conn: fix StdNetBind fallback on Windows

If RIO is unavailable, NewWinRingBind() falls back to StdNetBind.
StdNetBind uses x/net/ipv{4,6}.PacketConn for sending and receiving
datagrams, specifically via the {Read,Write}Batch methods.
These methods are unimplemented on Windows and will return runtime
errors as a result. This commit updates StdNetBind to fall back to the
standard library net package for Windows.

Signed-off-by: James Tucker <[email protected]>
Signed-off-by: Jordan Whited <[email protected]>

Author: jwhited

conn/bind_std.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"net"
 	"net/netip"
+	"runtime"
 	"strconv"
 	"sync"
 	"syscall"
@@ -22,15 +23,16 @@ var (
 	_ Bind = (*StdNetBind)(nil)
 )
 
-// StdNetBind implements Bind for all platforms except Windows.
+// StdNetBind implements Bind for all platforms. While Windows has its own Bind
+// (see bind_windows.go), it may fall back to StdNetBind.
 type StdNetBind struct {
 	mu           sync.Mutex // protects following fields
 	ipv4         *net.UDPConn
 	ipv6         *net.UDPConn
 	blackhole4   bool
 	blackhole6   bool
-	ipv4PC       *ipv4.PacketConn
-	ipv6PC       *ipv6.PacketConn
+	ipv4PC       *ipv4.PacketConn // will be nil on Windows
+	ipv6PC       *ipv6.PacketConn // will be nil on Windows
 	udpAddrPool  sync.Pool
 	ipv4MsgsPool sync.Pool
 	ipv6MsgsPool sync.Pool
@@ -184,8 +186,12 @@ again:
 		return nil, 0, syscall.EAFNOSUPPORT
 	}
 
-	s.ipv4PC = ipv4.NewPacketConn(s.ipv4)
-	s.ipv6PC = ipv6.NewPacketConn(s.ipv6)
+	// x/net/ipv{4,6} packages do not implement PacketConn.{Read,Write}Batch()
+	// for Windows (runtime error).
+	if runtime.GOOS != "windows" {
+		s.ipv4PC = ipv4.NewPacketConn(s.ipv4)
+		s.ipv6PC = ipv6.NewPacketConn(s.ipv6)
+	}
 
 	return fns, uint16(port), nil
 }
@@ -196,9 +202,19 @@ func (s *StdNetBind) receiveIPv4(buffs [][]byte, sizes []int, eps []Endpoint) (n
 	for i := range buffs {
 		(*msgs)[i].Buffers[0] = buffs[i]
 	}
-	numMsgs, err := s.ipv4PC.ReadBatch(*msgs, 0)
-	if err != nil {
-		return 0, err
+	var numMsgs int
+	if runtime.GOOS != "windows" {
+		numMsgs, err = s.ipv4PC.ReadBatch(*msgs, 0)
+		if err != nil {
+			return 0, err
+		}
+	} else {
+		msg := &(*msgs)[0]
+		msg.N, msg.NN, _, msg.Addr, err = s.ipv4.ReadMsgUDP(msg.Buffers[0], msg.OOB)
+		if err != nil {
+			return 0, err
+		}
+		numMsgs = 1
 	}
 	for i := 0; i < numMsgs; i++ {
 		msg := &(*msgs)[i]
@@ -217,9 +233,19 @@ func (s *StdNetBind) receiveIPv6(buffs [][]byte, sizes []int, eps []Endpoint) (n
 	for i := range buffs {
 		(*msgs)[i].Buffers[0] = buffs[i]
 	}
-	numMsgs, err := s.ipv6PC.ReadBatch(*msgs, 0)
-	if err != nil {
-		return 0, err
+	var numMsgs int
+	if runtime.GOOS != "windows" {
+		numMsgs, err = s.ipv6PC.ReadBatch(*msgs, 0)
+		if err != nil {
+			return 0, err
+		}
+	} else {
+		msg := &(*msgs)[0]
+		msg.N, msg.NN, _, msg.Addr, err = s.ipv6.ReadMsgUDP(msg.Buffers[0], msg.OOB)
+		if err != nil {
+			return 0, err
+		}
+		numMsgs = 1
 	}
 	for i := 0; i < numMsgs; i++ {
 		msg := &(*msgs)[i]
@@ -301,12 +327,21 @@ func (s *StdNetBind) send4(conn *ipv4.PacketConn, ep Endpoint, buffs [][]byte) e
 		err   error
 		start int
 	)
-	for {
-		n, err = conn.WriteBatch((*msgs)[start:len(buffs)], 0)
-		if err != nil || n == len((*msgs)[start:len(buffs)]) {
-			break
+	if runtime.GOOS != "windows" {
+		for {
+			n, err = conn.WriteBatch((*msgs)[start:len(buffs)], 0)
+			if err != nil || n == len((*msgs)[start:len(buffs)]) {
+				break
+			}
+			start += n
+		}
+	} else {
+		for i, buff := range buffs {
+			_, _, err = s.ipv4.WriteMsgUDP(buff, (*msgs)[i].OOB, ua)
+			if err != nil {
+				break
+			}
 		}
-		start += n
 	}
 	s.udpAddrPool.Put(ua)
 	s.ipv4MsgsPool.Put(msgs)
@@ -330,12 +365,21 @@ func (s *StdNetBind) send6(conn *ipv6.PacketConn, ep Endpoint, buffs [][]byte) e
 		err   error
 		start int
 	)
-	for {
-		n, err = conn.WriteBatch((*msgs)[start:len(buffs)], 0)
-		if err != nil || n == len((*msgs)[start:len(buffs)]) {
-			break
+	if runtime.GOOS != "windows" {
+		for {
+			n, err = conn.WriteBatch((*msgs)[start:len(buffs)], 0)
+			if err != nil || n == len((*msgs)[start:len(buffs)]) {
+				break
+			}
+			start += n
+		}
+	} else {
+		for i, buff := range buffs {
+			_, _, err = s.ipv6.WriteMsgUDP(buff, (*msgs)[i].OOB, ua)
+			if err != nil {
+				break
+			}
 		}
-		start += n
 	}
 	s.udpAddrPool.Put(ua)
 	s.ipv6MsgsPool.Put(msgs)