Upgraded use of AWS Ruby SDK for S3

When S3DownloadStrategy is detected in DownloadStrategyDetector an attempt
is made to install & require the aws-sdk-s3 gem.

The AWS S3 SDK is used to sign the URL and handed off to curl_download.

Library/Homebrew/download_strategy.rb

@@ -473,16 +473,6 @@ end
 # distribution.  (It will work for public buckets as well.)
 class S3DownloadStrategy < CurlDownloadStrategy
   def _fetch
-    # Put the aws gem requirement here (vs top of file) so it's only
-    # a dependency of S3 users, not all Homebrew users
-    require "rubygems"
-    begin
-      require "aws-sdk-v1"
-    rescue LoadError
-      onoe "Install the aws-sdk gem into the gem repo used by brew."
-      raise
-    end
-
     if @url !~ %r{^https?://([^.].*)\.s3\.amazonaws\.com/(.+)$}
       raise "Bad S3 URL: " + @url
     end
@@ -492,12 +482,12 @@ class S3DownloadStrategy < CurlDownloadStrategy
     ENV["AWS_ACCESS_KEY_ID"] = ENV["HOMEBREW_AWS_ACCESS_KEY_ID"]
     ENV["AWS_SECRET_ACCESS_KEY"] = ENV["HOMEBREW_AWS_SECRET_ACCESS_KEY"]
 
-    obj = AWS::S3.new.buckets[bucket].objects[key]
     begin
-      s3url = obj.url_for(:get)
-    rescue AWS::Errors::MissingCredentialsError
+      signer = Aws::S3::Presigner.new
+      s3url = signer.presigned_url :get_object, bucket: bucket, key: key
+    rescue Aws::Sigv4::Errors::MissingCredentialsError
       ohai "AWS credentials missing, trying public URL instead."
-      s3url = obj.public_url
+      s3url = @url
     end
 
     curl_download s3url, to: temporary_path
@@ -1116,6 +1106,9 @@ class DownloadStrategyDetector
   def self.detect(url, strategy = nil)
     if strategy.nil?
       detect_from_url(url)
+    elsif strategy == S3DownloadStrategy
+      require_aws_sdk
+      strategy
     elsif strategy.is_a?(Class) && strategy < AbstractDownloadStrategy
       strategy
     elsif strategy.is_a?(Symbol)
@@ -1169,4 +1162,9 @@ class DownloadStrategyDetector
       raise "Unknown download strategy #{symbol} was requested."
     end
   end
+
+  def self.require_aws_sdk
+    Homebrew.install_gem! "aws-sdk-s3", "~> 1.8"
+    require "aws-sdk-s3"
+  end
 end

Library/Homebrew/test/download_strategies_spec.rb

@@ -200,6 +200,26 @@ describe GitDownloadStrategy do
   end
 end
 
+describe S3DownloadStrategy do
+  subject { described_class.new(name, resource) }
+  let(:name) { "foo" }
+  let(:url) { "http://bucket.s3.amazonaws.com/foo.tar.gz" }
+  let(:resource) { double(Resource, url: url, mirrors: [], specs: {}, version: nil) }
+
+  describe "#_fetch" do
+    subject { described_class.new(name, resource)._fetch }
+
+    context "when given Bad S3 URL" do
+      let(:url) { "http://example.com/foo.tar.gz" }
+      it "should raise Bad S3 URL error" do
+        expect {
+          subject._fetch
+        }.to raise_error(RuntimeError)
+      end
+    end
+  end
+end
+
 describe CurlDownloadStrategy do
   subject { described_class.new(name, resource) }
   let(:name) { "foo" }
@@ -226,8 +246,9 @@ end
 
 describe DownloadStrategyDetector do
   describe "::detect" do
-    subject { described_class.detect(url) }
+    subject { described_class.detect(url, strategy) }
     let(:url) { Object.new }
+    let(:strategy) { nil }
 
     context "when given Git URL" do
       let(:url) { "git://example.com/foo.git" }
@@ -239,6 +260,15 @@ describe DownloadStrategyDetector do
       it { is_expected.to eq(GitHubGitDownloadStrategy) }
     end
 
+    context "when given strategy = S3DownloadStrategy" do
+      let(:url) { "https://bkt.s3.amazonaws.com/key.tar.gz" }
+      let(:strategy) { S3DownloadStrategy }
+      it "requires aws-sdk-s3" do
+        allow(DownloadStrategyDetector).to receive(:require_aws_sdk).and_return(true)
+        is_expected.to eq(S3DownloadStrategy)
+      end
+    end
+
     it "defaults to cURL" do
       expect(subject).to eq(CurlDownloadStrategy)
     end