net: add Buffers type, do writev on unix

No fast path currently for solaris, windows, nacl, plan9.

Fixes #13451

Change-Id: I24b3233a2e3a57fc6445e276a5c0d7b097884007
Reviewed-on: https://go-review.googlesource.com/29951Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/fd_unix.go

@@ -29,6 +29,9 @@ type netFD struct {
 	laddr       Addr
 	raddr       Addr
 
+	// writev cache.
+	iovecs *[]syscall.Iovec
+
 	// wait server
 	pd pollDesc
 }

src/net/net.go

@@ -604,3 +604,66 @@ func acquireThread() {
 func releaseThread() {
 	<-threadLimit
 }
+
+// buffersWriter is the interface implemented by Conns that support a
+// "writev"-like batch write optimization.
+// writeBuffers should fully consume and write all chunks from the
+// provided Buffers, else it should report a non-nil error.
+type buffersWriter interface {
+	writeBuffers(*Buffers) (int64, error)
+}
+
+var testHookDidWritev = func(wrote int) {}
+
+// Buffers contains zero or more runs of bytes to write.
+//
+// On certain machines, for certain types of connections, this is
+// optimized into an OS-specific batch write operation (such as
+// "writev").
+type Buffers [][]byte
+
+var (
+	_ io.WriterTo = (*Buffers)(nil)
+	_ io.Reader   = (*Buffers)(nil)
+)
+
+func (v *Buffers) WriteTo(w io.Writer) (n int64, err error) {
+	if wv, ok := w.(buffersWriter); ok {
+		return wv.writeBuffers(v)
+	}
+	for _, b := range *v {
+		nb, err := w.Write(b)
+		n += int64(nb)
+		if err != nil {
+			v.consume(n)
+			return n, err
+		}
+	}
+	v.consume(n)
+	return n, nil
+}
+
+func (v *Buffers) Read(p []byte) (n int, err error) {
+	for len(p) > 0 && len(*v) > 0 {
+		n0 := copy(p, (*v)[0])
+		v.consume(int64(n0))
+		p = p[n0:]
+		n += n0
+	}
+	if len(*v) == 0 {
+		err = io.EOF
+	}
+	return
+}
+
+func (v *Buffers) consume(n int64) {
+	for len(*v) > 0 {
+		ln0 := int64(len((*v)[0]))
+		if ln0 > n {
+			(*v)[0] = (*v)[0][n:]
+			return
+		}
+		n -= ln0
+		*v = (*v)[1:]
+	}
+}

src/net/net_test.go

@@ -414,3 +414,38 @@ func TestZeroByteRead(t *testing.T) {
 		}
 	}
 }
+
+// withTCPConnPair sets up a TCP connection between two peers, then
+// runs peer1 and peer2 concurrently. withTCPConnPair returns when
+// both have completed.
+func withTCPConnPair(t *testing.T, peer1, peer2 func(c *TCPConn) error) {
+	ln, err := newLocalListener("tcp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+	errc := make(chan error, 2)
+	go func() {
+		c1, err := ln.Accept()
+		if err != nil {
+			errc <- err
+			return
+		}
+		defer c1.Close()
+		errc <- peer1(c1.(*TCPConn))
+	}()
+	go func() {
+		c2, err := Dial("tcp", ln.Addr().String())
+		if err != nil {
+			errc <- err
+			return
+		}
+		defer c2.Close()
+		errc <- peer2(c2.(*TCPConn))
+	}()
+	for i := 0; i < 2; i++ {
+		if err := <-errc; err != nil {
+			t.Fatal(err)
+		}
+	}
+}

src/net/writev_test.go

+// Copyright 2016 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.
+
+package net
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"reflect"
+	"runtime"
+	"sync"
+	"testing"
+)
+
+func TestBuffers_read(t *testing.T) {
+	const story = "once upon a time in Gopherland ... "
+	buffers := Buffers{
+		[]byte("once "),
+		[]byte("upon "),
+		[]byte("a "),
+		[]byte("time "),
+		[]byte("in "),
+		[]byte("Gopherland ... "),
+	}
+	got, err := ioutil.ReadAll(&buffers)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != story {
+		t.Errorf("read %q; want %q", got, story)
+	}
+	if len(buffers) != 0 {
+		t.Errorf("len(buffers) = %d; want 0", len(buffers))
+	}
+}
+
+func TestBuffers_consume(t *testing.T) {
+	tests := []struct {
+		in      Buffers
+		consume int64
+		want    Buffers
+	}{
+		{
+			in:      Buffers{[]byte("foo"), []byte("bar")},
+			consume: 0,
+			want:    Buffers{[]byte("foo"), []byte("bar")},
+		},
+		{
+			in:      Buffers{[]byte("foo"), []byte("bar")},
+			consume: 2,
+			want:    Buffers{[]byte("o"), []byte("bar")},
+		},
+		{
+			in:      Buffers{[]byte("foo"), []byte("bar")},
+			consume: 3,
+			want:    Buffers{[]byte("bar")},
+		},
+		{
+			in:      Buffers{[]byte("foo"), []byte("bar")},
+			consume: 4,
+			want:    Buffers{[]byte("ar")},
+		},
+		{
+			in:      Buffers{nil, nil, nil, []byte("bar")},
+			consume: 1,
+			want:    Buffers{[]byte("ar")},
+		},
+		{
+			in:      Buffers{nil, nil, nil, []byte("foo")},
+			consume: 0,
+			want:    Buffers{[]byte("foo")},
+		},
+		{
+			in:      Buffers{nil, nil, nil},
+			consume: 0,
+			want:    Buffers{},
+		},
+	}
+	for i, tt := range tests {
+		in := tt.in
+		in.consume(tt.consume)
+		if !reflect.DeepEqual(in, tt.want) {
+			t.Errorf("%d. after consume(%d) = %+v, want %+v", i, tt.consume, in, tt.want)
+		}
+	}
+}
+
+func TestBuffers_WriteTo(t *testing.T) {
+	for _, name := range []string{"WriteTo", "Copy"} {
+		for _, size := range []int{0, 10, 1023, 1024, 1025} {
+			t.Run(fmt.Sprintf("%s/%d", name, size), func(t *testing.T) {
+				testBuffer_writeTo(t, size, name == "Copy")
+			})
+		}
+	}
+}
+
+func testBuffer_writeTo(t *testing.T, chunks int, useCopy bool) {
+	oldHook := testHookDidWritev
+	defer func() { testHookDidWritev = oldHook }()
+	var writeLog struct {
+		sync.Mutex
+		log []int
+	}
+	testHookDidWritev = func(size int) {
+		writeLog.Lock()
+		writeLog.log = append(writeLog.log, size)
+		writeLog.Unlock()
+	}
+	var want bytes.Buffer
+	for i := 0; i < chunks; i++ {
+		want.WriteByte(byte(i))
+	}
+
+	withTCPConnPair(t, func(c *TCPConn) error {
+		buffers := make(Buffers, chunks)
+		for i := range buffers {
+			buffers[i] = want.Bytes()[i : i+1]
+		}
+		var n int64
+		var err error
+		if useCopy {
+			n, err = io.Copy(c, &buffers)
+		} else {
+			n, err = buffers.WriteTo(c)
+		}
+		if err != nil {
+			return err
+		}
+		if len(buffers) != 0 {
+			return fmt.Errorf("len(buffers) = %d; want 0", len(buffers))
+		}
+		if n != int64(want.Len()) {
+			return fmt.Errorf("Buffers.WriteTo returned %d; want %d", n, want.Len())
+		}
+		return nil
+	}, func(c *TCPConn) error {
+		all, err := ioutil.ReadAll(c)
+		if !bytes.Equal(all, want.Bytes()) || err != nil {
+			return fmt.Errorf("client read %q, %v; want %q, nil", all, err, want.Bytes())
+		}
+
+		writeLog.Lock() // no need to unlock
+		var gotSum int
+		for _, v := range writeLog.log {
+			gotSum += v
+		}
+
+		var wantSum int
+		var wantMinCalls int
+		switch runtime.GOOS {
+		case "darwin", "dragonfly", "freebsd", "linux", "netbsd", "openbsd":
+			wantSum = want.Len()
+			v := chunks
+			for v > 0 {
+				wantMinCalls++
+				v -= 1024
+			}
+		}
+		if len(writeLog.log) < wantMinCalls {
+			t.Errorf("write calls = %v < wanted min %v", len(writeLog.log), wantMinCalls)
+		}
+		if gotSum != wantSum {
+			t.Errorf("writev call sum  = %v; want %v", gotSum, wantSum)
+		}
+		return nil
+	})
+}

src/net/writev_unix.go

+// Copyright 2016 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 darwin dragonfly freebsd linux netbsd openbsd
+
+package net
+
+import (
+	"io"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+func (c *conn) writeBuffers(v *Buffers) (int64, error) {
+	if !c.ok() {
+		return 0, syscall.EINVAL
+	}
+	n, err := c.fd.writeBuffers(v)
+	if err != nil {
+		return n, &OpError{Op: "writev", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
+	}
+	return n, nil
+}
+
+func (fd *netFD) writeBuffers(v *Buffers) (n int64, err error) {
+	if err := fd.writeLock(); err != nil {
+		return 0, err
+	}
+	defer fd.writeUnlock()
+	if err := fd.pd.prepareWrite(); err != nil {
+		return 0, err
+	}
+
+	var iovecs []syscall.Iovec
+	if fd.iovecs != nil {
+		iovecs = *fd.iovecs
+	}
+	// TODO: read from sysconf(_SC_IOV_MAX)? The Linux default is
+	// 1024 and this seems conservative enough for now. Darwin's
+	// UIO_MAXIOV also seems to be 1024.
+	maxVec := 1024
+
+	for len(*v) > 0 {
+		iovecs = iovecs[:0]
+		for _, chunk := range *v {
+			if len(chunk) == 0 {
+				continue
+			}
+			iovecs = append(iovecs, syscall.Iovec{Base: &chunk[0]})
+			iovecs[len(iovecs)-1].SetLen(len(chunk))
+			if len(iovecs) == maxVec {
+				break
+			}
+		}
+		if len(iovecs) == 0 {
+			break
+		}
+		fd.iovecs = &iovecs // cache
+
+		wrote, _, e0 := syscall.Syscall(syscall.SYS_WRITEV,
+			uintptr(fd.sysfd),
+			uintptr(unsafe.Pointer(&iovecs[0])),
+			uintptr(len(iovecs)))
+		if wrote < 0 {
+			wrote = 0
+		}
+		testHookDidWritev(int(wrote))
+		n += int64(wrote)
+		v.consume(int64(wrote))
+		if e0 == syscall.EAGAIN {
+			if err = fd.pd.waitWrite(); err == nil {
+				continue
+			}
+		} else if e0 != 0 {
+			err = syscall.Errno(e0)
+		}
+		if err != nil {
+			break
+		}
+		if n == 0 {
+			err = io.ErrUnexpectedEOF
+			break
+		}
+	}
+	if _, ok := err.(syscall.Errno); ok {
+		err = os.NewSyscallError("writev", err)
+	}
+	return n, err
+}

src/syscall/syscall_nacl.go

@@ -296,3 +296,5 @@ func RouteRIB(facility, param int) ([]byte, error)                { return nil,
 func ParseRoutingMessage(b []byte) ([]RoutingMessage, error)      { return nil, ENOSYS }
 func ParseRoutingSockaddr(msg RoutingMessage) ([]Sockaddr, error) { return nil, ENOSYS }
 func SysctlUint32(name string) (value uint32, err error)          { return 0, ENOSYS }
+
+type Iovec struct{} // dummy