os: add SyscallConn method for os.File

Fixes #24331

Change-Id: I119c09a4259d852cdf8ea31b3e03e6f09a5f7bda
Reviewed-on: https://go-review.googlesource.com/c/155517Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/file.go

@@ -473,3 +473,12 @@ func (f *File) SetReadDeadline(t time.Time) error {
 func (f *File) SetWriteDeadline(t time.Time) error {
 	return f.setWriteDeadline(t)
 }
+
+// SyscallConn returns a raw file.
+// This implements the syscall.Conn interface.
+func (f *File) SyscallConn() (syscall.RawConn, error) {
+	if err := f.checkValid("SyscallConn"); err != nil {
+		return nil, err
+	}
+	return newRawConn(f)
+}

src/os/file_plan9.go

@@ -534,3 +534,21 @@ func (f *File) checkValid(op string) error {
 	}
 	return nil
 }
+
+type rawConn struct{}
+
+func (c *rawConn) Control(f func(uintptr)) error {
+	return syscall.EPLAN9
+}
+
+func (c *rawConn) Read(f func(uintptr) bool) error {
+	return syscall.EPLAN9
+}
+
+func (c *rawConn) Write(f func(uintptr) bool) error {
+	return syscall.EPLAN9
+}
+
+func newRawConn(file *File) (*rawConn, error) {
+	return nil, syscall.EPLAN9
+}

src/os/os_unix_test.go

@@ -22,6 +22,9 @@ func init() {
 	isReadonlyError = func(err error) bool { return err == syscall.EROFS }
 }
 
+// For TestRawConnReadWrite.
+type syscallDescriptor = int
+
 func checkUidGid(t *testing.T, path string, uid, gid int) {
 	dir, err := Lstat(path)
 	if err != nil {

src/os/os_windows_test.go

@@ -26,6 +26,9 @@ import (
 	"unsafe"
 )
 
+// For TestRawConnReadWrite.
+type syscallDescriptor = syscall.Handle
+
 func TestSameWindowsFile(t *testing.T) {
 	temp, err := ioutil.TempDir("", "TestSameWindowsFile")
 	if err != nil {

src/os/rawconn.go

+// Copyright 2018 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 !plan9
+
+package os
+
+import (
+	"runtime"
+)
+
+// rawConn implements syscall.RawConn.
+type rawConn struct {
+	file *File
+}
+
+func (c *rawConn) Control(f func(uintptr)) error {
+	if err := c.file.checkValid("SyscallConn.Control"); err != nil {
+		return err
+	}
+	err := c.file.pfd.RawControl(f)
+	runtime.KeepAlive(c.file)
+	return err
+}
+
+func (c *rawConn) Read(f func(uintptr) bool) error {
+	if err := c.file.checkValid("SyscallConn.Read"); err != nil {
+		return err
+	}
+	err := c.file.pfd.RawRead(f)
+	runtime.KeepAlive(c.file)
+	return err
+}
+
+func (c *rawConn) Write(f func(uintptr) bool) error {
+	if err := c.file.checkValid("SyscallConn.Write"); err != nil {
+		return err
+	}
+	err := c.file.pfd.RawWrite(f)
+	runtime.KeepAlive(c.file)
+	return err
+}
+
+func newRawConn(file *File) (*rawConn, error) {
+	return &rawConn{file: file}, nil
+}

src/os/rawconn_test.go

+// Copyright 2018 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.
+
+// Test use of raw connections.
+// +build !plan9,!nacl,!js
+
+package os_test
+
+import (
+	"os"
+	"syscall"
+	"testing"
+)
+
+func TestRawConnReadWrite(t *testing.T) {
+	t.Parallel()
+
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer r.Close()
+	defer w.Close()
+
+	rconn, err := r.SyscallConn()
+	if err != nil {
+		t.Fatal(err)
+	}
+	wconn, err := w.SyscallConn()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var operr error
+	err = wconn.Write(func(s uintptr) bool {
+		_, operr = syscall.Write(syscallDescriptor(s), []byte{'b'})
+		return operr != syscall.EAGAIN
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if operr != nil {
+		t.Fatal(err)
+	}
+
+	var n int
+	buf := make([]byte, 1)
+	err = rconn.Read(func(s uintptr) bool {
+		n, operr = syscall.Read(syscallDescriptor(s), buf)
+		return operr != syscall.EAGAIN
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if operr != nil {
+		t.Fatal(operr)
+	}
+	if n != 1 {
+		t.Errorf("read %d bytes, expected 1", n)
+	}
+	if buf[0] != 'b' {
+		t.Errorf("read %q, expected %q", buf, "b")
+	}
+}

src/syscall/net.go

@@ -26,7 +26,7 @@ type RawConn interface {
 	Write(f func(fd uintptr) (done bool)) error
 }
 
-// Conn is implemented by some types in the net package to provide
+// Conn is implemented by some types in the net and os packages to provide
 // access to the underlying file descriptor or handle.
 type Conn interface {
 	// SyscallConn returns a raw network connection.