cipd: Refactor client to make it more readable.

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

Index: go/src/infra/tools/cipd/local/manifest.go
diff --git a/go/src/infra/tools/cipd/local/manifest.go b/go/src/infra/tools/cipd/local/manifest.go
new file mode 100644
index 0000000000000000000000000000000000000000..5f7b0045fc59b7dae56b51849d41ca95fc856a96
--- /dev/null
+++ b/go/src/infra/tools/cipd/local/manifest.go
@@ -0,0 +1,53 @@
+// 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
+}