Method Load

internal/backend/cache/backend.go:154–197

Load loads a file from the cache or the backend.

(ctx context.Context, h backend.Handle, length int, offset int64, consumer func(rd io.Reader) error)

// Load loads a file from the cache or the backend.
func (b *Backend) Load(ctx context.Context, h backend.Handle, length int, offset int64, consumer func(rd io.Reader) error) error {
	b.inProgressMutex.Lock()
	waitForFinish, inProgress := b.inProgress[h]
	b.inProgressMutex.Unlock()

	if inProgress {
		debug.Log("downloading %v is already in progress, waiting for finish", h)
		<-waitForFinish
		debug.Log("downloading %v finished", h)
	}

	// try loading from cache without checking that the handle is actually cached
	inCache, err := b.loadFromCache(h, length, offset, consumer)
	if inCache {
		if err != nil {
			debug.Log("error loading %v from cache: %v", h, err)
		}
		// the caller must explicitly use cache.Forget() to remove the cache entry
		return err
	}

	// if we don't automatically cache this file type, fall back to the backend
	if !autoCacheTypes(h) {
		debug.Log("Load(%v, %v, %v): delegating to backend", h, length, offset)
		return b.Backend.Load(ctx, h, length, offset, consumer)
	}

	debug.Log("auto-store %v in the cache", h)
	err = b.cacheFile(ctx, h)
	if err != nil {
		return err
	}

	inCache, err = b.loadFromCache(h, length, offset, consumer)
	if inCache {
		if err != nil {
			debug.Log("error loading %v from cache: %v", h, err)
		}
		return err
	}

	debug.Log("error caching %v: %v, falling back to backend", h, err)
	return b.Backend.Load(ctx, h, length, offset, consumer)
}

// Stat tests whether the backend has a file. If it does not exist but still
// exists in the cache, it is removed from the cache.