Basic filter implementation, similar to Sinatra.

spec/middleware/filters_spec.cr

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+require "../spec_helper"
+
+describe "Kemal::Middleware::Filters" do
+  it "executes code before home request" do
+    test_filter = FilterTest.new
+    test_filter.modified = "false"
+
+    filter = Kemal::Middleware::Filter.new
+    filter.add :before, "/greetings", {} of Symbol => String { test_filter.modified = "true" }
+
+    kemal = Kemal::RouteHandler.new
+    kemal.add_route "GET", "/greetings" { test_filter.modified }
+
+    test_filter.modified.should eq("false")
+    request = HTTP::Request.new("GET", "/greetings")
+    create_request_and_return_io(filter, request)
+    io_with_context = create_request_and_return_io(kemal, request)
+    client_response = HTTP::Client::Response.from_io(io_with_context, decompress: false)
+    client_response.body.should eq("true")
+  end
+end
+
+class FilterTest
+  property modified
+end