read stdin, maybe, if it has data.

main.go

package stdinMaybe

import (
	"bytes"
	"errors"
	"io"
	"os"
	"time"
)

// TryReadStdin is a non blocking func to read stdin
func TryReadStdin() (io.Reader, error) {
	var ret bytes.Buffer
	signalAllDone := make(chan error)
	signalCopyErr := make(chan error)
	go func() {
		temp := make([]byte, 1024)
		for {
			n, readErr := os.Stdin.Read(temp)
			if n == 0 && ret.Len() == 0 {
				signalCopyErr <- &EmptyDataError{errors.New("Empty stdin")}
			}
			if readErr != nil && readErr != io.EOF {
				signalCopyErr <- readErr
			}
			if n == 0 && readErr == nil {
				break
			}
			_, writeErr := ret.Write(temp[:n])
			temp = temp[:0]
			if writeErr != nil {
				signalCopyErr <- writeErr
			}
			if readErr == io.EOF {
				break
			}
			if writeErr == io.EOF {
				break
			}
		}
		signalCopyErr <- nil
	}()
	go func() {
		select {
		case signalAllDone <- <-signalCopyErr:
		case <-time.After(time.Millisecond * 100):
			signalAllDone <- &EmptyDataError{errors.New("Empty stdin")}
		}
	}()
	return &ret, <-signalAllDone
}

// EmptyDataError to signal empty feed.
type EmptyDataError struct {
	error
}

// Empty returns true.
func (e EmptyDataError) Empty() bool {
	return true
}

// EmptyDataErrorer is the contract to signal an empty feed.
type EmptyDataErrorer interface {
	Empty() bool
}

// IsEmpty is an helper to determine if the error is about an empty feed.
func IsEmpty(err error) bool {
	if err == nil {
		return false
	}
	_, ok := err.(EmptyDataErrorer)
	return ok
}