net: use same sendFile for freebsd/dragonfly and solaris

FreeBSD/Dragonfly and Solaris have identical implementations of
sendFile. Keep one and adjust the comments accordingly.

Change-Id: I77b0f88a4816dd6e40f5cb33919c44606401ac6b
Reviewed-on: https://go-review.googlesource.com/104915
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/src/net/sendfile_unix_alt.go b/src/net/sendfile_unix_alt.go
new file mode 100644
index 0000000000..97aeebbed2
--- /dev/null
+++ b/src/net/sendfile_unix_alt.go
@@ -0,0 +1,67 @@
+// 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.
+
+// +build dragonfly freebsd solaris
+
+package net
+
+import (
+	"internal/poll"
+	"io"
+	"os"
+)
+
+// 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 error, handled bool) {
+	// FreeBSD, DragonFly and Solaris use 0 as the "until EOF" value.
+	// If you pass in more bytes than the file contains, it will
+	// loop back to the beginning ad nauseam until it's sent
+	// exactly the number of bytes told to. As such, we need to
+	// know exactly how many bytes to send.
+	var remain int64 = 0
+
+	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
+	}
+
+	if remain == 0 {
+		fi, err := f.Stat()
+		if err != nil {
+			return 0, err, false
+		}
+
+		remain = fi.Size()
+	}
+
+	// The other quirk with FreeBSD/DragonFly/Solaris's sendfile
+	// implementation is that it doesn't use the current position
+	// of the file -- if you pass it offset 0, it starts from
+	// offset 0. There's no way to tell it "start from current
+	// position", so we have to manage that explicitly.
+	pos, err := f.Seek(0, io.SeekCurrent)
+	if err != nil {
+		return 0, err, false
+	}
+
+	written, err = poll.SendFile(&c.pfd, int(f.Fd()), pos, remain)
+
+	if lr != nil {
+		lr.N = remain - written
+	}
+	return written, wrapSyscallError("sendfile", err), written > 0
+}