How to pass data from go to a subprocess (via exec.Command), but without restarting the subprocess (i.e. write/read all the time)?

Question

go

There is this code:

cfCmd := exec.Command("perl", "./test.pl")
    cfIn, _ := cfCmd.StdinPipe()
    cfOut, _ := cfCmd.StdoutPipe()
    err := cfCmd.Start()
    if err != nil { 
    	fmt.Print(err.Error()) 
    	os.Exit(1) 
    } 
    cfIn.Write([]byte(task))
    cfIn.Close()
    cfBytes, _ := ioutil.ReadAll(cfOut)
    cfCmd.Wait()
    
    res := "\n>>> Server: test.pl " + fmt.Sprint(id) + " вернул: \n" + string(cfBytes)

But the problem is that I only need to run test.pl once, and then write data to it and read responses.
How to do it correctly in golang?

Answer 1

Do not close cfIn, write data there, but read from cfOut, in different goroutines.

For example, so

package main

import (
  "bufio"
  "fmt"
  "io"
  "os"
  "os/exec"
  "strings"
)

func main() {
  cfCmd := exec.Command("perl", "test.pl")
  cfIn, err := cfCmd.StdinPipe()
  if err != nil {
    panic(err)
  }
  cfOut, err := cfCmd.StdoutPipe()
  if err != nil {
    panic(err)
  }

  err = cfCmd.Start()
  if err != nil {
    panic(err)
  }

  go ProcessStdin(cfIn)
  ProcessStdout(cfOut)

  err = cfCmd.Wait()
  if err != nil {
    panic(err)
  }
}

func ProcessStdin(stdin io.WriteCloser) {
  defer stdin.Close()
  stdin.Write([]byte("some task"))
  stdin.Write([]byte("some other task"))
  // ......
}

func ProcessStdout(stdout io.ReadCloser) {
  defer stdout.Close()

  rd := bufio.NewReader(stdout)
  for {
    line, err := rd.ReadString('\n')
    if err != nil {
      fmt.Println("Error reading stdout:", err)
      os.Exit(1)
    }
    line = strings.TrimSpace(line)

    fmt.Println("Got line from a process:", line)
  }
}

Don't forget to do it in your perl program.
Otherwise, perl won't flush the stdout buffer and you won't get anything in the interactive.