Rewind rack.input when parsing request body

CHANGELOG.md

@@ -5,6 +5,11 @@
 - Reuse `define_dynamic_method` and `define_maybe_yield` methods in `RageController::API` from `Rage::Internal` by [@numice](https://github.com/numice) (#273).
 - Add the `form_actions` router configuration (#278).
 
+### Fixed
+
+- [OpenAPI] Fix SystemStackError in Alba parser with circular associations (#268).
+- Rewind `rack.input` when parsing request body (#279).
+
 ## [1.23.0] - 2026-04-15
 
 ### Fixed
@@ -29,7 +34,6 @@
 
 ### Fixed
 
-- [OpenAPI] Fix SystemStackError in Alba parser with circular associations.
 - Only parse request body as multipart if the request is multipart by [p8](https://github.com/p8) (#256).
 
 ## [1.22.0] - 2026-03-12

lib/rage/params_parser.rb

@@ -14,9 +14,9 @@ def self.prepare(env, url_params)
     end
 
     request_params = if content_type.start_with?("application/json")
-      json_parse(env["rack.input"].read)
+      json_parse(env["rack.input"].tap { |io| io.rewind }.read)
     elsif content_type.start_with?("application/x-www-form-urlencoded")
-      Iodine::Rack::Utils.parse_urlencoded_nested_query(env["rack.input"].read)
+      Iodine::Rack::Utils.parse_urlencoded_nested_query(env["rack.input"].tap { |io| io.rewind }.read)
     elsif content_type.start_with?("multipart/form-data")
       Iodine::Rack::Utils.parse_multipart(env["rack.input"], content_type)
     end

spec/params_parser_spec.rb

@@ -22,7 +22,7 @@
       "multipart/form-data; boundary=--aa123"
     end
   end
-  let(:rack_input) { instance_double(StringIO, read: body) }
+  let(:rack_input) { instance_double(StringIO, read: body, rewind: 0) }
 
   let(:env) do
     {
@@ -330,4 +330,52 @@
       end
     end
   end
+
+  context "when rack.input has been consumed by middleware" do
+    let(:url_params) { {} }
+
+    context "with json body" do
+      let(:raw_body) { '{"id":5,"name":"test"}' }
+      let(:rack_input) { StringIO.new(raw_body) }
+      let(:env) do
+        {
+          "IODINE_HAS_BODY" => true,
+          "QUERY_STRING" => "",
+          "CONTENT_TYPE" => "application/json",
+          "rack.input" => rack_input
+        }
+      end
+
+      before do
+        rack_input.read
+        allow(JSON).to receive(:parse).with(raw_body, symbolize_names: true).and_return({ id: 5, name: "test" })
+      end
+
+      it "can still parse the body after rewind" do
+        expect(subject).to eq({ id: 5, name: "test" })
+      end
+    end
+
+    context "with urlencoded body" do
+      let(:raw_body) { "id=15&name=test" }
+      let(:rack_input) { StringIO.new(raw_body) }
+      let(:env) do
+        {
+          "IODINE_HAS_BODY" => true,
+          "QUERY_STRING" => "",
+          "CONTENT_TYPE" => "application/x-www-form-urlencoded",
+          "rack.input" => rack_input
+        }
+      end
+
+      before do
+        rack_input.read
+        allow(Iodine::Rack::Utils).to receive(:parse_urlencoded_nested_query).with(raw_body).and_return({ id: "15", name: "test" })
+      end
+
+      it "can still parse the body after rewind" do
+        expect(subject).to eq({ id: "15", name: "test" })
+      end
+    end
+  end
 end