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// Copyright 2021 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package lisafs
import "golang.org/x/sys/unix"
// Communicator is a server side utility which represents exactly how the
// server is communicating with the client.
type Communicator interface {
// PayloadBuf returns a slice to the payload section of its internal buffer
// where the message can be marshalled. The handlers should use this to
// populate the payload buffer with the message.
//
// The payload buffer contents *should* be preserved across calls with
// different sizes. Note that this is not a guarantee, because a compromised
// owner of a "shared" payload buffer can tamper with its contents anytime,
// even when it's not its turn to do so.
PayloadBuf(size uint32) []byte
// SndRcvMessage sends message m. The caller must have populated PayloadBuf()
// with payloadLen bytes. The caller expects to receive wantFDs FDs.
// Any received FDs must be accessible via ReleaseFDs(). It returns the
// response message along with the response payload length.
SndRcvMessage(m MID, payloadLen uint32, wantFDs uint8) (MID, uint32, error)
// DonateFD makes fd non-blocking and starts tracking it. The next call to
// ReleaseFDs will include fd in the order it was added. Communicator takes
// ownership of fd. Server side should call this.
DonateFD(fd int) error
// Track starts tracking fd. The next call to ReleaseFDs will include fd in
// the order it was added. Communicator takes ownership of fd. Client side
// should use this for accumulating received FDs.
TrackFD(fd int)
// ReleaseFDs returns the accumulated FDs and stops tracking them. The
// ownership of the FDs is transferred to the caller.
ReleaseFDs() []int
}
// fdTracker is a partial implementation of Communicator. It can be embedded in
// Communicator implementations to keep track of FD donations.
type fdTracker struct {
fds []int
}
// DonateFD implements Communicator.DonateFD.
func (d *fdTracker) DonateFD(fd int) error {
// Make sure the FD is non-blocking.
if err := unix.SetNonblock(fd, true); err != nil {
unix.Close(fd)
return err
}
d.TrackFD(fd)
return nil
}
// TrackFD implements Communicator.TrackFD.
func (d *fdTracker) TrackFD(fd int) {
d.fds = append(d.fds, fd)
}
// ReleaseFDs implements Communicator.ReleaseFDs.
func (d *fdTracker) ReleaseFDs() []int {
ret := d.fds
d.fds = d.fds[:0]
return ret
}
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