github.com/google/trillian-examples@v0.0.0-20240520080811-0d40d35cef0e/binary_transparency/firmware/cmd/ft_witness/internal/ws/store.go (about)

     1  // Copyright 2021 Google LLC. All Rights Reserved.
     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  //     http://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 ws contains a Witness Store backed by a file.
    16  package ws
    17  
    18  import (
    19  	"fmt"
    20  	"os"
    21  	"sync"
    22  )
    23  
    24  const (
    25  	fileMask = 0755
    26  )
    27  
    28  // Storage is a Witness Storage intended for storing witness checkpoints.
    29  // Currently a simple file is used as a storage mechanism
    30  type Storage struct {
    31  	fp        string
    32  	storeLock sync.Mutex
    33  }
    34  
    35  // NewStorage creates a new WS that uses the given file as DB backend.
    36  // The DB will be initialized if needed.
    37  func NewStorage(fp string) (*Storage, error) {
    38  	ws := &Storage{
    39  		fp: fp,
    40  	}
    41  	return ws, ws.init()
    42  }
    43  
    44  // init creates the file storage
    45  func (ws *Storage) init() error {
    46  	// Check if the file exists, if not create one
    47  	f, err := os.OpenFile(ws.fp, os.O_RDWR|os.O_CREATE, os.ModePerm)
    48  	if err != nil {
    49  		return fmt.Errorf("failed to open file: %w", err)
    50  	}
    51  	if err := f.Close(); err != nil {
    52  		return fmt.Errorf("failed to close file: %w", err)
    53  	}
    54  	return nil
    55  }
    56  
    57  // StoreCP saves the given checkpoint into DB.
    58  func (ws *Storage) StoreCP(wcp []byte) error {
    59  	ws.storeLock.Lock()
    60  	defer ws.storeLock.Unlock()
    61  
    62  	return os.WriteFile(ws.fp, wcp, fileMask)
    63  }
    64  
    65  // RetrieveCP gets the checkpoint previously stored.
    66  func (ws *Storage) RetrieveCP() ([]byte, error) {
    67  	ws.storeLock.Lock()
    68  	defer ws.storeLock.Unlock()
    69  	return os.ReadFile(ws.fp)
    70  }