✨ Refactor ResponseHelper and add ResponderHandler

- Modified ResponseHelper.Body signature to return an io.Reader and an error.
- Updated ResponseHandler.ServeHTTP to handle errors from ResponseHelper.Body.
- Implemented JSONResponse and JSONResponseWithStatus functions for easier JSON responses.
- Added comprehensive unit tests for JSON response handling, including error scenarios.
- Extended Helper.ResponderHandler with a new test case to ensure proper error handling and response generation.
- Resolved linting issues related to dynamic error definition and function length in tests.

handler.go

@@ -1,13 +1,44 @@
 package ezhandler
 
-import "net/http"
+import (
+	"io"
+	"net/http"
+)
 
+// Handler is similar to [http.Handler], but also may return an error.
 type Handler interface {
 	ServeHTTP(w http.ResponseWriter, r *http.Request) error
 }
 
+// HandlerFunc is similar to [http.HandlerFunc] but it can also return an error.
 type HandlerFunc func(w http.ResponseWriter, r *http.Request) error
 
+var _ Handler = HandlerFunc(nil)
+
 func (fn HandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request) error {
 	return fn(w, r)
 }
+
+// ResponseHandler is similar to HandlerFunc but returns a [ResponseHelper], instead of passing an [http.ResponseWriter].
+type ResponseHandler func(r *http.Request) (resp ResponseHelper, err error)
+
+var _ Handler = ResponseHandler(nil)
+
+func (fn ResponseHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) error {
+	resp, err := fn(r)
+	if err != nil {
+		return err
+	}
+	w.WriteHeader(resp.Status())
+	for key, values := range resp.Headers() {
+		for _, val := range values {
+			w.Header().Add(key, val)
+		}
+	}
+	body, err := resp.Body()
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(w, body)
+	return err
+}

helper.go

@@ -34,3 +34,9 @@ func (help *Helper) HandlerFunc(hnd HandlerFunc) http.Handler {
 		}
 	})
 }
+
+// ResponderHandler returns an [http.Handler] for the provided [ResponderHandler].
+// If hnd returns an error, an appropriate error response is written using the ErrorHandler.
+func (help *Helper) ResponderHandler(hnd ResponseHandler) http.Handler {
+	return help.Handler(hnd)
+}

helper_test.go

@@ -44,6 +44,14 @@ func runHelperTest(t *testing.T, name string, handlerErr, expectedErr error, exp
 				return handlerErr
 			})
 			wrappedHandler = helper.HandlerFunc(mockHandlerFunc)
+		case "ResponderHandler":
+			mockResponseHandler := ezhandler.ResponseHandler(func(r *http.Request) (ezhandler.ResponseHelper, error) {
+				if handlerErr != nil {
+					return nil, handlerErr
+				}
+				return ezhandler.JSONResponse(map[string]string{"status": "ok"}), nil
+			})
+			wrappedHandler = helper.ResponderHandler(mockResponseHandler)
 		}
 
 		wrappedHandler.ServeHTTP(rec, req)
@@ -61,3 +69,8 @@ func TestHelper_HandlerFunc(t *testing.T) {
 	runHelperTest(t, "no error", nil, nil, false, "HandlerFunc")
 	runHelperTest(t, "with error", errTest, errTest, true, "HandlerFunc")
 }
+
+func TestHelper_ResponderHandler(t *testing.T) {
+	runHelperTest(t, "no error", nil, nil, false, "ResponderHandler")
+	runHelperTest(t, "with error", errTest, errTest, true, "ResponderHandler")
+}

response.go

@@ -0,0 +1,56 @@
+package ezhandler
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+)
+
+// ResponseHelper is a simpler way to return a response.
+type ResponseHelper interface {
+	// Body returns the body of the response. It is written to an [http.ResponseWriter].
+	Body() (io.Reader, error)
+	// Status should be a valid HTTP status.
+	Status() int
+	// Headers returns headers that should be added to the response.
+	Headers() http.Header
+}
+
+type jsonResponse struct {
+	value  any
+	status int
+}
+
+var _ ResponseHelper = new(jsonResponse)
+
+func (j *jsonResponse) Body() (io.Reader, error) {
+	b, err := json.Marshal(j.value)
+	if err != nil {
+		return nil, err
+	}
+	return bytes.NewReader(b), nil
+}
+
+func (j *jsonResponse) Status() int {
+	return j.status
+}
+
+func (j *jsonResponse) Headers() http.Header {
+	header := make(http.Header)
+	header.Set("Content-Type", "application/json")
+	return header
+}
+
+// JSONResponse returns a [ResponseHelper] that JSON encodes value with a 200 response.
+func JSONResponse(value any) ResponseHelper {
+	return JSONResponseWithStatus(value, http.StatusOK)
+}
+
+// JSONResponseWithStatus returns a [ResponseHelper] that JSON encodes value with the provided status.
+func JSONResponseWithStatus(value any, status int) ResponseHelper {
+	return &jsonResponse{
+		value:  value,
+		status: status,
+	}
+}

response_test.go

@@ -0,0 +1,163 @@
+package ezhandler_test
+
+import (
+	"codeberg.org/danjones000/ezhandler"
+	"encoding/json"
+	"errors"
+	"github.com/stretchr/testify/assert"
+
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+var errCircularMarshal = errors.New("json: unsupported value: encountered a cycle")
+
+func TestJSONResponse(t *testing.T) {
+	type testData struct {
+		Message string `json:"message"`
+		Code    int    `json:"code"`
+	}
+
+	data := testData{Message: "Hello", Code: 200}
+	respHelper := ezhandler.JSONResponse(data)
+
+	assert.Equal(t, http.StatusOK, respHelper.Status())
+
+	headers := respHelper.Headers()
+	assert.Equal(t, "application/json", headers.Get("Content-Type"))
+
+	body, err := respHelper.Body()
+	assert.NoError(t, err)
+	assert.NotNil(t, body)
+
+	var decodedData testData
+	err = json.NewDecoder(body).Decode(&decodedData)
+	assert.NoError(t, err)
+	assert.Equal(t, data, decodedData)
+}
+
+func TestJSONResponseWithStatus(t *testing.T) {
+	type testData struct {
+		Key string `json:"key"`
+	}
+
+	data := testData{Key: "value"}
+	customStatus := http.StatusCreated
+	respHelper := ezhandler.JSONResponseWithStatus(data, customStatus)
+
+	assert.Equal(t, customStatus, respHelper.Status())
+
+	headers := respHelper.Headers()
+	assert.Equal(t, "application/json", headers.Get("Content-Type"))
+
+	body, err := respHelper.Body()
+	assert.NoError(t, err)
+	assert.NotNil(t, body)
+
+	var decodedData testData
+	err = json.NewDecoder(body).Decode(&decodedData)
+	assert.NoError(t, err)
+	assert.Equal(t, data, decodedData)
+}
+
+func TestJSONResponse_BodyError(t *testing.T) {
+	// This type cannot be marshaled to JSON due to a circular reference
+	type Circular struct {
+		Self *Circular
+	}
+	data := Circular{}
+	data.Self = &data
+
+	respHelper := ezhandler.JSONResponse(data)
+
+	body, err := respHelper.Body()
+	assert.Error(t, err)
+	assert.Nil(t, body)
+}
+
+func TestResponseHandler_ServeHTTP_JSONResponse(t *testing.T) {
+	type testData struct {
+		Message string `json:"message"`
+	}
+
+	tests := []struct {
+		name           string
+		handler        ezhandler.ResponseHandler
+		expectedStatus int
+		expectedBody   string
+		expectedError  error
+	}{
+		{
+			name: "successful JSON response",
+			handler: ezhandler.ResponseHandler(func(r *http.Request) (ezhandler.ResponseHelper, error) {
+				return ezhandler.JSONResponse(testData{Message: "success"}), nil
+			}),
+			expectedStatus: http.StatusOK,
+			expectedBody:   "{\"message\":\"success\"}",
+			expectedError:  nil,
+		},
+		{
+			name: "JSON response with custom status",
+			handler: ezhandler.ResponseHandler(func(r *http.Request) (ezhandler.ResponseHelper, error) {
+				return ezhandler.JSONResponseWithStatus(testData{Message: "created"}, http.StatusCreated), nil
+			}),
+			expectedStatus: http.StatusCreated,
+			expectedBody:   "{\"message\":\"created\"}",
+			expectedError:  nil,
+		},
+		{
+			name: "error from ResponseHandler",
+			handler: ezhandler.ResponseHandler(func(r *http.Request) (ezhandler.ResponseHelper, error) {
+				return nil, errTest // Using errTest from helper_test.go
+			}),
+			expectedStatus: http.StatusOK, // Status won't be set if handler returns error before writing header
+			expectedBody:   "",
+			expectedError:  errTest,
+		},
+		{
+			name: "error from Body() method",
+			handler: ezhandler.ResponseHandler(func(r *http.Request) (ezhandler.ResponseHelper, error) {
+				type Circular struct {
+					Self *Circular
+				}
+				data := Circular{}
+				data.Self = &data
+				return ezhandler.JSONResponse(data), nil
+			}),
+			expectedStatus: http.StatusOK, // Status won't be set if Body() returns error
+			expectedBody:   "",
+			expectedError:  errCircularMarshal, // The error is returned by ServeHTTP, not the handler func
+		},
+	}
+
+	for _, tt := range tests {
+		runResponseHandlerTest(t, tt)
+	}
+}
+
+func runResponseHandlerTest(t *testing.T, tt struct {
+	name           string
+	handler        ezhandler.ResponseHandler
+	expectedStatus int
+	expectedBody   string
+	expectedError  error
+}) {
+	t.Run(tt.name, func(t *testing.T) {
+		req := httptest.NewRequest(http.MethodGet, "/", http.NoBody)
+		rec := httptest.NewRecorder()
+
+		err := tt.handler.ServeHTTP(rec, req)
+
+		if tt.expectedError != nil {
+			assert.ErrorContains(t, err, tt.expectedError.Error())
+		} else {
+			assert.NoError(t, err)
+			assert.Equal(t, tt.expectedStatus, rec.Code)
+			assert.Equal(t, tt.expectedBody, rec.Body.String())
+			if tt.expectedBody != "" {
+				assert.Equal(t, "application/json", rec.Header().Get("Content-Type"))
+			}
+		}
+	})
+}