make it easier for external middleware implementations

runnables/httpserver/middleware/logger.go

@@ -18,7 +18,7 @@ func Logger(logger *slog.Logger) Middleware {
 			start := time.Now()
 
 			// Create a response writer wrapper to capture status code
-			rw := &responseWriter{
+			rw := &ResponseWriter{
 				ResponseWriter: w,
 				statusCode:     http.StatusOK, // Default status code
 			}

runnables/httpserver/middleware/metrics.go

@@ -15,7 +15,7 @@ func MetricCollector() Middleware {
 			start := time.Now()
 
 			// Create a response writer wrapper to capture status code
-			rw := &responseWriter{
+			rw := &ResponseWriter{
 				ResponseWriter: w,
 				statusCode:     http.StatusOK, // Default status code
 			}

runnables/httpserver/middleware/metrics_test.go

@@ -63,7 +63,7 @@ func TestMetricCollector(t *testing.T) {
 	t.Run("captures status code in responseWriter", func(t *testing.T) {
 		// Setup direct responseWriter (without middleware)
 		rec := httptest.NewRecorder()
-		rw := &responseWriter{
+		rw := &ResponseWriter{
 			ResponseWriter: rec,
 			statusCode:     http.StatusOK, // Default
 		}

runnables/httpserver/middleware/middleware.go

@@ -1,31 +1,46 @@
+// Package middleware provides HTTP middleware utilities for wrapping http.HandlerFunc with additional functionality such as logging, metrics, and response inspection.
 package middleware
 
 import (
 	"net/http"
 )
 
 // Middleware is a function that takes an http.HandlerFunc and returns a new http.HandlerFunc
-// which may execute code before and/or after calling the original handler.
+// which may execute code before and/or after calling the original handler. It is commonly used
+// for cross-cutting concerns such as logging, authentication, and metrics.
 type Middleware func(http.HandlerFunc) http.HandlerFunc
 
-// responseWriter is a wrapper for http.ResponseWriter that captures the status code.
-type responseWriter struct {
+// ResponseWriter is a wrapper for http.ResponseWriter that captures the status code and the number of bytes written.
+// It is useful in middleware for logging, metrics, and conditional logic based on the response.
+type ResponseWriter struct {
 	http.ResponseWriter
-	statusCode int
-	written    bool
+	statusCode   int
+	written      bool
+	bytesWritten int
 }
 
 // WriteHeader captures the status code and calls the underlying WriteHeader.
-func (rw *responseWriter) WriteHeader(statusCode int) {
-	rw.statusCode = statusCode
+func (rw *ResponseWriter) WriteHeader(statusCode int) {
 	rw.written = true
+	rw.statusCode = statusCode
 	rw.ResponseWriter.WriteHeader(statusCode)
 }
 
-// Write captures that a response has been written and calls the underlying Write.
-func (rw *responseWriter) Write(b []byte) (int, error) {
-	if !rw.written {
-		rw.written = true
-	}
-	return rw.ResponseWriter.Write(b)
+// Write captures that a response has been written, counts the bytes, and calls the underlying Write.
+func (rw *ResponseWriter) Write(b []byte) (int, error) {
+	rw.written = true
+	n, err := rw.ResponseWriter.Write(b)
+	rw.bytesWritten += n
+	return n, err
+}
+
+// Status returns the HTTP status code that was written to the response.
+// If no status code was explicitly set, it returns 0.
+func (rw *ResponseWriter) Status() int {
+	return rw.statusCode
+}
+
+// BytesWritten returns the total number of bytes written to the response body.
+func (rw *ResponseWriter) BytesWritten() int {
+	return rw.bytesWritten
 }

runnables/httpserver/middleware/middleware_test.go

@@ -12,7 +12,7 @@ import (
 func TestResponseWriter(t *testing.T) {
 	t.Run("WriteHeader sets status code", func(t *testing.T) {
 		rec := httptest.NewRecorder()
-		rw := &responseWriter{
+		rw := &ResponseWriter{
 			ResponseWriter: rec,
 			statusCode:     http.StatusOK, // Default
 		}
@@ -30,7 +30,7 @@ func TestResponseWriter(t *testing.T) {
 
 	t.Run("Write sets written flag", func(t *testing.T) {
 		rec := httptest.NewRecorder()
-		rw := &responseWriter{
+		rw := &ResponseWriter{
 			ResponseWriter: rec,
 			statusCode:     http.StatusOK,
 			written:        false,
@@ -51,7 +51,7 @@ func TestResponseWriter(t *testing.T) {
 
 	t.Run("Write doesn't change written flag if already set", func(t *testing.T) {
 		rec := httptest.NewRecorder()
-		rw := &responseWriter{
+		rw := &ResponseWriter{
 			ResponseWriter: rec,
 			statusCode:     http.StatusOK,
 			written:        true, // Already set
@@ -69,7 +69,7 @@ func TestResponseWriter(t *testing.T) {
 		// Create a test middleware that uses the responseWriter
 		testMiddleware := func(next http.HandlerFunc) http.HandlerFunc {
 			return func(w http.ResponseWriter, r *http.Request) {
-				rw := &responseWriter{
+				rw := &ResponseWriter{
 					ResponseWriter: w,
 					statusCode:     http.StatusOK,
 				}
@@ -99,4 +99,44 @@ func TestResponseWriter(t *testing.T) {
 		assert.Equal(t, http.StatusCreated, rec.Code)
 		assert.Equal(t, "Created", rec.Body.String())
 	})
+
+	t.Run("Status() returns correct status", func(t *testing.T) {
+		rec := httptest.NewRecorder()
+		rw := &ResponseWriter{
+			ResponseWriter: rec,
+			statusCode:     http.StatusOK,
+		}
+
+		// No WriteHeader called yet
+		assert.Equal(t, http.StatusOK, rw.Status())
+
+		rw.WriteHeader(http.StatusTeapot)
+		assert.Equal(t, http.StatusTeapot, rw.Status())
+	})
+
+	t.Run("BytesWritten() returns correct count", func(t *testing.T) {
+		rec := httptest.NewRecorder()
+		rw := &ResponseWriter{
+			ResponseWriter: rec,
+			statusCode:     http.StatusOK,
+		}
+
+		// No bytes written yet
+		assert.Equal(t, 0, rw.BytesWritten())
+
+		_, err := rw.Write([]byte("foo"))
+		assert.NoError(t, err)
+		_, err = rw.Write([]byte("barbaz"))
+		assert.NoError(t, err)
+		assert.Equal(t, 9, rw.BytesWritten())
+	})
+
+	t.Run("Status() and BytesWritten() default values", func(t *testing.T) {
+		rec := httptest.NewRecorder()
+		rw := &ResponseWriter{
+			ResponseWriter: rec,
+		}
+		assert.Equal(t, 0, rw.Status())
+		assert.Equal(t, 0, rw.BytesWritten())
+	})
 }