1 files changed, 569 insertions, 0 deletions
diff --git a/pkg/unet/unet.go b/pkg/unet/unet.go
new file mode 100644
index 000000000..d843f19cf
--- /dev/null
+++ b/pkg/unet/unet.go
@@ -0,0 +1,569 @@
+// Copyright 2018 The gVisor 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 unet provides a minimal net package based on Unix Domain Sockets.
+//
+// This does no pooling, and should only be used for a limited number of
+// connections in a Go process. Don't use this package for arbitrary servers.
+package unet
+
+import (
+	"errors"
+	"sync/atomic"
+	"syscall"
+
+	"gvisor.dev/gvisor/pkg/gate"
+)
+
+// backlog is used for the listen request.
+const backlog = 16
+
+// errClosing is returned by wait if the Socket is in the process of closing.
+var errClosing = errors.New("Socket is closing")
+
+// errMessageTruncated indicates that data was lost because the provided buffer
+// was too small.
+var errMessageTruncated = errors.New("message truncated")
+
+// socketType returns the appropriate type.
+func socketType(packet bool) int {
+	if packet {
+		return syscall.SOCK_SEQPACKET
+	}
+	return syscall.SOCK_STREAM
+}
+
+// socket creates a new host socket.
+func socket(packet bool) (int, error) {
+	// Make a new socket.
+	fd, err := syscall.Socket(syscall.AF_UNIX, socketType(packet), 0)
+	if err != nil {
+		return 0, err
+	}
+
+	return fd, nil
+}
+
+// eventFD returns a new event FD with initial value 0.
+func eventFD() (int, error) {
+	f, _, e := syscall.Syscall(syscall.SYS_EVENTFD2, 0, 0, 0)
+	if e != 0 {
+		return -1, e
+	}
+	return int(f), nil
+}
+
+// Socket is a connected unix domain socket.
+type Socket struct {
+	// gate protects use of fd.
+	gate gate.Gate
+
+	// fd is the bound socket.
+	//
+	// fd must be read atomically, and only remains valid if read while
+	// within gate.
+	fd int32
+
+	// efd is an event FD that is signaled when the socket is closing.
+	//
+	// efd is immutable and remains valid until Close/Release.
+	efd int
+
+	// race is an atomic variable used to avoid triggering the race
+	// detector. See comment in SocketPair below.
+	race *int32
+}
+
+// NewSocket returns a socket from an existing FD.
+//
+// NewSocket takes ownership of fd.
+func NewSocket(fd int) (*Socket, error) {
+	// fd must be non-blocking for non-blocking syscall.Accept in
+	// ServerSocket.Accept.
+	if err := syscall.SetNonblock(fd, true); err != nil {
+		return nil, err
+	}
+
+	efd, err := eventFD()
+	if err != nil {
+		return nil, err
+	}
+
+	return &Socket{
+		fd:  int32(fd),
+		efd: efd,
+	}, nil
+}
+
+// finish completes use of s.fd by evicting any waiters, closing the gate, and
+// closing the event FD.
+func (s *Socket) finish() error {
+	// Signal any blocked or future polls.
+	//
+	// N.B. eventfd writes must be 8 bytes.
+	if _, err := syscall.Write(s.efd, []byte{1, 0, 0, 0, 0, 0, 0, 0}); err != nil {
+		return err
+	}
+
+	// Close the gate, blocking until all FD users leave.
+	s.gate.Close()
+
+	return syscall.Close(s.efd)
+}
+
+// Close closes the socket.
+func (s *Socket) Close() error {
+	// Set the FD in the socket to -1, to ensure that all future calls to
+	// FD/Release get nothing and Close calls return immediately.
+	fd := int(atomic.SwapInt32(&s.fd, -1))
+	if fd < 0 {
+		// Already closed or closing.
+		return syscall.EBADF
+	}
+
+	// Shutdown the socket to cancel any pending accepts.
+	s.shutdown(fd)
+
+	if err := s.finish(); err != nil {
+		return err
+	}
+
+	return syscall.Close(fd)
+}
+
+// Release releases ownership of the socket FD.
+//
+// The returned FD is non-blocking.
+//
+// Any concurrent or future callers of Socket methods will receive EBADF.
+func (s *Socket) Release() (int, error) {
+	// Set the FD in the socket to -1, to ensure that all future calls to
+	// FD/Release get nothing and Close calls return immediately.
+	fd := int(atomic.SwapInt32(&s.fd, -1))
+	if fd < 0 {
+		// Already closed or closing.
+		return -1, syscall.EBADF
+	}
+
+	if err := s.finish(); err != nil {
+		return -1, err
+	}
+
+	return fd, nil
+}
+
+// FD returns the FD for this Socket.
+//
+// The FD is non-blocking and must not be made blocking.
+//
+// N.B. os.File.Fd makes the FD blocking. Use of Release instead of FD is
+// strongly preferred.
+//
+// The returned FD cannot be used safely if there may be concurrent callers to
+// Close or Release.
+//
+// Use Release to take ownership of the FD.
+func (s *Socket) FD() int {
+	return int(atomic.LoadInt32(&s.fd))
+}
+
+// enterFD enters the FD gate and returns the FD value.
+//
+// If enterFD returns ok, s.gate.Leave must be called when done with the FD.
+// Callers may only block while within the gate using s.wait.
+//
+// The returned FD is guaranteed to remain valid until s.gate.Leave.
+func (s *Socket) enterFD() (int, bool) {
+	if !s.gate.Enter() {
+		return -1, false
+	}
+
+	fd := int(atomic.LoadInt32(&s.fd))
+	if fd < 0 {
+		s.gate.Leave()
+		return -1, false
+	}
+
+	return fd, true
+}
+
+// SocketPair creates a pair of connected sockets.
+func SocketPair(packet bool) (*Socket, *Socket, error) {
+	// Make a new pair.
+	fds, err := syscall.Socketpair(syscall.AF_UNIX, socketType(packet)|syscall.SOCK_CLOEXEC, 0)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// race is an atomic variable used to avoid triggering the race
+	// detector. We have to fool TSAN into thinking there is a race
+	// variable between our two sockets. We only use SocketPair in tests
+	// anyway.
+	//
+	// NOTE(b/27107811): This is purely due to the fact that the raw
+	// syscall does not serve as a boundary for the sanitizer.
+	var race int32
+	a, err := NewSocket(fds[0])
+	if err != nil {
+		syscall.Close(fds[0])
+		syscall.Close(fds[1])
+		return nil, nil, err
+	}
+	a.race = &race
+	b, err := NewSocket(fds[1])
+	if err != nil {
+		a.Close()
+		syscall.Close(fds[1])
+		return nil, nil, err
+	}
+	b.race = &race
+	return a, b, nil
+}
+
+// Connect connects to a server.
+func Connect(addr string, packet bool) (*Socket, error) {
+	fd, err := socket(packet)
+	if err != nil {
+		return nil, err
+	}
+
+	// Connect the socket.
+	usa := &syscall.SockaddrUnix{Name: addr}
+	if err := syscall.Connect(fd, usa); err != nil {
+		syscall.Close(fd)
+		return nil, err
+	}
+
+	return NewSocket(fd)
+}
+
+// ControlMessage wraps around a byte array and provides functions for parsing
+// as a Unix Domain Socket control message.
+type ControlMessage []byte
+
+// EnableFDs enables receiving FDs via control message.
+//
+// This guarantees only a MINIMUM number of FDs received. You may receive MORE
+// than this due to the way FDs are packed. To be specific, the number of
+// receivable buffers will be rounded up to the nearest even number.
+//
+// This must be called prior to ReadVec if you want to receive FDs.
+func (c *ControlMessage) EnableFDs(count int) {
+	*c = make([]byte, syscall.CmsgSpace(count*4))
+}
+
+// ExtractFDs returns the list of FDs in the control message.
+//
+// Either this or CloseFDs should be used after EnableFDs.
+func (c *ControlMessage) ExtractFDs() ([]int, error) {
+	msgs, err := syscall.ParseSocketControlMessage(*c)
+	if err != nil {
+		return nil, err
+	}
+	var fds []int
+	for _, msg := range msgs {
+		thisFds, err := syscall.ParseUnixRights(&msg)
+		if err != nil {
+			// Different control message.
+			return nil, err
+		}
+		for _, fd := range thisFds {
+			if fd >= 0 {
+				fds = append(fds, fd)
+			}
+		}
+	}
+	return fds, nil
+}
+
+// CloseFDs closes the list of FDs in the control message.
+//
+// Either this or ExtractFDs should be used after EnableFDs.
+func (c *ControlMessage) CloseFDs() {
+	fds, _ := c.ExtractFDs()
+	for _, fd := range fds {
+		if fd >= 0 {
+			syscall.Close(fd)
+		}
+	}
+}
+
+// PackFDs packs the given list of FDs in the control message.
+//
+// This must be used prior to WriteVec.
+func (c *ControlMessage) PackFDs(fds ...int) {
+	*c = ControlMessage(syscall.UnixRights(fds...))
+}
+
+// UnpackFDs clears the control message.
+func (c *ControlMessage) UnpackFDs() {
+	*c = nil
+}
+
+// SocketWriter wraps an individual send operation.
+//
+// The normal entrypoint is WriteVec.
+type SocketWriter struct {
+	socket   *Socket
+	to       []byte
+	blocking bool
+	race     *int32
+
+	ControlMessage
+}
+
+// Writer returns a writer for this socket.
+func (s *Socket) Writer(blocking bool) SocketWriter {
+	return SocketWriter{socket: s, blocking: blocking, race: s.race}
+}
+
+// Write implements io.Writer.Write.
+func (s *Socket) Write(p []byte) (int, error) {
+	r := s.Writer(true)
+	return r.WriteVec([][]byte{p})
+}
+
+// GetSockOpt gets the given socket option.
+func (s *Socket) GetSockOpt(level int, name int, b []byte) (uint32, error) {
+	fd, ok := s.enterFD()
+	if !ok {
+		return 0, syscall.EBADF
+	}
+	defer s.gate.Leave()
+
+	return getsockopt(fd, level, name, b)
+}
+
+// SetSockOpt sets the given socket option.
+func (s *Socket) SetSockOpt(level, name int, b []byte) error {
+	fd, ok := s.enterFD()
+	if !ok {
+		return syscall.EBADF
+	}
+	defer s.gate.Leave()
+
+	return setsockopt(fd, level, name, b)
+}
+
+// GetSockName returns the socket name.
+func (s *Socket) GetSockName() ([]byte, error) {
+	fd, ok := s.enterFD()
+	if !ok {
+		return nil, syscall.EBADF
+	}
+	defer s.gate.Leave()
+
+	var buf []byte
+	l := syscall.SizeofSockaddrAny
+
+	for {
+		// If the buffer is not large enough, allocate a new one with the hint.
+		buf = make([]byte, l)
+		l, err := getsockname(fd, buf)
+		if err != nil {
+			return nil, err
+		}
+
+		if l <= uint32(len(buf)) {
+			return buf[:l], nil
+		}
+	}
+}
+
+// GetPeerName returns the peer name.
+func (s *Socket) GetPeerName() ([]byte, error) {
+	fd, ok := s.enterFD()
+	if !ok {
+		return nil, syscall.EBADF
+	}
+	defer s.gate.Leave()
+
+	var buf []byte
+	l := syscall.SizeofSockaddrAny
+
+	for {
+		// See above.
+		buf = make([]byte, l)
+		l, err := getpeername(fd, buf)
+		if err != nil {
+			return nil, err
+		}
+
+		if l <= uint32(len(buf)) {
+			return buf[:l], nil
+		}
+	}
+}
+
+// GetPeerCred returns the peer's unix credentials.
+func (s *Socket) GetPeerCred() (*syscall.Ucred, error) {
+	fd, ok := s.enterFD()
+	if !ok {
+		return nil, syscall.EBADF
+	}
+	defer s.gate.Leave()
+
+	return syscall.GetsockoptUcred(fd, syscall.SOL_SOCKET, syscall.SO_PEERCRED)
+}
+
+// SocketReader wraps an individual receive operation.
+//
+// This may be used for doing vectorized reads and/or sending additional
+// control messages (e.g. FDs). The normal entrypoint is ReadVec.
+//
+// One of ExtractFDs or DisposeFDs must be called if EnableFDs is used.
+type SocketReader struct {
+	socket   *Socket
+	source   []byte
+	blocking bool
+	race     *int32
+
+	ControlMessage
+}
+
+// Reader returns a reader for this socket.
+func (s *Socket) Reader(blocking bool) SocketReader {
+	return SocketReader{socket: s, blocking: blocking, race: s.race}
+}
+
+// Read implements io.Reader.Read.
+func (s *Socket) Read(p []byte) (int, error) {
+	r := s.Reader(true)
+	return r.ReadVec([][]byte{p})
+}
+
+func (s *Socket) shutdown(fd int) error {
+	// Shutdown the socket to cancel any pending accepts.
+	return syscall.Shutdown(fd, syscall.SHUT_RDWR)
+}
+
+// Shutdown closes the socket for read and write.
+func (s *Socket) Shutdown() error {
+	fd, ok := s.enterFD()
+	if !ok {
+		return syscall.EBADF
+	}
+	defer s.gate.Leave()
+
+	return s.shutdown(fd)
+}
+
+// ServerSocket is a bound unix domain socket.
+type ServerSocket struct {
+	socket *Socket
+}
+
+// NewServerSocket returns a socket from an existing FD.
+func NewServerSocket(fd int) (*ServerSocket, error) {
+	s, err := NewSocket(fd)
+	if err != nil {
+		return nil, err
+	}
+	return &ServerSocket{socket: s}, nil
+}
+
+// Bind creates and binds a new socket.
+func Bind(addr string, packet bool) (*ServerSocket, error) {
+	fd, err := socket(packet)
+	if err != nil {
+		return nil, err
+	}
+
+	// Do the bind.
+	usa := &syscall.SockaddrUnix{Name: addr}
+	if err := syscall.Bind(fd, usa); err != nil {
+		syscall.Close(fd)
+		return nil, err
+	}
+
+	return NewServerSocket(fd)
+}
+
+// BindAndListen creates, binds and listens on a new socket.
+func BindAndListen(addr string, packet bool) (*ServerSocket, error) {
+	s, err := Bind(addr, packet)
+	if err != nil {
+		return nil, err
+	}
+
+	// Start listening.
+	if err := s.Listen(); err != nil {
+		s.Close()
+		return nil, err
+	}
+
+	return s, nil
+}
+
+// Listen starts listening on the socket.
+func (s *ServerSocket) Listen() error {
+	fd, ok := s.socket.enterFD()
+	if !ok {
+		return syscall.EBADF
+	}
+	defer s.socket.gate.Leave()
+
+	return syscall.Listen(fd, backlog)
+}
+
+// Accept accepts a new connection.
+//
+// This is always blocking.
+//
+// Preconditions:
+//  * ServerSocket is listening (Listen called).
+func (s *ServerSocket) Accept() (*Socket, error) {
+	fd, ok := s.socket.enterFD()
+	if !ok {
+		return nil, syscall.EBADF
+	}
+	defer s.socket.gate.Leave()
+
+	for {
+		nfd, _, err := syscall.Accept(fd)
+		switch err {
+		case nil:
+			return NewSocket(nfd)
+		case syscall.EAGAIN:
+			err = s.socket.wait(false)
+			if err == errClosing {
+				err = syscall.EBADF
+			}
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+}
+
+// Close closes the server socket.
+//
+// This must only be called once.
+func (s *ServerSocket) Close() error {
+	return s.socket.Close()
+}
+
+// FD returns the socket's file descriptor.
+//
+// See Socket.FD.
+func (s *ServerSocket) FD() int {
+	return s.socket.FD()
+}
+
+// Release releases ownership of the socket's file descriptor.
+//
+// See Socket.Release.
+func (s *ServerSocket) Release() (int, error) {
+	return s.socket.Release()
+}