fix: detect non-interactive stdio and use "normal" IO operations (#204)

pkg/stdio/stdio.go

@@ -1,17 +1,52 @@
 package stdio
 
-import "io"
+import (
+	"bufio"
+	"io"
+	"os"
+
+	"github.com/AlecAivazis/survey/v2/terminal"
+	"github.com/mattn/go-isatty"
+)
 
 const MinPasswordLen = 8
 
 type StdIO interface {
-	io.Writer
+	// Write prints some bytes to stdout.
+	Write(p []byte) (n int, err error)
+	// WriteErr prints some bytes to stderr.
 	WriteErr(p []byte) (n int, err error)
+	// Banner displays informational text to the user.
 	Banner(message string) error
+	// Error displays an error message to the user.
 	Error(message string) error
-	InputIsInteractive() bool
+	// IsInteractive signals whether interactive I/O is supported.
+	IsInteractive() bool
+	// GetStringInput prompts the user for arbitrary input.
 	GetStringInput(prompt, defaultValue string) (string, error)
+	// GetSecret prompts the user for a secret.
 	GetSecret(prompt string, minLen int) (string, error)
+	// GetPassword prompts the user for a secret twice, and inputs must match.
+	// Uses stdio.MinPasswordLen as the minimum input length
 	GetPassword(prompt string) (string, error)
+	// GetConfirm asks the user for a y/n answer to a prompt.
 	GetConfirm(prompt string) bool
 }
+
+func newTerminalStdio(in terminal.FileReader, out terminal.FileWriter, err io.Writer) StdIO {
+	interactiveIn := isatty.IsTerminal(in.Fd()) || isatty.IsCygwinTerminal(in.Fd())
+	interactiveOut := isatty.IsTerminal(out.Fd()) || isatty.IsCygwinTerminal(out.Fd())
+
+	if interactiveIn && interactiveOut {
+		return &interactiveStdio{in: in, out: out, err: err}
+	}
+
+	return &noninteractiveStdio{
+		in:  bufio.NewScanner(in),
+		out: out,
+		err: err,
+	}
+}
+
+// TerminalStdio interacts with users over stdin/stdout/stderr.
+var TerminalStdio = newTerminalStdio(os.Stdin, os.Stdout, os.Stderr)