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// Copyright 2018 The Go Cloud Development Kit Authors
//
// 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
//
// https://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 fileblob
import (
"encoding/json"
"fmt"
"os"
)
const attrsExt = ".attrs"
var errAttrsExt = fmt.Errorf("file extension %q is reserved", attrsExt)
// xattrs stores extended attributes for an object. The format is like
// filesystem extended attributes, see
// https://www.freedesktop.org/wiki/CommonExtendedAttributes.
type xattrs struct {
CacheControl string `json:"user.cache_control"`
ContentDisposition string `json:"user.content_disposition"`
ContentEncoding string `json:"user.content_encoding"`
ContentLanguage string `json:"user.content_language"`
ContentType string `json:"user.content_type"`
Metadata map[string]string `json:"user.metadata"`
MD5 []byte `json:"md5"`
}
// setAttrs creates a "path.attrs" file along with blob to store the attributes,
// it uses JSON format.
func setAttrs(path string, xa xattrs) error {
f, err := os.Create(path + attrsExt)
if err != nil {
return err
}
if err := json.NewEncoder(f).Encode(xa); err != nil {
f.Close()
os.Remove(f.Name())
return err
}
return f.Close()
}
// getAttrs looks at the "path.attrs" file to retrieve the attributes and
// decodes them into a xattrs struct. It doesn't return error when there is no
// such .attrs file.
func getAttrs(path string) (xattrs, error) {
f, err := os.Open(path + attrsExt)
if err != nil {
if os.IsNotExist(err) {
// Handle gracefully for non-existent .attr files.
return xattrs{
ContentType: "application/octet-stream",
}, nil
}
return xattrs{}, err
}
xa := new(xattrs)
if err := json.NewDecoder(f).Decode(xa); err != nil {
f.Close()
return xattrs{}, err
}
return *xa, f.Close()
}
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