tailscale/net/wsconn/wsconn.go

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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package wsconn contains an adapter type that turns
// a websocket connection into a net.Conn. It a temporary fork of the
// netconn.go file from the nhooyr.io/websocket package while we wait for
// https://github.com/nhooyr/websocket/pull/350 to be merged.
package wsconn
import (
"context"
"fmt"
"io"
"math"
"net"
"os"
"sync"
"sync/atomic"
"time"
"nhooyr.io/websocket"
)
// NetConn converts a *websocket.Conn into a net.Conn.
//
// It's for tunneling arbitrary protocols over WebSockets.
// Few users of the library will need this but it's tricky to implement
// correctly and so provided in the library.
// See https://github.com/nhooyr/websocket/issues/100.
//
// Every Write to the net.Conn will correspond to a message write of
// the given type on *websocket.Conn.
//
// The passed ctx bounds the lifetime of the net.Conn. If cancelled,
// all reads and writes on the net.Conn will be cancelled.
//
// If a message is read that is not of the correct type, the connection
// will be closed with StatusUnsupportedData and an error will be returned.
//
// Close will close the *websocket.Conn with StatusNormalClosure.
//
// When a deadline is hit, the connection will be closed. This is
// different from most net.Conn implementations where only the
// reading/writing goroutines are interrupted but the connection is kept alive.
//
// The Addr methods will return a mock net.Addr that returns "websocket" for Network
// and "websocket/unknown-addr" for String.
//
// A received StatusNormalClosure or StatusGoingAway close frame will be translated to
// io.EOF when reading.
//
// The given remoteAddr will be the value of the returned conn's
// RemoteAddr().String(). For best compatibility with consumers of
// conns, the string should be an ip:port if available, but in the
// absence of that it can be any string that describes the remote
// endpoint, or the empty string to makes RemoteAddr() return a place
// holder value.
func NetConn(ctx context.Context, c *websocket.Conn, msgType websocket.MessageType, remoteAddr string) net.Conn {
nc := &netConn{
c: c,
msgType: msgType,
remoteAddr: remoteAddr,
}
var writeCancel context.CancelFunc
nc.writeContext, writeCancel = context.WithCancel(ctx)
nc.writeTimer = time.AfterFunc(math.MaxInt64, func() {
nc.afterWriteDeadline.Store(true)
if nc.writing.Load() {
writeCancel()
}
})
if !nc.writeTimer.Stop() {
<-nc.writeTimer.C
}
var readCancel context.CancelFunc
nc.readContext, readCancel = context.WithCancel(ctx)
nc.readTimer = time.AfterFunc(math.MaxInt64, func() {
nc.afterReadDeadline.Store(true)
if nc.reading.Load() {
readCancel()
}
})
if !nc.readTimer.Stop() {
<-nc.readTimer.C
}
return nc
}
type netConn struct {
c *websocket.Conn
msgType websocket.MessageType
remoteAddr string
writeTimer *time.Timer
writeContext context.Context
writing atomic.Bool
afterWriteDeadline atomic.Bool
readTimer *time.Timer
readContext context.Context
reading atomic.Bool
afterReadDeadline atomic.Bool
readMu sync.Mutex
eofed bool
reader io.Reader
}
var _ net.Conn = &netConn{}
func (c *netConn) Close() error {
return c.c.Close(websocket.StatusNormalClosure, "")
}
func (c *netConn) Write(p []byte) (int, error) {
if c.afterWriteDeadline.Load() {
return 0, os.ErrDeadlineExceeded
}
if swapped := c.writing.CompareAndSwap(false, true); !swapped {
panic("Concurrent writes not allowed")
}
defer c.writing.Store(false)
err := c.c.Write(c.writeContext, c.msgType, p)
if err != nil {
return 0, err
}
return len(p), nil
}
func (c *netConn) Read(p []byte) (int, error) {
if c.afterReadDeadline.Load() {
return 0, os.ErrDeadlineExceeded
}
c.readMu.Lock()
defer c.readMu.Unlock()
if swapped := c.reading.CompareAndSwap(false, true); !swapped {
panic("Concurrent reads not allowed")
}
defer c.reading.Store(false)
if c.eofed {
return 0, io.EOF
}
if c.reader == nil {
typ, r, err := c.c.Reader(c.readContext)
if err != nil {
switch websocket.CloseStatus(err) {
case websocket.StatusNormalClosure, websocket.StatusGoingAway:
c.eofed = true
return 0, io.EOF
}
return 0, err
}
if typ != c.msgType {
err := fmt.Errorf("unexpected frame type read (expected %v): %v", c.msgType, typ)
c.c.Close(websocket.StatusUnsupportedData, err.Error())
return 0, err
}
c.reader = r
}
n, err := c.reader.Read(p)
if err == io.EOF {
c.reader = nil
err = nil
}
return n, err
}
type websocketAddr struct {
addr string
}
func (a websocketAddr) Network() string {
return "websocket"
}
func (a websocketAddr) String() string {
if a.addr != "" {
return a.addr
}
return "websocket/unknown-addr"
}
func (c *netConn) RemoteAddr() net.Addr {
return websocketAddr{c.remoteAddr}
}
func (c *netConn) LocalAddr() net.Addr {
return websocketAddr{""}
}
func (c *netConn) SetDeadline(t time.Time) error {
c.SetWriteDeadline(t)
c.SetReadDeadline(t)
return nil
}
func (c *netConn) SetWriteDeadline(t time.Time) error {
if t.IsZero() {
c.writeTimer.Stop()
} else {
c.writeTimer.Reset(time.Until(t))
}
c.afterWriteDeadline.Store(false)
return nil
}
func (c *netConn) SetReadDeadline(t time.Time) error {
if t.IsZero() {
c.readTimer.Stop()
} else {
c.readTimer.Reset(time.Until(t))
}
c.afterReadDeadline.Store(false)
return nil
}