mesh-cli: carry what a pipe or a file gives standard input with the line, at most 64 KiB

So a secret reaches the controller's terminal without standing on a command line:
mesh-cli secret accept <node> <module> <name> --from - < file. A terminal is never read, more than the
bound is refused before anything is asked, and nothing carried is printed. mesh-sdk moves to f047d0a.

modules/mesh-cli/cmd/mesh-cli/main_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"context"
+	"io"
 	"net"
 	"path/filepath"
 	"strings"
@@ -11,6 +12,13 @@ import (
 	"git.novox.be/novox/mesh-sdk/go/cli"
 )
 
+// The tests' own standard input is the runner's, which may be a pipe nobody closes: read as a terminal unless a test
+// says otherwise.
+func init() { standardInput = func() (io.Reader, bool) { return nil, true } }
+
+// lastStdin is the standard input the engine was last given.
+var lastStdin []byte
+
 // engine answers one connection on a socket of the test's own as the node-engine would, and says what it was asked.
 func engine(t *testing.T, answer cli.Answer) <-chan []string {
 	t.Helper()
@@ -24,6 +32,7 @@ func engine(t *testing.T, answer cli.Answer) <-chan []string {
 	socket = path
 	t.Cleanup(func() { socket = before })
 	asked := make(chan []string, 1)
+	lastStdin = nil
 	go func() {
 		conn, err := l.Accept()
 		if err != nil {
@@ -34,6 +43,7 @@ func engine(t *testing.T, answer cli.Answer) <-chan []string {
 		if err != nil {
 			return
 		}
+		lastStdin = req.Stdin
 		asked <- req.Line
 		_ = cli.WriteAnswer(conn, answer)
 	}()
@@ -104,3 +114,42 @@ func TestAnOutcomeNotKnownIsSaid(t *testing.T) {
 		t.Fatalf("exit %d, said %q", code, errOut.String())
 	}
 }
+
+// A pipe's or a file's standard input goes with the line, whole; a terminal's is never read; more than the bound is
+// refused and nothing is asked (novox/hq ADR 0259 §10).
+func TestStandardInputGoesWithTheLineAndATerminalIsNeverRead(t *testing.T) {
+	t.Setenv("MESH_VERB", "")
+	was := standardInput
+	t.Cleanup(func() { standardInput = was })
+	secret := "123456789:the-bot-token\n"
+
+	standardInput = func() (io.Reader, bool) { return strings.NewReader(secret), false }
+	asked := engine(t, cli.Answer{Terminal: true})
+	var out, errOut bytes.Buffer
+	if code := run(context.Background(), []string{"secret", "accept", "anchor", "telegram", "telegram-token", "--from", "-"},
+		&out, &errOut); code != 0 {
+		t.Fatalf("exit %d: %s", code, errOut.String())
+	}
+	<-asked
+	if string(lastStdin) != secret {
+		t.Fatalf("the engine was given %q", lastStdin)
+	}
+	if strings.Contains(out.String()+errOut.String(), "bot-token") {
+		t.Fatal("mesh-cli printed what it carried")
+	}
+
+	standardInput = func() (io.Reader, bool) { return strings.NewReader("typed"), true }
+	asked = engine(t, cli.Answer{})
+	_ = run(context.Background(), []string{"status"}, &out, &errOut)
+	<-asked
+	if len(lastStdin) != 0 {
+		t.Fatalf("a terminal's input was read: %q", lastStdin)
+	}
+
+	standardInput = func() (io.Reader, bool) { return bytes.NewReader(make([]byte, cli.MaxStdin+1)), false }
+	errOut.Reset()
+	if code := run(context.Background(), []string{"secret", "accept", "a", "b", "c", "--from", "-"}, &out, &errOut); code == 0 ||
+		!strings.Contains(errOut.String(), "nothing was asked") {
+		t.Fatalf("more than the bound was asked: %d %s", code, errOut.String())
+	}
+}