| // Copyright 2022 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Package cache implements a simple file-based cache. |
| package cache |
| |
| import ( |
| "fmt" |
| "io" |
| "os" |
| "path/filepath" |
| "time" |
| ) |
| |
| // A Cache is a directory holding cached data. |
| type Cache struct { |
| dir string |
| disabled bool |
| } |
| |
| // Disabled returns a Cache that is always empty. |
| // Reads always return no result, and writes succeed but are discarded. |
| func Disabled() *Cache { |
| return &Cache{disabled: true} |
| } |
| |
| // Create returns a cache using the named subdirectory |
| // of the user's cache directory. |
| // For example, on macOS, Create("myprog") uses $HOME/Library/Caches/myprog. |
| // Create creates the directory if it does not already exist. |
| func Create(name string) (*Cache, error) { |
| dir, err := os.UserCacheDir() |
| if err != nil { |
| return nil, err |
| } |
| dir = filepath.Join(dir, name) |
| if err := os.MkdirAll(dir, 0777); err != nil { |
| return nil, err |
| } |
| return &Cache{dir: dir}, nil |
| } |
| |
| // Read reads the file with the given name in the cache. |
| // It returns the file content, its last modification time, |
| // and any error encountered. |
| // If the file does not exist in the cache, Read returns nil, time.Time{}, nil. |
| func (c *Cache) Read(name string) ([]byte, time.Time, error) { |
| if c.disabled { |
| return nil, time.Time{}, nil |
| } |
| if c.dir == "" { |
| return nil, time.Time{}, fmt.Errorf("use of zero Cache") |
| } |
| f, err := os.Open(filepath.Join(c.dir, name)) |
| if err != nil { |
| if os.IsNotExist(err) { |
| err = nil |
| } |
| return nil, time.Time{}, err |
| } |
| defer f.Close() |
| info, err := f.Stat() |
| if err != nil { |
| return nil, time.Time{}, err |
| } |
| data, err := io.ReadAll(f) |
| if err != nil { |
| return nil, time.Time{}, err |
| } |
| return data, info.ModTime(), nil |
| } |
| |
| // Write writes data to the file with the given name in the cache. |
| func (c *Cache) Write(name string, data []byte) error { |
| if c.disabled { |
| return nil |
| } |
| if c.dir == "" { |
| return fmt.Errorf("use of zero Cache") |
| } |
| return os.WriteFile(filepath.Join(c.dir, name), data, 0666) |
| } |