simples3 : Simple no frills AWS S3 Library using REST with V4 Signing

Overview

SimpleS3 is a Go library for manipulating objects in S3 buckets using REST API calls or Presigned URLs signed using AWS Signature Version 4.

Features:

• Simple, intuitive API following Go idioms
• Complete S3 operations - Upload, Download, Delete, List, Details
• Multipart upload - Large file support with parallel uploads, progress tracking, and resumability
• Bucket management - Create, Delete, and List buckets
• AWS Signature Version 4 signing
• Custom endpoint support (MinIO, DigitalOcean Spaces, etc.)
• Simple List API with pagination, prefix filtering, and delimiter grouping
• Iterator-based ListAll for memory-efficient large bucket iteration (Go 1.23+)
• Presigned URL generation for secure browser uploads/downloads (including multipart)
• IAM credential support for EC2 instances
• Comprehensive test coverage
• Zero dependencies - uses only Go standard library

Install

go get github.com/rhnvrm/simples3

Quick Start

package main

import (
    "log"
    "os"
    "github.com/rhnvrm/simples3"
)

func main() {
    // Initialize S3 client
    s3 := simples3.New("us-east-1", "your-access-key", "your-secret-key")

    // Upload a file
    file, err := os.Open("my-file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    resp, err := s3.FileUpload(simples3.UploadInput{
        Bucket:      "my-bucket",
        ObjectKey:   "my-file.txt",
        ContentType: "text/plain",
        FileName:    "my-file.txt",
        Body:        file,
    })
    if err != nil {
        log.Fatal(err)
    }

    log.Printf("File uploaded successfully: %+v", resp)
}

API Reference

Bucket Operations

List All Buckets

// List all buckets for the AWS account
result, err := s3.ListBuckets(simples3.ListBucketsInput{})
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Found %d buckets:\n", len(result.Buckets))
for _, bucket := range result.Buckets {
    fmt.Printf("- %s (created: %s)\n", bucket.Name, bucket.CreationDate)
}

// Owner information is also available
fmt.Printf("Owner: %s (%s)\n", result.Owner.DisplayName, result.Owner.ID)

Create a Bucket

// Create a new bucket
output, err := s3.CreateBucket(simples3.CreateBucketInput{
    Bucket: "my-new-bucket",
    Region: "us-east-1", // Optional, defaults to client region
})
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Bucket created at: %s\n", output.Location)

Delete a Bucket

// Delete an empty bucket
err := s3.DeleteBucket(simples3.DeleteBucketInput{
    Bucket: "my-old-bucket",
})
if err != nil {
    log.Fatal(err)
}

// Note: The bucket must be empty before deletion

File Operations

Upload Files

// POST upload (recommended for browsers)
resp, err := s3.FileUpload(simples3.UploadInput{
    Bucket:      "my-bucket",
    ObjectKey:   "path/to/file.txt",
    ContentType: "text/plain",
    FileName:    "file.txt",
    Body:        file,
})

// PUT upload (simpler for programmatic use)
resp, err := s3.FilePut(simples3.UploadInput{
    Bucket:      "my-bucket",
    ObjectKey:   "path/to/file.txt",
    ContentType: "text/plain",
    Body:        file,
})

Download Files

// Download file
file, err := s3.FileDownload(simples3.DownloadInput{
    Bucket:    "my-bucket",
    ObjectKey: "path/to/file.txt",
})
if err != nil {
    log.Fatal(err)
}
defer file.Close()

// Read the content
data, err := io.ReadAll(file)
if err != nil {
    log.Fatal(err)
}

Delete Files

err := s3.FileDelete(simples3.DeleteInput{
    Bucket:    "my-bucket",
    ObjectKey: "path/to/file.txt",
})

Copy Objects

// Copy object within same bucket
output, err := s3.CopyObject(simples3.CopyObjectInput{
    SourceBucket: "my-bucket",
    SourceKey:    "original/file.txt",
    DestBucket:   "my-bucket",
    DestKey:      "copied/file.txt",
})

// Copy across buckets
output, err := s3.CopyObject(simples3.CopyObjectInput{
    SourceBucket: "source-bucket",
    SourceKey:    "file.txt",
    DestBucket:   "dest-bucket",
    DestKey:      "file.txt",
})

// Copy with metadata replacement
output, err := s3.CopyObject(simples3.CopyObjectInput{
    SourceBucket:      "my-bucket",
    SourceKey:         "file.txt",
    DestBucket:        "my-bucket",
    DestKey:           "file-copy.txt",
    MetadataDirective: "REPLACE",
    ContentType:       "application/json",
    CustomMetadata:    map[string]string{"version": "2"},
})

Batch Delete Files

// Delete multiple objects in one request (up to 1000)
output, err := s3.DeleteObjects(simples3.DeleteObjectsInput{
    Bucket:  "my-bucket",
    Objects: []string{"file1.txt", "file2.txt", "file3.txt"},
    Quiet:   false,
})
if err != nil {
    log.Fatal(err)
}

// Check results
for _, deleted := range output.Deleted {
    fmt.Printf("Deleted: %s\n", deleted.Key)
}
for _, errItem := range output.Errors {
    fmt.Printf("Failed to delete %s: %s\n", errItem.Key, errItem.Message)
}

Get File Details

details, err := s3.FileDetails(simples3.DetailsInput{
    Bucket:    "my-bucket",
    ObjectKey: "path/to/file.txt",
})
if err != nil {
    log.Fatal(err)
}

log.Printf("File size: %s bytes", details.ContentLength)
log.Printf("Last modified: %s", details.LastModified)
log.Printf("Content type: %s", details.ContentType)

List Objects

SimpleS3 provides a clean, easy-to-use List API that follows the same pattern as other library methods:

Simple Listing

// List all objects in a bucket
result, err := s3.List(simples3.ListInput{
    Bucket: "my-bucket",
})
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Found %d objects:\n", len(result.Objects))
for _, obj := range result.Objects {
    fmt.Printf("- %s (%d bytes)\n", obj.Key, obj.Size)
}

Advanced Listing with Options

// List with prefix filtering and pagination
result, err := s3.List(simples3.ListInput{
    Bucket:    "my-bucket",
    Prefix:    "documents/",
    Delimiter: "/",
    MaxKeys:   100,
})
if err != nil {
    log.Fatal(err)
}

// Process objects
for _, obj := range result.Objects {
    fmt.Printf("%s (%d bytes)\n", obj.Key, obj.Size)
}

// Process "directories" (common prefixes)
for _, prefix := range result.CommonPrefixes {
    fmt.Printf("%s/\n", prefix)
}

Iterator-based Listing (Go 1.23+)

// Use the new ListAll method for memory-efficient iteration
s3 := simples3.New("us-east-1", "your-access-key", "your-secret-key")

// Iterate over all objects with automatic pagination and error handling
seq, finish := s3.ListAll(simples3.ListInput{
    Bucket: "my-bucket",
    Prefix: "documents/", // Optional filtering
})

for obj := range seq {
    fmt.Printf("%s (%d bytes)\n", obj.Key, obj.Size)
}

// Check for any errors that occurred during iteration
if err := finish(); err != nil {
    log.Fatalf("Error during iteration: %v", err)
}

Handle Pagination (Legacy)

// Handle large result sets with pagination
func listAllObjects(s3 *simples3.S3, bucket string) ([]simples3.Object, error) {
    var allObjects []simples3.Object
    var continuationToken string

    for {
        // List objects with continuation token
        result, err := s3.List(simples3.ListInput{
            Bucket:            bucket,
            ContinuationToken: continuationToken,
            MaxKeys:          1000, // Maximum page size
        })
        if err != nil {
            return nil, err
        }

        // Add current page objects to our collection
        allObjects = append(allObjects, result.Objects...)

        // Check if there are more pages
        if !result.IsTruncated {
            break
        }

        // Set token for next page
        continuationToken = result.NextContinuationToken
    }

    return allObjects, nil
}

// Usage example
func main() {
    s3 := simples3.New("us-east-1", "your-access-key", "your-secret-key")

    allObjects, err := listAllObjects(s3, "my-bucket")
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("Total objects: %d\n", len(allObjects))
    for _, obj := range allObjects {
        fmt.Printf("- %s (%d bytes)\n", obj.Key, obj.Size)
    }
}

Multipart Upload

For large files (>100MB), use multipart upload for better performance, resumability, and parallel uploads.

High-Level API (Recommended)

The easiest way to upload large files:

file, err := os.Open("large-video.mp4")
if err != nil {
    log.Fatal(err)
}
defer file.Close()

// FileUploadMultipart automatically handles chunking and parallel uploads
output, err := s3.FileUploadMultipart(simples3.MultipartUploadInput{
    Bucket:      "my-bucket",
    ObjectKey:   "videos/large-video.mp4",
    Body:        file,
    ContentType: "video/mp4",
    PartSize:    10 * 1024 * 1024, // 10MB parts (optional, default 5MB)
    Concurrency: 5,                 // Upload 5 parts in parallel (optional, default 1)
    OnProgress: func(info simples3.ProgressInfo) {
        fmt.Printf("\rProgress: %.1f%% (%d/%d parts)",
            float64(info.UploadedBytes)/float64(info.TotalBytes)*100,
            info.CurrentPart, info.TotalParts)
    },
})
if err != nil {
    log.Fatal(err)
}

fmt.Printf("\nUploaded: %s (ETag: %s)\n", output.Key, output.ETag)

Low-Level API (Advanced)

For more control over the upload process:

// 1. Initiate multipart upload
initOutput, err := s3.InitiateMultipartUpload(simples3.InitiateMultipartUploadInput{
    Bucket:      "my-bucket",
    ObjectKey:   "large-file.bin",
    ContentType: "application/octet-stream",
})
if err != nil {
    log.Fatal(err)
}

// 2. Upload parts (can be done in parallel or resumed later)
var completedParts []simples3.CompletedPart
partSize := int64(10 * 1024 * 1024) // 10MB

for partNum := 1; partNum <= totalParts; partNum++ {
    // Read part data
    partData := getPartData(partNum, partSize) // Your function to get part data

    output, err := s3.UploadPart(simples3.UploadPartInput{
        Bucket:     "my-bucket",
        ObjectKey:  "large-file.bin",
        UploadID:   initOutput.UploadID,
        PartNumber: partNum,
        Body:       bytes.NewReader(partData),
        Size:       int64(len(partData)),
    })
    if err != nil {
        // Abort on error
        s3.AbortMultipartUpload(simples3.AbortMultipartUploadInput{
            Bucket:    "my-bucket",
            ObjectKey: "large-file.bin",
            UploadID:  initOutput.UploadID,
        })
        log.Fatal(err)
    }

    completedParts = append(completedParts, simples3.CompletedPart{
        PartNumber: output.PartNumber,
        ETag:       output.ETag,
    })
}

// 3. Complete the upload
result, err := s3.CompleteMultipartUpload(simples3.CompleteMultipartUploadInput{
    Bucket:    "my-bucket",
    ObjectKey: "large-file.bin",
    UploadID:  initOutput.UploadID,
    Parts:     completedParts,
})
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Upload completed: %s\n", result.ETag)

List Uploaded Parts

Query which parts have been uploaded (useful for resuming uploads):

output, err := s3.ListParts(simples3.ListPartsInput{
    Bucket:    "my-bucket",
    ObjectKey: "large-file.bin",
    UploadID:  uploadID,
})
if err != nil {
    log.Fatal(err)
}

for _, part := range output.Parts {
    fmt.Printf("Part %d: %d bytes (ETag: %s)\n",
        part.PartNumber, part.Size, part.ETag)
}

Abort Multipart Upload

Cancel an in-progress upload and clean up parts:

err := s3.AbortMultipartUpload(simples3.AbortMultipartUploadInput{
    Bucket:    "my-bucket",
    ObjectKey: "large-file.bin",
    UploadID:  uploadID,
})

Browser-Based Multipart Upload

Generate presigned URLs for each part to enable direct browser uploads:

// Backend: Initiate and generate presigned URLs
initOutput, _ := s3.InitiateMultipartUpload(simples3.InitiateMultipartUploadInput{
    Bucket:    "my-bucket",
    ObjectKey: "client-upload.bin",
})

// Generate presigned URL for part 1
presignedURL := s3.GeneratePresignedUploadPartURL(simples3.PresignedMultipartInput{
    Bucket:        "my-bucket",
    ObjectKey:     "client-upload.bin",
    UploadID:      initOutput.UploadID,
    PartNumber:    1,
    ExpirySeconds: 3600,
})

// Frontend: Upload directly to S3 using the presigned URL (via PUT request)
// Then send ETags back to backend for completion

Presigned URLs

Generate secure URLs for browser-based uploads/downloads:

// Generate presigned URL for download
url := s3.GeneratePresignedURL(simples3.PresignedInput{
    Bucket:        "my-bucket",
    ObjectKey:     "private-file.pdf",
    Method:        "GET",
    ExpirySeconds: 3600, // 1 hour
})

// Users can now download directly: <a href="{{url}}">Download</a>

Custom Endpoints

Use with MinIO, DigitalOcean Spaces, or other S3-compatible services:

// MinIO
s3 := simples3.New("us-east-1", "minioadmin", "minioadmin")
s3.SetEndpoint("http://localhost:9000")

// DigitalOcean Spaces
s3 := simples3.New("nyc3", "your-access-key", "your-secret-key")
s3.SetEndpoint("https://nyc3.digitaloceanspaces.com")

IAM Credentials

On EC2 instances, use IAM roles automatically:

s3, err := simples3.NewUsingIAM("us-east-1")
if err != nil {
    log.Fatal(err)
}
// Automatically uses instance IAM role

Development

Setup Development Environment

# Clone the repository
git clone https://github.com/rhnvrm/simples3.git
cd simples3

# Using Nix (recommended)
nix develop

# Or using direnv
direnv allow

# Start local MinIO for testing
just setup

# Run tests
just test-local

Testing

The library includes comprehensive tests that run against a local MinIO instance:

# Run all tests (without MinIO)
just test

# Run tests with local MinIO
just test-local

# Run specific test
go test -v -run TestList

Available Commands

just              # List all commands
just test         # Run tests without MinIO
just test-local   # Run tests with MinIO (includes setup)
just setup        # Setup development environment
just minio-up      # Start MinIO container
just minio-down    # Stop MinIO container
just clean         # Clean up everything
just status        # Check development environment status

Environment Variables

For development and testing:

export AWS_S3_REGION="us-east-1"
export AWS_S3_ACCESS_KEY="minioadmin"
export AWS_S3_SECRET_KEY="minioadmin"
export AWS_S3_ENDPOINT="http://localhost:9000"
export AWS_S3_BUCKET="testbucket"

Contributing

Contributions welcome! Check ROADMAP.md for planned features. Please add tests and ensure just test-local passes before submitting PRs.

Author

Rohan Verma hello@rohanverma.net

License

BSD-2-Clause-FreeBSD