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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
}