pkg/util/fdchannel.go

/*
Copyright 2018 The Kubernetes Authors.
Copyright 2022 Google LLC

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

    https://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 util

import (
	"errors"
	"net"
	"syscall"

	"k8s.io/klog/v2"
)

func SendMsg(via net.Conn, fd int, msg []byte) error {
	klog.V(4).Info("get the underlying socket")
	conn, ok := via.(*net.UnixConn)
	if !ok {
		return errors.New("failed to cast via to *net.UnixConn")
	}
	connf, err := conn.File()
	if err != nil {
		return err
	}
	socket := int(connf.Fd())
	defer connf.Close()

	klog.V(4).Infof("calling sendmsg...")
	rights := syscall.UnixRights(fd)

	return syscall.Sendmsg(socket, msg, rights, nil, 0)
}

func RecvMsg(via net.Conn) (int, []byte, error) {
	klog.V(4).Info("get the underlying socket")
	conn, ok := via.(*net.UnixConn)
	if !ok {
		return 0, nil, errors.New("failed to cast via to *net.UnixConn")
	}
	connf, err := conn.File()
	if err != nil {
		return 0, nil, err
	}
	socket := int(connf.Fd())
	defer connf.Close()

	klog.V(4).Info("calling recvmsg...")
	buf := make([]byte, syscall.CmsgSpace(4))
	b := make([]byte, 5000)
	//nolint:dogsled
	n, _, _, _, err := syscall.Recvmsg(socket, b, buf, 0)
	if err != nil {
		return 0, nil, err
	}
	klog.V(4).Infof("received message of %d bytes", n)

	klog.V(4).Info("parsing SCM...")
	var msgs []syscall.SocketControlMessage
	msgs, err = syscall.ParseSocketControlMessage(buf)
	if err != nil {
		return 0, nil, err
	}

	klog.V(4).Info("parsing SCM_RIGHTS...")
	fds, err := syscall.ParseUnixRights(&msgs[0])
	if err != nil {
		return 0, nil, err
	}

	return fds[0], b[:n], err
}