Is the output from ssh guaranteed to be retrieved? - go

Question

I use the ssh package to connect to a Linux server and retrieve the output of commands. The helper function I wrote for that is below:
func sshRunCommand(host string, command string) (output string, err error) {
keyData, err := ioutil.ReadFile("srv.private.openssh")
if err != nil {
return "", err
}
key, err := ssh.ParsePrivateKey(keyData)
if err != nil {
return "", err
}
// Authentication
config := &ssh.ClientConfig{
User: "root",
HostKeyCallback: ssh.InsecureIgnoreHostKey(),
Auth: []ssh.AuthMethod{
ssh.PublicKeys(key),
},
}
// Connect
client, err := ssh.Dial("tcp", net.JoinHostPort(host, "22"), config)
if err != nil {
return "", err
}
// Create a session. It is one session per command.
session, err := client.NewSession()
if err != nil {
return "", err
}
defer session.Close()
var b bytes.Buffer
session.Stdout = &b // 👈 this is the place I am concerned with
// Finally, run the command
err = session.Run(command)
return b.String(), err
}
This command usually works fine: it always connects but randomly does not return the output.
Before going further in my investigations, I wanted to make sure that the output buffer is flushed before returning the output. Is this the case?

Answer 1

In this use-case/issue, you can see stdout and stderr being linked to the same buffer.
See if that helps in your case.
sess, err := client.NewSession()
if err != nil {
log.Fatal("Failed to create session: ", err)
}
defer sess.Close()
stdin, err := sess.StdinPipe()
if err != nil {
log.Fatal(err)
}
var b bytes.Buffer
sess.Stdout = &b
sess.Stderr = &b
err = sess.Shell()
if err != nil {
log.Fatal(err)
}
...
_, err = fmt.Fprintf(stdin, "%s\n", cmd)