fix: detect storage:exec TTY with isatty, not ModeCharDevice

/dev/null is a character device but not a terminal. Treating it as a TTY
made docker run -it fail under docker exec without -t, which broke the
Dokku-in-Docker storage bats job in CI.

plugins/storage/commands_entries.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/dokku/dokku/plugins/common"
+	"github.com/mattn/go-isatty"
 )
 
 // CommandCreateInput captures the flags accepted by storage:create.
@@ -422,14 +423,16 @@ func CommandExec(input CommandExecInput) error {
 
 // stdinModes inspects os.Stdin to decide whether docker / the k8s exec
 // SDK should request an interactive session and a TTY.
+//
+// TTY detection uses isatty rather than ModeCharDevice: /dev/null is a
+// character device but not a terminal, and treating it as a TTY makes
+// docker run -it fail with "cannot attach stdin to a TTY-enabled
+// container because stdin is not a terminal" (e.g. docker exec without
+// -t, as in CI).
 func stdinModes() (interactive bool, tty bool) {
+	tty = isatty.IsTerminal(os.Stdin.Fd()) || isatty.IsCygwinTerminal(os.Stdin.Fd())
 	fi, err := os.Stdin.Stat()
-	if err != nil || fi == nil {
+	hasStdinData := err == nil && fi != nil && fi.Mode()&os.ModeNamedPipe != 0
-		return false, false
-	}
-	mode := fi.Mode()
-	tty = mode&os.ModeCharDevice != 0
-	hasStdinData := mode&os.ModeNamedPipe != 0
 	interactive = tty || hasStdinData
 	return interactive, tty
 }

plugins/storage/commands_entries_test.go

@@ -1,6 +1,7 @@
 package storage
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 
@@ -218,3 +219,47 @@ func TestCommandSetPersistsAndValidates(t *testing.T) {
 	Expect(err).To(HaveOccurred())
 	Expect(err.Error()).To(ContainSubstring("does not exist"))
 }
+
+// TestStdinModesDevNullIsNotTTY guards the CI / docker-exec path: stdin is
+// often /dev/null, which is a character device but not a terminal. ModeCharDevice
+// alone would request docker run -it and fail attach.
+func TestStdinModesDevNullIsNotTTY(t *testing.T) {
+	devNull, err := os.Open(os.DevNull)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer devNull.Close()
+
+	old := os.Stdin
+	os.Stdin = devNull
+	t.Cleanup(func() { os.Stdin = old })
+
+	interactive, tty := stdinModes()
+	if tty {
+		t.Fatalf("expected tty=false for /dev/null, got tty=true interactive=%v", interactive)
+	}
+	if interactive {
+		t.Fatalf("expected interactive=false for /dev/null, got interactive=true")
+	}
+}
+
+func TestStdinModesNamedPipeIsInteractiveWithoutTTY(t *testing.T) {
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r.Close()
+	defer w.Close()
+
+	old := os.Stdin
+	os.Stdin = r
+	t.Cleanup(func() { os.Stdin = old })
+
+	interactive, tty := stdinModes()
+	if tty {
+		t.Fatalf("expected tty=false for a pipe, got tty=true")
+	}
+	if !interactive {
+		t.Fatalf("expected interactive=true for a named pipe")
+	}
+}

plugins/storage/go.mod

@@ -5,6 +5,7 @@ go 1.26.2
 require (
 	github.com/dokku/dokku/plugins/common v0.0.0-00010101000000-000000000000
 	github.com/dokku/dokku/plugins/docker-options v0.0.0-00010101000000-000000000000
+	github.com/mattn/go-isatty v0.0.24
 	github.com/onsi/gomega v1.44.0
 	github.com/spf13/pflag v1.0.10
 )
@@ -17,7 +18,6 @@ require (
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
 	github.com/kr/fs v0.1.0 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
-	github.com/mattn/go-isatty v0.0.24 // indirect
 	github.com/melbahja/goph v1.5.2 // indirect
 	github.com/otiai10/copy v1.14.1 // indirect
 	github.com/otiai10/mint v1.6.3 // indirect