cipd: Refactor client to make it more readable.

go/src/infra/tools/cipd/local/manifest.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 local
+
+import (
+        "encoding/json"
+        "io"
+        "io/ioutil"
+)
+
+// Name of the directory inside an installation root reserved for cipd stuff.
+const SiteServiceDir = ".cipd"
+
+// Name of the directory inside the package reserved for cipd stuff.
+const packageServiceDir = ".cipdpkg"
+
+// Name of the manifest file inside the package.
+const manifestName = packageServiceDir + "/manifest.json"
+
+// Format version to write to the manifest file.
+const manifestFormatVersion = "1"
+
+// Manifest defines structure of manifest.json file.
+type Manifest struct {
+        FormatVersion string `json:"format_version"`
+        PackageName   string `json:"package_name"`
+}
+
+// readManifest reads and decodes manifest JSON from io.Reader.
+func readManifest(r io.Reader) (Manifest, error) {

[nodir, 2015/05/13 01:25:29]

nit: if you give names to return values, there will be less code in this func

[Vadim Sh., 2015/05/13 03:08:06]

Done.

+        blob, err := ioutil.ReadAll(r)
+        if err != nil {
+                return Manifest{}, err
+        }
+        manifest := Manifest{}
+        err = json.Unmarshal(blob, &manifest)
+        if err != nil {
+                return Manifest{}, err
+        }
+        return manifest, nil
+}
+
+// writeManifest encodes and writes manifest JSON to io.Writer.
+func writeManifest(m *Manifest, w io.Writer) error {

[nodir, 2015/05/13 01:25:29]

How do you judge whether a func should be a method or a func?

[Vadim Sh., 2015/05/13 03:08:06]

I flip a coin...

Basically, for immutable types I prefer functions. For stateful types - methods.

+        data, err := json.MarshalIndent(m, "", "  ")
+        if err != nil {
+                return err
+        }
+        _, err = w.Write(data)
+        return err
+}