s3

dp-s3

Client to interact with AWS S3

Getting started

Setting up AWS credentials

In order to access AWS S3, this library will require your access key id and access secret key. You can either setup a default profile in ~/.aws/credentials file:

[default]
aws_access_key_id=<id>
aws_secret_access_key=<secret>
region=eu-west-1

Or export the values as environmental variables:

export AWS_ACCESS_KEY_ID=<id>
export AWS_SECRET_ACCESS_KEY=<secret>

More information in Amazon documentation

Setting up IAM policy

The functionality implemented by this library requires that the user has some permissions defined by an IAM policy.

• Health-check functionality performs a HEAD bucket operation, requiring allowed s3:ListBucket for all resources.

• Get functionality requires allowed s3:GetObject for the objects under the hierarchy you want to allow (e.g. my-bucket/prefix/*).

• Upload (PUT) functionality requires allowed s3:PutObject for the objects under the hierarchy you want to allow (e.g. my-bucket/prefix/*).

• Multipart upload functionality requires allowed s3:PutObject, s3:GetObject, s3:AbortMultipartUpload, s3:ListMultipartUploadParts for objects under the hierarchy you want to allow (e.g. my-bucket/prefix/*); and s3:ListBucketMultipartUploads for the bucket (e.g. my-bucket).

Please, see our terraform repository for more information.

S3 Client Usage

The S3 client wraps the necessary AWS SDK structs and offers functionality to check buckets, and read and write objects from/to S3.

The client is configured with a specific bucket and region, note that the bucket needs to be created in the region that you provide in order to access it.

There are 2 available constructors:

• Constructor without AWS session (will create a new session):

import dps3 "github.com/ONSdigital/dp-s3/v2"

s3cli := dps3.NewClient(region, bucket)

• Constructor with AWS session (will reuse the provided session):

import dps3 "github.com/ONSdigital/dp-s3/v2"

s3cli := dps3.NewClientWithSession(bucket, awsSession)

It is recommended to create a single AWS session in your service and reuse it if you need other clients. The client offers a session getter: s3cli.Session()

A bucket name getter is also offered for convenience: s3cli.BucketName()

Get

The S3 client exposes functions to get S3 objects by using the vanilla SDK or the crypto client, for user-defined encryption keys.

Functions that have the suffix WithPSK allow you to provide a psk for encryption. For example:

• Get an un-encrypted object from S3

file, err := s3cli.Get("my/s3/file")

• Get an encrypted object from S3, using a psk:

file, err := s3cli.GetWithPSK("my/s3/file", psk)

You can get a file's metadata via a Head call:

out, err := s3cli.Head("my/s3/file")

Upload

The client also wraps the AWS SDK s3manager uploader, which is a high level client to upload files which automatically splits large files into chunks and uploads them concurrently.

This offers functionality to put objects in S3 in a single func call, hiding the low level details of chunking. More information here

Functions that have the suffix WithPSK allow you to provide a psk for encryption and functions with the suffix WithContext allow you to pass a context, which may be cancelled to abort the operation. For example:

• Upload an un-encrypted object to S3

result, err := s3cli.Upload(
    &s3manager.UploadInput{
		Body:   file.Reader,
		Key:    &filename,
	},
)

• Upload an encrypted object to S3, using a psk:

result, err := s3cli.UploadWithPSK(
    &s3manager.UploadInput{
		Body:   file.Reader,
		Key:    &filename,
	},
    psk,
)

• Upload an encrypted object to S3, passing a context:

result, err := s3cli.UploadWithPSKAndContext(
    ctx,
    &s3manager.UploadInput{
		Body:   file.Reader,
		Key:    &filename,
	},
    psk,
)

Multipart Upload

You may use the low-level AWS SDK s3 client multipart upload methods

and upload objects using multipart upload, which is an AWS SDK functionality to perform uploads in chunks. More information here

The minimum chunk size allowed in AWS S3 is 5 MegaBytes (MB) if any chunks (excluding the final chunk) are under this size a ErrChunkTooSmall error will be returned from UploadPart and UploadPartWithPsk functions when all chunks have been uploaded.

URL

S3Url is a structure intended to be used for S3 URL string manipulation in its different formats. To create a new structure you need to provide region, bucketName and object key, and optionally the scheme:

s3Url, err := func NewURL(region, bucket, s3ObjectKey)
s3Url, err := func NewURLWithScheme(scheme, region, bucket, s3ObjectKey)

If you want to parse a URL into an s3Url object, you can use ParseURL() method, providing the format style:

s3Url, err := ParseURL(rawURL, URLStyle)

Once you have a valid s3Url object, you can obtain the URL string representation in the required format style by calling String() method:

str, err := s3Url.String(URLStyle)

The following URL styles are supported:

• PathStyle: https://s3-eu-west-1.amazonaws.com/myBucket/my/s3/object/key
• GlobalPathStyle: https://s3.amazonaws.com/myBucket/my/s3/object/key
• VirtualHostedStyle: https://myBucket.s3-eu-west-1.amazonaws.com/my/s3/object/key
• GlobalVirtualHostedStyle: https://myBucket.s3.amazonaws.com/my/s3/object/key
• AliasVirtualHostedStyle: 'https://myBucket/my/s3/object/key

More information in S3 official documentation

Health check

The S3 checker function performs a HEAD bucket operation . The health check will succeed only if the bucket can be accessed using the client (i.e. client must be authenticated correctly, bucket must exist and have been created in the same region as the client).

Read the Health Check Specification for details.

After creating an S3 client as described above, call s3 health checker with s3cli.Checker(context.Background()) and this will return a check object:

{
    "name": "string",
    "status": "string",
    "message": "string",
    "status_code": "int",
    "last_checked": "ISO8601 - UTC date time",
    "last_success": "ISO8601 - UTC date time",
    "last_failure": "ISO8601 - UTC date time"
}

Contributing

See CONTRIBUTING for details.

License

Copyright © 2020, Office for National Statistics (https://www.ons.gov.uk)

Released under MIT license, see LICENSE for details.