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diff --git a/lib/raindrops/middleware.rb b/lib/raindrops/middleware.rb
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+# -*- encoding: binary -*-
+require 'raindrops'
+
+# Raindrops middleware should be loaded at the top of Rack
+# middleware stack before other middlewares for maximum accuracy.
+class Raindrops
+class Middleware < ::Struct.new(:app, :stats, :path, :tcp, :unix)
+
+  # :stopdoc:
+  Stats = Raindrops::Struct.new(:calling, :writing)
+  PATH_INFO = "PATH_INFO"
+  # :startdoc:
+
+  def initialize(app, opts = {})
+    super(app, opts[:stats] || Stats.new, opts[:path] || "/_raindrops")
+    if tmp = opts[:listeners]
+      self.tcp = tmp.grep(/\A[^:]+:\d+\z/)
+      self.unix = tmp.grep(%r{\A/})
+      self.tcp = nil if tcp.empty?
+      self.unix = nil if unix.empty?
+    end
+  end
+
+  # standard Rack endpoing
+  def call(env)
+    env[PATH_INFO] == path ? stats_response : dup._call(env)
+  end
+
+  def _call(env)
+    stats.incr_calling
+    status, headers, self.app = app.call(env)
+
+    # the Rack server will start writing headers soon after this method
+    stats.incr_writing
+    [ status, headers, self ]
+    ensure
+      stats.decr_calling
+  end
+
+  # yield to the Rack server here for writing
+  def each(&block)
+    app.each(&block)
+  end
+
+  # the Rack server should call this after #each (usually ensure-d)
+  def close
+    stats.decr_writing
+    ensure
+      app.close if app.respond_to?(:close)
+  end
+
+  def stats_response
+    body = "calling: #{stats.calling}\n" \
+           "writing: #{stats.writing}\n"
+
+    if defined?(Linux)
+      Linux.tcp_listener_stats(tcp).each do |addr,stats|
+        body << "#{addr} active: #{stats.active}\n" \
+                "#{addr} queued: #{stats.queued}\n"
+      end if tcp
+      Linux.unix_listener_stats(unix).each do |addr,stats|
+        body << "#{addr} active: #{stats.active}\n" \
+                "#{addr} queued: #{stats.queued}\n"
+      end if unix
+    end
+
+    headers = {
+      "Content-Type" => "text/plain",
+      "Content-Length" => body.size.to_s,
+    }
+    [ 200, headers, [ body ] ]
+  end
+
+end
+end