Basic filter implementation, similar to Sinatra.

src/kemal/middleware/filters.cr

@@ -0,0 +1,52 @@
+module Kemal::Middleware
+  # Kemal::Filter handle all code that should be evaluated before and after
+  # every request
+  class Filter < HTTP::Handler
+    def initialize
+      @tree = Radix::Tree.new
+    end
+
+    def add(type, path, options, &block : HTTP::Server::Context -> _)
+      node = radix_path type, path
+      @tree.add node, Block.new &block
+    end
+
+    def call(context)
+      process_filter(context, :before)
+      call_next(context)
+      process_filter(context, :after)
+    end
+
+    private def process_filter(context, type)
+      lookup = @tree.find radix_path(type, context.request.path)
+      if lookup.found? && lookup.payload.is_a? Block
+        block = lookup.payload as Block
+        block.block.call(context)
+      end
+    end
+
+    private def radix_path(type : Symbol, path)
+      "/#{type}#{path}"
+    end
+  end
+
+  class Block
+    property block
+    def initialize(&@block : HTTP::Server::Context -> _)
+    end
+  end
+end
+
+def add_filters
+  Kemal.config.add_handler Kemal::Filters::Filter.new
+end
+
+def before(path = "*", options = {} of Symbol => String, &block : HTTP::Server::Context -> _)
+  filter = Kemal.config.handlers.first as Kemal::Filters::Filter
+  filter.add :before, path, options, &block
+end
+
+def after(path = "*", options = {} of Symbol => String, &block : HTTP::Server::Context -> _)
+  filter = Kemal.config.handlers.first as Kemal::Filters::Filter
+  filter.add :after, path, options, &block
+end