// cmdStream executes a command, and returns its stdout as a stream.
// If the command fails to run or doesn't complete successfully, an error
// will be returned, including anything written on stderr.
func cmdStream(cmd *exec.Cmd, input io.Reader) (io.ReadCloser, <-chan struct{}, error) {
chdone := make(chan struct{})
cmd.Stdin = input
pipeR, pipeW := io.Pipe()
cmd.Stdout = pipeW
var errBuf bytes.Buffer
cmd.Stderr = &errBuf
// Run the command and return the pipe
if err := cmd.Start(); err != nil {
return nil, nil, err
}
// Copy stdout to the returned pipe
go func() {
if err := cmd.Wait(); err != nil {
pipeW.CloseWithError(fmt.Errorf("%s: %s", err, errBuf.String()))
} else {
pipeW.Close()
}
close(chdone)
}()
return pipeR, chdone, nil
}
