LogDog: Add Butler Output package.

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

Index: client/internal/logdog/butler/output/output.go
diff --git a/client/internal/logdog/butler/output/output.go b/client/internal/logdog/butler/output/output.go
new file mode 100644
index 0000000000000000000000000000000000000000..e59a00bbc761e06f8c80738ea2c4707ad4cc87cb
--- /dev/null
+++ b/client/internal/logdog/butler/output/output.go
@@ -0,0 +1,102 @@
+// 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 output
+
+import (
+	"fmt"
+
+	"github.com/luci/luci-go/common/logdog/protocol"
+)
+
+// Output is a sink endpoint for groups of messages.
+//
+// An Output's methods must be goroutine-safe.
+//
+// Note that there is no guarantee that any of the bundles passed through an
+// Output are ordered.
+type Output interface {
+	// SendBundle sends a constructed ButlerLogBundle through the Output.
+	//
+	// If an error is returned, it indicates a failure to send the bundle.
+	// If there is a data error or a message type is not supported by the
+	// Output, it should log the error and return nil.
+	SendBundle(*protocol.ButlerLogBundle) error
+
+	// MaxSize returns the maximum number of bytes that this Output can process
+	// with a single send. A return value <=0 indicates that there si no fixed
+	// maximum size for this Output.
+	//
+	// Since it is impossible for callers to know the actual size of the message
+	// that is being submitted, and since message batching may cluster across
+	// size boundaries, this should be a conservative estimate.
+	MaxSize() int
+
+	// Collect current Output stats.
+	Stats() Stats
+
+	// Close closes the Output, blocking until any buffered actions are flushed.
+	Close()
+}
+
+// Stats is an interface to query Output statistics.
+//
+// An Output's ability to keep statistics varies with its implementation
+// details. Currently, Stats are for debugging/information purposes only.
+type Stats interface {
+	fmt.Stringer
+
+	// SentBytes returns the number of bytes
+	SentBytes() int
+	// SentMessages returns the number of successfully transmitted messages.
+	SentMessages() int
+	// DiscardedMessages returns the number of discarded messages.
+	DiscardedMessages() int
+	// Errors returns the number of errors encountered during operation.
+	Errors() int
+}
+
+// StatsBase is a simple implementation of the Stats interface.
+type StatsBase struct {
+	F struct {
+		SentBytes         int // The number of bytes sent.
+		SentMessages      int // The number of messages sent.
+		DiscardedMessages int // The number of messages that have been discarded.
+		Errors            int // The number of errors encountered.
+	}
+}
+
+var _ Stats = (*StatsBase)(nil)
+
+func (s *StatsBase) String() string {
+	return fmt.Sprintf("%+v", s.F)
+}
+
+// SentBytes implements Stas.
+func (s *StatsBase) SentBytes() int {
+	return s.F.SentBytes
+}
+
+// SentMessages implements Stas.
+func (s *StatsBase) SentMessages() int {
+	return s.F.SentMessages
+}
+
+// DiscardedMessages implements Stas.
+func (s *StatsBase) DiscardedMessages() int {
+	return s.F.DiscardedMessages
+}
+
+// Errors implements Stas.
+func (s *StatsBase) Errors() int {
+	return s.F.Errors
+}
+
+// Merge merges the values from one Stats block into another.
+func (s *StatsBase) Merge(o Stats) {
+	s.F.SentBytes += o.SentBytes()
+	s.F.SentMessages += o.SentMessages()
+	s.F.DiscardedMessages += o.DiscardedMessages()
+	s.F.Errors += o.Errors()
+}