Adding upstream version 0.28.1.

Signed-off-by: Daniel Baumann <daniel@debian.org>

tools/filesystem/internal/fileblob/attrs.go

@@ -0,0 +1,84 @@
+package fileblob
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+// Largely copied from gocloud.dev/blob/fileblob to apply the same
+// retrieve and write side-car .attrs rules.
+//
+// -------------------------------------------------------------------
+// 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.
+// -------------------------------------------------------------------
+
+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()
+}