Merge 69089318-download-cache-redirects to master

[Completes #69089318]

Author: nebhale

lib/java_buildpack/util/cache/download_cache.rb

@@ -100,9 +100,16 @@ def evict(uri)
           Timeout::Error
         ].freeze
 
+        REDIRECT_TYPES = [
+          Net::HTTPMovedPermanently,
+          Net::HTTPFound,
+          Net::HTTPSeeOther,
+          Net::HTTPTemporaryRedirect
+        ].freeze
+
         TIMEOUT_SECONDS = 10.freeze
 
-        private_constant :FAILURE_LIMIT, :HTTP_ERRORS, :TIMEOUT_SECONDS
+        private_constant :FAILURE_LIMIT, :HTTP_ERRORS, :REDIRECT_TYPES, :TIMEOUT_SECONDS
 
         def attempt(http, request, cached_file)
           downloaded = false
@@ -117,6 +124,8 @@ def attempt(http, request, cached_file)
               downloaded = true
             elsif response.is_a? Net::HTTPNotModified
               @logger.debug { 'Cached copy up to date' }
+            elsif redirect?(response)
+              downloaded = update URI(response['Location']), cached_file
             else
               fail InferredNetworkFailure, "Bad response: #{response}"
             end
@@ -204,6 +213,10 @@ def proxy(uri)
           Net::HTTP::Proxy(proxy_uri.host, proxy_uri.port, proxy_uri.user, proxy_uri.password)
         end
 
+        def redirect?(response)
+          REDIRECT_TYPES.any? { |t| response.is_a? t }
+        end
+
         def request(uri, cached_file)
           request = Net::HTTP::Get.new(uri.request_uri)
 

spec/java_buildpack/util/cache/download_cache_spec.rb

@@ -85,6 +85,17 @@
     expect_complete_cache mutable_cache_root
   end
 
+  it 'should follow redirects' do
+    stub_request(:get, uri)
+    .to_return(status: 301, headers: { Location: uri_secure })
+    stub_request(:get, uri_secure)
+    .to_return(status: 200, body: 'foo-cached', headers: { Etag: 'foo-etag', 'Last-Modified' => 'foo-last-modified' })
+
+    expect { |b| download_cache.get uri, &b }.to yield_with_args(be_a(File), true)
+                                                 .and yield_file_with_content(/foo-cached/)
+    expect_complete_cache mutable_cache_root
+  end
+
   it 'should retry failed downloads' do
     stub_request(:get, uri)
     .to_raise(SocketError)