Make use to #media_type instead of #content_type to avoid false negatives (e.g., multipart/form-data; boundary=...)

lib/hanami/action/mime.rb

@@ -222,11 +222,13 @@ def enforce_accept(request, config)
         # @since 2.0.0
         # @api private
         def enforce_content_type(request, config)
-          content_type = request.content_type
+          # Compare media type (without parameters) instead of full Content-Type header
+          # to avoid false negatives (e.g., multipart/form-data; boundary=...)
+          media_type = request.media_type
 
-          return if content_type.nil?
+          return if media_type.nil?
 
-          return if accepted_mime_type?(content_type, config)
+          return if accepted_mime_type?(media_type, config)
 
           yield
         end

spec/integration/hanami/controller/mime_type_spec.rb

@@ -58,6 +58,15 @@
       end
     end
 
+    context "when uploading a file to an action with format multipart/form-data configured" do
+      it "does not return 415 for valid multipart/form-data request with boundary" do
+        response = app.post("/upload", "CONTENT_TYPE" => "multipart/form-data; boundary=----abc123")
+
+        expect(response.status).to eq(200)
+        expect(response.body).to eq("multipart/form-data; boundary=----abc123")
+      end
+    end
+
     context "when Content-Type are sent and formats are configured to accept all" do
       it "accepts the request with a custom content type" do
         response = app.get("/relaxed", "CONTENT_TYPE" => "application/custom")

spec/support/fixtures.rb

@@ -1597,6 +1597,16 @@ def handle(*, res)
     end
   end
 
+  class UploadAction < Hanami::Action
+    config.formats.add :multipart, "multipart/form-data"
+    config.format :multipart
+
+    def handle(req, res)
+      res.format = :txt
+      res.body = req.content_type
+    end
+  end
+
   class Restricted < Hanami::Action
     config.formats.add :custom, "application/custom"
 
@@ -1641,6 +1651,7 @@ def initialize
         get "/custom_from_accept", to: Mimes::CustomFromAccept.new
         get "/strict",             to: Mimes::Strict.new
         get "/relaxed",            to: Mimes::Relaxed.new
+        post "/upload",            to: Mimes::UploadAction.new
       end
     end