github.com/SaurabhDubey-Groww/go-cloud@v0.0.0-20221124105541-b26c29285fd8/blob/fileblob/attrs.go (about)

     1  // Copyright 2018 The Go Cloud Development Kit Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     https://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package fileblob
    16  
    17  import (
    18  	"encoding/json"
    19  	"fmt"
    20  	"os"
    21  )
    22  
    23  const attrsExt = ".attrs"
    24  
    25  var errAttrsExt = fmt.Errorf("file extension %q is reserved", attrsExt)
    26  
    27  // xattrs stores extended attributes for an object. The format is like
    28  // filesystem extended attributes, see
    29  // https://www.freedesktop.org/wiki/CommonExtendedAttributes.
    30  type xattrs struct {
    31  	CacheControl       string            `json:"user.cache_control"`
    32  	ContentDisposition string            `json:"user.content_disposition"`
    33  	ContentEncoding    string            `json:"user.content_encoding"`
    34  	ContentLanguage    string            `json:"user.content_language"`
    35  	ContentType        string            `json:"user.content_type"`
    36  	Metadata           map[string]string `json:"user.metadata"`
    37  	MD5                []byte            `json:"md5"`
    38  }
    39  
    40  // setAttrs creates a "path.attrs" file along with blob to store the attributes,
    41  // it uses JSON format.
    42  func setAttrs(path string, xa xattrs) error {
    43  	f, err := os.Create(path + attrsExt)
    44  	if err != nil {
    45  		return err
    46  	}
    47  	if err := json.NewEncoder(f).Encode(xa); err != nil {
    48  		f.Close()
    49  		os.Remove(f.Name())
    50  		return err
    51  	}
    52  	return f.Close()
    53  }
    54  
    55  // getAttrs looks at the "path.attrs" file to retrieve the attributes and
    56  // decodes them into a xattrs struct. It doesn't return error when there is no
    57  // such .attrs file.
    58  func getAttrs(path string) (xattrs, error) {
    59  	f, err := os.Open(path + attrsExt)
    60  	if err != nil {
    61  		if os.IsNotExist(err) {
    62  			// Handle gracefully for non-existent .attr files.
    63  			return xattrs{
    64  				ContentType: "application/octet-stream",
    65  			}, nil
    66  		}
    67  		return xattrs{}, err
    68  	}
    69  	xa := new(xattrs)
    70  	if err := json.NewDecoder(f).Decode(xa); err != nil {
    71  		f.Close()
    72  		return xattrs{}, err
    73  	}
    74  	return *xa, f.Close()
    75  }