windows: delegate Read, Write, Fd, Name to the file passed to newMaster

console_windows.go

@@ -62,6 +62,8 @@ func (m *master) initStdios() {
 }
 
 type master struct {
+	f File
+
 	in     windows.Handle
 	inMode uint32
 
@@ -153,22 +155,23 @@ func (m *master) Close() error {
 }
 
 func (m *master) Read(b []byte) (int, error) {
-	return os.Stdin.Read(b)
+	return m.f.Read(b)
 }
 
 func (m *master) Write(b []byte) (int, error) {
-	return os.Stdout.Write(b)
+	return m.f.Write(b)
 }
 
 func (m *master) Fd() uintptr {
-	return uintptr(m.in)
+	return m.f.Fd()
 }
 
-// on windows, console can only be made from os.Std{in,out,err}, hence there
-// isnt a single name here we can use. Return a dummy "console" value in this
-// case should be sufficient.
+// Name returns the name of the underlying file the console was created from
+// (for example "/dev/stdout"). It intentionally no longer returns a fixed
+// "console" string so the reported name matches the originating file,
+// consistent with the Unix implementation.
 func (m *master) Name() string {
-	return "console"
+	return m.f.Name()
 }
 
 // makeInputRaw puts the terminal (Windows Console) connected to the given
@@ -209,11 +212,19 @@ func checkConsole(f File) error {
 	return nil
 }
 
+// newMaster creates a Console from one of the process's standard streams
+// (os.Stdin, os.Stdout, or os.Stderr); any other file is rejected.
+//
+// Read, Write, Fd, and Name are delegated to f. The console-mode operations
+// (SetRaw, Reset, Size, and DisableEcho) act on the process's standard
+// handles rather than f alone: on Windows these streams share a single
+// underlying console object, so mode and size queries apply to that console
+// as a whole.
 func newMaster(f File) (Console, error) {
 	if f != os.Stdin && f != os.Stdout && f != os.Stderr {
 		return nil, errors.New("creating a console from a file is not supported on windows")
 	}
-	m := &master{}
+	m := &master{f: f}
 	m.initStdios()
 	return m, nil
 }

console_windows_test.go

@@ -0,0 +1,177 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package console
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"testing"
+)
+
+// TestMaster_DelegatesToFile verifies that a master delegates Read, Write,
+// Fd, and Name to the file it was constructed with, rather than the
+// process's global os.Stdin/os.Stdout. The Write case is the regression
+// test for https://github.com/containerd/console/issues/83, where output
+// written to a console created from a non-stdout stream leaked to stdout.
+//
+// The master is backed by an os.Pipe so the assertions exercise real I/O
+// without requiring an attached console, allowing the test to run anywhere.
+func TestMaster_DelegatesToFile(t *testing.T) {
+	t.Run("WriteGoesToFile", func(t *testing.T) {
+		r, w, err := os.Pipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer r.Close()
+		defer w.Close()
+
+		want := []byte("written via master")
+
+		// Drain the pipe concurrently so Write does not block.
+		type result struct {
+			data []byte
+			err  error
+		}
+		done := make(chan result, 1)
+		go func() {
+			data, err := io.ReadAll(r)
+			done <- result{data, err}
+		}()
+
+		m := &master{f: w}
+		if _, err := m.Write(want); err != nil {
+			t.Fatalf("Write: %v", err)
+		}
+		w.Close()
+
+		got := <-done
+		if got.err != nil {
+			t.Fatalf("reading pipe: %v", got.err)
+		}
+		if string(got.data) != string(want) {
+			t.Errorf("Write reached the wrong stream: pipe got %q, want %q", got.data, want)
+		}
+	})
+
+	t.Run("ReadComesFromFile", func(t *testing.T) {
+		r, w, err := os.Pipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer r.Close()
+		defer w.Close()
+
+		want := []byte("read via master")
+		go func() {
+			w.Write(want)
+			w.Close()
+		}()
+
+		m := &master{f: r}
+		got, err := io.ReadAll(m)
+		if err != nil {
+			t.Fatalf("Read: %v", err)
+		}
+		if string(got) != string(want) {
+			t.Errorf("Read drew from the wrong stream: got %q, want %q", got, want)
+		}
+	})
+
+	t.Run("FdAndName", func(t *testing.T) {
+		r, w, err := os.Pipe()
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer r.Close()
+		defer w.Close()
+
+		m := &master{f: w}
+		if got, want := m.Fd(), w.Fd(); got != want {
+			t.Errorf("Fd() = %v, want %v", got, want)
+		}
+		if m.Fd() == os.Stdout.Fd() {
+			t.Error("Fd() returned os.Stdout's descriptor; expected the provided file's")
+		}
+		if got, want := m.Name(), w.Name(); got != want {
+			t.Errorf("Name() = %q, want %q", got, want)
+		}
+	})
+}
+
+// TestConsoleFromFile_Delegation is an end-to-end test that exercises
+// the public ConsoleFromFile API with real console handles.
+//
+// Because "go test" redirects standard streams to pipes, the test
+// spawns itself as a subprocess with stdin/stdout connected to the real
+// console devices (CONIN$/CONOUT$); the subprocess's stderr is captured
+// so failures are reported with detail. This is the same helper-process
+// pattern used in the Go standard library (os/exec tests).
+func TestConsoleFromFile_Delegation(t *testing.T) {
+	if os.Getenv("CONSOLE_E2E_SUBPROCESS") == "1" {
+		// Subprocess: stdin and stdout are wired to the real console.
+		// stderr is captured by the parent and used to report diagnostics.
+		var failed bool
+		for _, f := range []*os.File{os.Stdin, os.Stdout} {
+			c, err := ConsoleFromFile(f)
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "ConsoleFromFile(%s): %v\n", f.Name(), err)
+				failed = true
+				continue
+			}
+			if got, want := c.Fd(), f.Fd(); got != want {
+				fmt.Fprintf(os.Stderr, "ConsoleFromFile(%s).Fd() = %v, want %v\n", f.Name(), got, want)
+				failed = true
+			}
+			if got, want := c.Name(), f.Name(); got != want {
+				fmt.Fprintf(os.Stderr, "ConsoleFromFile(%s).Name() = %q, want %q\n", f.Name(), got, want)
+				failed = true
+			}
+		}
+		if failed {
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+
+	conin, err := os.OpenFile("CONIN$", os.O_RDWR, 0)
+	if err != nil {
+		t.Skip("no console available:", err)
+	}
+	defer conin.Close()
+
+	conout, err := os.OpenFile("CONOUT$", os.O_RDWR, 0)
+	if err != nil {
+		t.Skip("no console available:", err)
+	}
+	defer conout.Close()
+
+	// stdin and stdout go to the real console (what we are testing); stderr is
+	// captured so subprocess diagnostics surface in the failure message.
+	var stderr bytes.Buffer
+	cmd := exec.Command(os.Args[0], "-test.run=^TestConsoleFromFile_Delegation$")
+	cmd.Env = append(os.Environ(), "CONSOLE_E2E_SUBPROCESS=1")
+	cmd.Stdin = conin
+	cmd.Stdout = conout
+	cmd.Stderr = &stderr
+
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("subprocess failed: %v\n%s", err, stderr.String())
+	}
+}