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/* ipp-usb - HTTP reverse proxy, backed by IPP-over-USB connection to device
*
* Copyright (C) 2020 and up by Alexander Pevzner (pzz@apevzner.com)
* See LICENSE for license terms and conditions
*
* Demonization
*/
package main
import (
"bytes"
"errors"
"fmt"
"io"
"os"
"strings"
"syscall"
"unicode"
)
// #include <unistd.h>
import "C"
// CloseStdInOutErr closes stdin/stdout/stderr handles
func CloseStdInOutErr() error {
nul, err := syscall.Open(os.DevNull, syscall.O_RDONLY, 0644)
if err != nil {
return fmt.Errorf("Open %q: %s", os.DevNull, err)
}
defer syscall.Close(nul)
// Note, syscall.Dup2 is not implemented on old Go
// versions for ARM64 Linux. So we use C.dup2 as a
// portable workaround
C.dup2(C.int(nul), 0)
C.dup2(C.int(nul), 1)
C.dup2(C.int(nul), 2)
return nil
}
// Daemon runs ipp-usb program in background
func Daemon() error {
// Obtain path to program's executable
exe, err := os.Executable()
if err != nil {
return err
}
// Create stdout/stderr pipes
rstdout, wstdout, err := os.Pipe()
if err != nil {
return fmt.Errorf("pipe(): %s", err)
}
rstderr, wstderr, err := os.Pipe()
if err != nil {
return fmt.Errorf("pipe(): %s", err)
}
devnull, err := os.Open(os.DevNull)
if err != nil {
return fmt.Errorf("Open %q: %s", os.DevNull, err)
}
// Initialize process attributes
attr := &os.ProcAttr{
Files: []*os.File{devnull, wstdout, wstderr},
Sys: &syscall.SysProcAttr{
Setsid: true,
},
}
// Initialize process arguments
args := []string{}
for _, arg := range os.Args {
if arg != "-bg" {
args = append(args, arg)
}
}
// Start new process
proc, err := os.StartProcess(exe, args, attr)
if err != nil {
return err
}
// Collect its initialization output
wstdout.Close()
wstderr.Close()
stdout := &bytes.Buffer{}
stderr := &bytes.Buffer{}
io.Copy(stdout, rstdout)
io.Copy(stderr, rstderr)
if stdout.Len() != 0 {
os.Stdout.Write(stdout.Bytes())
}
// Check for an error
if stderr.Len() > 0 {
s := strings.TrimFunc(stderr.String(), unicode.IsSpace)
proc.Kill() // Just in case
return errors.New(s)
}
proc.Release()
return nil
}
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