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Use go-events package

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Signed-off-by: Elliot Pahl <elliot.pahl@gmail.com>
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Elliot Pahl 2018-03-14 11:08:11 +11:00 • committed by Derek McGowan
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# Compiled Object files, Static and Dynamic libs (Shared Objects)
*.o
*.a
*.so
# Folders
_obj
_test
# Architecture specific extensions/prefixes
*.[568vq]
[568vq].out
*.cgo1.go
*.cgo2.c
_cgo_defun.c
_cgo_gotypes.go
_cgo_export.*
_testmain.go
*.exe
*.test
*.prof

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# Contributing to Docker open source projects
Want to hack on go-events? Awesome! Here are instructions to get you started.
go-events is part of the [Docker](https://www.docker.com) project, and
follows the same rules and principles. If you're already familiar with the way
Docker does things, you'll feel right at home.
Otherwise, go read Docker's
[contributions guidelines](https://github.com/docker/docker/blob/master/CONTRIBUTING.md),
[issue triaging](https://github.com/docker/docker/blob/master/project/ISSUE-TRIAGE.md),
[review process](https://github.com/docker/docker/blob/master/project/REVIEWING.md) and
[branches and tags](https://github.com/docker/docker/blob/master/project/BRANCHES-AND-TAGS.md).
For an in-depth description of our contribution process, visit the
contributors guide: [Understand how to contribute](https://docs.docker.com/opensource/workflow/make-a-contribution/)
### Sign your work
The sign-off is a simple line at the end of the explanation for the patch. Your
signature certifies that you wrote the patch or otherwise have the right to pass
it on as an open-source patch. The rules are pretty simple: if you can certify
the below (from [developercertificate.org](http://developercertificate.org/)):
```
Developer Certificate of Origin
Version 1.1
Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
660 York Street, Suite 102,
San Francisco, CA 94110 USA
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.
```
Then you just add a line to every git commit message:
Signed-off-by: Joe Smith <joe.smith@email.com>
Use your real name (sorry, no pseudonyms or anonymous contributions.)
If you set your `user.name` and `user.email` git configs, you can sign your
commit automatically with `git commit -s`.

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See the License for the specific language governing permissions and
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# go-events maintainers file
#
# This file describes who runs the docker/go-events project and how.
# This is a living document - if you see something out of date or missing, speak up!
#
# It is structured to be consumable by both humans and programs.
# To extract its contents programmatically, use any TOML-compliant parser.
#
# This file is compiled into the MAINTAINERS file in docker/opensource.
#
[Org]
[Org."Core maintainers"]
people = [
"aaronlehmann",
"aluzzardi",
"lk4d4",
"stevvooe",
]
[people]
# A reference list of all people associated with the project.
# All other sections should refer to people by their canonical key
# in the people section.
# ADD YOURSELF HERE IN ALPHABETICAL ORDER
[people.aaronlehmann]
Name = "Aaron Lehmann"
Email = "aaron.lehmann@docker.com"
GitHub = "aaronlehmann"
[people.aluzzardi]
Name = "Andrea Luzzardi"
Email = "al@docker.com"
GitHub = "aluzzardi"
[people.lk4d4]
Name = "Alexander Morozov"
Email = "lk4d4@docker.com"
GitHub = "lk4d4"
[people.stevvooe]
Name = "Stephen Day"
Email = "stephen.day@docker.com"
GitHub = "stevvooe"

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# Docker Events Package
[![GoDoc](https://godoc.org/github.com/docker/go-events?status.svg)](https://godoc.org/github.com/docker/go-events)
[![Circle CI](https://circleci.com/gh/docker/go-events.svg?style=shield)](https://circleci.com/gh/docker/go-events)
The Docker `events` package implements a composable event distribution package
for Go.
Originally created to implement the [notifications in Docker Registry
2](https://github.com/docker/distribution/blob/master/docs/notifications.md),
we've found the pattern to be useful in other applications. This package is
most of the same code with slightly updated interfaces. Much of the internals
have been made available.
## Usage
The `events` package centers around a `Sink` type. Events are written with
calls to `Sink.Write(event Event)`. Sinks can be wired up in various
configurations to achieve interesting behavior.
The canonical example is that employed by the
[docker/distribution/notifications](https://godoc.org/github.com/docker/distribution/notifications)
package. Let's say we have a type `httpSink` where we'd like to queue
notifications. As a rule, it should send a single http request and return an
error if it fails:
```go
func (h *httpSink) Write(event Event) error {
p, err := json.Marshal(event)
if err != nil {
return err
}
body := bytes.NewReader(p)
resp, err := h.client.Post(h.url, "application/json", body)
if err != nil {
return err
}
defer resp.Body.Close()
if resp.Status != 200 {
return errors.New("unexpected status")
}
return nil
}
// implement (*httpSink).Close()
```
With just that, we can start using components from this package. One can call
`(*httpSink).Write` to send events as the body of a post request to a
configured URL.
### Retries
HTTP can be unreliable. The first feature we'd like is to have some retry:
```go
hs := newHTTPSink(/*...*/)
retry := NewRetryingSink(hs, NewBreaker(5, time.Second))
```
We now have a sink that will retry events against the `httpSink` until they
succeed. The retry will backoff for one second after 5 consecutive failures
using the breaker strategy.
### Queues
This isn't quite enough. We we want a sink that doesn't block while we are
waiting for events to be sent. Let's add a `Queue`:
```go
queue := NewQueue(retry)
```
Now, we have an unbounded queue that will work through all events sent with
`(*Queue).Write`. Events can be added asynchronously to the queue without
blocking the current execution path. This is ideal for use in an http request.
### Broadcast
It usually turns out that you want to send to more than one listener. We can
use `Broadcaster` to support this:
```go
var broadcast = NewBroadcaster() // make it available somewhere in your application.
broadcast.Add(queue) // add your queue!
broadcast.Add(queue2) // and another!
```
With the above, we can now call `broadcast.Write` in our http handlers and have
all the events distributed to each queue. Because the events are queued, not
listener blocks another.
### Extending
For the most part, the above is sufficient for a lot of applications. However,
extending the above functionality can be done implementing your own `Sink`. The
behavior and semantics of the sink can be completely dependent on the
application requirements. The interface is provided below for reference:
```go
type Sink {
Write(Event) error
Close() error
}
```
Application behavior can be controlled by how `Write` behaves. The examples
above are designed to queue the message and return as quickly as possible.
Other implementations may block until the event is committed to durable
storage.
## Copyright and license
Copyright © 2016 Docker, Inc. go-events is licensed under the Apache License,
Version 2.0. See [LICENSE](LICENSE) for the full license text.

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package events
import (
"fmt"
"sync"
"github.com/sirupsen/logrus"
)
// Broadcaster sends events to multiple, reliable Sinks. The goal of this
// component is to dispatch events to configured endpoints. Reliability can be
// provided by wrapping incoming sinks.
type Broadcaster struct {
sinks []Sink
events chan Event
adds chan configureRequest
removes chan configureRequest
shutdown chan struct{}
closed chan struct{}
once sync.Once
}
// NewBroadcaster appends one or more sinks to the list of sinks. The
// broadcaster behavior will be affected by the properties of the sink.
// Generally, the sink should accept all messages and deal with reliability on
// its own. Use of EventQueue and RetryingSink should be used here.
func NewBroadcaster(sinks ...Sink) *Broadcaster {
b := Broadcaster{
sinks: sinks,
events: make(chan Event),
adds: make(chan configureRequest),
removes: make(chan configureRequest),
shutdown: make(chan struct{}),
closed: make(chan struct{}),
}
// Start the broadcaster
go b.run()
return &b
}
// Write accepts an event to be dispatched to all sinks. This method will never
// fail and should never block (hopefully!). The caller cedes the memory to the
// broadcaster and should not modify it after calling write.
func (b *Broadcaster) Write(event Event) error {
select {
case b.events <- event:
case <-b.closed:
return ErrSinkClosed
}
return nil
}
// Add the sink to the broadcaster.
//
// The provided sink must be comparable with equality. Typically, this just
// works with a regular pointer type.
func (b *Broadcaster) Add(sink Sink) error {
return b.configure(b.adds, sink)
}
// Remove the provided sink.
func (b *Broadcaster) Remove(sink Sink) error {
return b.configure(b.removes, sink)
}
type configureRequest struct {
sink Sink
response chan error
}
func (b *Broadcaster) configure(ch chan configureRequest, sink Sink) error {
response := make(chan error, 1)
for {
select {
case ch <- configureRequest{
sink: sink,
response: response}:
ch = nil
case err := <-response:
return err
case <-b.closed:
return ErrSinkClosed
}
}
}
// Close the broadcaster, ensuring that all messages are flushed to the
// underlying sink before returning.
func (b *Broadcaster) Close() error {
b.once.Do(func() {
close(b.shutdown)
})
<-b.closed
return nil
}
// run is the main broadcast loop, started when the broadcaster is created.
// Under normal conditions, it waits for events on the event channel. After
// Close is called, this goroutine will exit.
func (b *Broadcaster) run() {
defer close(b.closed)
remove := func(target Sink) {
for i, sink := range b.sinks {
if sink == target {
b.sinks = append(b.sinks[:i], b.sinks[i+1:]...)
break
}
}
}
for {
select {
case event := <-b.events:
for _, sink := range b.sinks {
if err := sink.Write(event); err != nil {
if err == ErrSinkClosed {
// remove closed sinks
remove(sink)
continue
}
logrus.WithField("event", event).WithField("events.sink", sink).WithError(err).
Errorf("broadcaster: dropping event")
}
}
case request := <-b.adds:
// while we have to iterate for add/remove, common iteration for
// send is faster against slice.
var found bool
for _, sink := range b.sinks {
if request.sink == sink {
found = true
break
}
}
if !found {
b.sinks = append(b.sinks, request.sink)
}
// b.sinks[request.sink] = struct{}{}
request.response <- nil
case request := <-b.removes:
remove(request.sink)
request.response <- nil
case <-b.shutdown:
// close all the underlying sinks
for _, sink := range b.sinks {
if err := sink.Close(); err != nil && err != ErrSinkClosed {
logrus.WithField("events.sink", sink).WithError(err).
Errorf("broadcaster: closing sink failed")
}
}
return
}
}
}
func (b *Broadcaster) String() string {
// Serialize copy of this broadcaster without the sync.Once, to avoid
// a data race.
b2 := map[string]interface{}{
"sinks": b.sinks,
"events": b.events,
"adds": b.adds,
"removes": b.removes,
"shutdown": b.shutdown,
"closed": b.closed,
}
return fmt.Sprint(b2)
}

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package events
import (
"fmt"
"sync"
)
// Channel provides a sink that can be listened on. The writer and channel
// listener must operate in separate goroutines.
//
// Consumers should listen on Channel.C until Closed is closed.
type Channel struct {
C chan Event
closed chan struct{}
once sync.Once
}
// NewChannel returns a channel. If buffer is zero, the channel is
// unbuffered.
func NewChannel(buffer int) *Channel {
return &Channel{
C: make(chan Event, buffer),
closed: make(chan struct{}),
}
}
// Done returns a channel that will always proceed once the sink is closed.
func (ch *Channel) Done() chan struct{} {
return ch.closed
}
// Write the event to the channel. Must be called in a separate goroutine from
// the listener.
func (ch *Channel) Write(event Event) error {
select {
case ch.C <- event:
return nil
case <-ch.closed:
return ErrSinkClosed
}
}
// Close the channel sink.
func (ch *Channel) Close() error {
ch.once.Do(func() {
close(ch.closed)
})
return nil
}
func (ch *Channel) String() string {
// Serialize a copy of the Channel that doesn't contain the sync.Once,
// to avoid a data race.
ch2 := map[string]interface{}{
"C": ch.C,
"closed": ch.closed,
}
return fmt.Sprint(ch2)
}

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package events
import "fmt"
var (
// ErrSinkClosed is returned if a write is issued to a sink that has been
// closed. If encountered, the error should be considered terminal and
// retries will not be successful.
ErrSinkClosed = fmt.Errorf("events: sink closed")
)

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package events
// Event marks items that can be sent as events.
type Event interface{}
// Sink accepts and sends events.
type Sink interface {
// Write an event to the Sink. If no error is returned, the caller will
// assume that all events have been committed to the sink. If an error is
// received, the caller may retry sending the event.
Write(event Event) error
// Close the sink, possibly waiting for pending events to flush.
Close() error
}

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package events
// Matcher matches events.
type Matcher interface {
Match(event Event) bool
}
// MatcherFunc implements matcher with just a function.
type MatcherFunc func(event Event) bool
// Match calls the wrapped function.
func (fn MatcherFunc) Match(event Event) bool {
return fn(event)
}
// Filter provides an event sink that sends only events that are accepted by a
// Matcher. No methods on filter are goroutine safe.
type Filter struct {
dst Sink
matcher Matcher
closed bool
}
// NewFilter returns a new filter that will send to events to dst that return
// true for Matcher.
func NewFilter(dst Sink, matcher Matcher) Sink {
return &Filter{dst: dst, matcher: matcher}
}
// Write an event to the filter.
func (f *Filter) Write(event Event) error {
if f.closed {
return ErrSinkClosed
}
if f.matcher.Match(event) {
return f.dst.Write(event)
}
return nil
}
// Close the filter and allow no more events to pass through.
func (f *Filter) Close() error {
// TODO(stevvooe): Not all sinks should have Close.
if f.closed {
return nil
}
f.closed = true
return f.dst.Close()
}

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package events
import (
"container/list"
"sync"
"github.com/sirupsen/logrus"
)
// Queue accepts all messages into a queue for asynchronous consumption
// by a sink. It is unbounded and thread safe but the sink must be reliable or
// events will be dropped.
type Queue struct {
dst Sink
events *list.List
cond *sync.Cond
mu sync.Mutex
closed bool
}
// NewQueue returns a queue to the provided Sink dst.
func NewQueue(dst Sink) *Queue {
eq := Queue{
dst: dst,
events: list.New(),
}
eq.cond = sync.NewCond(&eq.mu)
go eq.run()
return &eq
}
// Write accepts the events into the queue, only failing if the queue has
// been closed.
func (eq *Queue) Write(event Event) error {
eq.mu.Lock()
defer eq.mu.Unlock()
if eq.closed {
return ErrSinkClosed
}
eq.events.PushBack(event)
eq.cond.Signal() // signal waiters
return nil
}
// Close shutsdown the event queue, flushing
func (eq *Queue) Close() error {
eq.mu.Lock()
defer eq.mu.Unlock()
if eq.closed {
return nil
}
// set closed flag
eq.closed = true
eq.cond.Signal() // signal flushes queue
eq.cond.Wait() // wait for signal from last flush
return eq.dst.Close()
}
// run is the main goroutine to flush events to the target sink.
func (eq *Queue) run() {
for {
event := eq.next()
if event == nil {
return // nil block means event queue is closed.
}
if err := eq.dst.Write(event); err != nil {
// TODO(aaronl): Dropping events could be bad depending
// on the application. We should have a way of
// communicating this condition. However, logging
// at a log level above debug may not be appropriate.
// Eventually, go-events should not use logrus at all,
// and should bubble up conditions like this through
// error values.
logrus.WithFields(logrus.Fields{
"event": event,
"sink": eq.dst,
}).WithError(err).Debug("eventqueue: dropped event")
}
}
}
// next encompasses the critical section of the run loop. When the queue is
// empty, it will block on the condition. If new data arrives, it will wake
// and return a block. When closed, a nil slice will be returned.
func (eq *Queue) next() Event {
eq.mu.Lock()
defer eq.mu.Unlock()
for eq.events.Len() < 1 {
if eq.closed {
eq.cond.Broadcast()
return nil
}
eq.cond.Wait()
}
front := eq.events.Front()
block := front.Value.(Event)
eq.events.Remove(front)
return block
}

260
vendor/github.com/docker/go-events/retry.go generated vendored Normal file
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@ -0,0 +1,260 @@
package events
import (
"fmt"
"math/rand"
"sync"
"sync/atomic"
"time"
"github.com/sirupsen/logrus"
)
// RetryingSink retries the write until success or an ErrSinkClosed is
// returned. Underlying sink must have p > 0 of succeeding or the sink will
// block. Retry is configured with a RetryStrategy. Concurrent calls to a
// retrying sink are serialized through the sink, meaning that if one is
// in-flight, another will not proceed.
type RetryingSink struct {
sink Sink
strategy RetryStrategy
closed chan struct{}
once sync.Once
}
// NewRetryingSink returns a sink that will retry writes to a sink, backing
// off on failure. Parameters threshold and backoff adjust the behavior of the
// circuit breaker.
func NewRetryingSink(sink Sink, strategy RetryStrategy) *RetryingSink {
rs := &RetryingSink{
sink: sink,
strategy: strategy,
closed: make(chan struct{}),
}
return rs
}
// Write attempts to flush the events to the downstream sink until it succeeds
// or the sink is closed.
func (rs *RetryingSink) Write(event Event) error {
logger := logrus.WithField("event", event)
retry:
select {
case <-rs.closed:
return ErrSinkClosed
default:
}
if backoff := rs.strategy.Proceed(event); backoff > 0 {
select {
case <-time.After(backoff):
// TODO(stevvooe): This branch holds up the next try. Before, we
// would simply break to the "retry" label and then possibly wait
// again. However, this requires all retry strategies to have a
// large probability of probing the sync for success, rather than
// just backing off and sending the request.
case <-rs.closed:
return ErrSinkClosed
}
}
if err := rs.sink.Write(event); err != nil {
if err == ErrSinkClosed {
// terminal!
return err
}
logger := logger.WithError(err) // shadow!!
if rs.strategy.Failure(event, err) {
logger.Errorf("retryingsink: dropped event")
return nil
}
logger.Errorf("retryingsink: error writing event, retrying")
goto retry
}
rs.strategy.Success(event)
return nil
}
// Close closes the sink and the underlying sink.
func (rs *RetryingSink) Close() error {
rs.once.Do(func() {
close(rs.closed)
})
return nil
}
func (rs *RetryingSink) String() string {
// Serialize a copy of the RetryingSink without the sync.Once, to avoid
// a data race.
rs2 := map[string]interface{}{
"sink": rs.sink,
"strategy": rs.strategy,
"closed": rs.closed,
}
return fmt.Sprint(rs2)
}
// RetryStrategy defines a strategy for retrying event sink writes.
//
// All methods should be goroutine safe.
type RetryStrategy interface {
// Proceed is called before every event send. If proceed returns a
// positive, non-zero integer, the retryer will back off by the provided
// duration.
//
// An event is provided, by may be ignored.
Proceed(event Event) time.Duration
// Failure reports a failure to the strategy. If this method returns true,
// the event should be dropped.
Failure(event Event, err error) bool
// Success should be called when an event is sent successfully.
Success(event Event)
}
// Breaker implements a circuit breaker retry strategy.
//
// The current implementation never drops events.
type Breaker struct {
threshold int
recent int
last time.Time
backoff time.Duration // time after which we retry after failure.
mu sync.Mutex
}
var _ RetryStrategy = &Breaker{}
// NewBreaker returns a breaker that will backoff after the threshold has been
// tripped. A Breaker is thread safe and may be shared by many goroutines.
func NewBreaker(threshold int, backoff time.Duration) *Breaker {
return &Breaker{
threshold: threshold,
backoff: backoff,
}
}
// Proceed checks the failures against the threshold.
func (b *Breaker) Proceed(event Event) time.Duration {
b.mu.Lock()
defer b.mu.Unlock()
if b.recent < b.threshold {
return 0
}
return b.last.Add(b.backoff).Sub(time.Now())
}
// Success resets the breaker.
func (b *Breaker) Success(event Event) {
b.mu.Lock()
defer b.mu.Unlock()
b.recent = 0
b.last = time.Time{}
}
// Failure records the failure and latest failure time.
func (b *Breaker) Failure(event Event, err error) bool {
b.mu.Lock()
defer b.mu.Unlock()
b.recent++
b.last = time.Now().UTC()
return false // never drop events.
}
var (
// DefaultExponentialBackoffConfig provides a default configuration for
// exponential backoff.
DefaultExponentialBackoffConfig = ExponentialBackoffConfig{
Base: time.Second,
Factor: time.Second,
Max: 20 * time.Second,
}
)
// ExponentialBackoffConfig configures backoff parameters.
//
// Note that these parameters operate on the upper bound for choosing a random
// value. For example, at Base=1s, a random value in [0,1s) will be chosen for
// the backoff value.
type ExponentialBackoffConfig struct {
// Base is the minimum bound for backing off after failure.
Base time.Duration
// Factor sets the amount of time by which the backoff grows with each
// failure.
Factor time.Duration
// Max is the absolute maxiumum bound for a single backoff.
Max time.Duration
}
// ExponentialBackoff implements random backoff with exponentially increasing
// bounds as the number consecutive failures increase.
type ExponentialBackoff struct {
failures uint64 // consecutive failure counter (needs to be 64-bit aligned)
config ExponentialBackoffConfig
}
// NewExponentialBackoff returns an exponential backoff strategy with the
// desired config. If config is nil, the default is returned.
func NewExponentialBackoff(config ExponentialBackoffConfig) *ExponentialBackoff {
return &ExponentialBackoff{
config: config,
}
}
// Proceed returns the next randomly bound exponential backoff time.
func (b *ExponentialBackoff) Proceed(event Event) time.Duration {
return b.backoff(atomic.LoadUint64(&b.failures))
}
// Success resets the failures counter.
func (b *ExponentialBackoff) Success(event Event) {
atomic.StoreUint64(&b.failures, 0)
}
// Failure increments the failure counter.
func (b *ExponentialBackoff) Failure(event Event, err error) bool {
atomic.AddUint64(&b.failures, 1)
return false
}
// backoff calculates the amount of time to wait based on the number of
// consecutive failures.
func (b *ExponentialBackoff) backoff(failures uint64) time.Duration {
if failures <= 0 {
// proceed normally when there are no failures.
return 0
}
factor := b.config.Factor
if factor <= 0 {
factor = DefaultExponentialBackoffConfig.Factor
}
backoff := b.config.Base + factor*time.Duration(1<<(failures-1))
max := b.config.Max
if max <= 0 {
max = DefaultExponentialBackoffConfig.Max
}
if backoff > max || backoff < 0 {
backoff = max
}
// Choose a uniformly distributed value from [0, backoff).
return time.Duration(rand.Int63n(int64(backoff)))
}