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

pkg/stdio/noninteractive.go

@@ -0,0 +1,73 @@
+package stdio
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strings"
+)
+
+// noninteractiveStdio interacts with stdin/stdout/stderr as files, with no user interaction.
+type noninteractiveStdio struct {
+	in  *bufio.Scanner
+	out io.Writer
+	err io.Writer
+}
+
+func (t *noninteractiveStdio) Write(p []byte) (int, error) {
+	return t.out.Write(p)
+}
+
+func (t *noninteractiveStdio) WriteErr(p []byte) (int, error) {
+	return t.err.Write(p)
+}
+
+func (t *noninteractiveStdio) Banner(message string) error {
+	_, err := fmt.Fprintf(t.out, "> %s\n", message)
+	return err
+}
+
+func (t *noninteractiveStdio) Error(message string) error {
+	_, err := fmt.Fprintf(t.err, "X %s\n", message)
+	return err
+}
+
+func (t *noninteractiveStdio) IsInteractive() bool {
+	return false
+}
+
+func (t *noninteractiveStdio) GetStringInput(prompt, defaultValue string) (string, error) {
+	if inLine := t.readStdinLine(); inLine != "" {
+		return inLine, nil
+	}
+	if defaultValue != "" {
+		return defaultValue, nil
+	}
+	return "", fmt.Errorf("couldn't get input for prompt %q: no data on stdin", prompt)
+}
+
+func (t *noninteractiveStdio) GetSecret(prompt string, minLen int) (string, error) {
+	inLine := t.readStdinLine()
+	if len(inLine) >= minLen {
+		return inLine, nil
+	} else if minLen > 0 {
+		return "", fmt.Errorf("value for prompt %q is too short: min length is %d", prompt, minLen)
+	}
+	return "", nil
+}
+
+func (t *noninteractiveStdio) GetPassword(prompt string) (string, error) {
+	return t.GetSecret(prompt, MinPasswordLen)
+}
+
+func (t *noninteractiveStdio) GetConfirm(prompt string) (answer bool) {
+	return strings.HasPrefix(t.readStdinLine(), "y")
+}
+
+// readStdinLine returns the first line of text on stdin, or empty string if stdin is at EOF.
+func (t *noninteractiveStdio) readStdinLine() string {
+	if !t.in.Scan() {
+		return ""
+	}
+	return t.in.Text()
+}