quick: Add yaml format support (#3833)

quick Save() and Load() infers config file's format from
file name extension.

pkg/quick/encoding.go

@@ -0,0 +1,142 @@
+/*
+ * Quick - Quick key value store for config files and persistent state files
+ *
+ * Quick (C) 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package quick
+
+import (
+	"bytes"
+	"encoding/json"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+
+	yaml "gopkg.in/yaml.v2"
+)
+
+// ConfigEncoding is a generic interface which
+// marshal/unmarshal configuration.
+type ConfigEncoding interface {
+	Unmarshal([]byte, interface{}) error
+	Marshal(interface{}) ([]byte, error)
+}
+
+// YAML encoding implements ConfigEncoding
+type yamlEncoding struct{}
+
+func (y yamlEncoding) Unmarshal(b []byte, v interface{}) error {
+	return yaml.Unmarshal(b, v)
+}
+
+func (y yamlEncoding) Marshal(v interface{}) ([]byte, error) {
+	return yaml.Marshal(v)
+}
+
+// JSON encoding implements ConfigEncoding
+type jsonEncoding struct{}
+
+func (j jsonEncoding) Unmarshal(b []byte, v interface{}) error {
+	err := json.Unmarshal(b, v)
+	if err != nil {
+		// Try to return a sophisticated json error message if possible
+		switch err := err.(type) {
+		case *json.SyntaxError:
+			return FormatJSONSyntaxError(bytes.NewReader(b), err)
+		default:
+			return err
+		}
+	}
+	return nil
+}
+
+func (j jsonEncoding) Marshal(v interface{}) ([]byte, error) {
+	return json.MarshalIndent(v, "", "\t")
+}
+
+// Convert a file extension to the appropriate struct capable
+// to marshal/unmarshal data
+func ext2EncFormat(fileExtension string) ConfigEncoding {
+	// Lower the file extension
+	ext := strings.ToLower(fileExtension)
+	ext = strings.TrimPrefix(ext, ".")
+	// Return the appropriate encoder/decoder according
+	// to the extension
+	switch ext {
+	case "yml", "yaml":
+		// YAML
+		return yamlEncoding{}
+	default:
+		// JSON
+		return jsonEncoding{}
+	}
+}
+
+// toMarshaller returns the right marshal function according
+// to the given file extension
+func toMarshaller(ext string) func(interface{}) ([]byte, error) {
+	return ext2EncFormat(ext).Marshal
+}
+
+// toUnmarshaller returns the right marshal function according
+// to the given file extension
+func toUnmarshaller(ext string) func([]byte, interface{}) error {
+	return ext2EncFormat(ext).Unmarshal
+}
+
+// saveFileConfig marshals with the right encoding format
+// according to the filename extension, if no extension is
+// provided, json will be selected.
+func saveFileConfig(filename string, v interface{}) error {
+	// Fetch filename's extension
+	ext := filepath.Ext(filename)
+	// Marshal data
+	dataBytes, err := toMarshaller(ext)(v)
+	if err != nil {
+		return err
+	}
+	if runtime.GOOS == "windows" {
+		dataBytes = []byte(strings.Replace(string(dataBytes), "\n", "\r\n", -1))
+	}
+	// Save data.
+	return writeFile(filename, dataBytes)
+
+}
+
+// loadFileConfig unmarshals the file's content with the right
+// decoder format according to the filename extension. If no
+// extension is provided, json will be selected by default.
+func loadFileConfig(filename string, v interface{}) error {
+	_, err := os.Stat(filename)
+	if err != nil {
+		return err
+	}
+	fileData, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return err
+	}
+	if runtime.GOOS == "windows" {
+		fileData = []byte(strings.Replace(string(fileData), "\r\n", "\n", -1))
+	}
+	ext := filepath.Ext(filename)
+	// Unmarshal file's content
+	if err := toUnmarshaller(ext)(fileData, v); err != nil {
+		return err
+	}
+	return nil
+}