io, net, http: sendfile support

Speeds up static fileserver, avoiding kernel/userspace copies.

Numbers: downloading 14 MB AppEngine Go SDK with ab (Apache Bench)
with 5 threads:

Before/after numbers:

CPU:
user    0m3.910s
sys     0m23.650s
->
user    0m0.720s
sys     0m4.890s

Time taken for tests:   8.906 seconds
->
Time taken for tests:   8.545 seconds

Percentage of the requests served within a certain time (ms)
50%     44
66%     45
75%     46
80%     46
90%     48
95%     51
98%     59
99%     71
100     74 (longest request)
->
50%     42
66%     43
75%     43
80%     44
90%     46
95%     57
98%     62
99%     63
100%    64 (longest request)

R=iant, gary.burd, rsc, bradfitz
CC=golang-dev
https://golang.org/cl/4543071

src/pkg/http/server.go

@@ -119,6 +119,27 @@ type response struct {
 	closeAfterReply bool
 }
 
+type writerOnly struct {
+	io.Writer
+}
+
+func (r *response) ReadFrom(src io.Reader) (n int64, err os.Error) {
+	// Flush before checking r.chunking, as Flush will call
+	// WriteHeader if it hasn't been called yet, and WriteHeader
+	// is what sets r.chunking.
+	r.Flush()
+	if !r.chunking {
+		if rf, ok := r.conn.rwc.(io.ReaderFrom); ok {
+			n, err = rf.ReadFrom(src)
+			r.written += n
+			return
+		}
+	}
+	// Fall back to default io.Copy implementation.
+	// Use wrapper to hide r.ReadFrom from io.Copy.
+	return io.Copy(writerOnly{r}, src)
+}
+
 // Create new connection from rwc.
 func newConn(rwc net.Conn, handler Handler) (c *conn, err os.Error) {
 	c = new(conn)

src/pkg/io/io.go

@@ -303,22 +303,26 @@ func Copy(dst Writer, src Reader) (written int64, err os.Error) {
 
 // LimitReader returns a Reader that reads from r
 // but stops with os.EOF after n bytes.
-func LimitReader(r Reader, n int64) Reader { return &limitedReader{r, n} }
+// The underlying implementation is a *LimitedReader.
+func LimitReader(r Reader, n int64) Reader { return &LimitedReader{r, n} }
 
-type limitedReader struct {
+// A LimitedReader reads from R but limits the amount of
-	r Reader
+// data returned to just N bytes. Each call to Read
-	n int64
+// updates N to reflect the new amount remaining.
+type LimitedReader struct {
+	R Reader // underlying reader
+	N int64  // max bytes remaining
 }
 
-func (l *limitedReader) Read(p []byte) (n int, err os.Error) {
+func (l *LimitedReader) Read(p []byte) (n int, err os.Error) {
-	if l.n <= 0 {
+	if l.N <= 0 {
 		return 0, os.EOF
 	}
-	if int64(len(p)) > l.n {
+	if int64(len(p)) > l.N {
-		p = p[0:l.n]
+		p = p[0:l.N]
 	}
-	n, err = l.r.Read(p)
+	n, err = l.R.Read(p)
-	l.n -= int64(n)
+	l.N -= int64(n)
 	return
 }
 

src/pkg/net/Makefile

@@ -23,12 +23,13 @@ GOFILES=\
 	unixsock.go\
 
 GOFILES_freebsd=\
-	newpollserver.go\
+	dnsclient.go\
+	dnsconfig.go\
 	fd.go\
 	file.go\
-	dnsconfig.go\
+	newpollserver.go\
-	dnsclient.go\
 	port.go\
+	sendfile_stub.go\
 	sock_bsd.go\
 
 CGOFILES_freebsd=\
@@ -36,12 +37,13 @@ CGOFILES_freebsd=\
 	cgo_unix.go\
 
 GOFILES_darwin=\
-	newpollserver.go\
+	dnsclient.go\
+	dnsconfig.go\
 	fd.go\
 	file.go\
-	dnsconfig.go\
+	newpollserver.go\
-	dnsclient.go\
 	port.go\
+	sendfile_stub.go\
 	sock_bsd.go\
 
 CGOFILES_darwin=\
@@ -49,14 +51,18 @@ CGOFILES_darwin=\
 	cgo_unix.go\
 
 GOFILES_linux=\
-	newpollserver.go\
+	dnsclient.go\
+	dnsconfig.go\
 	fd.go\
 	file.go\
-	dnsconfig.go\
+	newpollserver.go\
-	dnsclient.go\
 	port.go\
+	sendfile_linux.go\
 	sock_linux.go\
 
+GOFILES_plan9=\
+	sendfile_stub.go\
+
 ifeq ($(GOARCH),arm)
 # ARM has no cgo, so use the stubs.
 GOFILES_linux+=cgo_stub.go
@@ -68,8 +74,9 @@ endif
 
 GOFILES_windows=\
 	cgo_stub.go\
-	resolv_windows.go\
 	file_windows.go\
+	resolv_windows.go\
+	sendfile_stub.go\
 	sock_windows.go\
 
 GOFILES+=$(GOFILES_$(GOOS))

src/pkg/net/sendfile_linux.go

@@ -0,0 +1,84 @@
+// Copyright 2011 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 (
+	"io"
+	"os"
+	"syscall"
+)
+
+// maxSendfileSize is the largest chunk size we ask the kernel to copy
+// at a time.
+const maxSendfileSize int = 4 << 20
+
+// sendFile copies the contents of r to c using the sendfile
+// system call to minimize copies.
+//
+// if handled == true, sendFile returns the number of bytes copied and any
+// non-EOF error.
+//
+// if handled == false, sendFile performed no work.
+func sendFile(c *netFD, r io.Reader) (written int64, err os.Error, handled bool) {
+	var remain int64 = 1 << 62 // by default, copy until EOF
+
+	lr, ok := r.(*io.LimitedReader)
+	if ok {
+		remain, r = lr.N, lr.R
+		if remain <= 0 {
+			return 0, nil, true
+		}
+	}
+	f, ok := r.(*os.File)
+	if !ok {
+		return 0, nil, false
+	}
+
+	c.wio.Lock()
+	defer c.wio.Unlock()
+	c.incref()
+	defer c.decref()
+	if c.wdeadline_delta > 0 {
+		// This is a little odd that we're setting the timeout
+		// for the entire file but Write has the same issue
+		// (if one slurps the whole file into memory and
+		// do one large Write). At least they're consistent.
+		c.wdeadline = pollserver.Now() + c.wdeadline_delta
+	} else {
+		c.wdeadline = 0
+	}
+
+	dst := c.sysfd
+	src := f.Fd()
+	for remain > 0 {
+		n := maxSendfileSize
+		if int64(n) > remain {
+			n = int(remain)
+		}
+		n, errno := syscall.Sendfile(dst, src, nil, n)
+		if n > 0 {
+			written += int64(n)
+			remain -= int64(n)
+		}
+		if n == 0 && errno == 0 {
+			break
+		}
+		if errno == syscall.EAGAIN && c.wdeadline >= 0 {
+			pollserver.WaitWrite(c)
+			continue
+		}
+		if errno != 0 {
+			// This includes syscall.ENOSYS (no kernel
+			// support) and syscall.EINVAL (fd types which
+			// don't implement sendfile together)
+			err = &OpError{"sendfile", c.net, c.raddr, os.Errno(errno)}
+			break
+		}
+	}
+	if lr != nil {
+		lr.N = remain
+	}
+	return written, err, written > 0
+}

src/pkg/net/sendfile_stub.go

@@ -0,0 +1,14 @@
+// Copyright 2011 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 (
+	"io"
+	"os"
+)
+
+func sendFile(c *netFD, r io.Reader) (n int64, err os.Error, handled bool) {
+	return 0, nil, false
+}

src/pkg/net/sock.go

@@ -7,6 +7,7 @@
 package net
 
 import (
+	"io"
 	"os"
 	"reflect"
 	"syscall"
@@ -153,3 +154,14 @@ type UnknownSocketError struct {
 func (e *UnknownSocketError) String() string {
 	return "unknown socket address type " + reflect.TypeOf(e.sa).String()
 }
+
+type writerOnly struct {
+	io.Writer
+}
+
+// Fallback implementation of io.ReaderFrom's ReadFrom, when sendfile isn't
+// applicable.
+func genericReadFrom(w io.Writer, r io.Reader) (n int64, err os.Error) {
+	// Use wrapper to hide existing r.ReadFrom from io.Copy.
+	return io.Copy(writerOnly{w}, r)
+}

src/pkg/net/tcpsock.go

@@ -7,6 +7,7 @@
 package net
 
 import (
+	"io"
 	"os"
 	"syscall"
 )
@@ -95,6 +96,14 @@ func (c *TCPConn) Read(b []byte) (n int, err os.Error) {
 	return c.fd.Read(b)
 }
 
+// ReadFrom implements the io.ReaderFrom ReadFrom method.
+func (c *TCPConn) ReadFrom(r io.Reader) (int64, os.Error) {
+	if n, err, handled := sendFile(c.fd, r); handled {
+		return n, err
+	}
+	return genericReadFrom(c, r)
+}
+
 // Write implements the net.Conn Write method.
 func (c *TCPConn) Write(b []byte) (n int, err os.Error) {
 	if !c.ok() {