net: reduce allocation size in ReadFromUDP

Switch to concrete types. Bring your own object to fill in.

Allocate just enough for the IP byte slice.
The allocation is now just 4 bytes for IPv4,
which puts it in the tiny allocator, which is much faster.

name                  old time/op    new time/op    delta
WriteToReadFromUDP-8    13.7µs ± 1%    13.4µs ± 2%   -2.49%  (p=0.000 n=10+10)

name                  old alloc/op   new alloc/op   delta
WriteToReadFromUDP-8     32.0B ± 0%      4.0B ± 0%  -87.50%  (p=0.000 n=10+10)

name                  old allocs/op  new allocs/op  delta
WriteToReadFromUDP-8      1.00 ± 0%      1.00 ± 0%     ~     (all equal)

Windows is temporarily stubbed out.

Updates #43451

Change-Id: Ief506f891b401d28715d22dce6ebda037941924e
Reviewed-on: https://go-review.googlesource.com/c/go/+/331490
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Damien Neil <dneil@google.com>

8 files changed, 197 insertions, 7 deletions

diff --git a/api/next.txt b/api/next.txt
index 8d2ee73f79..4dbaae3cf2 100644
--- a/api/next.txt
+++ b/api/next.txt
@@ -1,52 +1,104 @@
+pkg syscall (darwin-amd64), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (darwin-amd64), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (darwin-amd64), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (darwin-amd64), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (darwin-amd64-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (darwin-amd64-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (darwin-amd64-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (darwin-amd64-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (freebsd-386), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (freebsd-386), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (freebsd-386), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (freebsd-386), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (freebsd-386-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (freebsd-386-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (freebsd-386-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (freebsd-386-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (freebsd-amd64), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (freebsd-amd64), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (freebsd-amd64), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (freebsd-amd64), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (freebsd-amd64-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (freebsd-amd64-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (freebsd-amd64-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (freebsd-amd64-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (freebsd-arm), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (freebsd-arm), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (freebsd-arm), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (freebsd-arm), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (freebsd-arm-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (freebsd-arm-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (freebsd-arm-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (freebsd-arm-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (linux-386), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (linux-386), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (linux-386), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (linux-386), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (linux-386-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (linux-386-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (linux-386-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (linux-386-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (linux-amd64), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (linux-amd64), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (linux-amd64), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (linux-amd64), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (linux-amd64-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (linux-amd64-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (linux-amd64-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (linux-amd64-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (linux-arm), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (linux-arm), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (linux-arm), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (linux-arm), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (linux-arm-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (linux-arm-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (linux-arm-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (linux-arm-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-386), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-386), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-386), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-386), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-386-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-386-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-386-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-386-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-amd64), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-amd64), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-amd64), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-amd64), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-amd64-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-amd64-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-amd64-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-amd64-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-arm), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-arm), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-arm), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-arm), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-arm-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-arm-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-arm-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-arm-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-arm64), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-arm64), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-arm64), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-arm64), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (netbsd-arm64-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (netbsd-arm64-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (netbsd-arm64-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (netbsd-arm64-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (openbsd-386), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (openbsd-386), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (openbsd-386), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (openbsd-386), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (openbsd-386-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (openbsd-386-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (openbsd-386-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (openbsd-386-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (openbsd-amd64), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (openbsd-amd64), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (openbsd-amd64), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (openbsd-amd64), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
+pkg syscall (openbsd-amd64-cgo), func RecvfromInet4(int, []uint8, int, *SockaddrInet4) (int, error)
+pkg syscall (openbsd-amd64-cgo), func RecvfromInet6(int, []uint8, int, *SockaddrInet6) (int, error)
 pkg syscall (openbsd-amd64-cgo), func SendtoInet4(int, []uint8, int, SockaddrInet4) error
 pkg syscall (openbsd-amd64-cgo), func SendtoInet6(int, []uint8, int, SockaddrInet6) error
diff --git a/src/internal/poll/fd_unix.go b/src/internal/poll/fd_unix.go
index 51d15f6abc..60b59df2e3 100644
--- a/src/internal/poll/fd_unix.go
+++ b/src/internal/poll/fd_unix.go
@@ -230,6 +230,60 @@ func (fd *FD) ReadFrom(p []byte) (int, syscall.Sockaddr, error) {
 	}
 }
 
+// ReadFrom wraps the recvfrom network call for IPv4.
+func (fd *FD) ReadFromInet4(p []byte, from *syscall.SockaddrInet4) (int, error) {
+	if err := fd.readLock(); err != nil {
+		return 0, err
+	}
+	defer fd.readUnlock()
+	if err := fd.pd.prepareRead(fd.isFile); err != nil {
+		return 0, err
+	}
+	for {
+		n, err := syscall.RecvfromInet4(fd.Sysfd, p, 0, from)
+		if err != nil {
+			if err == syscall.EINTR {
+				continue
+			}
+			n = 0
+			if err == syscall.EAGAIN && fd.pd.pollable() {
+				if err = fd.pd.waitRead(fd.isFile); err == nil {
+					continue
+				}
+			}
+		}
+		err = fd.eofError(n, err)
+		return n, err
+	}
+}
+
+// ReadFrom wraps the recvfrom network call for IPv6.
+func (fd *FD) ReadFromInet6(p []byte, from *syscall.SockaddrInet6) (int, error) {
+	if err := fd.readLock(); err != nil {
+		return 0, err
+	}
+	defer fd.readUnlock()
+	if err := fd.pd.prepareRead(fd.isFile); err != nil {
+		return 0, err
+	}
+	for {
+		n, err := syscall.RecvfromInet6(fd.Sysfd, p, 0, from)
+		if err != nil {
+			if err == syscall.EINTR {
+				continue
+			}
+			n = 0
+			if err == syscall.EAGAIN && fd.pd.pollable() {
+				if err = fd.pd.waitRead(fd.isFile); err == nil {
+					continue
+				}
+			}
+		}
+		err = fd.eofError(n, err)
+		return n, err
+	}
+}
+
 // ReadMsg wraps the recvmsg network call.
 func (fd *FD) ReadMsg(p []byte, oob []byte, flags int) (int, int, int, syscall.Sockaddr, error) {
 	if err := fd.readLock(); err != nil {
diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index 3dada32985..14e8f4965b 100644
--- a/src/internal/poll/fd_windows.go
+++ b/src/internal/poll/fd_windows.go
@@ -593,6 +593,24 @@ func (fd *FD) ReadFrom(buf []byte) (int, syscall.Sockaddr, error) {
 	return n, sa, nil
 }
 
+// ReadFrom wraps the recvfrom network call for IPv4.
+func (fd *FD) ReadFromInet4(buf []byte, sa4 *syscall.SockaddrInet4) (int, error) {
+	n, sa, err := fd.ReadFrom(buf)
+	if sa != nil {
+		*sa4 = *(sa.(*syscall.SockaddrInet4))
+	}
+	return n, err
+}
+
+// ReadFrom wraps the recvfrom network call for IPv6.
+func (fd *FD) ReadFromInet6(buf []byte, sa6 *syscall.SockaddrInet6) (int, error) {
+	n, sa, err := fd.ReadFrom(buf)
+	if sa != nil {
+		*sa6 = *(sa.(*syscall.SockaddrInet6))
+	}
+	return n, err
+}
+
 // Write implements io.Writer.
 func (fd *FD) Write(buf []byte) (int, error) {
 	if err := fd.writeLock(); err != nil {
diff --git a/src/net/fd_posix.go b/src/net/fd_posix.go
index a0675b2072..38e5a8d61d 100644
--- a/src/net/fd_posix.go
+++ b/src/net/fd_posix.go
@@ -63,6 +63,17 @@ func (fd *netFD) readFrom(p []byte) (n int, sa syscall.Sockaddr, err error) {
 	runtime.KeepAlive(fd)
 	return n, sa, wrapSyscallError(readFromSyscallName, err)
 }
+func (fd *netFD) readFromInet4(p []byte, from *syscall.SockaddrInet4) (n int, err error) {
+	n, err = fd.pfd.ReadFromInet4(p, from)
+	runtime.KeepAlive(fd)
+	return n, wrapSyscallError(readFromSyscallName, err)
+}
+
+func (fd *netFD) readFromInet6(p []byte, from *syscall.SockaddrInet6) (n int, err error) {
+	n, err = fd.pfd.ReadFromInet6(p, from)
+	runtime.KeepAlive(fd)
+	return n, wrapSyscallError(readFromSyscallName, err)
+}
 
 func (fd *netFD) readMsg(p []byte, oob []byte, flags int) (n, oobn, retflags int, sa syscall.Sockaddr, err error) {
 	n, oobn, retflags, sa, err = fd.pfd.ReadMsg(p, oob, flags)
diff --git a/src/net/net_fake.go b/src/net/net_fake.go
index feb51968dd..48419be670 100644
--- a/src/net/net_fake.go
+++ b/src/net/net_fake.go
@@ -266,6 +266,14 @@ func sysSocket(family, sotype, proto int) (int, error) {
 
 func (fd *netFD) readFrom(p []byte) (n int, sa syscall.Sockaddr, err error) {
 	return 0, nil, syscall.ENOSYS
+
+}
+func (fd *netFD) readFromInet4(p []byte, sa *syscall.SockaddrInet4) (n int, err error) {
+	return 0, syscall.ENOSYS
+}
+
+func (fd *netFD) readFromInet6(p []byte, sa *syscall.SockaddrInet6) (n int, err error) {
+	return 0, syscall.ENOSYS
 }
 
 func (fd *netFD) readMsg(p []byte, oob []byte, flags int) (n, oobn, retflags int, sa syscall.Sockaddr, err error) {
diff --git a/src/net/udpsock_posix.go b/src/net/udpsock_posix.go
index b71be09217..3a333ca243 100644
--- a/src/net/udpsock_posix.go
+++ b/src/net/udpsock_posix.go
@@ -44,13 +44,25 @@ func (a *UDPAddr) toLocal(net string) sockaddr {
 }
 
 func (c *UDPConn) readFrom(b []byte, addr *UDPAddr) (int, *UDPAddr, error) {
-	n, sa, err := c.fd.readFrom(b)
-	switch sa := sa.(type) {
-	case *syscall.SockaddrInet4:
-		*addr = UDPAddr{IP: sa.Addr[0:], Port: sa.Port}
-	case *syscall.SockaddrInet6:
-		*addr = UDPAddr{IP: sa.Addr[0:], Port: sa.Port, Zone: zoneCache.name(int(sa.ZoneId))}
-	default:
+	var n int
+	var err error
+	switch c.fd.family {
+	case syscall.AF_INET:
+		var from syscall.SockaddrInet4
+		n, err = c.fd.readFromInet4(b, &from)
+		if err == nil {
+			ip := from.Addr // copy from.Addr; ip escapes, so this line allocates 4 bytes
+			*addr = UDPAddr{IP: ip[:], Port: from.Port}
+		}
+	case syscall.AF_INET6:
+		var from syscall.SockaddrInet6
+		n, err = c.fd.readFromInet6(b, &from)
+		if err == nil {
+			ip := from.Addr // copy from.Addr; ip escapes, so this line allocates 16 bytes
+			*addr = UDPAddr{IP: ip[:], Port: from.Port, Zone: zoneCache.name(int(from.ZoneId))}
+		}
+	}
+	if err != nil {
 		// No sockaddr, so don't return UDPAddr.
 		addr = nil
 	}
diff --git a/src/syscall/net_js.go b/src/syscall/net_js.go
index 17799148bd..2998c2159c 100644
--- a/src/syscall/net_js.go
+++ b/src/syscall/net_js.go
@@ -92,6 +92,14 @@ func Recvfrom(fd int, p []byte, flags int) (n int, from Sockaddr, err error) {
 	return 0, nil, ENOSYS
 }
 
+func RecvfromInet4(fd int, p []byte, flags int, from *SockaddrInet4) (n int, err error) {
+	return 0, ENOSYS
+}
+
+func RecvfromInet6(fd int, p []byte, flags int, from *SockaddrInet6) (n int, err error) {
+	return 0, ENOSYS
+}
+
 func Sendto(fd int, p []byte, flags int, to Sockaddr) error {
 	return ENOSYS
 }
diff --git a/src/syscall/syscall_unix.go b/src/syscall/syscall_unix.go
index 60aeae14de..101e39c7d0 100644
--- a/src/syscall/syscall_unix.go
+++ b/src/syscall/syscall_unix.go
@@ -292,6 +292,33 @@ func Recvfrom(fd int, p []byte, flags int) (n int, from Sockaddr, err error) {
 	return
 }
 
+func RecvfromInet4(fd int, p []byte, flags int, from *SockaddrInet4) (n int, err error) {
+	var rsa RawSockaddrAny
+	var socklen _Socklen = SizeofSockaddrAny
+	if n, err = recvfrom(fd, p, flags, &rsa, &socklen); err != nil {
+		return
+	}
+	pp := (*RawSockaddrInet4)(unsafe.Pointer(&rsa))
+	port := (*[2]byte)(unsafe.Pointer(&pp.Port))
+	from.Port = int(port[0])<<8 + int(port[1])
+	from.Addr = pp.Addr
+	return
+}
+
+func RecvfromInet6(fd int, p []byte, flags int, from *SockaddrInet6) (n int, err error) {
+	var rsa RawSockaddrAny
+	var socklen _Socklen = SizeofSockaddrAny
+	if n, err = recvfrom(fd, p, flags, &rsa, &socklen); err != nil {
+		return
+	}
+	pp := (*RawSockaddrInet6)(unsafe.Pointer(&rsa))
+	port := (*[2]byte)(unsafe.Pointer(&pp.Port))
+	from.Port = int(port[0])<<8 + int(port[1])
+	from.ZoneId = pp.Scope_id
+	from.Addr = pp.Addr
+	return
+}
+
 func SendtoInet4(fd int, p []byte, flags int, to SockaddrInet4) (err error) {
 	ptr, n, err := to.sockaddr()
 	if err != nil {