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// 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 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()

        dst := c.sysfd

        src := f.Fd()

        for remain > 0 {

                n := maxSendfileSize

                if int64(n) > remain {

                        n = int(remain)

                }

                n, err1 := syscall.Sendfile(dst, src, nil, n)

                if n > 0 {

                        written += int64(n)

                        remain -= int64(n)

                }

                if n == 0 && err1 == nil {

                        break

                }

                if err1 == syscall.EAGAIN && c.wdeadline >= 0 {

                        pollserver.WaitWrite(c)

                        continue

                }

                if err1 != nil {

                        // 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, err1}

                        break

                }

        }

        if lr != nil {

                lr.N = remain

        }

        return written, err, written > 0

}