1	/*
     2	Copyright 2012 The Perkeep Authors
     3	
     4	Licensed under the Apache License, Version 2.0 (the "License");
     5	you may not use this file except in compliance with the License.
     6	You may obtain a copy of the License at
     7	
     8	     http://www.apache.org/licenses/LICENSE-2.0
     9	
    10	Unless required by applicable law or agreed to in writing, software
    11	distributed under the License is distributed on an "AS IS" BASIS,
    12	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13	See the License for the specific language governing permissions and
    14	limitations under the License.
    15	*/
    16	
    17	/*
    18	Package local implements functionality common to both the "localdisk" and
    19	"diskpacked" storage mechanisms.
    20	*/
    21	package local // import "perkeep.org/pkg/blobserver/local"
    22	
    23	import (
    24		"bytes"
    25		"crypto/rand"
    26		"fmt"
    27		"io"
    28		"os"
    29		"path/filepath"
    30		"time"
    31	)
    32	
    33	type Generationer struct {
    34		root string
    35	}
    36	
    37	// NewGenerationer returns a struct for implementing blobserver.Generationer
    38	func NewGenerationer(rootDir string) *Generationer {
    39		return &Generationer{rootDir}
    40	}
    41	
    42	func (g Generationer) generationFile() string {
    43		return filepath.Join(g.root, "GENERATION.dat")
    44	}
    45	
    46	// StorageGeneration returns the generation's initialization time,
    47	// and the random string. If the GENERATION.dat file does not exist under
    48	// root yet, then creates it now (by calling ResetGeneration).
    49	func (g Generationer) StorageGeneration() (initTime time.Time, random string, err error) {
    50		f, err := os.Open(g.generationFile())
    51		if os.IsNotExist(err) {
    52			if err = g.ResetStorageGeneration(); err != nil {
    53				return
    54			}
    55			f, err = os.Open(g.generationFile())
    56		}
    57		if err != nil {
    58			return
    59		}
    60		defer f.Close()
    61		bs, err := io.ReadAll(f)
    62		if err != nil {
    63			return
    64		}
    65		if i := bytes.IndexByte(bs, '\n'); i != -1 {
    66			bs = bs[:i]
    67		}
    68		if fi, err := f.Stat(); err == nil {
    69			initTime = fi.ModTime()
    70		}
    71		random = string(bs)
    72		return
    73	}
    74	
    75	// ResetStorageGeneration reinitializes the generation by recreating the
    76	// GENERATION.dat file with a new random string
    77	func (g Generationer) ResetStorageGeneration() error {
    78		var buf bytes.Buffer
    79		if _, err := io.CopyN(&buf, rand.Reader, 20); err != nil {
    80			return err
    81		}
    82		hex := fmt.Sprintf("%x", buf.Bytes())
    83		buf.Reset()
    84		buf.WriteString(hex)
    85		buf.WriteString(`
    86	
    87	This file's random string on the first line is an optimization and
    88	paranoia facility for clients.
    89	
    90	If the client sees the same random string in multiple upload sessions,
    91	it assumes that the blobserver still has all the same blobs, and also
    92	it's the same server.  This mechanism is not fundamental to
    93	Perkeep's operation: the client could also check each blob before
    94	uploading, or enumerate all blobs from the server too.  This is purely
    95	an optimization so clients can mix this value into their "is this file
    96	uploaded?" local cache keys.
    97	
    98	If you deleted any blobs (or suspect any were corrupted), it's best to
    99	delete this file so clients can safely re-upload them.
   100	
   101	`)
   102	
   103		return os.WriteFile(g.generationFile(), buf.Bytes(), 0644)
   104	}