DownloadStrategyDetector recognizes s3 URL scheme

DownloadStrategyDetector now detects URLs with the s3:// prefix, e.g.:
  s3://my-bucket/path/to/key/tarball.tar.gz

Library/Homebrew/download_strategy.rb

@@ -473,7 +473,8 @@ end
 # distribution.  (It will work for public buckets as well.)
 class S3DownloadStrategy < CurlDownloadStrategy
   def _fetch
-    if @url !~ %r{^https?://([^.].*)\.s3\.amazonaws\.com/(.+)$}
+    if @url !~ %r{^https?://([^.].*)\.s3\.amazonaws\.com/(.+)$} &&
+       @url !~ %r{^s3://([^.].*?)/(.+)$}
       raise "Bad S3 URL: " + @url
     end
     bucket = Regexp.last_match(1)
@@ -1141,6 +1142,9 @@ class DownloadStrategyDetector
       SubversionDownloadStrategy
     when %r{^https?://(.+?\.)?sourceforge\.net/hgweb/}
       MercurialDownloadStrategy
+    when %r{^s3://}
+      require_aws_sdk
+      S3DownloadStrategy
     else
       CurlDownloadStrategy
     end

Library/Homebrew/test/download_strategies_spec.rb

@@ -260,6 +260,14 @@ describe DownloadStrategyDetector do
       it { is_expected.to eq(GitHubGitDownloadStrategy) }
     end
 
+    context "when given an S3 URL" do
+      let(:url) { "s3://bucket/homebrew/brew.tar.gz" }
+      it "returns S3DownloadStrategy" do
+        allow(DownloadStrategyDetector).to receive(:require_aws_sdk).and_return(true)
+        is_expected.to eq(S3DownloadStrategy)
+      end
+    end
+
     context "when given strategy = S3DownloadStrategy" do
       let(:url) { "https://bkt.s3.amazonaws.com/key.tar.gz" }
       let(:strategy) { S3DownloadStrategy }