bastion 0.57.0

client-go/pair_terminal.go

@@ -0,0 +1,66 @@
+package main
+
+// pair_terminal.go: the one question `pair` asks a person, on a local machine
+// that already serves a Host: whether to add another.
+//
+// A local bastion used to serve one Host, full stop, because on a single-user
+// machine a second Host appearing meant someone else had got a token onto the
+// box. A person who uses two Hosts (a Cloud machine beside the platform one)
+// could not pair the second at all. Now the second is added when the person at
+// this machine says so, and only then: the answer is read from the controlling
+// terminal, never from standard input, so a token piped in by a script or an
+// installer (which feeds the pairing code through standard input) cannot add a
+// Host by itself. With no terminal there is nobody to ask, and the pair is
+// refused.
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// errNoTerminal: this process has no controlling terminal to ask on.
+var errNoTerminal = errors.New("no terminal")
+
+// openTerminal opens the controlling terminal for one question: a reader for
+// the answer, a writer for the question, and a close. A variable so a test can
+// stand in a person; nothing else assigns it.
+var openTerminal = openControllingTerminal
+
+// terminalSafeName is a Host name as the question shows it. newHost is the
+// handle the token carries, which nothing has checked yet: whoever made the
+// token chose it, and a control character or an escape sequence in it could
+// rewrite the question on the person's screen. A plain host name is shown as
+// it is; anything else is quoted, every such byte escaped.
+func terminalSafeName(name string) string {
+	if validHostName(name) {
+		return name
+	}
+	return strconv.QuoteToASCII(name)
+}
+
+// confirmAddHost asks whether to add newHost beside serving, the Host this
+// local machine already serves. True only for a typed y or yes.
+func confirmAddHost(serving, newHost string) (bool, error) {
+	in, out, closeTerm, err := openTerminal()
+	if err != nil {
+		return false, fmt.Errorf("this computer already serves your Host %s, and adding another needs a yes typed "+
+			"at this computer, but this run has no terminal to ask in. Run the same command in a terminal "+
+			"window on this computer; nothing was paired", serving)
+	}
+	defer closeTerm()
+	fmt.Fprintf(out, "This computer already serves your Host %s. Add %s as well? It gets a pairing of its own,\n"+
+		"and `privatae-bastion ui` shows what each Host may do here. [y/N] ", terminalSafeName(serving), terminalSafeName(newHost))
+	line, err := bufio.NewReader(io.LimitReader(in, 256)).ReadString('\n')
+	if err != nil && !errors.Is(err, io.EOF) {
+		return false, fmt.Errorf("could not read the answer (%v); nothing was paired", err)
+	}
+	switch strings.ToLower(strings.TrimSpace(line)) {
+	case "y", "yes":
+		return true, nil
+	}
+	return false, nil
+}