LogDog: Add Butler Output package.

client/internal/logdog/butler/output/gcps/gcpsOutput.go

Index: client/internal/logdog/butler/output/gcps/gcpsOutput.go
diff --git a/client/internal/logdog/butler/output/gcps/gcpsOutput.go b/client/internal/logdog/butler/output/gcps/gcpsOutput.go
new file mode 100644
index 0000000000000000000000000000000000000000..a7c8b41309d22d530516f70d3a459480c2bda7b1
--- /dev/null
+++ b/client/internal/logdog/butler/output/gcps/gcpsOutput.go
@@ -0,0 +1,210 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package gcps
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/luci/luci-go/client/internal/logdog/butler/output"
+	"github.com/luci/luci-go/client/logdog/butlerproto"
+	"github.com/luci/luci-go/common/gcloud/gcps"
+	"github.com/luci/luci-go/common/logdog/protocol"
+	log "github.com/luci/luci-go/common/logging"
+	"github.com/luci/luci-go/common/recordio"
+	"github.com/luci/luci-go/common/retry"
+	"golang.org/x/net/context"
+	"google.golang.org/cloud/pubsub"

[estaab, 2015/11/19 23:57:24]

I think some encapsulation is being broken here - gcps seems to be the interface
we want to use to interact with this package, not use it directly. Can you
possibly just add

package gcps

type Message struct {
  pubsub.Message
}

to gcps so we can remove this? If that's not valid go or against some idioms
then nevermind. :)

[dnj, 2015/11/20 01:55:12]

"gcps" package is never used outside of the pubsub package (and the CLI
interface to couple to it). I don't see the value in this abstraction.

[estaab, 2015/11/20 04:37:28]

Besides clean abstraction being a general good practice I can think of at least
one practical reason: if cloud ever releases a v2 API none of this code will
need to change, just luci-go/common/gcloud/gcps. Less likely: we switch to
another pubsub implementation. Since it's easy I'm not sure what the argument
against abstracting it is. I guess the only reason pubsub is abstracted at all
is for the testability of this file?

Perhaps leaky abstractions are more common in go since building is fast. In C++
or java you'd be able to run gcpsOutput_test without building any underlying
pubsub code, making binaries smaller and causing fewer tests to trigger when
doing an affected tests dependency calculation on a patch.

[dnj (Google), 2015/11/20 04:45:48]

Yeah, Pub/Sub abstraction is in place so we can test. This is directly bound to
the interface, and I'd kill the abstraction too if it weren't necessary to do
proper testing.

If Pub/Sub upgrades to a v2 API, this code may have to change, as will the
abstraction. It's a fairly dead-simple interface. If I built a "send this data
through Pub/Sub" interface, it'd basically be the Pub/Sub interface, so not much
to gain by shielding this code from it.

[estaab, 2015/11/20 05:15:48]

Ok, that's fine. I think it's a good habit but it seems reasonable to have a
thin abstraction for testability.

+)
+
+// Config is a configuration structure for GCPS output.
+type Config struct {
+	// Pubsub is the Pub/Sub instance to use.
+	PubSub gcps.PubSub
+
+	// Topic is the name of the Cloud Pub/Sub topic to publish to.
+	Topic gcps.Topic
+
+	// Compress, if true, enables zlib compression.
+	Compress bool
+}
+
+// Validate validates the Output configuration.
+func (c *Config) Validate() error {
+	if c.PubSub == nil {
+		return errors.New("gcps: no pub/sub instance configured")
+	}
+	if err := c.Topic.Validate(); err != nil {
+		return fmt.Errorf("gcps: invalid Topic [%s]: %s", c.Topic, err)
+	}
+	return nil
+}
+
+// gcpsBuffer
+type gcpsBuffer struct {
+	bytes.Buffer // Output buffer for published message data.
+
+	frameWriter recordio.Writer
+	protoWriter *butlerproto.Writer
+}
+
+// Butler Output that sends messages into Google Cloud PubSub as compressed
+// protocol buffer blobs.
+type gcpsOutput struct {
+	*Config
+
+	ctx        context.Context // Retained context object.
+	bufferPool sync.Pool       // Pool of reusable gcpsBuffer instances.
+
+	statsMu sync.Mutex
+	stats   output.StatsBase
+}
+
+// New instantiates a new GCPS output.
+func New(ctx context.Context, c Config) output.Output {
+	o := gcpsOutput{
+		Config: &c,
+		ctx:    ctx,
+	}
+	o.bufferPool.New = func() interface{} { return &gcpsBuffer{} }
+	o.ctx = log.SetField(o.ctx, "output", &o)
+	return &o
+}
+
+func (o *gcpsOutput) String() string {
+	return fmt.Sprintf("gcps(%s)", o.Topic)
+}
+
+func (o *gcpsOutput) SendBundle(bundle *protocol.ButlerLogBundle) error {
+	st := output.StatsBase{}
+	defer o.mergeStats(&st)
+
+	b := o.bufferPool.Get().(*gcpsBuffer)
+	defer o.bufferPool.Put(b)
+
+	message, err := o.buildMessage(b, bundle)
+	if err != nil {
+		log.Errorf(log.SetError(o.ctx, err), "Failed to build PubSub Message from bundle.")

[estaab, 2015/11/19 23:57:24]

Do the rules about lowercase first letter and no punctuation apply here?

[dnj, 2015/11/20 01:55:12]

Nope, this isn't a Go error, it's a logging error message.

+		st.F.DiscardedMessages++
+		st.F.Errors++
+		return err
+	}
+	if len(message.Data) > gcps.MaxPublishSize {
+		log.Fields{
+			"messageSize":   len(message.Data),
+			"maxPubSubSize": gcps.MaxPublishSize,
+		}.Errorf(o.ctx, "Constructed message exceeds Pub/Sub maximum size.")
+		return errors.New("gcps: bundle contents violate Pub/Sub size limit")
+	}
+	if err := o.publishMessages([]*pubsub.Message{message}); err != nil {
+		st.F.DiscardedMessages++
+		st.F.Errors++
+		return err
+	}
+
+	st.F.SentBytes += len(message.Data)
+	st.F.SentMessages++
+	return nil
+}
+
+func (*gcpsOutput) MaxSize() int {
+	return gcps.MaxPublishSize / 2
+}
+
+func (o *gcpsOutput) Stats() output.Stats {
+	o.statsMu.Lock()
+	defer o.statsMu.Unlock()
+
+	statsCopy := o.stats
+	return &statsCopy
+}
+
+func (o *gcpsOutput) Close() {
+	// Nothing to do.
+}
+
+// buildMessage constructs a Pub/Sub Message out of LogDog frames.
+//
+// The first frame will be a ButlerMetadata message describing the second
+// frame. The second frame will be a ButlerLogBundle containing the bundle
+// data.
+func (o *gcpsOutput) buildMessage(buf *gcpsBuffer, bundle *protocol.ButlerLogBundle) (*pubsub.Message, error) {
+	if buf.protoWriter == nil {
+		buf.protoWriter = &butlerproto.Writer{
+			Compress:          o.Compress,
+			CompressThreshold: butlerproto.DefaultCompressThreshold,
+		}
+	}
+
+	// Clear our buffer and (re)initialize our frame writer.
+	buf.Reset()
+	if buf.frameWriter == nil {
+		buf.frameWriter = recordio.NewWriter(buf)
+	} else {
+		buf.frameWriter.Reset(buf)
+	}
+
+	if err := buf.protoWriter.WriteWith(buf.frameWriter, bundle); err != nil {
+		return nil, err
+	}
+
+	return &pubsub.Message{
+		Data: buf.Bytes(),
+	}, nil
+}
+
+// publishMessages handles an individual publish request. It will indefinitely
+// retry transient errors until the publish succeeds.
+func (o *gcpsOutput) publishMessages(messages []*pubsub.Message) error {
+	var messageIDs []string
+	count := 0
+	err := retry.Retry(o.ctx, retry.TransientOnly(o.publishRetryIterator()), func() error {
+		ids, err := o.PubSub.Publish(o.Topic, messages...)
+		if err != nil {
+			return err
+		}
+		messageIDs = ids
+		return nil
+	}, func(err error, d time.Duration) {
+		log.Fields{
+			log.ErrorKey: err,
+			"count":      count,
+			"delay":      d,
+		}.Warningf(o.ctx, "Transient publish error; retrying.")
+		count++
+	})
+	if err != nil {
+		log.Errorf(log.SetError(o.ctx, err), "Failed to send PubSub message.")
+		return err
+	}
+
+	log.Debugf(log.SetField(o.ctx, "messageIds", messageIDs), "Published messages.")
+	return nil
+}
+
+func (o *gcpsOutput) mergeStats(s output.Stats) {
+	o.statsMu.Lock()
+	defer o.statsMu.Unlock()
+
+	o.stats.Merge(s)
+}
+
+// publishRetryIterator returns a retry.Iterator configured for publish
+// requests.
+//
+// Note that this iterator has no retry upper bound. It will continue retrying
+// indefinitely until success.
+func (*gcpsOutput) publishRetryIterator() retry.Iterator {
+	return &retry.ExponentialBackoff{
+		Limited: retry.Limited{
+			Delay: 500 * time.Millisecond,
+		},
+		Multiplier: 3.0,
+		MaxDelay:   15 * time.Second,
+	}
+}