Add logic to override CORS headers

cache.go

@@ -146,8 +146,9 @@ func (client *Client) Middleware() echo.MiddlewareFunc {
 					}
 				} else {
 					b, ok := client.adapter.Get(key)
-					response := BytesToResponse(b)
 					if ok {
+						response := BytesToResponse(b)
+						response.Header = client.rewriteCorsHeaders(response.Header, c.Response().Header())
 						if response.Expiration.After(time.Now()) {
 							response.LastAccess = time.Now()
 							response.Frequency++
@@ -209,6 +210,19 @@ func (client *Client) Middleware() echo.MiddlewareFunc {
 	}
 }
 
+func (client *Client) rewriteCorsHeaders(cachedHeaders http.Header, responseHeaders http.Header) http.Header {
+	corsHeaders := []string{
+		"Access-Control-Allow-Origin",
+		"Access-Control-Allow-Credentials",
+	}
+	for _, h := range corsHeaders {
+		if val := responseHeaders.Get(h); val != "" {
+			cachedHeaders.Set(h, val)
+		}
+	}
+	return cachedHeaders
+}
+
 func (client *Client) cacheableMethod(method string) bool {
 	for _, m := range client.methods {
 		if method == m {

cache_test.go

@@ -12,6 +12,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/coinpaprika/echo-http-cache/adapter/memory"
 	"github.com/labstack/echo/v4"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -231,6 +232,51 @@ func TestMiddleware(t *testing.T) {
 	}
 }
 
+func TestCorsHeaders(t *testing.T) {
+	e := echo.New()
+
+	handler := func(c echo.Context) error {
+		return c.String(http.StatusOK, "ok")
+	}
+	memoryAdapter, err := memory.NewAdapter()
+	require.NoError(t, err)
+
+	client, _ := NewClient(
+		ClientWithAdapter(memoryAdapter),
+		ClientWithTTL(1*time.Minute),
+	)
+
+	cacheMiddleware := client.Middleware()
+
+	req, err := http.NewRequest(http.MethodGet, "/test", nil)
+	require.NoError(t, err)
+	rec := httptest.NewRecorder()
+
+	// simulate CORS middleware
+	rec.Header().Add("Access-Control-Allow-Origin", "http://localhost:8181")
+	rec.Header().Add("Access-Control-Allow-Credentials", "true")
+
+	c := e.NewContext(req, rec)
+	_ = cacheMiddleware(handler)(c)
+
+	assert.Equal(t, "http://localhost:8181", rec.Header().Get("Access-Control-Allow-Origin"))
+	assert.Equal(t, "true", rec.Header().Get("Access-Control-Allow-Credentials"))
+
+	secondRec := httptest.NewRecorder()
+
+	// simulate CORS middleware
+	secondRec.Header().Add("Access-Control-Allow-Origin", "http://coinpaprika.com")
+	secondRec.Header().Add("Access-Control-Allow-Credentials", "true")
+
+	secondC := e.NewContext(req, secondRec)
+	_ = cacheMiddleware(handler)(secondC)
+
+	assert.Equal(t, "http://coinpaprika.com", secondRec.Header().Get("Access-Control-Allow-Origin"))
+	assert.Equal(t, "true", secondRec.Header().Get("Access-Control-Allow-Credentials"))
+	time.Sleep(time.Second)
+}
+
+
 func TestRestrictedPaths(t *testing.T) {
 	tests := []struct {
 		name        string