sinatra.diff

diff --git a/lib/sinatra/base.rb b/lib/sinatra/base.rb
index 9718363..eea1729 100644
--- a/lib/sinatra/base.rb
+++ b/lib/sinatra/base.rb
@@ -1360,12 +1360,18 @@ module Sinatra
 
     # Fixes encoding issues by
     # * defaulting to UTF-8
-    # * casting params to Encoding.default_external
+    # * casting params to default_encoding
     #
     # The latter might not be necessary if Rack handles it one day.
     # Keep an eye on Rack's LH #100.
     def force_encoding(*args) settings.force_encoding(*args) end
     if defined? Encoding
+      if Encoding.default_external == Encoding::ASCII
+        set :default_encoding, "utf-8"
+      else
+        set :default_encoding, Encoding.default_external.to_s.downcase
+      end
+
       def self.force_encoding(data, encoding = default_encoding)
         return if data == settings || data.is_a?(Tempfile)
         if data.respond_to? :force_encoding
@@ -1390,7 +1396,6 @@ module Sinatra
     set :sessions, false
     set :logging, false
     set :method_override, false
-    set :default_encoding, "utf-8"
     set :add_charset, [/^text\//, 'application/javascript', 'application/xml', 'application/xhtml+xml']
 
     # explicitly generating a session secret eagerly to play nice with preforking

tilt.diff

diff --git a/lib/tilt/template.rb b/lib/tilt/template.rb
index 4852ee0..ba63706 100644
--- a/lib/tilt/template.rb
+++ b/lib/tilt/template.rb
@@ -60,11 +60,19 @@ module Tilt
       @compiled_method = {}
 
       # used on 1.9 to set the encoding if it is not set elsewhere (like a magic comment)
-      # currently only used if template compiles to ruby
       @default_encoding = @options.delete :default_encoding
+      @default_encoding ||= Encoding.default_external if defined? Encoding.default_external
+
+      # decide how to load template data
+      @reader = block || begin
+        if File.respond_to? :binread
+          lambda { |t| File.read(@file, :encoding => @default_encoding, :mode => 'rb') }
+        else
+          lambda { |t| File.read(@file) }
+        end
+      end
 
-      # load template data and prepare (uses binread to avoid encoding issues)
-      @reader = block || lambda { |t| File.respond_to?(:binread) ? File.binread(@file) : File.read(@file) }
+      # actually load template data and prepare
       @data = @reader.call(self)
       prepare
     end

Looks great!

The Sinatra patch needs adjustments (we also need to set default_encoding on 1.8, since we use it for HTTP headers).

Why you need to convert from ASCII to UTF8 ? If one have their source in ascii and want to keep them in ascii ?

if Encoding.default_external == Encoding::ASCII
  set :default_encoding, "utf-8"
else
  set :default_encoding, Encoding.default_external.to_s.downcase
end

See discussion (default value, error on deployment), it might even be possible that the server starts and crashes as soon as a user submits UTF-8 characters in a from.

Okey, thanks for the explanation! Great work!