writing twice to the same sub process golang - go

Question

I have a simple scp function that is just a wrapper over the scp cli tool.
type credential struct {
username string
password string
host string
port string
}
func scpFile(filepath, destpath string, c *credential) error {
cmd := exec.Command("scp", filepath, c.username+"#"+c.host+":"+destpath)
if err := cmd.Run(); err != nil {
return err
}
fmt.Println("done")
return nil
}
This works just fine now I want to add the capability of putting in a password the SSH if scp needs it. This is what I came up with
func scpFile(filepath, destpath string, c *credential) error {
cmd := exec.Command("scp", filepath, c.username+"#"+c.host+":"+destpath)
stdin, err := cmd.StdinPipe()
if err != nil {
return err
}
defer stdin.Close()
if err := cmd.Start(); err != nil {
return err
}
io.WriteString(stdin, c.password+"\n")
cmd.Wait()
fmt.Println("done")
return nil
}
This does not work as the password prompt just hangs there. I tried adding a 1 second sleep before I re write to stdin thinking maybe I was writing the password to fast but did not make a difference.

Answer 1

So I was able to find a work around by instead of trying to send the password to stdin I create a ssh session and scp a file through the ssh session. Here is the new scpFile function:
func scpFile(filePath, destinationPath string, session *ssh.Session) error {
defer session.Close()
f, err := os.Open(filePath)
if err != nil {
return err
}
defer f.Close()
s, err := f.Stat()
if err != nil {
return err
}
go func() {
w, _ := session.StdinPipe()
defer w.Close()
fmt.Fprintf(w, "C%#o %d %s\n", s.Mode().Perm(), s.Size(), path.Base(filePath))
io.Copy(w, f)
fmt.Fprint(w, "\x00")
}()
cmd := fmt.Sprintf("scp -t %s", destinationPath)
if err := session.Run(cmd); err != nil {
return err
}
return nil
}
This could probably be made better but the main idea is there