S3: permit uploading files larger than 5 GB

Use multipart uploads for files larger than 100 MB. Dynamically calculate part size based on total object size and maximum part count.

3 files changed, 69 insertions, 6 deletions

diff --git a/activestorage/CHANGELOG.md b/activestorage/CHANGELOG.md
index 957591ec0a..956567e08a 100644
--- a/activestorage/CHANGELOG.md
+++ b/activestorage/CHANGELOG.md
@@ -1,3 +1,24 @@
+*  The S3 service now permits uploading files larger than 5 gigabytes.
 
+   When uploading a file greater than 100 megabytes in size, the service
+   transparently switches to [multipart uploads](https://docs.aws.amazon.com/AmazonS3/latest/dev/mpuoverview.html)
+   using a part size computed from the file's total size and S3's part count limit.
+
+   No application changes are necessary to take advantage of this feature. You
+   can customize the default 100 MB multipart upload threshold in your S3
+   service's configuration:
+
+   ```yaml
+   production:
+     service: s3
+     access_key_id: <%= Rails.application.credentials.dig(:aws, :access_key_id) %>
+     secret_access_key: <%= Rails.application.credentials.dig(:aws, :secret_access_key) %>
+     region: us-east-1
+     bucket: my-bucket
+     upload:
+       multipart_threshold: <%= 250.megabytes %>
+   ```
+
+   *George Claghorn*
 
 Please check [6-0-stable](https://github.com/rails/rails/blob/6-0-stable/activestorage/CHANGELOG.md) for previous changes.
diff --git a/activestorage/lib/active_storage/service/s3_service.rb b/activestorage/lib/active_storage/service/s3_service.rb
index c7e4ec96a2..e4bd57048a 100644
--- a/activestorage/lib/active_storage/service/s3_service.rb
+++ b/activestorage/lib/active_storage/service/s3_service.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+gem "aws-sdk-s3", "~> 1.14"
+
 require "aws-sdk-s3"
 require "active_support/core_ext/numeric/bytes"
 
@@ -7,20 +9,24 @@ module ActiveStorage
   # Wraps the Amazon Simple Storage Service (S3) as an Active Storage service.
   # See ActiveStorage::Service for the generic API documentation that applies to all services.
   class Service::S3Service < Service
-    attr_reader :client, :bucket, :upload_options
+    attr_reader :client, :bucket
+    attr_reader :multipart_upload_threshold, :upload_options
 
     def initialize(bucket:, upload: {}, **options)
       @client = Aws::S3::Resource.new(**options)
       @bucket = @client.bucket(bucket)
 
+      @multipart_upload_threshold = upload.fetch(:multipart_threshold, 100.megabytes)
       @upload_options = upload
     end
 
     def upload(key, io, checksum: nil, content_type: nil, **)
       instrument :upload, key: key, checksum: checksum do
-        object_for(key).put(upload_options.merge(body: io, content_md5: checksum, content_type: content_type))
-      rescue Aws::S3::Errors::BadDigest
-        raise ActiveStorage::IntegrityError
+        if io.size < multipart_upload_threshold
+          upload_with_single_part key, io, checksum: checksum, content_type: content_type
+        else
+          upload_with_multipart key, io, content_type: content_type
+        end
       end
     end
 
@@ -94,6 +100,24 @@ module ActiveStorage
     end
 
     private
+      MAXIMUM_UPLOAD_PARTS_COUNT = 10000
+      MINIMUM_UPLOAD_PART_SIZE   = 5.megabytes
+
+      def upload_with_single_part(key, io, checksum: nil, content_type: nil)
+        object_for(key).put(body: io, content_md5: checksum, content_type: content_type, **upload_options)
+      rescue Aws::S3::Errors::BadDigest
+        raise ActiveStorage::IntegrityError
+      end
+
+      def upload_with_multipart(key, io, content_type: nil)
+        part_size = [ io.size.fdiv(MAXIMUM_UPLOAD_PARTS_COUNT).ceil, MINIMUM_UPLOAD_PART_SIZE ].max
+
+        object_for(key).upload_stream(content_type: content_type, part_size: part_size, **upload_options) do |out|
+          IO.copy_stream(io, out)
+        end
+      end
+
+
       def object_for(key)
         bucket.object(key)
       end
diff --git a/activestorage/test/service/s3_service_test.rb b/activestorage/test/service/s3_service_test.rb
index 74c0aa0405..b9120770e6 100644
--- a/activestorage/test/service/s3_service_test.rb
+++ b/activestorage/test/service/s3_service_test.rb
@@ -46,8 +46,7 @@ if SERVICE_CONFIGURATIONS[:s3]
     end
 
     test "uploading with server-side encryption" do
-      config  = SERVICE_CONFIGURATIONS.deep_merge(s3: { upload: { server_side_encryption: "AES256" } })
-      service = ActiveStorage::Service.configure(:s3, config)
+      service = build_service(upload: { server_side_encryption: "AES256" })
 
       begin
         key  = SecureRandom.base58(24)
@@ -77,6 +76,25 @@ if SERVICE_CONFIGURATIONS[:s3]
     ensure
       @service.delete key
     end
+
+    test "uploading a large object in multiple parts" do
+      service = build_service(upload: { multipart_threshold: 5.megabytes })
+
+      begin
+        key  = SecureRandom.base58(24)
+        data = SecureRandom.bytes(8.megabytes)
+
+        service.upload key, StringIO.new(data), checksum: Digest::MD5.base64digest(data)
+        assert data == service.download(key)
+      ensure
+        service.delete key
+      end
+    end
+
+    private
+      def build_service(configuration)
+        ActiveStorage::Service.configure :s3, SERVICE_CONFIGURATIONS.deep_merge(s3: configuration)
+      end
   end
 else
   puts "Skipping S3 Service tests because no S3 configuration was supplied"