < 3; i++ {
pipes[i].r, pipes[i].w, err = os.Pipe()
if err != nil {
return nil, fmt.Errorf("container_daemon: create pipe: %s", err)
}
}
cmd.Stdin = pipes[0].r
cmd.Stdout = pipes[1].w
cmd.Stderr = pipes[2].w
exitStatusR, err := wireExit(cmd, w.Runner)
if err != nil {
for _, p := range pipes {
p.r.Close()
p.w.Close()
}
return nil, err
}
return []*os.File{pipes[0].w, pipes[1].r, pipes[2].r, exitStatusR}, nil
}
func wireExit(cmd *exec.Cmd, runner Runner) (*os.File, error) {
exitR, exitW, err := os.Pipe()
if err != nil {
return nil, fmt.Errorf("container_daemon: create pipe: %s", err)
}
stdout := cmd.Stdout
stderr := cmd.Stderr
if err := runner.Start(cmd); err != nil {
return nil, fmt.Errorf("container_daemon: start: %s", err)
}
go handleCompletion(runner, cmd, exitW, stdout, stderr)
return exitR, nil
}
func handleCompletion(runner Runner, cmd *exec.Cmd, exitW *os.File, stdout, stderr io.Writer) {
defer exitW.Close()
defer tryClose(stdout)
if stderr != stdout {
defer tryClose(stderr)
}
status := runner.Wait(cmd)
exitW.Write([]byte{status})
}
func tryClose(w io.Writer) {
if wc, ok := w.(io.WriteCloser); ok {
wc.Close()
}
}