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// Copyright 2018 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 eventchannel contains functionality for sending any protobuf message
// on a socketpair.
//
// The wire format is a uvarint length followed by a binary protobuf.Any
// message.
package eventchannel
import (
"encoding/binary"
"fmt"
"syscall"
"google.golang.org/protobuf/encoding/prototext"
"google.golang.org/protobuf/proto"
pb "gvisor.dev/gvisor/pkg/eventchannel/eventchannel_go_proto"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/unet"
)
// Emitter emits a proto message.
type Emitter interface {
// Emit writes a single eventchannel message to an emitter. Emit should
// return hangup = true to indicate an emitter has "hung up" and no further
// messages should be directed to it.
Emit(msg proto.Message) (hangup bool, err error)
// Close closes this emitter. Emit cannot be used after Close is called.
Close() error
}
// DefaultEmitter is the default emitter. Calls to Emit and AddEmitter are sent
// to this Emitter.
var DefaultEmitter = &multiEmitter{}
// Emit is a helper method that calls DefaultEmitter.Emit.
func Emit(msg proto.Message) error {
_, err := DefaultEmitter.Emit(msg)
return err
}
// AddEmitter is a helper method that calls DefaultEmitter.AddEmitter.
func AddEmitter(e Emitter) {
DefaultEmitter.AddEmitter(e)
}
// multiEmitter is an Emitter that forwards messages to multiple Emitters.
type multiEmitter struct {
// mu protects emitters.
mu sync.Mutex
// emitters is initialized lazily in AddEmitter.
emitters map[Emitter]struct{}
}
// Emit emits a message using all added emitters.
func (me *multiEmitter) Emit(msg proto.Message) (bool, error) {
me.mu.Lock()
defer me.mu.Unlock()
var err error
for e := range me.emitters {
hangup, eerr := e.Emit(msg)
if eerr != nil {
if err == nil {
err = fmt.Errorf("error emitting %v: on %v: %v", msg, e, eerr)
} else {
err = fmt.Errorf("%v; on %v: %v", err, e, eerr)
}
// Log as well, since most callers ignore the error.
log.Warningf("Error emitting %v on %v: %v", msg, e, eerr)
}
if hangup {
log.Infof("Hangup on eventchannel emitter %v.", e)
delete(me.emitters, e)
}
}
return false, err
}
// AddEmitter adds a new emitter.
func (me *multiEmitter) AddEmitter(e Emitter) {
me.mu.Lock()
defer me.mu.Unlock()
if me.emitters == nil {
me.emitters = make(map[Emitter]struct{})
}
me.emitters[e] = struct{}{}
}
// Close closes all emitters. If any Close call errors, it returns the first
// one encountered.
func (me *multiEmitter) Close() error {
me.mu.Lock()
defer me.mu.Unlock()
var err error
for e := range me.emitters {
if eerr := e.Close(); err == nil && eerr != nil {
err = eerr
}
delete(me.emitters, e)
}
return err
}
// socketEmitter emits proto messages on a socket.
type socketEmitter struct {
socket *unet.Socket
}
// SocketEmitter creates a new event channel based on the given fd.
//
// SocketEmitter takes ownership of fd.
func SocketEmitter(fd int) (Emitter, error) {
s, err := unet.NewSocket(fd)
if err != nil {
return nil, err
}
return &socketEmitter{
socket: s,
}, nil
}
// Emit implements Emitter.Emit.
func (s *socketEmitter) Emit(msg proto.Message) (bool, error) {
any, err := newAny(msg)
if err != nil {
return false, err
}
bufMsg, err := proto.Marshal(any)
if err != nil {
return false, err
}
// Wire format is uvarint message length followed by binary proto.
p := make([]byte, binary.MaxVarintLen64)
n := binary.PutUvarint(p, uint64(len(bufMsg)))
p = append(p[:n], bufMsg...)
for done := 0; done < len(p); {
n, err := s.socket.Write(p[done:])
if err != nil {
return (err == syscall.EPIPE), err
}
done += n
}
return false, nil
}
// Close implements Emitter.Emit.
func (s *socketEmitter) Close() error {
return s.socket.Close()
}
// debugEmitter wraps an emitter to emit stringified event messages. This is
// useful for debugging -- when the messages are intended for humans.
type debugEmitter struct {
inner Emitter
}
// DebugEmitterFrom creates a new event channel emitter by wrapping an existing
// raw emitter.
func DebugEmitterFrom(inner Emitter) Emitter {
return &debugEmitter{
inner: inner,
}
}
func (d *debugEmitter) Emit(msg proto.Message) (bool, error) {
text, err := prototext.Marshal(msg)
if err != nil {
return false, err
}
ev := &pb.DebugEvent{
Name: string(msg.ProtoReflect().Descriptor().FullName()),
Text: string(text),
}
return d.inner.Emit(ev)
}
func (d *debugEmitter) Close() error {
return d.inner.Close()
}
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