[release-branch.go1.15] internal/poll: netpollcheckerr before sendfile

In net/http package, the ServeContent/ServeFile doesn't check the I/O
timeout error from chunkWriter or *net.TCPConn, which means that both
HTTP status and headers might be missing when WriteTimeout happens. If
the poll.SendFile() doesn't check the *poll.FD state before sending
data, the client will only receive the response body with status and
report "malformed http response/status code".

This patch is to enable netpollcheckerr before sendfile, which should
align with normal *poll.FD.Write() and Splice().

For #43822
Fixes #44294

Change-Id: I32517e3f261bab883a58b577b813ef189214b954
Reviewed-on: https://go-review.googlesource.com/c/go/+/285914
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
(cherry picked from commit f0d23c9dbb)
Reviewed-on: https://go-review.googlesource.com/c/go/+/296530
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/internal/poll/sendfile_bsd.go

@@ -18,6 +18,10 @@ func SendFile(dstFD *FD, src int, pos, remain int64) (int64, error) {
 		return 0, err
 	}
 	defer dstFD.writeUnlock()
+	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
+		return 0, err
+	}
+
 	dst := int(dstFD.Sysfd)
 	var written int64
 	var err error

src/internal/poll/sendfile_linux.go

@@ -16,6 +16,9 @@ func SendFile(dstFD *FD, src int, remain int64) (int64, error) {
 		return 0, err
 	}
 	defer dstFD.writeUnlock()
+	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
+		return 0, err
+	}
 
 	dst := int(dstFD.Sysfd)
 	var written int64

src/internal/poll/sendfile_solaris.go

@@ -20,6 +20,9 @@ func SendFile(dstFD *FD, src int, pos, remain int64) (int64, error) {
 		return 0, err
 	}
 	defer dstFD.writeUnlock()
+	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
+		return 0, err
+	}
 
 	dst := int(dstFD.Sysfd)
 	var written int64

src/net/sendfile_test.go

@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"crypto/sha256"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -314,3 +315,66 @@ func TestSendfilePipe(t *testing.T) {
 
 	wg.Wait()
 }
+
+// Issue 43822: tests that returns EOF when conn write timeout.
+func TestSendfileOnWriteTimeoutExceeded(t *testing.T) {
+	ln, err := newLocalListener("tcp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+
+	errc := make(chan error, 1)
+	go func(ln Listener) (retErr error) {
+		defer func() {
+			errc <- retErr
+			close(errc)
+		}()
+
+		conn, err := ln.Accept()
+		if err != nil {
+			return err
+		}
+		defer conn.Close()
+
+		// Set the write deadline in the past(1h ago). It makes
+		// sure that it is always write timeout.
+		if err := conn.SetWriteDeadline(time.Now().Add(-1 * time.Hour)); err != nil {
+			return err
+		}
+
+		f, err := os.Open(newton)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+
+		_, err = io.Copy(conn, f)
+		if errors.Is(err, os.ErrDeadlineExceeded) {
+			return nil
+		}
+
+		if err == nil {
+			err = fmt.Errorf("expected ErrDeadlineExceeded, but got nil")
+		}
+		return err
+	}(ln)
+
+	conn, err := Dial("tcp", ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+
+	n, err := io.Copy(ioutil.Discard, conn)
+	if err != nil {
+		t.Fatalf("expected nil error, but got %v", err)
+	}
+	if n != 0 {
+		t.Fatalf("expected receive zero, but got %d byte(s)", n)
+	}
+
+	if err := <-errc; err != nil {
+		t.Fatal(err)
+	}
+}