3 files changed, 39 insertions, 0 deletions
diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 99c3ac3c04..74711c0320 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -62,6 +62,19 @@
     persistent between requests so if you need to manipulate the environment
     for your test you need to do it before the cookie jar is created.
 
+## Rails 3.1.2 (unreleased) ##
+
+*   Implement a workaround for a bug in ruby-1.9.3p0 where an error would be raised
+    while attempting to convert a template from one encoding to another.
+
+    Please see http://redmine.ruby-lang.org/issues/5564 for details of the bug.
+
+    The workaround is to load all conversions into memory ahead of time, and will
+    only happen if the ruby version is *exactly* 1.9.3p0. The hope is obviously that
+    the underlying problem will be resolved in the next patchlevel release of
+    1.9.3.
+
+    *Jon Leighton*
 
 ## Rails 3.1.1 (unreleased) ##
 
diff --git a/actionpack/lib/action_view/data/encoding_conversions.dump b/actionpack/lib/action_view/data/encoding_conversions.dump
new file mode 100644
index 0000000000..18d7cd448b
--- /dev/null
+++ b/actionpack/lib/action_view/data/encoding_conversions.dump
diff --git a/actionpack/lib/action_view/template.rb b/actionpack/lib/action_view/template.rb
index 10797c010f..1f1a8f7867 100644
--- a/actionpack/lib/action_view/template.rb
+++ b/actionpack/lib/action_view/template.rb
@@ -3,6 +3,32 @@ require 'active_support/core_ext/object/blank'
 require 'active_support/core_ext/object/try'
 require 'active_support/core_ext/kernel/singleton_class'
 
+if RUBY_ENGINE == 'ruby' && RUBY_VERSION == '1.9.3' && RUBY_PATCHLEVEL == 0
+  # This is a hack to work around a bug in Ruby 1.9.3p0:
+  # http://redmine.ruby-lang.org/issues/5564
+  #
+  # Basically, at runtime we may need to perform some encoding conversions on the templates,
+  # but if the converter hasn't been loaded by Ruby beforehand (i.e. now), then it won't be
+  # able to find it (due to a  bug).
+  #
+  # However, we don't know what conversions we may need to do a runtime. So we load up a
+  # marshal-dumped structure which contains a pre-generated list of all the possible conversions,
+  # and we load all of them.
+  #
+  # In my testing this increased the process size by about 3.9 MB (after the conversions array
+  # is GC'd) and took around 170ms to run, which seems acceptable for a workaround.
+  #
+  # The script to dump the conversions is: https://gist.github.com/1342729
+
+  filename    = File.join(File.dirname(__FILE__), 'data', 'encoding_conversions.dump')
+  conversions = Marshal.load(File.read(filename))
+  conversions.each do |from, to_array|
+    to_array.each do |to|
+      Encoding::Converter.new(from, to)
+    end
+  end
+end
+
 module ActionView
   # = Action View Template
   class Template