Storage
storage is a Go package which abstracts file systems (local, in-memory, Google Cloud Storage, S3) into a few interfaces. It includes convenience wrappers for simplifying common file system use cases such as caching, prefix isolation and more!
Requirements
Installation
$ go get code.sajari.com/storageUsage
For full documentation see: http://godoc.org/code.sajari.com/storage/.
All storage in this package follow two simple interfaces designed for using file systems.
type FS interface {
Walker
// Open opens an existing file at path in the filesystem. Callers must close the
// File when done to release all underlying resources.
Open(ctx context.Context, path string) (*File, error)
// Create makes a new file in the filesystem. Callers must close the
// returned WriteCloser and check the error to be sure that the file
// was successfully written.
Create(ctx context.Context, path string) (io.WriteCloser, error)
// Delete removes a file from the filesystem.
Delete(ctx context.Context, path string) error
}
// WalkFn is a function type which is passed to Walk.
type WalkFn func(path string) error
// Walker is an interface which defines the Walk method.
type Walker interface {
// Walk traverses a path listing by prefix, calling fn with each object path rewritten
// to be relative to the underlying filesystem and provided path.
Walk(ctx context.Context, path string, fn WalkFn) error
}Local
Local is the default implementation of a local file system (i.e. using os.Open etc).
local := storage.Local("/some/root/path")
f, err := local.Open(context.Background(), "file.json") // will open "/some/root/path/file.json"
if err != nil {
// ...
}
// ...
f.Close()Memory
Mem is the default in-memory implementation of a file system.
mem := storage.Mem()
wc, err := mem.Create(context.Background(), "file.txt")
if err != nil {
// ...
}
if _, err := io.WriteString(wc, "Hello World!"); err != nil {
// ...
}
if err := wc.Close(); err != nil {
// ...
}And now:
f, err := mem.Open(context.Background(), "file.txt")
if err != nil {
// ...
}
// ...
f.Close()Google Cloud Storage
CloudStorage is the default implementation of Google Cloud Storage. This uses https://godoc.org/golang.org/x/oauth2/google#DefaultTokenSource for autentication.
store := storage.CloudStorage{Bucket:"some-bucket"}
f, err := store.Open(context.Background(), "file.json") // will fetch "gs://some-bucket/file.json"
if err != nil {
// ...
}
// ...
f.Close()S3
Not yet implemented! Watch this space.
Wrappers and Helpers
Simple Caching
To use Cloud Storage as a source file system, but cache all opened files in a local filesystem:
src := storage.CloudStorage{Bucket:"some-bucket"}
local := storage.Local("/scratch-space")
fs := storage.Cache(src, local)
f, err := fs.Open(context.Background(), "file.json") // will try src then jump to cache ("gs://some-bucket/file.json")
if err != nil {
// ...
}
// ...
f.Close()
f, err := fs.Open(context.Background(), "file.json") // should now be cached ("/scratch-space/file.json")
if err != nil {
// ...
}
// ...
f.Close()This is particularly useful when distributing files across multiple regions or between cloud providers. For instance, we could add the following code to the previous example:
mainSrc := storage.CloudStorage{Bucket:"some-bucket-in-another-region"}
fs2 := storage.Cache(mainSrc, fs) // fs is from previous snippet
// Open will:
// 1. Try local (see above)
// 2. Try gs://some-bucket
// 3. Try gs://some-bucket-in-another-region, which will be cached in gs://some-bucket and then local on its
// way back to the caller.
f, err := fs2.Open(context.Background(), "file.json") // will fetch "gs://some-bucket-in-another-region/file.json"
if err != nil {
// ...
}
// ...
f.Close()
f, err := fs2.Open(context.Background(), "file.json") // will fetch "/scratch-space/file.json"
if err != nil {
// ...
}
// ...
f.Close()Adding prefixes to paths
If you're writing code that relies on a set directory structure, it can be very messy to have to pass path-patterns around. You can avoid this by wrapping storage.FS implementations with storage.Prefix that rewrites all incoming paths.
modelFS := storage.Prefix(rootFS, "models/")
f, err := modelFS.Open(context.Background(), "file.json") // will call rootFS.Open with path "models/file.json"
if err != nil {
// ...
}
// ...
f.Close()It's also now simple to write wrapper functions to abstract out more complex directory structures.
func UserFS(fs storage.FS, userID, mediaType string) FS {
return storage.Prefix(fs, fmt.Sprintf("%v/%v", userID, userType))
}
userFS := UserFS(rootFS, "1111", "pics")
f, err := userFS.Open(context.Background(), "beach.png") // will call rootFS.Open with path "1111/pics/beach.png"
if err != nil {
// ...
}
// ...
f.Close()