os: if descriptor is non-blocking, retain that in Fd method

For #58408
Fixes #60211

Change-Id: I30f5678b46e15121865b19d1c0f82698493fad4e
Reviewed-on: https://go-review.googlesource.com/c/go/+/495079


Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

src/internal/syscall/unix/nonblocking.go

@@ -19,3 +19,7 @@ func IsNonblock(fd int) (nonblocking bool, err error) {
 	}
 	return flag&syscall.O_NONBLOCK != 0, nil
 }
+
+func HasNonblockFlag(flag int) bool {
+	return flag&syscall.O_NONBLOCK != 0
+}

src/internal/syscall/unix/nonblocking_js.go

@@ -9,3 +9,7 @@ package unix
 func IsNonblock(fd int) (nonblocking bool, err error) {
 	return false, nil
 }
+
+func HasNonblockFlag(flag int) bool {
+	return false
+}

src/internal/syscall/unix/nonblocking_libc.go

@@ -19,6 +19,10 @@ func IsNonblock(fd int) (nonblocking bool, err error) {
 	return flag&syscall.O_NONBLOCK != 0, nil
 }
 
+func HasNonblockFlag(flag int) bool {
+	return flag&syscall.O_NONBLOCK != 0
+}
+
 // Implemented in the syscall package.
 //
 //go:linkname fcntl syscall.fcntl

src/internal/syscall/unix/nonblocking_wasip1.go

@@ -19,6 +19,10 @@ func IsNonblock(fd int) (nonblocking bool, err error) {
 	return flags&syscall.FDFLAG_NONBLOCK != 0, nil
 }
 
+func HasNonblockFlag(flag int) bool {
+	return flag&syscall.FDFLAG_NONBLOCK != 0
+}
+
 // This helper is implemented in the syscall package. It means we don't have
 // to redefine the fd_fdstat_get host import or the fdstat struct it
 // populates.

src/os/fifo_test.go

@@ -8,6 +8,7 @@ package os_test
 
 import (
 	"errors"
+	"internal/syscall/unix"
 	"internal/testenv"
 	"io/fs"
 	"os"
@@ -155,3 +156,52 @@ func TestNonPollable(t *testing.T) {
 		}
 	}
 }
+
+// Issue 60211.
+func TestOpenFileNonBlocking(t *testing.T) {
+	exe, err := os.Executable()
+	if err != nil {
+		t.Skipf("can't find executable: %v", err)
+	}
+	f, err := os.OpenFile(exe, os.O_RDONLY|syscall.O_NONBLOCK, 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	nonblock, err := unix.IsNonblock(int(f.Fd()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !nonblock {
+		t.Errorf("file opened with O_NONBLOCK but in blocking mode")
+	}
+}
+
+func TestNewFileNonBlocking(t *testing.T) {
+	var p [2]int
+	if err := syscall.Pipe(p[:]); err != nil {
+		t.Fatal(err)
+	}
+	if err := syscall.SetNonblock(p[0], true); err != nil {
+		t.Fatal(err)
+	}
+	f := os.NewFile(uintptr(p[0]), "pipe")
+	nonblock, err := unix.IsNonblock(p[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !nonblock {
+		t.Error("pipe blocking after NewFile")
+	}
+	fd := f.Fd()
+	if fd != uintptr(p[0]) {
+		t.Errorf("Fd returned %d, want %d", fd, p[0])
+	}
+	nonblock, err = unix.IsNonblock(p[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !nonblock {
+		t.Error("pipe blocking after Fd")
+	}
+}

src/os/file_unix.go

@@ -116,12 +116,12 @@ const (
 	// kindNewFile means that the descriptor was passed to us via NewFile.
 	kindNewFile newFileKind = iota
 	// kindOpenFile means that the descriptor was opened using
-	// Open, Create, or OpenFile.
+	// Open, Create, or OpenFile (without O_NONBLOCK).
 	kindOpenFile
 	// kindPipe means that the descriptor was opened using Pipe.
 	kindPipe
-	// kindNonBlock means that the descriptor was passed to us via NewFile,
-	// and the descriptor is already in non-blocking mode.
+	// kindNonBlock means that the descriptor is already in
+	// non-blocking mode.
 	kindNonBlock
 	// kindNoPoll means that we should not put the descriptor into
 	// non-blocking mode, because we know it is not a pipe or FIFO.
@@ -184,7 +184,9 @@ func newFile(fd uintptr, name string, kind newFileKind) *File {
 	clearNonBlock := false
 	if pollable {
 		if kind == kindNonBlock {
-			f.nonblock = true
+			// The descriptor is already in non-blocking mode.
+			// We only set f.nonblock if we put the file into
+			// non-blocking mode.
 		} else if err := syscall.SetNonblock(fdi, true); err == nil {
 			f.nonblock = true
 			clearNonBlock = true
@@ -263,7 +265,12 @@ func openFileNolog(name string, flag int, perm FileMode) (*File, error) {
 		syscall.CloseOnExec(r)
 	}
 
-	f := newFile(uintptr(r), name, kindOpenFile)
+	kind := kindOpenFile
+	if unix.HasNonblockFlag(flag) {
+		kind = kindNonBlock
+	}
+
+	f := newFile(uintptr(r), name, kind)
 	f.pfd.SysFile = s
 	return f, nil
 }