LogDog: Fix archival Get/Tail implementations.

common/iotools/countingreader.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package iotools
 
 import (
         "io"
 )
 
 // CountingReader is an io.Reader that counts the number of bytes that are read.
 type CountingReader struct {
         io.Reader // The underlying io.Reader.
 
-        count int64
+        Count int64

[dnj, 2016/10/19 23:18:59]

This is trivial enough that I don't mind combining it. No reason not to offer
direct access to this, and I use it below to clear the count periodically.

 }
 
 var _ io.Reader = (*CountingReader)(nil)
 
 // Read implements io.Reader.
 func (c *CountingReader) Read(buf []byte) (int, error) {
         amount, err := c.Reader.Read(buf)
-        c.count += int64(amount)
+        c.Count += int64(amount)
         return amount, err
 }
 
 // ReadByte implements io.ByteReader.
 func (c *CountingReader) ReadByte() (byte, error) {
         // If our underlying reader is a ByteReader, use its ReadByte directly.
         if br, ok := c.Reader.(io.ByteReader); ok {
                 b, err := br.ReadByte()
                 if err == nil {
-                        c.count++
+                        c.Count++
                 }
                 return b, err
         }
 
         data := []byte{0}
         amount, err := c.Reader.Read(data)
         if amount != 0 {
-                c.count += int64(amount)
+                c.Count += int64(amount)
                 return data[0], err
         }
         return 0, err
 }
-
-// Count returns the number of bytes that have been read.
-func (c *CountingReader) Count() int64 {
-        return c.count
-}