LogDog: Add Butler Output package.

common/logdog/butlerproto/doc.go

 // 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 butlerproto implements the LogDog Butler wire protocol. This protocol
 // wraps Butler messages that are published to Cloud Pub/Sub for LogDog
 // consumption.
 //
 // The protocol begins with a set of header bytes to identify and parameterize
 // the remaining data, followed by the data itself.
 //
 // Note that the Pub/Sub layer is assumed to provide both a total length (so no
 // need to length-prefix) and integrity (so no need to checksum).
 //
 // Header
 //
 // The header is a fixed four bytes which positively identify the message as a
 // Butler Pub/Sub message and describe the remaining data. Variant parameters
 // can use different magic numbers to identify different parameters.
 //
 // Two magic numbers are currently defined:
 //   - 0x10 0x6d 0x06 0x00 (LogDog protocol ButlerLogBundle Raw)
 //   - 0x10 0x6d 0x06 0x62 (LogDog protocol ButlerLogBundle GZip compressed)
 //
 // Data
 //
 // The data component is described by the header, and consists of all data in
 // the Pub/Sub message past the last header byte.
 package butlerproto