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package dirivcache
import (
"log"
"strings"
"sync"
"time"
)
const (
maxEntries = 100
expireTime = 1 * time.Second
)
type cacheEntry struct {
// DirIV of the directory.
iv []byte
// Relative ciphertext path of the directory.
cDir string
}
// DirIVCache stores up to "maxEntries" directory IVs.
type DirIVCache struct {
// data in the cache, indexed by relative plaintext path
// of the directory.
data map[string]cacheEntry
// The DirIV of the root directory gets special treatment because it
// cannot change (the root directory cannot be renamed or deleted).
// It is unaffected by the expiry timer and cache clears.
rootDirIV []byte
// expiry is the time when the whole cache expires.
// The cached entry might become out-of-date if the ciphertext directory is
// modified behind the back of gocryptfs. Having an expiry time limits the
// inconstancy to one second, like attr_timeout does for the kernel
// getattr cache.
expiry time.Time
sync.RWMutex
}
// Lookup - fetch entry for "dir" (relative plaintext path) from the cache.
// Returns the directory IV and the relative encrypted path, or (nil, "")
// if the entry was not found.
func (c *DirIVCache) Lookup(dir string) (iv []byte, cDir string) {
c.RLock()
defer c.RUnlock()
if dir == "" {
return c.rootDirIV, ""
}
if c.data == nil {
return nil, ""
}
if time.Since(c.expiry) > 0 {
c.data = nil
return nil, ""
}
v := c.data[dir]
return v.iv, v.cDir
}
// Store - write an entry for directory "dir" into the cache.
// Arguments:
// dir ... relative plaintext path
// iv .... directory IV
// cDir .. relative ciphertext path
func (c *DirIVCache) Store(dir string, iv []byte, cDir string) {
c.Lock()
defer c.Unlock()
if dir == "" {
c.rootDirIV = iv
}
// Sanity check: plaintext and chiphertext paths must have the same number
// of segments
if strings.Count(dir, "/") != strings.Count(cDir, "/") {
log.Panicf("inconsistent number of path segments: dir=%q cDir=%q", dir, cDir)
}
// Clear() may have cleared c.data: re-initialize
if c.data == nil {
c.data = make(map[string]cacheEntry, maxEntries)
// Set expiry time one second into the future
c.expiry = time.Now().Add(expireTime)
}
// Delete a random entry from the map if reached maxEntries
if len(c.data) >= maxEntries {
for k := range c.data {
delete(c.data, k)
break
}
}
c.data[dir] = cacheEntry{iv, cDir}
}
// Clear ... clear the cache.
// Called from fusefrontend when directories are renamed or deleted.
func (c *DirIVCache) Clear() {
c.Lock()
defer c.Unlock()
// Will be re-initialized in the next Store()
c.data = nil
}
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