Golang io.Copy blocks in internal ReadFrom - go

Question

I am building a terminal emulator in golang and I was trying to run detached processes from which I can copy output and display it to the user but the io.Copy function blocks and hence I cannot continue to the output part
I looked in the source code and it blocks in the internal ReadFrom method, I cannot understand why this is happening
package main
import (
"bytes"
"fmt"
"io"
"os"
)
func main() {
inputReader, inputWriter, _ := os.Pipe()
outputReader, outputWriter, _ := os.Pipe()
io.Copy(inputWriter, bytes.NewReader([]byte("\n")))
stdin := inputReader
stdout := outputWriter
stderr := outputWriter
var attr = os.ProcAttr{
Dir: "/tmp",
Env: nil,
Files: []*os.File{
stdin,
stdout,
stderr,
},
Sys: nil,
}
process, startProcessErr := os.StartProcess("/usr/bin/ls", []string{"ls"}, &attr)
if startProcessErr != nil {
panic(startProcessErr)
}
if releaseProcessErr := process.Release(); releaseProcessErr != nil {
panic(releaseProcessErr)
}
var output bytes.Buffer
io.Copy(&output, outputReader)
fmt.Println(output)
}
Maybe it is because I release the process but I dont think it should happen

Answer 1

The call io.Copy(&output, outputReader) blocks until read on outputReader returns EOF or some other error. Read on outputReader does not return EOF because the write side of the pipe is still open in the parent process. Fix by closing the writer in the parent process.
...
if releaseProcessErr := process.Release(); releaseProcessErr != nil {
panic(releaseProcessErr)
}
outputWriter.Close() // <-- add this line
var output bytes.Buffer
io.Copy(&output, outputReader)
fmt.Println(output)
...
Use the os/exec package to simplify the code:
cmd := exec.Command("/usr/bin/ls")
cmd.Dir = "/tmp"
output, err := cmd.CombinedOutput()
if err != nil {
log.Fatal(err)
}
fmt.Println(string(output))