b2

A Go library for the Backblaze B2 Cloud Storage API.

Contents

1. API Support
2. Install
3. Setup
4. Usage
   1. Authentication
   2. Upload File
   3. Upload Large File
   4. Download File
   5. Delete a File
   6. List Files

API Support

The following API endpoints and functionality are currently supported:

• Authentication
  • b2_authorize_account
• Uploading a file
  • b2_get_upload_url
  • b2_upload_file
• Uploading a large file (multi-part upload)
  • b2_start_large_file
  • b2_get_upload_part_url
  • b2_upload_part
  • b2_finish_large_file
  • b2_cancel_large_file
• Downloading a file
  • b2_download_file_by_id
• Deleting a file
  • b2_delete_file_version

The project is being actively developed, and more functionality will likely be added in the near future. Existing functionality is unlikely to change and should be considered stable.

Install

go get github.com/benbusby/b2

Setup

To use this library with B2, create an account on backblaze.com, create a new bucket (or use an existing one) and follow the following steps to create an Application Key:

1. Select Account > Application Keys > Add New Application Key
2. Name the key and select which bucket the key should have access to
3. Save the keyID and applicationKey values

Local Storage Only

If you just want to use the library functions to write files to your machine for testing, you can skip creating a Backblaze account and just use one of the "dummy" authentication methods outlined below in Authentication.

Usage

Authentication

You can authenticate with Backblaze B2 using b2.AuthorizeAccount(keyID, key), where keyID is either an application or master key ID, and key is the actual key contents. b2.AuthorizeAccount returns a b2.Auth struct:

type Auth struct {
	AbsoluteMinimumPartSize int    `json:"absoluteMinimumPartSize"`
	AccountID               string `json:"accountId"`
	Allowed                 struct {
		BucketID     string   `json:"bucketId"`
		BucketName   string   `json:"bucketName"`
		Capabilities []string `json:"capabilities"`
		NamePrefix   any      `json:"namePrefix"`
	} `json:"allowed"`
	APIURL              string `json:"apiUrl"`
	AuthorizationToken  string `json:"authorizationToken"`
	DownloadURL         string `json:"downloadUrl"`
	RecommendedPartSize int    `json:"recommendedPartSize"`
	S3APIURL            string `json:"s3ApiUrl"`
}

Most B2 functions have a receiver type of Auth and will use the AuthorizationToken field to authenticate requests.

---

Functions

func AuthorizeAccount(
	b2BucketKeyId string,
	b2BucketKey string,
) (Service, AuthV2, error)

func AuthorizeAccountV2(
    b2BucketKeyId string,
    b2BucketKey string,
) (Service, AuthV3, error)

func AuthorizeDummyAccount(
	path string,
) (Service, error)

func AuthorizeLimitedDummyAccount(
	path string,
	storageLimit int,
) (Service, error)

---

Example

# Authenticate with B2
b2, err := b2.AuthorizeAccount(
	os.Getenv("B2_BUCKET_KEY_ID"),
	os.Getenv("B2_BUCKET_KEY"))

# Create dummy authentication
b2, err := b2.AuthorizeDummyAccount("/tmp")

# Create dummy authentication w/ 1GB storage limit
b2, err := b2.AuthorizeLimitedDummyAccount("local-bucket", 1024*1024*1024)

Upload File

Uploading a regular (non-chunked) file involves fetching the upload parameters first (unique upload URL, token, etc), and then sending your file data, a SHA-1 checksum for the data, and the file name.

Note that although the endpoint for retrieving upload data is named b2_get_upload_url, the returned struct contains more than just a URL. Most importantly, it contains the required auth token for actually uploading the file.

After uploading, you'll receive a struct with fields such as FileID that you can use to access or delete the file later.

---

Functions

Get upload URL:

func (b2Service Service) GetUploadURL() (FileInfo, error)

Upload file:

func (b2Info FileInfo) UploadFile(
	filename string,
	checksum string,
	contents []byte,
) (File, error)

---

Example

b2, _ := b2.AuthorizeAccount(
	os.Getenv("B2_BUCKET_KEY_ID"),
	os.Getenv("B2_BUCKET_KEY"))

b2Uploader, _ := b2.GetUploadURL()

data := []byte("test")

h := sha1.New()
h.Write(data)
checksum := fmt.Sprintf("%x", h.Sum(nil))

file, err := b2Uploader.UploadFile(
	"myfile.txt",
	checksum,
	data)

// save/store `file.FileID` somewhere in order to access it later

Upload Large File

Uploading a large file requires extra steps to "start" and "stop" uploading, which will depend on how many chunks of data you're sending. Each chunk of file data needs to be at least 5mb, except for the final chunk. You cannot use the large file upload process to upload files <5mb.

The basic flow of uploading a large file is:

1. Start the file
2. Get the upload info for a chunk
3. Upload the chunks of data until finished
4. Stop the file

You'll also need to track each checksum as you upload data, since finishing a large file requires an array of past checksums to finalize the upload.

The finalized large file struct, like the normal B2 file struct, contains metadata that you may want in order to access the file later.

---

Function(s)

Start large file:

func (b2Service Service) StartLargeFile(filename string) (StartFile, error)

Get upload part URL:

func (b2Service Service) GetUploadPartURL(b2File StartFile) (FilePartInfo, error)

Upload file part:

func (b2PartInfo FilePartInfo) UploadFilePart(
	chunkNum int,
	checksum string,
	contents []byte,
) error

Finish large file:

func (b2Service Service) FinishLargeFile(
	fileID string,
	checksums []string,
) (LargeFile, error)

Cancel large file:

func (b2Service Service) CancelLargeFile(fileID string) (bool, error)

---

Example

dataSize := 10485760
chunkSize := 5242880

data := make([]byte, dataSize) // empty, only for example
var checksums []string

b2, _ := b2.AuthorizeAccount(
	os.Getenv("B2_BUCKET_KEY_ID"),
	os.Getenv("B2_BUCKET_KEY"))

b2InitFile, _ := b2.StartLargeFile("mybigfile.mp4")
b2PartUploader, _ := b2.GetUploadPartURL(b2InitFile)

for i := 0; i < dataSize; i++ {
	start := i * chunkSize
	stop := i * chunkSize + chunkSize
	chunk := data[start:stop]

	h := sha1.New()
	h.Write(data)
	checksum := fmt.Sprintf("%x", h.Sum(nil))
	checksums = append(checksums, checksum)

	// B2 chunk numbering starts at 1, not 0
	err := info.UploadFilePart(i+1, checksum, chunk)

	if err != nil {
		panic(err)
	}
}

err = b2.FinishLargeFile(b2PartUploader.FileID, checksums)
if err != nil {
	panic(err)
}

Download File

Downloading a file can either be done in one request (likely only feasible for smaller files) or chunked, similar to how large files are uploaded but in reverse.

---

Functions

Multi-part download:

func (b2Service Service) PartialDownloadById(
	id string,
	begin int,
	end int,
) ([]byte, error)

Full download:

func (b2Service Service) DownloadById(id string) ([]byte, error)

---

Example (single request)

b2, _ := b2.AuthorizeAccount(
	os.Getenv("B2_BUCKET_KEY_ID"),
	os.Getenv("B2_BUCKET_KEY"))

id := getB2FileID() // value from UploadFile or FinishLargeFile

data, err := b2.DownloadById(id)

// do something with the file data

Example (multi request)

b2, _ := b2.AuthorizeAccount(
	os.Getenv("B2_BUCKET_KEY_ID"),
	os.Getenv("B2_BUCKET_KEY"))

id := getB2FileID() // value from UploadFile or FinishLargeFile
fileSize := getB2FileSize() // same note as above

chunkSize := 5242880
i := 0
var output []byte

for i < fileSize {
	start := i * chunkSize
	stop := i * chunkSize + chunkSize
	data, _ := auth.PartialDownloadById(id, start, stop)
	output = append(output, data...)
}

// do something with output (full file data)

Delete a File

Deleting a file requires both the file's ID, and the file's name. Both of these are returned in the final struct when uploading a file and should be stored somewhere if you want to delete the file later on.

---

Function

func (b2Service Service) DeleteFile(b2ID string, name string) bool

---

Example

b2, _ := b2.AuthorizeAccount(
	os.Getenv("B2_BUCKET_KEY_ID"),
	os.Getenv("B2_BUCKET_KEY"))

id, name := getB2FileInfo()

if b2.DeleteFile(id, name) {
	fmt.Println("File successfully deleted")
} else {
	return errors.New("failed to delete file")
}

List Files

Listing files requires the bucket ID that you're wanting to query, and can accept a few optional parameters for filtering.

---

Functions

func (b2Service Service) ListAllFiles(bucketID string) (FileList, error)

func (b2Service Service) ListNFiles(bucketID string, count int) (FileList, error)

func (b2Service Service) ListFiles(
	bucketID string,
	count int,
	startName string,
	startID string,
) (FileList, error)

---

Example

files, _ := b2.ListAllFiles(bucketID)

for _, file := range files.Files {
    // do something with `file`
}