cipd: Refactor client to make it more readable.

go/src/infra/tools/cipd/local/reader.go

 // Copyright 2014 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 cipd
+package local
 
 import (
         "archive/zip"
         "crypto/sha1"
         "encoding/hex"
         "fmt"
         "io"
         "io/ioutil"
         "os"
+
+        "infra/tools/cipd/common"
 )
 
 // PackageInstance represents a binary package file.
 type PackageInstance interface {
         // Close shuts down the package and its data provider.
         Close() error
-        // PackageName returns package name, as defined in the manifest.
-        PackageName() string
-        // InstanceID returns id that identifies particular built of the package. It's a hash of the package data.
-        InstanceID() string
+        // Pin identifies package name and concreted package instance ID of this package file.
+        Pin() common.Pin
         // Files returns a list of files inside the package.
         Files() []File
         // DataReader returns reader that reads raw package data.
         DataReader() io.ReadSeeker
 }
 
 // OpenInstance verifies package SHA1 hash (instanceID if not empty string) and
 // prepares a package instance for extraction. If the call succeeds,
 // PackageInstance takes ownership of io.ReadSeeker. If it also implements
 // io.Closer, it will be closed when package.Close() is called. If an error is
@@ skipping 144 matching lines @@
                 inst.data = nil
         }
         inst.dataSize = 0
         inst.instanceID = ""
         inst.zip = nil
         inst.files = []File{}
         inst.manifest = Manifest{}
         return nil
 }
 
-func (inst *packageInstance) InstanceID() string        { return inst.instanceID }
-func (inst *packageInstance) PackageName() string       { return inst.manifest.PackageName }
+func (inst *packageInstance) Pin() common.Pin {
+        return common.Pin{
+                PackageName: inst.manifest.PackageName,
+                InstanceID:  inst.instanceID,
+        }
+}
+
 func (inst *packageInstance) Files() []File             { return inst.files }
 func (inst *packageInstance) DataReader() io.ReadSeeker { return inst.data }
 
 ////////////////////////////////////////////////////////////////////////////////
 // Utilities.
 
 // readManifestFile decodes manifest file zipped inside the package.
 func readManifestFile(f File) (Manifest, error) {
         r, err := f.Open()
         if err != nil {
@@ skipping 59 matching lines @@
         r io.ReadSeeker
 }
 
 func (r *readerAt) ReadAt(data []byte, off int64) (int, error) {
         _, err := r.r.Seek(off, os.SEEK_SET)
         if err != nil {
                 return 0, err
         }
         return r.r.Read(data)
 }