chartmuseum/storage

Go library providing a common interface for working across multiple storage backends.

Supported storage backends:

• Local filesystem
• Amazon S3
• Google Cloud Storage
• Microsoft Azure Blob Storage
• Alibaba Cloud OSS Storage
• Openstack Object Storage
• Oracle Cloud Infrastructure Object Storage

This code was originally part of the Helm project, ChartMuseum, but has since been released as a standalone package for others to use in their own projects.

Primary Components

Backend (interface)

Backend is a common interface that is implemented by all the supported storage backends and their associated types:

type Backend interface {
    ListObjects(prefix string) ([]Object, error)
    GetObject(path string) (Object, error)
    PutObject(path string, content []byte) error
    DeleteObject(path string) error
}

Object (struct)

Object is a struct that represents a single storage object:

type Object struct {
    Path         string
    Content      []byte
    LastModified time.Time
}

ObjectSliceDiff (struct)

ObjectSliceDiff is a struct that represents overall changes between two Object slices:

type ObjectSliceDiff struct {
    Change  bool
    Removed []Object
    Added   []Object
    Updated []Object
}

GetObjectSliceDiff (function)

GetObjectSliceDiff is a function that takes two Object slices, compares them, and returns an ObjectSliceDiff:

func GetObjectSliceDiff(os1 []Object, os2 []Object) ObjectSliceDiff

Usage

Simple example

The following is a simple program that will upload a file either to an Azure Blob Storage bucket (container) or a Google Cloud Storage bucket based on the command line options provided:

// Usage: go run example.go <cloud> <bucket> <file>

package main

import (
	"fmt"
	"github.com/chartmuseum/storage"
	"io/ioutil"
	"os"
	"path/filepath"
)

type (
	Uploader struct {
		Backend storage.Backend
	}
)

func NewUploader(cloud string, bucket string) *Uploader {
	var backend storage.Backend
	switch cloud {
	case "azure":
		backend = storage.Backend(storage.NewMicrosoftBlobBackend(bucket, ""))
	case "google":
		backend = storage.Backend(storage.NewGoogleCSBackend(bucket, ""))
	default:
		panic("cloud provider " + cloud + " not supported")
	}
	uploader := Uploader{Backend: backend}
	fmt.Printf("uploader created (cloud: %s, bucket: %s)\n", cloud, bucket)
	return &uploader
}

func (uploader *Uploader) Upload(filename string) {
	basename := filepath.Base(filename)
	content, err := ioutil.ReadFile(filename)
	if err != nil {
		panic(err)
	}
	err = uploader.Backend.PutObject(basename, content)
	if err != nil {
		panic(err)
	}
	fmt.Printf("%s successfully uploaded\n", basename)
}

func main() {
	args := os.Args[1:]
	uploader := NewUploader(args[0], args[1])
	uploader.Upload(args[2])
}

Example of using to upload the file index.html to an Azure bucket:

go run example.go azure mycontainer index.html

Example of using to upload the file index.html to a Google Cloud bucket:

go run example.go google mybucket index.html

Per backend

Each supported storage backend has its own type that implements the Backend interface. All available types are described in detail on GoDoc.

In addition, authentication methods are based on the runtime environment and vary from cloud to cloud.