Added GDBM support and code examples.

README.md

@@ -10,12 +10,14 @@ Sinatra.
 
 Features
 --------
+
 * Throttles a Rack application by enforcing a minimum interval (by default,
   1 second) between subsequent HTTP requests from a particular client.
 * Compatible with any Rack application and any Rack-based framework.
 * Stores rate-limiting counters in any key/value store implementation that
   responds to `#[]`/`#[]=` (like Ruby's hashes) or to `#get`/`#set` (like
   memcached or Redis).
+* Compatible with the [gdbm][] binding included in Ruby's standard library.
 * Compatible with the [memcached][], [memcache-client][], [memcache][] and
   [redis][] gems.
 * Compatible with [Heroku][]'s [memcached add-on][Heroku memcache]
@@ -36,6 +38,11 @@ Examples
 
     use Rack::Throttle::Interval, :min => 3.0
 
+### Using GDBM to store rate-limiting counters
+
+    require 'gdbm'
+    use Rack::Throttle::Interval, :cache => GDBM.new('tmp/throttle.db')
+
 ### Using Memcached to store rate-limiting counters
 
     require 'memcached'
@@ -134,6 +141,7 @@ License
 information, see <http://unlicense.org/> or the accompanying UNLICENSE file.
 
 [Rack]:            http://rack.rubyforge.org/
+[gdbm]:            http://ruby-doc.org/stdlib/libdoc/gdbm/rdoc/classes/GDBM.html
 [memcached]:       http://rubygems.org/gems/memcached
 [memcache-client]: http://rubygems.org/gems/memcache-client
 [memcache]:        http://rubygems.org/gems/memcache

etc/gdbm.ru

@@ -0,0 +1,7 @@
+$:.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
+require 'rack/throttle'
+require 'gdbm'
+
+use Rack::Throttle::Interval, :min => 3.0, :cache => GDBM.new('/tmp/throttle.db')
+
+run lambda { |env| [200, {'Content-Type' => 'text/plain'}, "Hello, world!\n"] }

lib/rack/throttle/limiter.rb

@@ -122,7 +122,16 @@ def cache_get(key, default = nil)
     def cache_set(key, value)
       case
         when cache.respond_to?(:[]=)
-          cache[key] = value
+          begin
+            cache[key] = value
+          rescue TypeError => e
+            # GDBM throws a "TypeError: can't convert Float into String"
+            # exception when trying to store a Float. On the other hand, we
+            # don't want to unnecessarily coerce the value to a String for
+            # any stores that do support other data types (e.g. in-memory
+            # hash objects). So, this is a compromise.
+            cache[key] = value.to_s
+          end
         when cache.respond_to?(:set)
           cache.set(key, value)
       end