I'm writing a kubectl plugin to authenticate users, and I would like to prompt the user for a password after the plugin is invoked. From what I understand, it's fairly trivial to get input from STDIN, but I'm struggling seeing messages written to STDOUT. Currently my code looks like this:
In cmd/kubectl-myauth.go:
// This is mostly boilerplate, but it's needed for the MRE
// https://stackoverflow.com/help/minimal-reproducible-example
package myauth
import (...)
func main() {
pflag.CommandLine = pflag.NewFlagSet("kubectl-myauth", pflag.ExitOnError)
root := cmd.NewCmdAuthOp(genericclioptions.IOStreams{In: os.Stdin, Out: os.Stdout, ErrOut: os.Stderr})
if err := root.Execute(); err != nil {
os.Exit(1)
}
}
In pkg/cmd/auth.go:
package cmd
...
type AuthOpOptions struct {
configFlags *genericclioptions.ConfigFlags
resultingContext *api.Context
rawConfig api.Config
args []string
...
genericclioptions.IOStreams
}
func NewAuthOpOptions(streams genericclioptions.IOStreams) *AuthOpOptions {
return &AuthOpOptions{
configFlags: genericclioptions.NewConfigFlags(true),
IOStreams: streams,
}
}
func NewCmdAuthOp(streams genericclioptions.IOStreams) *cobra.Command {
o := NewAuthOpOptions(streams)
cmd := &cobra.Command{
RunE: func(c *cobra.Command, args []string) error {
return o.Run()
},
}
return cmd
}
func (o *AuthOpOptions) Run() error {
pass, err := getPassword(o)
if err != nil {
return err
}
// Do Auth Stuff
// Eventually print an ExecCredential to STDOUT
return nil
}
func getPassword(o *AuthOpOptions) (string, error) {
var reader *bufio.Reader
reader = nil
pass := ""
for pass == "" {
// THIS IS AN IMPORTANT LINE [1]
fmt.Fprintf(o.IOStreams.Out, "Password with which to authenticate:
")
// THE REST OF THIS IS STILL IMPORTANT, BUT LESS SO [2]
if reader == nil {
// The first time through, initialize the reader
reader = bufio.NewReader(o.IOStreams.In)
}
pass, err := reader.ReadString('
')
if err != nil {
return nil, err
}
pass = strings.Trim(pass, "
")
if pass == "" {
// ALSO THIS LINE IS IMPORTANT [3]
fmt.Fprintf(o.IOStreams.Out, `Read password was empty string.
Please input a valid password.
`)
}
}
return pass, nil
}
This works the way that I expect when running from outside of the kubectl context - namely, it prints the string, prompts for input, and continues. However, from inside the kubectl context, I believe the print between the first two all-caps comments ([1] and [2]) is being swallowed by kubectl listening on STDOUT. I can get around this by printing to STDERR, but that feels... wrong. Is there a way that I can bypass kubectl's consumption of STDOUT to communicate with the user?
TL;DR: kubectl appears to be swallowing all of STDOUT for kubectl plugins, but I want to prompt the user for input - is there a simple way to do this?
