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// Copyright 2015 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 poll
import "syscall"
// Not strictly needed, but very helpful for debugging, see issue #10221.
//go:cgo_import_dynamic _ _ "libsendfile.so"
//go:cgo_import_dynamic _ _ "libsocket.so"
// maxSendfileSize is the largest chunk size we ask the kernel to copy
// at a time.
const maxSendfileSize int = 4 << 20
// SendFile wraps the sendfile system call.
func SendFile(dstFD *FD, src int, pos, remain int64) (int64, error) {
if err := dstFD.writeLock(); err != nil {
return 0, err
}
defer dstFD.writeUnlock()
if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
return 0, err
}
dst := dstFD.Sysfd
var written int64
var err error
for remain > 0 {
n := maxSendfileSize
if int64(n) > remain {
n = int(remain)
}
pos1 := pos
n, err1 := syscall.Sendfile(dst, src, &pos1, n)
if err1 == syscall.EAGAIN || err1 == syscall.EINTR {
// partial write may have occurred
n = int(pos1 - pos)
}
if n > 0 {
pos += int64(n)
written += int64(n)
remain -= int64(n)
} else if n == 0 && err1 == nil {
break
}
if err1 == syscall.EAGAIN {
if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
continue
}
}
if err1 == syscall.EINTR {
continue
}
if err1 != nil {
// This includes syscall.ENOSYS (no kernel
// support) and syscall.EINVAL (fd types which
// don't implement sendfile)
err = err1
break
}
}
return written, err
}
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