Add Kemal::OverrideMethodHandler (#651)

spec/override_method_handler_spec.cr

@@ -0,0 +1,29 @@
+require "./spec_helper"
+
+describe "Kemal::OverrideMethodHandler" do
+  it "does not override method without _method for POST requests" do
+    request = HTTP::Request.new(
+      "POST",
+      "/",
+      body: "_not_method=PATCH",
+      headers: HTTP::Headers{"Content-Type" => "application/x-www-form-urlencoded; charset=UTF-8"}
+    )
+
+    context = create_request_and_return_io_and_context(Kemal::OverrideMethodHandler::INSTANCE, request)[1]
+
+    context.request.method.should eq "POST"
+  end
+
+  it "overrides method with _method for POST requests" do
+    request = HTTP::Request.new(
+      "POST",
+      "/",
+      body: "_method=PATCH",
+      headers: HTTP::Headers{"Content-Type" => "application/x-www-form-urlencoded; charset=UTF-8"}
+    )
+
+    context = create_request_and_return_io_and_context(Kemal::OverrideMethodHandler::INSTANCE, request)[1]
+
+    context.request.method.should eq "PATCH"
+  end
+end

src/kemal/override_method_handler.cr

@@ -0,0 +1,33 @@
+module Kemal
+  # Adds support for `_method` magic parameter to simulate PUT, PATCH, DELETE requests in an html form.
+  #
+  # This middleware is **not** in the default Kemal handlers. You need to explicitly add this to your handlers:
+  #
+  # ```ruby
+  # add_handler Kemal::OverrideMethodHandler
+  # ```
+  #
+  # **Important:** This middleware consumes `params.body` to read the `_method` magic parameter.
+  class OverrideMethodHandler
+    include HTTP::Handler
+    INSTANCE = new
+
+    ALLOWED_METHODS           = ["PUT", "PATCH", "DELETE"]
+    OVERRIDE_METHOD           = "POST"
+    OVERRIDE_METHOD_PARAM_KEY = "_method"
+
+    def call(context)
+      request = context.request
+      if request.method == OVERRIDE_METHOD
+        if context.params.body.has_key?(OVERRIDE_METHOD_PARAM_KEY) && override_method_valid?(context.params.body[OVERRIDE_METHOD_PARAM_KEY])
+          request.method = context.params.body["_method"].upcase
+        end
+      end
+      call_next(context)
+    end
+
+    private def override_method_valid?(override_method : String)
+      ALLOWED_METHODS.includes?(override_method.upcase)
+    end
+  end
+end