3 files changed, 225 insertions, 0 deletions
diff --git a/pkg/eventchannel/BUILD b/pkg/eventchannel/BUILD
new file mode 100644
index 000000000..ea0c587be
--- /dev/null
+++ b/pkg/eventchannel/BUILD
@@ -0,0 +1,33 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "eventchannel",
+    srcs = [
+        "event.go",
+    ],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/eventchannel",
+    visibility = ["//:sandbox"],
+    deps = [
+        ":eventchannel_go_proto",
+        "//pkg/log",
+        "//pkg/unet",
+        "@com_github_golang_protobuf//proto:go_default_library",
+        "@com_github_golang_protobuf//ptypes:go_default_library",
+    ],
+)
+
+proto_library(
+    name = "eventchannel_proto",
+    srcs = ["event.proto"],
+    visibility = ["//:sandbox"],
+)
+
+go_proto_library(
+    name = "eventchannel_go_proto",
+    importpath = "gvisor.googlesource.com/gvisor/pkg/eventchannel/eventchannel_go_proto",
+    proto = ":eventchannel_proto",
+    visibility = ["//:sandbox"],
+)
diff --git a/pkg/eventchannel/event.go b/pkg/eventchannel/event.go
new file mode 100644
index 000000000..bfd28256e
--- /dev/null
+++ b/pkg/eventchannel/event.go
@@ -0,0 +1,165 @@
+// Copyright 2018 Google Inc.
+//
+// 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"
+	"sync"
+	"syscall"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/golang/protobuf/ptypes"
+	pb "gvisor.googlesource.com/gvisor/pkg/eventchannel/eventchannel_go_proto"
+	"gvisor.googlesource.com/gvisor/pkg/log"
+	"gvisor.googlesource.com/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
+}
+
+var (
+	mu       sync.Mutex
+	emitters = make(map[Emitter]struct{})
+)
+
+// Emit emits a message using all added emitters.
+func Emit(msg proto.Message) error {
+	mu.Lock()
+	defer mu.Unlock()
+
+	var err error
+	for e := range 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(emitters, e)
+		}
+	}
+
+	return err
+}
+
+// AddEmitter adds a new emitter.
+func AddEmitter(e Emitter) {
+	mu.Lock()
+	defer mu.Unlock()
+	emitters[e] = struct{}{}
+}
+
+func marshal(msg proto.Message) ([]byte, error) {
+	anypb, err := ptypes.MarshalAny(msg)
+	if err != nil {
+		return nil, err
+	}
+
+	// Wire format is uvarint message length followed by binary proto.
+	bufMsg, err := proto.Marshal(anypb)
+	if err != nil {
+		return nil, err
+	}
+	p := make([]byte, binary.MaxVarintLen64)
+	n := binary.PutUvarint(p, uint64(len(bufMsg)))
+	return append(p[:n], bufMsg...), nil
+}
+
+// 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) {
+	p, err := marshal(msg)
+	if err != nil {
+		return false, err
+	}
+	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 wraping an existing
+// raw emitter.
+func DebugEmitterFrom(inner Emitter) Emitter {
+	return &debugEmitter{
+		inner: inner,
+	}
+}
+
+func (d *debugEmitter) Emit(msg proto.Message) (bool, error) {
+	ev := &pb.DebugEvent{
+		Name: proto.MessageName(msg),
+		Text: proto.MarshalTextString(msg),
+	}
+	return d.inner.Emit(ev)
+}
+
+func (d *debugEmitter) Close() error {
+	return d.inner.Close()
+}
diff --git a/pkg/eventchannel/event.proto b/pkg/eventchannel/event.proto
new file mode 100644
index 000000000..455f03658
--- /dev/null
+++ b/pkg/eventchannel/event.proto
@@ -0,0 +1,27 @@
+// Copyright 2018 Google Inc.
+//
+// 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.
+
+syntax = "proto3";
+
+package gvisor;
+
+// A debug event encapsulates any other event protobuf in text format. This is
+// useful because clients reading events emitted this way do not need to link
+// the event protobufs to display them in a human-readable format.
+message DebugEvent {
+  // Name of the inner message.
+  string name = 1;
+  // Text representation of the inner message content.
+  string text = 2;
+}