From 2279c4208e89a7824ad82b6d5936ad35ce4e7843 Mon Sep 17 00:00:00 2001
From: Juan Pablo Balarini <jpbalarini@gmail.com>
Date: Wed, 9 Nov 2022 16:56:57 -0300
Subject: [PATCH 1/4] Update assets.rb typo in comment

Saw a bad typo in a comment in the asset.rb file and this commit fix this.
---
 lib/sprockets/asset.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/sprockets/asset.rb b/lib/sprockets/asset.rb
index ef7e17a4f..439ebca54 100644
--- a/lib/sprockets/asset.rb
+++ b/lib/sprockets/asset.rb
@@ -137,7 +137,7 @@ def hexdigest
       DigestUtils.pack_hexdigest(digest)
     end
 
-    # Pubic: ETag String of Asset.
+    # Public: ETag String of Asset.
     def etag
       version = environment_version
 

From 33b0ade807c7b8d303cb1e05ea62426819256b14 Mon Sep 17 00:00:00 2001
From: Juan Pablo Balarini <jpbalarini@gmail.com>
Date: Wed, 9 Nov 2022 17:04:49 -0300
Subject: [PATCH 2/4] Update Changelog file

Update changelog with proposed changes for #768
---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4fe4f33cc..f1c8d7349 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@ Get upgrade notes from Sprockets 3.x to 4.x at https://github.com/rails/sprocket
 
 - Add support for Rack 3.0. Headers set by sprockets will now be lower case. [#758](https://github.com/rails/sprockets/pull/758)
 - Make `Sprockets::Utils.module_include` thread safe on JRuby. [#759](https://github.com/rails/sprockets/pull/759)
+- Fix typo in `asset.rb` file. [#768](https://github.com/rails/sprockets/pull/768) 
 
 ## 4.1.0
 

From 4be779f5f73bcf808fe26d4e8968b3f34f96d3a2 Mon Sep 17 00:00:00 2001
From: Hartley McGuire <skipkayhil@gmail.com>
Date: Sat, 29 Jul 2023 18:28:17 -0400
Subject: [PATCH 3/4] Fix Minitest constant name in tests

Minitest 5.19.0 removed the "ancient MiniTest compatibility layer" that
aliased `Minitest` as `MiniTest`. CI runs without a lock file so tests
are failing due to this new release.

This commit renames all of the tests to the correct `Minitest` constant
---
 test/sprockets_test.rb               |  2 +-
 test/test_babel_processor.rb         |  2 +-
 test/test_cache_store.rb             | 10 +++++-----
 test/test_closure_compressor.rb      |  2 +-
 test/test_coffee_script_processor.rb |  2 +-
 test/test_digest_utils.rb            |  2 +-
 test/test_eco_processor.rb           |  2 +-
 test/test_ejs_processor.rb           |  2 +-
 test/test_encoding_utils.rb          |  2 +-
 test/test_erb_processor.rb           |  2 +-
 test/test_http_utils.rb              |  2 +-
 test/test_jsminc_compressor.rb       |  2 +-
 test/test_jst_processor.rb           |  2 +-
 test/test_manifest_utils.rb          |  2 +-
 test/test_path_dependency_utils.rb   |  2 +-
 test/test_path_digest_utils.rb       |  2 +-
 test/test_path_utils.rb              |  2 +-
 test/test_processor_utils.rb         |  2 +-
 test/test_require.rb                 |  2 +-
 test/test_source_map_utils.rb        |  2 +-
 test/test_uglifier_compressor.rb     |  2 +-
 test/test_uri_utils.rb               |  2 +-
 test/test_utils.rb                   |  2 +-
 test/test_yui_compressor.rb          |  2 +-
 24 files changed, 28 insertions(+), 28 deletions(-)

diff --git a/test/sprockets_test.rb b/test/sprockets_test.rb
index 8b45d0aa1..f6da782b0 100644
--- a/test/sprockets_test.rb
+++ b/test/sprockets_test.rb
@@ -93,7 +93,7 @@ def test(name, &block)
   end
 end
 
-class Sprockets::TestCase < MiniTest::Test
+class Sprockets::TestCase < Minitest::Test
   extend Sprockets::TestDefinition
 
   FIXTURE_ROOT = File.join(__dir__, "fixtures")
diff --git a/test/test_babel_processor.rb b/test/test_babel_processor.rb
index 93cc1a166..bdabbaeaa 100644
--- a/test/test_babel_processor.rb
+++ b/test/test_babel_processor.rb
@@ -4,7 +4,7 @@
 require 'sprockets/cache'
 require 'sprockets/babel_processor'
 
-class TestBabelProcessor < MiniTest::Test
+class TestBabelProcessor < Minitest::Test
   def setup
     @env = Sprockets::Environment.new
     @env.append_path File.expand_path("../fixtures", __FILE__)
diff --git a/test/test_cache_store.rb b/test/test_cache_store.rb
index f4ed3ccc5..bbaa18867 100644
--- a/test/test_cache_store.rb
+++ b/test/test_cache_store.rb
@@ -85,7 +85,7 @@ def test_clear
   end
 end
 
-class TestNullStore < MiniTest::Test
+class TestNullStore < Minitest::Test
   def setup
     @_store = Sprockets::Cache::NullStore.new
     @store = Sprockets::Cache.new(Sprockets::Cache::NullStore.new)
@@ -99,7 +99,7 @@ def test_inspect
   include CacheStoreNullTests
 end
 
-class TestMemoryStore < MiniTest::Test
+class TestMemoryStore < Minitest::Test
   def setup
     @_store = Sprockets::Cache::MemoryStore.new
     @store = Sprockets::Cache.new(@_store)
@@ -132,7 +132,7 @@ def test_set_with_lru
   end
 end
 
-class TestZeroMemoryStore < MiniTest::Test
+class TestZeroMemoryStore < Minitest::Test
   def setup
     @_store = Sprockets::Cache::MemoryStore.new(0)
     @store = Sprockets::Cache.new(@_store)
@@ -145,7 +145,7 @@ def test_inspect
   include CacheStoreNullTests
 end
 
-class TestFileStore < MiniTest::Test
+class TestFileStore < Minitest::Test
   def setup
     @root = Dir::mktmpdir "sprockets-file-store"
     @_store = Sprockets::Cache::FileStore.new(@root)
@@ -180,7 +180,7 @@ def test_clear_store_dir_not_exist
   include CacheStoreTests
 end
 
-class TestZeroFileStore < MiniTest::Test
+class TestZeroFileStore < Minitest::Test
   def setup
     @tmpdir = Dir::mktmpdir "sprockets-file-store-zero"
     @_store = Sprockets::Cache::FileStore.new(@tmpdir, 0)
diff --git a/test/test_closure_compressor.rb b/test/test_closure_compressor.rb
index fe39c2a0c..fd73a8944 100644
--- a/test/test_closure_compressor.rb
+++ b/test/test_closure_compressor.rb
@@ -3,7 +3,7 @@
 require 'sprockets/cache'
 require 'sprockets/closure_compressor'
 
-class TestClosureCompressor < MiniTest::Test
+class TestClosureCompressor < Minitest::Test
   def test_compress_javascript
     input = {
       data: "function foo() {\n  return true;\n}",
diff --git a/test/test_coffee_script_processor.rb b/test/test_coffee_script_processor.rb
index 614460ebd..e5496ef16 100644
--- a/test/test_coffee_script_processor.rb
+++ b/test/test_coffee_script_processor.rb
@@ -5,7 +5,7 @@
 require 'sprockets/coffee_script_processor'
 require 'sprockets/source_map_utils'
 
-class TestCoffeeScriptProcessor < MiniTest::Test
+class TestCoffeeScriptProcessor < Minitest::Test
   def setup
     @env = Sprockets::Environment.new
     @env.append_path File.expand_path("../fixtures", __FILE__)
diff --git a/test/test_digest_utils.rb b/test/test_digest_utils.rb
index c0548070b..246afbd09 100644
--- a/test/test_digest_utils.rb
+++ b/test/test_digest_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/digest_utils'
 
-class TestDigestUtils < MiniTest::Test
+class TestDigestUtils < Minitest::Test
   include Sprockets::DigestUtils
 
   def test_detect_digest_class
diff --git a/test/test_eco_processor.rb b/test/test_eco_processor.rb
index 85b606481..d6903902d 100644
--- a/test/test_eco_processor.rb
+++ b/test/test_eco_processor.rb
@@ -3,7 +3,7 @@
 require 'sprockets/cache'
 require 'sprockets/eco_processor'
 
-class TestEcoProcessor < MiniTest::Test
+class TestEcoProcessor < Minitest::Test
   def test_compile_eco_template_to_js
     input = {
       content_type: 'application/javascript',
diff --git a/test/test_ejs_processor.rb b/test/test_ejs_processor.rb
index 4c306d001..99e72b051 100644
--- a/test/test_ejs_processor.rb
+++ b/test/test_ejs_processor.rb
@@ -3,7 +3,7 @@
 require 'sprockets/cache'
 require 'sprockets/ejs_processor'
 
-class TestEjsProcessor < MiniTest::Test
+class TestEjsProcessor < Minitest::Test
   def test_compile_ejs_template_to_js
     input = {
       content_type: 'application/javascript',
diff --git a/test/test_encoding_utils.rb b/test/test_encoding_utils.rb
index e276e2e3b..724d923ff 100644
--- a/test/test_encoding_utils.rb
+++ b/test/test_encoding_utils.rb
@@ -3,7 +3,7 @@
 require 'minitest/autorun'
 require 'sprockets/encoding_utils'
 
-class TestDigestUtils < MiniTest::Test
+class TestDigestUtils < Minitest::Test
   include Sprockets::EncodingUtils
 
   def test_deflate
diff --git a/test/test_erb_processor.rb b/test/test_erb_processor.rb
index 7ab0a88cb..d82127f1d 100644
--- a/test/test_erb_processor.rb
+++ b/test/test_erb_processor.rb
@@ -5,7 +5,7 @@
 require 'sprockets/erb_processor'
 require 'sass'
 
-class TestERBProcessor < MiniTest::Test
+class TestERBProcessor < Minitest::Test
 
   def uri_path(path)
     path = '/' + path if path[1] == ':' # Windows path / drive letter
diff --git a/test/test_http_utils.rb b/test/test_http_utils.rb
index b476dc568..9a042d32f 100644
--- a/test/test_http_utils.rb
+++ b/test/test_http_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/http_utils'
 
-class TestHTTPUtils < MiniTest::Test
+class TestHTTPUtils < Minitest::Test
   include Sprockets::HTTPUtils
 
   def test_match_mime_type
diff --git a/test/test_jsminc_compressor.rb b/test/test_jsminc_compressor.rb
index d7cfb6a8a..6e402c791 100644
--- a/test/test_jsminc_compressor.rb
+++ b/test/test_jsminc_compressor.rb
@@ -4,7 +4,7 @@
 unless RUBY_PLATFORM.include?('java')
   require 'sprockets/jsminc_compressor'
 
-  class TestJSMincCompressor < MiniTest::Test
+  class TestJSMincCompressor < Minitest::Test
 
     def test_compress_javascript
       input = {
diff --git a/test/test_jst_processor.rb b/test/test_jst_processor.rb
index d9d2e5d54..d7e16a60f 100644
--- a/test/test_jst_processor.rb
+++ b/test/test_jst_processor.rb
@@ -3,7 +3,7 @@
 require 'sprockets/cache'
 require 'sprockets/jst_processor'
 
-class TestJstProcessor < MiniTest::Test
+class TestJstProcessor < Minitest::Test
   def test_export_js_template_in_JST
     input = {
       name: 'users/show',
diff --git a/test/test_manifest_utils.rb b/test/test_manifest_utils.rb
index 02a1755bb..3f0beeb37 100644
--- a/test/test_manifest_utils.rb
+++ b/test/test_manifest_utils.rb
@@ -3,7 +3,7 @@
 require 'sprockets/manifest_utils'
 require 'logger'
 
-class TestManifestUtils < MiniTest::Test
+class TestManifestUtils < Minitest::Test
   include Sprockets::ManifestUtils
 
   def test_generate_manifest_path
diff --git a/test/test_path_dependency_utils.rb b/test/test_path_dependency_utils.rb
index 2159af4fa..9dd10f94a 100644
--- a/test/test_path_dependency_utils.rb
+++ b/test/test_path_dependency_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/path_dependency_utils'
 
-class TestPathDependencyUtils < MiniTest::Test
+class TestPathDependencyUtils < Minitest::Test
   include Sprockets::PathDependencyUtils
 
   def test_entries_with_dependencies
diff --git a/test/test_path_digest_utils.rb b/test/test_path_digest_utils.rb
index a62d5e550..1e93a1ce3 100644
--- a/test/test_path_digest_utils.rb
+++ b/test/test_path_digest_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/path_digest_utils'
 
-class TestPathDigestUtils < MiniTest::Test
+class TestPathDigestUtils < Minitest::Test
   include Sprockets::PathDigestUtils
 
   def test_file_stat_digest
diff --git a/test/test_path_utils.rb b/test/test_path_utils.rb
index 0464247ee..3e7c6dc93 100644
--- a/test/test_path_utils.rb
+++ b/test/test_path_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/path_utils'
 
-class TestPathUtils < MiniTest::Test
+class TestPathUtils < Minitest::Test
   include Sprockets::PathUtils
 
   DOSISH = File::ALT_SEPARATOR != nil
diff --git a/test/test_processor_utils.rb b/test/test_processor_utils.rb
index 01f92ae21..775d45e6f 100644
--- a/test/test_processor_utils.rb
+++ b/test/test_processor_utils.rb
@@ -37,7 +37,7 @@ def test_charset_supersedes_default
   end
 end
 
-class TestProcessorUtils < MiniTest::Test
+class TestProcessorUtils < Minitest::Test
   include Sprockets::ProcessorUtils
 
   class Processor
diff --git a/test/test_require.rb b/test/test_require.rb
index f356a718f..cfe110fba 100644
--- a/test/test_require.rb
+++ b/test/test_require.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 require 'minitest/autorun'
 
-class TestRequire < MiniTest::Test
+class TestRequire < Minitest::Test
   parallelize_me!
 
   ROOT = File.expand_path("../..", __FILE__)
diff --git a/test/test_source_map_utils.rb b/test/test_source_map_utils.rb
index 1fff15d7a..6ab0d2a2e 100644
--- a/test/test_source_map_utils.rb
+++ b/test/test_source_map_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/source_map_utils'
 
-class TestSourceMapUtils < MiniTest::Test
+class TestSourceMapUtils < Minitest::Test
 
   def deep_dup(object)
     Marshal.load( Marshal.dump(object) )
diff --git a/test/test_uglifier_compressor.rb b/test/test_uglifier_compressor.rb
index 0c4de5763..8c120b53e 100644
--- a/test/test_uglifier_compressor.rb
+++ b/test/test_uglifier_compressor.rb
@@ -4,7 +4,7 @@
 require 'sprockets/cache'
 require 'sprockets/uglifier_compressor'
 
-class TestUglifierCompressor < MiniTest::Test
+class TestUglifierCompressor < Minitest::Test
   def setup
     @env = Sprockets::Environment.new
     @env.append_path File.expand_path("../fixtures", __FILE__)
diff --git a/test/test_uri_utils.rb b/test/test_uri_utils.rb
index f3b946d47..8a9f7dbfc 100644
--- a/test/test_uri_utils.rb
+++ b/test/test_uri_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/uri_utils'
 
-class TestURIUtils < MiniTest::Test
+class TestURIUtils < Minitest::Test
   include Sprockets::URIUtils
 
   DOSISH = File::ALT_SEPARATOR != nil
diff --git a/test/test_utils.rb b/test/test_utils.rb
index 49f511d7b..65b009337 100644
--- a/test/test_utils.rb
+++ b/test/test_utils.rb
@@ -2,7 +2,7 @@
 require 'minitest/autorun'
 require 'sprockets/utils'
 
-class TestUtils < MiniTest::Test
+class TestUtils < Minitest::Test
   include Sprockets::Utils
 
   def test_duplicable
diff --git a/test/test_yui_compressor.rb b/test/test_yui_compressor.rb
index fe701234a..152033253 100644
--- a/test/test_yui_compressor.rb
+++ b/test/test_yui_compressor.rb
@@ -3,7 +3,7 @@
 require 'sprockets/cache'
 require 'sprockets/yui_compressor'
 
-class TestYUICompressor < MiniTest::Test
+class TestYUICompressor < Minitest::Test
   def test_compress_javascript
     input = {
       content_type: 'application/javascript',

From 5d795a7b19877118496ec1d2092d77db21171a4d Mon Sep 17 00:00:00 2001
From: Hartley McGuire <skipkayhil@gmail.com>
Date: Sat, 29 Jul 2023 17:34:44 -0400
Subject: [PATCH 4/4] Fix header casing compatibility with Rails 7

To support Rack 3, response headers in `Sprockets::Server` were all
downcased. However, this has led to issues with Rack 2 applications (ex.
Rails 7) since they still expect mixed case (ex. `Content-Type`)
headers.

To ensure compatibility with both Rack 2 and Rack 3 applications, this
commit makes the casing of the headers conditional on the Rack version.
Rack itself provides constants to do this easily for most of the headers
used (`Content-Type`, `Content-Length`, `Cache-Control`, and `ETag`) and
the rest are added as constants under `Rack::Server`.

As an alternative to this, the responses could instead be wrapped using
`Rack::Headers` (and `Rack::Utils::HeaderHash` in Rack 2), but making
the header casing conditional seems better to me because it is
relatively easier to implement and there will be less churn if/when Rack
2 support is eventually removed.
---
 CHANGELOG.md            |  1 +
 lib/sprockets/server.rb | 48 +++++++++++++++++++++++++----------------
 2 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1817f73ee..9e19c3a9e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 Get upgrade notes from Sprockets 3.x to 4.x at https://github.com/rails/sprockets/blob/master/UPGRADING.md
 
 - Fix for precompile issues when multiple extensions map to the same MIME type (eg. `.jpeg` / `.jpg`). [#781](https://github.com/rails/sprockets/pull/781)
+- Fix compatibility with Rack 2 applications. [#790](https://github.com/rails/sprockets/pull/790)
 
 ## 4.2.0
 
diff --git a/lib/sprockets/server.rb b/lib/sprockets/server.rb
index f3cdb4f54..c32ce2228 100644
--- a/lib/sprockets/server.rb
+++ b/lib/sprockets/server.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 require 'set'
 require 'time'
-require 'rack/utils'
+require 'rack'
 
 module Sprockets
   # `Server` is a concern mixed into `Environment` and
@@ -11,6 +11,16 @@ module Server
     # Supported HTTP request methods.
     ALLOWED_REQUEST_METHODS = ['GET', 'HEAD'].to_set.freeze
 
+    # :stopdoc:
+    if Gem::Version.new(Rack::RELEASE) < Gem::Version.new("3")
+      X_CASCADE = "X-Cascade"
+      VARY = "Vary"
+    else
+      X_CASCADE = "x-cascade"
+      VARY = "vary"
+    end
+    # :startdoc:
+
     # `call` implements the Rack 1.x specification which accepts an
     # `env` Hash and returns a three item tuple with the status code,
     # headers, and body.
@@ -148,39 +158,39 @@ def not_modified_response(env, etag)
       # Returns a 400 Forbidden response tuple
       def bad_request_response(env)
         if head_request?(env)
-          [ 400, { "content-type" => "text/plain", "content-length" => "0" }, [] ]
+          [ 400, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "0" }, [] ]
         else
-          [ 400, { "content-type" => "text/plain", "content-length" => "11" }, [ "Bad Request" ] ]
+          [ 400, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "11" }, [ "Bad Request" ] ]
         end
       end
 
       # Returns a 403 Forbidden response tuple
       def forbidden_response(env)
         if head_request?(env)
-          [ 403, { "content-type" => "text/plain", "content-length" => "0" }, [] ]
+          [ 403, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "0" }, [] ]
         else
-          [ 403, { "content-type" => "text/plain", "content-length" => "9" }, [ "Forbidden" ] ]
+          [ 403, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "9" }, [ "Forbidden" ] ]
         end
       end
 
       # Returns a 404 Not Found response tuple
       def not_found_response(env)
         if head_request?(env)
-          [ 404, { "content-type" => "text/plain", "content-length" => "0", "x-cascade" => "pass" }, [] ]
+          [ 404, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "0", X_CASCADE => "pass" }, [] ]
         else
-          [ 404, { "content-type" => "text/plain", "content-length" => "9", "x-cascade" => "pass" }, [ "Not found" ] ]
+          [ 404, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "9", X_CASCADE => "pass" }, [ "Not found" ] ]
         end
       end
 
       def method_not_allowed_response
-        [ 405, { "content-type" => "text/plain", "content-length" => "18" }, [ "Method Not Allowed" ] ]
+        [ 405, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "18" }, [ "Method Not Allowed" ] ]
       end
 
       def precondition_failed_response(env)
         if head_request?(env)
-          [ 412, { "content-type" => "text/plain", "content-length" => "0", "x-cascade" => "pass" }, [] ]
+          [ 412, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "0", X_CASCADE => "pass" }, [] ]
         else
-          [ 412, { "content-type" => "text/plain", "content-length" => "19", "x-cascade" => "pass" }, [ "Precondition Failed" ] ]
+          [ 412, { Rack::CONTENT_TYPE => "text/plain", Rack::CONTENT_LENGTH => "19", X_CASCADE => "pass" }, [ "Precondition Failed" ] ]
         end
       end
 
@@ -189,7 +199,7 @@ def precondition_failed_response(env)
       def javascript_exception_response(exception)
         err  = "#{exception.class.name}: #{exception.message}\n  (in #{exception.backtrace[0]})"
         body = "throw Error(#{err.inspect})"
-        [ 200, { "content-type" => "application/javascript", "content-length" => body.bytesize.to_s }, [ body ] ]
+        [ 200, { Rack::CONTENT_TYPE => "application/javascript", Rack::CONTENT_LENGTH => body.bytesize.to_s }, [ body ] ]
       end
 
       # Returns a CSS response that hides all elements on the page and
@@ -242,7 +252,7 @@ def css_exception_response(exception)
           }
         CSS
 
-        [ 200, { "content-type" => "text/css; charset=utf-8", "content-length" => body.bytesize.to_s }, [ body ] ]
+        [ 200, { Rack::CONTENT_TYPE => "text/css; charset=utf-8", Rack::CONTENT_LENGTH => body.bytesize.to_s }, [ body ] ]
       end
 
       # Escape special characters for use inside a CSS content("...") string
@@ -258,18 +268,18 @@ def cache_headers(env, etag)
         headers = {}
 
         # Set caching headers
-        headers["cache-control"] = +"public"
-        headers["etag"]          = %("#{etag}")
+        headers[Rack::CACHE_CONTROL] = +"public"
+        headers[Rack::ETAG]          = %("#{etag}")
 
         # If the request url contains a fingerprint, set a long
         # expires on the response
         if path_fingerprint(env["PATH_INFO"])
-          headers["cache-control"] << ", max-age=31536000, immutable"
+          headers[Rack::CACHE_CONTROL] << ", max-age=31536000, immutable"
 
         # Otherwise set `must-revalidate` since the asset could be modified.
         else
-          headers["cache-control"] << ", must-revalidate"
-          headers["vary"] = "Accept-Encoding"
+          headers[Rack::CACHE_CONTROL] << ", must-revalidate"
+          headers[VARY] = "Accept-Encoding"
         end
 
         headers
@@ -279,7 +289,7 @@ def headers(env, asset, length)
         headers = {}
 
         # Set content length header
-        headers["content-length"] = length.to_s
+        headers[Rack::CONTENT_LENGTH] = length.to_s
 
         # Set content type header
         if type = asset.content_type
@@ -287,7 +297,7 @@ def headers(env, asset, length)
           if type.start_with?("text/") && asset.charset
             type += "; charset=#{asset.charset}"
           end
-          headers["content-type"] = type
+          headers[Rack::CONTENT_TYPE] = type
         end
 
         headers.merge(cache_headers(env, asset.etag))