golang sendfile_windows 代码
文件路径：/src/internal/poll/sendfile_windows.go
/ 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 poll
import (
"io"
"syscall"
)
/ SendFile wraps the TransmitFile call.
func SendFile(fd *FD, src syscall.Handle, n int64) (written int64, err error) {
if fd.kind == kindPipe {
/ TransmitFile does not work with pipes
return 0, syscall.ESPIPE
}
if err := fd.writeLock(); err != nil {
return 0, err
}
defer fd.writeUnlock()
o := &fd.wop
o.handle = src
/ TODO(brainman): skip calling syscall.Seek if OS allows it
curpos, err := syscall.Seek(o.handle, 0, io.SeekCurrent)
if err != nil {
return 0, err
}
if n <= 0 { / We don't know the size of the file so infer it.
/ Find the number of bytes offset from curpos until the end of the file.
n, err = syscall.Seek(o.handle, -curpos, io.SeekEnd)
if err != nil {
return
}
/ Now seek back to the original position.
if _, err = syscall.Seek(o.handle, curpos, io.SeekStart); err != nil {
return
}
}
/ TransmitFile can be invoked in one call with at most
/ 2,147,483,646 bytes: the maximum value for a 32-bit integer minus 1.
/ See https://docs.microsoft.com/en-us/windows/win32/api/mswsock/nf-mswsock-transmitfile
const maxChunkSizePerCall = int64(0x7fffffff - 1)
for n > 0 {
chunkSize := maxChunkSizePerCall
if chunkSize > n {
chunkSize = n
}
o.qty = uint32(chunkSize)
o.o.Offset = uint32(curpos)
o.o.OffsetHigh = uint32(curpos >> 32)
nw, err := execIO(o, func(o *operation) error {
return syscall.TransmitFile(o.fd.Sysfd, o.handle, o.qty, 0, &o.o, nil, syscall.TF_WRITE_BEHIND)
})
if err != nil {
return written, err
}
curpos += int64(nw)
/ Some versions of Windows (Windows 10 1803) do not set
/ file position after TransmitFile completes.
/ So just use Seek to set file position.
if _, err = syscall.Seek(o.handle, curpos, io.SeekStart); err != nil {
return written, err
}
n -= int64(nw)
written += int64(nw)
}
return
}