How to download from public s3 bucket using golang - amazon-web-services

Question

I'm implementing a function to download a file from an s3 bucket. This worked fine when the bucket was private and I set the credentials
os.Setenv("AWS_ACCESS_KEY_ID", "test")
os.Setenv("AWS_SECRET_ACCESS_KEY", "test")
However, I made the s3 bucket public as described in here and now I want to download it without credentials.
func DownloadFromS3Bucket(bucket, item, path string) {
file, err := os.Create(filepath.Join(path, item))
if err != nil {
fmt.Printf("Error in downloading from file: %v \n", err)
os.Exit(1)
}
defer file.Close()
sess, _ := session.NewSession(&aws.Config{
Region: aws.String(constants.AWS_REGION)},
)
// Create a downloader with the session and custom options
downloader := s3manager.NewDownloader(sess, func(d *s3manager.Downloader) {
d.PartSize = 64 * 1024 * 1024 // 64MB per part
d.Concurrency = 6
})
numBytes, err := downloader.Download(file,
&s3.GetObjectInput{
Bucket: aws.String(bucket),
Key: aws.String(item),
})
if err != nil {
fmt.Printf("Error in downloading from file: %v \n", err)
os.Exit(1)
}
fmt.Println("Download completed", file.Name(), numBytes, "bytes")
}
But now I'm getting an error.
Error in downloading from file: NoCredentialProviders: no valid providers in chain. Deprecated.
For verbose messaging see aws.Config.CredentialsChainVerboseErrors
Any idea how to download it without credentials?

Answer 1

We can set Credentials: credentials.AnonymousCredentials when creating session. Following is the working code.
func DownloadFromS3Bucket(bucket, item, path string) {
file, err := os.Create(filepath.Join(path, item))
if err != nil {
fmt.Printf("Error in downloading from file: %v \n", err)
os.Exit(1)
}
defer file.Close()
sess, _ := session.NewSession(&aws.Config{
Region: aws.String(constants.AWS_REGION), Credentials: credentials.AnonymousCredentials},
)
// Create a downloader with the session and custom options
downloader := s3manager.NewDownloader(sess, func(d *s3manager.Downloader) {
d.PartSize = 64 * 1024 * 1024 // 64MB per part
d.Concurrency = 6
})
numBytes, err := downloader.Download(file,
&s3.GetObjectInput{
Bucket: aws.String(bucket),
Key: aws.String(item),
})
if err != nil {
fmt.Printf("Error in downloading from file: %v \n", err)
os.Exit(1)
}
fmt.Println("Download completed", file.Name(), numBytes, "bytes")
}