Jun 23, 2025 · Jun 24, 2025 · Jun 24, 2025 · Jun 24, 2025 · Jun 24, 2025 · Jun 24, 2025
diff --git a/coderd/files/cache.go b/coderd/files/cache.go
 "context"
 "io/fs"
 "sync"
 "sync/atomic"

 "github.com/google/uuid"
 "github.com/prometheus/client_golang/prometheus"

 // New returns a file cache that will fetch files from a database
 func New(registerer prometheus.Registerer, authz rbac.Authorizer) *Cache {
 return (&Cache{
 lock:  sync.Mutex{},
 data:  make(map[uuid.UUID]*cacheEntry),
 authz: authz,
 }).registerMetrics(registerer)
 return &Cache{
 lock:         sync.Mutex{},
 data:         make(map[uuid.UUID]*cacheEntry),
 authz:        authz,
 cacheMetrics: newCacheMetrics(registerer),
 }
 }

 func(c *Cache) registerMetrics(registerer prometheus.Registerer)*Cache {
 funcnewCacheMetrics(registerer prometheus.Registerer)cacheMetrics {
 subsystem := "file_cache"
 f := promauto.With(registerer)

 c.currentCacheSize = f.NewGauge(prometheus.GaugeOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_size_bytes_current",
 Help:      "The current amount of memory of all files currently open in the file cache.",
 })

 c.totalCacheSize = f.NewCounter(prometheus.CounterOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_size_bytes_total",
 Help:      "The total amount of memory ever opened in the file cache. This number never decrements.",
 })

 c.currentOpenFiles = f.NewGauge(prometheus.GaugeOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_current",
 Help:      "The count of unique files currently open in the file cache.",
 })

 c.totalOpenedFiles = f.NewCounter(prometheus.CounterOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_total",
 Help:      "The total count of unique files ever opened in the file cache.",
 })

 c.currentOpenFileReferences = f.NewGauge(prometheus.GaugeOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_file_refs_current",
 Help:      "The count of file references currently open in the file cache. Multiple references can be held for the same file.",
 })

 c.totalOpenFileReferences = f.NewCounterVec(prometheus.CounterOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_file_refs_total",
 Help:      "The total number of file references ever opened in the file cache. The 'hit' label indicates if the file was loaded from the cache.",
 }, []string{"hit"})

 return c
 return cacheMetrics{
 currentCacheSize: f.NewGauge(prometheus.GaugeOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_size_bytes_current",
 Help:      "The current amount of memory of all files currently open in the file cache.",
 }),

 totalCacheSize: f.NewCounter(prometheus.CounterOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_size_bytes_total",
 Help:      "The total amount of memory ever opened in the file cache. This number never decrements.",
 }),

 currentOpenFiles: f.NewGauge(prometheus.GaugeOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_current",
 Help:      "The count of unique files currently open in the file cache.",
 }),

 totalOpenedFiles: f.NewCounter(prometheus.CounterOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_files_total",
 Help:      "The total count of unique files ever opened in the file cache.",
 }),

 currentOpenFileReferences: f.NewGauge(prometheus.GaugeOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_file_refs_current",
 Help:      "The count of file references currently open in the file cache. Multiple references can be held for the same file.",
 }),

 totalOpenFileReferences: f.NewCounterVec(prometheus.CounterOpts{
 Namespace: "coderd",
 Subsystem: subsystem,
 Name:      "open_file_refs_total",
 Help:      "The total number of file references ever opened in the file cache. The 'hit' label indicates if the file was loaded from the cache.",
 }, []string{"hit"}),
 }
 }

 // Cache persists the files for template versions, and is used by dynamic
 totalCacheSize   prometheus.Counter
 }

 type cacheEntry struct {
 refCount atomic.Int32
 value    *lazy.ValueWithError[CacheEntryValue]

 close func()
 purge func()
 }

 type CacheEntryValue struct {
 fs.FS
 Object rbac.Object
 Size   int64
 }

 type cacheEntry struct {
 // refCount must only be accessed while the Cache lock is held.
 refCount int
 value    *lazy.ValueWithError[CacheEntryValue]
 }

 var _ fs.FS = (*CloseFS)(nil)

 // CloseFS is a wrapper around fs.FS that implements io.Closer. The Close()
 // mutex has been released, or we would continue to hold the lock until the
 // entire file has been fetched, which may be slow, and would prevent other
 // files from being fetched in parallel.
 it, err := c.prepare(ctx, db, fileID).Load()
 e := c.prepare(db, fileID)
 ev, err := e.value.Load()
 if err != nil {
 c.release(fileID)
 e.close()
 e.purge()
 return nil, err
 }

 // We always run the fetch under a system context and actor, so we need to check the caller's
 // context manually before returning.

 // Check if the caller's context was canceled
 if err := ctx.Err(); err != nil {
 e.close()
 return nil, err
 }

 // Check that the caller is authorized to access the file
 subject, ok := dbauthz.ActorFromContext(ctx)
 if !ok {
 e.close()
 return nil, dbauthz.ErrNoActor
 }
 // Always check the caller can actually read the file.
 if err := c.authz.Authorize(ctx, subject, policy.ActionRead, it.Object); err != nil {
 c.release(fileID)
 if err := c.authz.Authorize(ctx, subject, policy.ActionRead, ev.Object); err != nil {
 e.close()
 return nil, err
 }

 varonce sync.Once
 varcloseOnce sync.Once
 return &CloseFS{
 FS:it.FS,
 FS:ev.FS,
 close: func() {
 // sync.Once makes the Close() idempotent, so we can call it
 // multiple times without worrying about double-releasing.
 once.Do(func() { c.release(fileID) })
 closeOnce.Do(func() {
 e.close()
 })
 },
 }, nil
 }

 func (c *Cache) prepare(ctx context.Context,db database.Store, fileID uuid.UUID) *lazy.ValueWithError[CacheEntryValue] {
 func (c *Cache) prepare(db database.Store, fileID uuid.UUID) *cacheEntry {
 c.lock.Lock()
 defer c.lock.Unlock()

 hitLabel := "true"
 entry, ok := c.data[fileID]
 if !ok {
 value := lazy.NewWithError(func() (CacheEntryValue, error) {
 val, err := fetch(ctx, db, fileID)
 hitLabel = "false"

 // Always add to the cache size the bytes of the file loaded.
 if err == nil {
 var purgeOnce sync.Once
 entry = &cacheEntry{
 value: lazy.NewWithError(func() (CacheEntryValue, error) {
 val, err := fetch(db, fileID)
 if err != nil {
 return val, err
 }

 // Add the size of the file to the cache size metrics.
 c.currentCacheSize.Add(float64(val.Size))
 c.totalCacheSize.Add(float64(val.Size))
 }

 return val, err
 })

 entry = &cacheEntry{
 value:    value,
 refCount: 0,
 return val, err
 }),

 close: func() {
 entry.refCount.Add(-1)
 c.currentOpenFileReferences.Dec()
 // Safety: Another thread could grab a reference to this value between
 // this check and entering `purge`, which will grab the cache lock. This
 // is annoying, and may lead to temporary duplication of the file in
 // memory, but is better than the deadlocking potential of other
 // approaches we tried to solve this.
 if entry.refCount.Load() > 0 {
 return
 }

 entry.purge()
 },

 purge: func() {
 purgeOnce.Do(func() {
 c.purge(fileID)
 })
 },
 }
 c.data[fileID] = entry

 c.currentOpenFiles.Inc()
 c.totalOpenedFiles.Inc()
 hitLabel = "false"
 }

 c.currentOpenFileReferences.Inc()
 c.totalOpenFileReferences.WithLabelValues(hitLabel).Inc()
 entry.refCount++
 return entry.value
 entry.refCount.Add(1)
 return entry
 }

 // release decrements the reference count for the given fileID, and frees the
 // backing data if there are no further references being held.
 //
 // release should only be called after a successful call to Acquire using the Release()
 // method on the returned *CloseFS.
 func (c *Cache) release(fileID uuid.UUID) {
 // purge immediately removes an entry from the cache, even if it has open
 // references.
 func (c *Cache) purge(fileID uuid.UUID) {
 c.lock.Lock()
 defer c.lock.Unlock()

 entry, ok := c.data[fileID]
 if !ok {
 // If we land here, it's almost certainly because a bug already happened,
 // and we're freeing something that's already been freed, or we're calling
 // this function with an incorrect ID. Should this function return an error?
 return
 }

 c.currentOpenFileReferences.Dec()
 entry.refCount--
 if entry.refCount > 0 {
 // If we land here, it's probably because of a fetch attempt that
 // resulted in an error, and got purged already. It may also be an
 // erroneous extra close, but we can't really distinguish between those
 // two cases currently.
 return
 }

 // Purge the file from the cache.
 c.currentOpenFiles.Dec()

 ev, err := entry.value.Load()
 if err == nil {
 c.currentCacheSize.Add(-1 * float64(ev.Size))
 return len(c.data)
 }

 func fetch(ctx context.Context, store database.Store, fileID uuid.UUID) (CacheEntryValue, error) {
 // Make sure the read does not fail due to authorization issues.
 // Authz is checked on the Acquire call, so this is safe.
 func fetch(store database.Store, fileID uuid.UUID) (CacheEntryValue, error) {
 // Because many callers can be waiting on the same file fetch concurrently, we
 // want to prevent any failures that would cause them all to receive errors
 // because the caller who initiated the fetch would fail.
 // - We always run the fetch with an uncancelable context, and then check
 //   context cancellation for each acquirer afterwards.
 // - We always run the fetch as a system user, and then check authorization
 //   for each acquirer afterwards.
 // This prevents a canceled context or an unauthorized user from "holding up
 // the queue".
 //nolint:gocritic
 file, err := store.GetFileByID(dbauthz.AsFileReader(ctx), fileID)
 file, err := store.GetFileByID(dbauthz.AsFileReader(context.Background()), fileID)
 if err != nil {
 return CacheEntryValue{}, xerrors.Errorf("failed to read file from database: %w", err)
 }