unix: add methods to manipulate *FdSet

Add Set, Clear, IsSet and Zero methods to manipulate an *FdSet. These
implement the same functionality as the FD_SET, FD_CLR, FD_ISSET and
FD_ZERO macros in <sys/select.h>.

Change-Id: I6b7bccb98e58ee5e719096ed5743f6edcd232840
Reviewed-on: https://go-review.googlesource.com/c/sys/+/205397
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/fdset.go

@@ -0,0 +1,29 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package unix
+
+// Set adds fd to the set fds.
+func (fds *FdSet) Set(fd int) {
+	fds.Bits[fd/NFDBITS] |= (1 << (uintptr(fd) % NFDBITS))
+}
+
+// Clear removes fd from the set fds.
+func (fds *FdSet) Clear(fd int) {
+	fds.Bits[fd/NFDBITS] &^= (1 << (uintptr(fd) % NFDBITS))
+}
+
+// IsSet returns whether fd is in the set fds.
+func (fds *FdSet) IsSet(fd int) bool {
+	return fds.Bits[fd/NFDBITS]&(1<<(uintptr(fd)%NFDBITS)) != 0
+}
+
+// Zero clears the set fds.
+func (fds *FdSet) Zero() {
+	for i := range fds.Bits {
+		fds.Bits[i] = 0
+	}
+}

unix/fdset_test.go

@@ -0,0 +1,53 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package unix_test
+
+import (
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestFdSet(t *testing.T) {
+	var fdSet unix.FdSet
+	fdSet.Zero()
+	for fd := 0; fd < unix.FD_SETSIZE; fd++ {
+		if fdSet.IsSet(fd) {
+			t.Fatalf("Zero did not clear fd %d", fd)
+		}
+		fdSet.Set(fd)
+	}
+
+	for fd := 0; fd < unix.FD_SETSIZE; fd++ {
+		if !fdSet.IsSet(fd) {
+			t.Fatalf("IsSet(%d): expected true, got false", fd)
+		}
+	}
+
+	fdSet.Zero()
+	for fd := 0; fd < unix.FD_SETSIZE; fd++ {
+		if fdSet.IsSet(fd) {
+			t.Fatalf("Zero did not clear fd %d", fd)
+		}
+	}
+
+	for fd := 1; fd < unix.FD_SETSIZE; fd += 2 {
+		fdSet.Set(fd)
+	}
+
+	for fd := 0; fd < unix.FD_SETSIZE; fd++ {
+		if fd&0x1 == 0x1 {
+			if !fdSet.IsSet(fd) {
+				t.Fatalf("IsSet(%d): expected true, got false", fd)
+			}
+		} else {
+			if fdSet.IsSet(fd) {
+				t.Fatalf("IsSet(%d): expected false, got true", fd)
+			}
+		}
+	}
+}

unix/syscall_bsd_test.go

@@ -87,11 +87,10 @@ func TestSelect(t *testing.T) {
 	}
 
 	rFdSet := &unix.FdSet{}
-	fd := rr.Fd()
-	// FD_SET(fd, rFdSet)
-	rFdSet.Bits[fd/unix.NFDBITS] |= (1 << (fd % unix.NFDBITS))
+	fd := int(rr.Fd())
+	rFdSet.Set(fd)
 
-	n, err = unix.Select(int(fd+1), rFdSet, nil, nil, nil)
+	n, err = unix.Select(fd+1, rFdSet, nil, nil, nil)
 	if err != nil {
 		t.Fatalf("Select: %v", err)
 	}

unix/syscall_linux_test.go

@@ -274,11 +274,10 @@ func TestSelect(t *testing.T) {
 	}
 
 	rFdSet := &unix.FdSet{}
-	fd := rr.Fd()
-	// FD_SET(fd, rFdSet)
-	rFdSet.Bits[fd/unix.NFDBITS] |= (1 << (fd % unix.NFDBITS))
+	fd := int(rr.Fd())
+	rFdSet.Set(fd)
 
-	n, err = unix.Select(int(fd+1), rFdSet, nil, nil, nil)
+	n, err = unix.Select(fd+1, rFdSet, nil, nil, nil)
 	if err != nil {
 		t.Fatalf("Select: %v", err)
 	}

unix/syscall_solaris_test.go

@@ -52,11 +52,10 @@ func TestSelect(t *testing.T) {
 	}
 
 	rFdSet := &unix.FdSet{}
-	fd := rr.Fd()
-	// FD_SET(fd, rFdSet)
-	rFdSet.Bits[fd/unix.NFDBITS] |= (1 << (fd % unix.NFDBITS))
+	fd := int(rr.Fd())
+	rFdSet.Set(fd)
 
-	n, err = unix.Select(int(fd+1), rFdSet, nil, nil, nil)
+	n, err = unix.Select(fd+1, rFdSet, nil, nil, nil)
 	if err != nil {
 		t.Fatalf("Select: %v", err)
 	}