| // 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 ( |
| "internal/poll" |
| "io" |
| "os" |
| "syscall" |
| ) |
| |
| // sendFile copies the contents of r to c using the TransmitFile |
| // 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(fd *netFD, r io.Reader) (written int64, err error, handled bool) { |
| var n int64 = 0 // by default, copy until EOF. |
| |
| lr, ok := r.(*io.LimitedReader) |
| if ok { |
| n, r = lr.N, lr.R |
| if n <= 0 { |
| return 0, nil, true |
| } |
| } |
| |
| f, ok := r.(*os.File) |
| if !ok { |
| return 0, nil, false |
| } |
| |
| // 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) |
| |
| switch { |
| case n <= maxChunkSizePerCall: |
| // The file is within sendfile's limits. |
| written, err = doSendFile(fd, lr, f, n) |
| |
| default: |
| // Now invoke doSendFile on the file in chunks of upto 2GiB per chunk. |
| for lr.N > 0 { // lr.N is decremented in every successful invocation of doSendFile. |
| chunkSize := maxChunkSizePerCall |
| if chunkSize > lr.N { |
| chunkSize = lr.N |
| } |
| var nw int64 |
| nw, err = doSendFile(fd, lr, f, chunkSize) |
| if err != nil { |
| break |
| } |
| written += nw |
| } |
| } |
| |
| // If any byte was copied, regardless of any error |
| // encountered mid-way, handled must be set to true. |
| return written, err, written > 0 |
| } |
| |
| // doSendFile is a helper to invoke poll.SendFile. |
| // It will decrement lr.N by the number of written bytes. |
| func doSendFile(fd *netFD, lr *io.LimitedReader, f *os.File, remain int64) (written int64, err error) { |
| done, err := poll.SendFile(&fd.pfd, syscall.Handle(f.Fd()), remain) |
| if err != nil { |
| return 0, wrapSyscallError("transmitfile", err) |
| } |
| if lr != nil { |
| lr.N -= int64(done) |
| } |
| return int64(done), nil |
| } |