Address pull request comments

* Simplify scrypt constants with const block
* Add key store constructors and make their types private
* Simplify key store and file namings to be less Java Enterprise™
* Change test error logging to use t.Error(err)
* Reduce number of naked returns (just like my ex-gf)
* Simplify file reading path code

crypto/key_store_plain.go

@@ -0,0 +1,114 @@
+/*
+	This file is part of go-ethereum
+
+	go-ethereum is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Lesser General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	go-ethereum is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU Lesser General Public License
+	along with go-ethereum.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * @authors
+ * 	Gustav Simonsson <gustav.simonsson@gmail.com>
+ * @date 2015
+ *
+ */
+
+package crypto
+
+import (
+	"code.google.com/p/go-uuid/uuid"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/user"
+	"path"
+)
+
+// TODO: rename to KeyStore when replacing existing KeyStore
+type KeyStore2 interface {
+	GenerateNewKey(string) (*Key, error)     // create and store new key, optionally using auth string
+	GetKey(*uuid.UUID, string) (*Key, error) // key from id and auth string
+	StoreKey(*Key, string) error             // store key optionally using auth string
+	DeleteKey(*uuid.UUID, string) error      // delete key by id and auth string
+}
+
+type keyStorePlain struct {
+	keysDirPath string
+}
+
+// TODO: copied from cmd/ethereum/flags.go
+func DefaultDataDir() string {
+	usr, _ := user.Current()
+	return path.Join(usr.HomeDir, ".ethereum")
+}
+
+func NewKeyStorePlain(path string) KeyStore2 {
+	ks := new(keyStorePlain)
+	ks.keysDirPath = path
+	return ks
+}
+
+func (ks keyStorePlain) GenerateNewKey(auth string) (key *Key, err error) {
+	return GenerateNewKeyDefault(ks, auth)
+}
+
+func GenerateNewKeyDefault(ks KeyStore2, auth string) (key *Key, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("GenerateNewKey error: %v", r)
+		}
+	}()
+	key = NewKey()
+	err = ks.StoreKey(key, auth)
+	return key, err
+}
+
+func (ks keyStorePlain) GetKey(keyId *uuid.UUID, auth string) (key *Key, err error) {
+	fileContent, err := GetKeyFile(ks.keysDirPath, keyId)
+	if err != nil {
+		return nil, err
+	}
+
+	key = new(Key)
+	err = json.Unmarshal(fileContent, key)
+	return key, err
+}
+
+func (ks keyStorePlain) StoreKey(key *Key, auth string) (err error) {
+	keyJSON, err := json.Marshal(key)
+	if err != nil {
+		return err
+	}
+	err = WriteKeyFile(key.Id.String(), ks.keysDirPath, keyJSON)
+	return err
+}
+
+func (ks keyStorePlain) DeleteKey(keyId *uuid.UUID, auth string) (err error) {
+	keyDirPath := path.Join(ks.keysDirPath, keyId.String())
+	err = os.RemoveAll(keyDirPath)
+	return err
+}
+
+func GetKeyFile(keysDirPath string, keyId *uuid.UUID) (fileContent []byte, err error) {
+	id := keyId.String()
+	return ioutil.ReadFile(path.Join(keysDirPath, id, id))
+}
+
+func WriteKeyFile(id string, keysDirPath string, content []byte) (err error) {
+	keyDirPath := path.Join(keysDirPath, id)
+	keyFilePath := path.Join(keyDirPath, id)
+	err = os.MkdirAll(keyDirPath, 0700) // read, write and dir search for user
+	if err != nil {
+		return err
+	}
+	return ioutil.WriteFile(keyFilePath, content, 0600) // read, write for user
+}