3 files changed, 52 insertions, 10 deletions
diff --git a/activestorage/app/models/active_storage/blob.rb b/activestorage/app/models/active_storage/blob.rb
index 9f2ed1e5ac..664a53a778 100644
--- a/activestorage/app/models/active_storage/blob.rb
+++ b/activestorage/app/models/active_storage/blob.rb
@@ -127,7 +127,7 @@ class ActiveStorage::Blob < ActiveRecord::Base
   # Hiding the +service_url+ behind a redirect also gives you the power to change services without updating all URLs. And
   # it allows permanent URLs that redirect to the +service_url+ to be cached in the view.
   def service_url(expires_in: 5.minutes, disposition: :inline)
-    service.url key, expires_in: expires_in, disposition: disposition, filename: filename, content_type: content_type
+    service.url key, expires_in: expires_in, disposition: "#{disposition}; #{filename.parameters}", filename: filename, content_type: content_type
   end
 
   # Returns a URL that can be used to directly upload a file for this blob on the service. This URL is intended to be
diff --git a/activestorage/app/models/active_storage/filename.rb b/activestorage/app/models/active_storage/filename.rb
index 6a9889addf..c2ad5c844c 100644
--- a/activestorage/app/models/active_storage/filename.rb
+++ b/activestorage/app/models/active_storage/filename.rb
@@ -9,21 +9,23 @@ class ActiveStorage::Filename
     @filename = filename
   end
 
-  # Filename.new("racecar.jpg").extname # => ".jpg"
-  def extname
-    File.extname(@filename)
+  # Filename.new("racecar.jpg").base # => "racecar"
+  def base
+    File.basename @filename, extension_with_delimiter
   end
 
-  # Filename.new("racecar.jpg").extension # => "jpg"
-  def extension
-    extname.from(1)
+  # Filename.new("racecar.jpg").extension_with_delimiter # => ".jpg"
+  def extension_with_delimiter
+    File.extname @filename
   end
 
-  # Filename.new("racecar.jpg").base # => "racecar"
-  def base
-    File.basename(@filename, extname)
+  # Filename.new("racecar.jpg").extension_without_delimiter # => "jpg"
+  def extension_without_delimiter
+    extension_with_delimiter.from(1).to_s
   end
 
+  alias_method :extension, :extension_without_delimiter
+
   # Filename.new("foo:bar.jpg").sanitized # => "foo-bar.jpg"
   # Filename.new("foo/bar.jpg").sanitized # => "foo-bar.jpg"
   #
@@ -32,6 +34,10 @@ class ActiveStorage::Filename
     @filename.encode(Encoding::UTF_8, invalid: :replace, undef: :replace, replace: "�").strip.tr("\u{202E}%$|:;/\t\r\n\\", "-")
   end
 
+  def parameters
+    Parameters.new self
+  end
+
   # Returns the sanitized version of the filename.
   def to_s
     sanitized.to_s
diff --git a/activestorage/app/models/active_storage/filename/parameters.rb b/activestorage/app/models/active_storage/filename/parameters.rb
new file mode 100644
index 0000000000..58ce198d38
--- /dev/null
+++ b/activestorage/app/models/active_storage/filename/parameters.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+class ActiveStorage::Filename::Parameters
+  attr_reader :filename
+
+  def initialize(filename)
+    @filename = filename
+  end
+
+  def combined
+    "#{ascii}; #{utf8}"
+  end
+
+  TRADITIONAL_ESCAPED_CHAR = /[^ A-Za-z0-9!#$+.^_`|~-]/
+
+  def ascii
+    'filename="' + percent_escape(I18n.transliterate(filename.sanitized), TRADITIONAL_ESCAPED_CHAR) + '"'
+  end
+
+  RFC_5987_ESCAPED_CHAR = /[^A-Za-z0-9!#$&+.^_`|~-]/
+
+  def utf8
+    "filename*=UTF-8''" + percent_escape(filename.sanitized, RFC_5987_ESCAPED_CHAR)
+  end
+
+  def to_s
+    combined
+  end
+
+  private
+    def percent_escape(string, pattern)
+      string.gsub(pattern) do |char|
+        char.bytes.map { |byte| "%%%02X" % byte }.join
+      end
+    end
+end