Backblaze B2 is a cost-effective cloud storage solution favored by developers for its simplicity and scalability. In this guide, we explore efficient techniques to import files from Backblaze B2 using Go, covering environment setup, file transfer, error handling, and performance optimization.

Understanding the Backblaze B2 API

Backblaze B2 provides a RESTful API that enables you to interact with cloud storage programmatically. It supports operations such as file upload, download, and listing. Although Backblaze does not offer an official Go SDK, the community-maintained library, gopkg.in/kothar/go-backblaze.v0, is a widely adopted solution for integrating B2 storage into Go applications.

Setting up your Go environment for Backblaze file importing

Before starting, ensure you have Go installed. Initialize your Go module and install the required dependencies. For these examples, we use:

  • go-backblaze v0.0.0-20210124194846-35409b867216
  • pb/v3 v3.1.0
  • golang.org/x/time/rate (latest version)

Use the following commands to set up your project:

go mod init backblaze-import
go get gopkg.in/kothar/go-backblaze.v0@v0.0.0-20210124194846-35409b867216
go get github.com/cheggaaa/pb/v3@v3.1.0
go get golang.org/x/time/rate

Using the Go SDK to connect to Backblaze B2

Establish a connection to Backblaze B2 using your account credentials. Replace 'YOUR_ACCOUNT_ID' and 'YOUR_APPLICATION_KEY' with your actual Backblaze B2 credentials.

package main

import (
    "context"
    "log"

    "gopkg.in/kothar/go-backblaze.v0"
)

func main() {
    ctx := context.Background()

    // Initialize the B2 client with your credentials.
    b2, err := backblaze.NewB2(backblaze.Credentials{
        AccountID:      "YOUR_ACCOUNT_ID",
        ApplicationKey: "YOUR_APPLICATION_KEY",
    })
    if err != nil {
        log.Fatalf("Failed to create B2 client: %v", err)
    }

    bucket, err := b2.Bucket("YOUR_BUCKET_NAME")
    if err != nil {
        log.Fatalf("Failed to get bucket: %v", err)
    }

    // Your code to interact with the bucket goes here.
    _ = bucket
    _ = ctx
}

This snippet initializes a B2 client and retrieves a reference to your bucket, allowing you to perform subsequent operations.

Implementing basic file import functionality in Go

The following function demonstrates how to download a single file from Backblaze B2. It creates a local file and streams the content directly from B2, ensuring efficient memory usage.

package main

import (
    "fmt"
    "io"
    "os"

    "gopkg.in/kothar/go-backblaze.v0"
)

func downloadFile(b2 *backblaze.B2, bucketName, fileName, localPath string) error {
    // Open the local file for writing.
    file, err := os.Create(localPath)
    if err != nil {
        return fmt.Errorf("failed to create local file: %v", err)
    }
    defer file.Close()

    // Retrieve the bucket.
    bucket, err := b2.Bucket(bucketName)
    if err != nil {
        return fmt.Errorf("failed to get bucket: %v", err)
    }

    // Download the file from B2.
    reader, err := bucket.DownloadFileByName(fileName)
    if err != nil {
        if b2Err, ok := err.(*backblaze.B2Error); ok {
            return fmt.Errorf("B2 error downloading file: %v (code: %s)", b2Err, b2Err.Code)
        }
        return fmt.Errorf("failed to download file: %v", err)
    }
    defer reader.Close()

    // Write the content to the local file.
    _, err = io.Copy(file, reader)
    if err != nil {
        return fmt.Errorf("failed to write file: %v", err)
    }

    return nil
}

Handling directories and batch imports: best practices

To import multiple files or entire directories, implement batch processing by listing files with a specific prefix and then downloading them iteratively. The example below creates the necessary local directory structure and downloads each file.

package main

import (
    "fmt"
    "os"
    "path/filepath"

    "gopkg.in/kothar/go-backblaze.v0"
)

func batchDownload(b2 *backblaze.B2, bucketName, prefix string) error {
    bucket, err := b2.Bucket(bucketName)
    if err != nil {
        return fmt.Errorf("failed to get bucket: %v", err)
    }

    files, err := bucket.ListFileNames(prefix, 1000)
    if err != nil {
        return fmt.Errorf("failed to list files: %v", err)
    }

    for _, file := range files {
        localPath := filepath.Join("downloads", file.Name)

        // Create the directory structure if needed.
        if dir := filepath.Dir(localPath); dir != "" {
            if err := os.MkdirAll(dir, 0755); err != nil {
                return fmt.Errorf("failed to create directory: %v", err)
            }
        }

        if err := downloadFile(b2, bucketName, file.Name, localPath); err != nil {
            return fmt.Errorf("failed to download %s: %v", file.Name, err)
        }
    }

    return nil
}

Error handling and debugging: ensuring smooth file transfers

Network issues and transient errors may occur during file transfers. Incorporate retries with exponential backoff to increase reliability. In the example below, the function attempts to download a file multiple times before failing.

package main

import (
    "fmt"
    "log"
    "time"

    "gopkg.in/kothar/go-backblaze.v0"
)

func downloadWithRetry(b2 *backblaze.B2, bucketName, fileName, localPath string, maxRetries int) error {
    var lastErr error
    for i := 0; i < maxRetries; i++ {
        err := downloadFile(b2, bucketName, fileName, localPath)
        if err == nil {
            return nil
        }

        lastErr = err
        if b2Err, ok := err.(*backblaze.B2Error); ok {
            // Do not retry on permanent errors.
            if b2Err.Status == 401 || b2Err.Status == 403 {
                return fmt.Errorf("permanent error: %v", err)
            }
        }

        wait := time.Duration(1<<uint(i)) * time.Second
        log.Printf("Retrying in %v...", wait)
        time.Sleep(wait)
    }
    return fmt.Errorf("failed after %d retries: %v", maxRetries, lastErr)
}

Progress tracking for large file transfers

For large file imports, tracking progress is beneficial. The following function uses the pb/v3 library to display a progress bar in the terminal while downloading a file.

package main

import (
    "fmt"
    "io"
    "os"

    "github.com/cheggaaa/pb/v3"
    "gopkg.in/kothar/go-backblaze.v0"
)

func downloadFileWithProgress(b2 *backblaze.B2, bucketName, fileName, localPath string) error {
    bucket, err := b2.Bucket(bucketName)
    if err != nil {
        return fmt.Errorf("failed to get bucket: %v", err)
    }

    // Retrieve file information.
    fileInfo, err := bucket.GetFileInfo(fileName)
    if err != nil {
        return fmt.Errorf("failed to get file info: %v", err)
    }

    // Open the local file for writing.
    localFile, err := os.Create(localPath)
    if err != nil {
        return fmt.Errorf("failed to create local file: %v", err)
    }
    defer localFile.Close()

    // Download the file from B2.
    reader, err := bucket.DownloadFileByName(fileName)
    if err != nil {
        return fmt.Errorf("failed to download file: %v", err)
    }
    defer reader.Close()

    // Set up the progress bar.
    bar := pb.Full.Start64(fileInfo.ContentLength)
    barReader := bar.NewProxyReader(reader)
    defer bar.Finish()

    // Write the content to the local file with progress tracking.
    _, err = io.Copy(localFile, barReader)
    if err != nil {
        return fmt.Errorf("failed to write file: %v", err)
    }

    return nil
}

Common pitfalls and troubleshooting tips

Memory management

For large files, stream downloads rather than loading entire files into memory. The previous examples demonstrate streaming content directly to disk, thereby optimizing memory usage.

Rate limiting

Backblaze B2 imposes rate limits on API calls. To avoid throttling, incorporate rate limiting in your application:

package main

import (
    "context"

    "golang.org/x/time/rate"
    "gopkg.in/kothar/go-backblaze.v0"
)

var limiter = rate.NewLimiter(rate.Limit(10), 1) // 10 requests per second

func rateLimitedDownload(b2 *backblaze.B2, bucketName, fileName, localPath string) error {
    if err := limiter.Wait(context.Background()); err != nil {
        return err
    }
    return downloadFile(b2, bucketName, fileName, localPath)
}

Handling network interruptions

Implement timeouts and cancellation contexts to gracefully handle network interruptions.

package main

import (
    "context"
    "fmt"
    "time"

    "gopkg.in/kothar/go-backblaze.v0"
)

func downloadFileWithTimeout(b2 *backblaze.B2, bucketName, fileName, localPath string, timeout time.Duration) error {
    ctx, cancel := context.WithTimeout(context.Background(), timeout)
    defer cancel()

    done := make(chan error, 1)
    go func() {
        done <- downloadFile(b2, bucketName, fileName, localPath)
    }()

    select {
    case err := <-done:
        return err
    case <-ctx.Done():
        return fmt.Errorf("download timed out after %v", timeout)
    }
}

Concurrent downloads with rate limiting

For handling a large number of files more efficiently, process downloads concurrently with controlled rate limiting. The example below demonstrates how to use Go's concurrency primitives to download files in parallel while adhering to rate limits.

package main

import (
    "context"
    "fmt"
    "os"
    "path/filepath"

    "golang.org/x/sync/errgroup"
    "gopkg.in/kothar/go-backblaze.v0"
)

func concurrentBatchDownload(b2 *backblaze.B2, bucketName, prefix string, maxConcurrency int) error {
    bucket, err := b2.Bucket(bucketName)
    if err != nil {
        return fmt.Errorf("failed to get bucket: %v", err)
    }

    files, err := bucket.ListFileNames(prefix, 1000)
    if err != nil {
        return fmt.Errorf("failed to list files: %v", err)
    }

    eg, _ := errgroup.WithContext(context.Background())
    sem := make(chan struct{}, maxConcurrency)

    for _, file := range files {
        file := file // capture variable
        sem <- struct{}{}
        eg.Go(func() error {
            defer func() { <-sem }()
            localPath := filepath.Join("downloads", file.Name)
            if dir := filepath.Dir(localPath); dir != "" {
                if err := os.MkdirAll(dir, 0755); err != nil {
                    return fmt.Errorf("failed to create directory: %v", err)
                }
            }
            // Download the file with retry logic.
            return downloadWithRetry(b2, bucketName, file.Name, localPath, 3)
        })
    }
    return eg.Wait()
}

Bucket lifecycle management best practices

Effective bucket lifecycle management is essential for maintaining a robust file storage system. Always verify that a bucket exists before performing operations. In production environments, you may want to implement routines that create, archive, or clean up buckets based on your usage policies.

package main

import (
    "fmt"

    "gopkg.in/kothar/go-backblaze.v0"
)

func ensureBucket(b2 *backblaze.B2, bucketName string) (*backblaze.Bucket, error) {
    bucket, err := b2.Bucket(bucketName)
    if err == nil {
        return bucket, nil
    }
    // Attempt to create the bucket if it does not exist.
    bucket, err = b2.CreateBucket(bucketName)
    if err != nil {
        return nil, fmt.Errorf("failed to create bucket: %v", err)
    }
    return bucket, nil
}

Conclusion and further resources

Importing files from Backblaze B2 using Go is straightforward when you apply best practices for error handling, concurrency, and bucket management. By integrating techniques such as exponential backoff, progress tracking, and rate limiting, you can build robust applications that efficiently handle both individual and bulk file transfers.

If you are looking for a managed solution for importing files from Backblaze B2, check out Transloadit's file importing service, which simplifies these complexities for you.