Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/http/response/xml/xml_test.go

@@ -0,0 +1,82 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package xml // import "miniflux.app/v2/internal/http/response/xml"
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestOKResponse(t *testing.T) {
+	r, err := http.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	w := httptest.NewRecorder()
+
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		OK(w, r, "Some XML")
+	})
+
+	handler.ServeHTTP(w, r)
+	resp := w.Result()
+
+	expectedStatusCode := http.StatusOK
+	if resp.StatusCode != expectedStatusCode {
+		t.Fatalf(`Unexpected status code, got %d instead of %d`, resp.StatusCode, expectedStatusCode)
+	}
+
+	expectedBody := `Some XML`
+	actualBody := w.Body.String()
+	if actualBody != expectedBody {
+		t.Fatalf(`Unexpected body, got %s instead of %s`, actualBody, expectedBody)
+	}
+
+	expectedContentType := "text/xml; charset=utf-8"
+	actualContentType := resp.Header.Get("Content-Type")
+	if actualContentType != expectedContentType {
+		t.Fatalf(`Unexpected content type, got %q instead of %q`, actualContentType, expectedContentType)
+	}
+}
+
+func TestAttachmentResponse(t *testing.T) {
+	r, err := http.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	w := httptest.NewRecorder()
+
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		Attachment(w, r, "file.xml", "Some XML")
+	})
+
+	handler.ServeHTTP(w, r)
+	resp := w.Result()
+
+	expectedStatusCode := http.StatusOK
+	if resp.StatusCode != expectedStatusCode {
+		t.Fatalf(`Unexpected status code, got %d instead of %d`, resp.StatusCode, expectedStatusCode)
+	}
+
+	expectedBody := `Some XML`
+	actualBody := w.Body.String()
+	if actualBody != expectedBody {
+		t.Fatalf(`Unexpected body, got %s instead of %s`, actualBody, expectedBody)
+	}
+
+	headers := map[string]string{
+		"Content-Type":        "text/xml; charset=utf-8",
+		"Content-Disposition": "attachment; filename=file.xml",
+	}
+
+	for header, expected := range headers {
+		actual := resp.Header.Get(header)
+		if actual != expected {
+			t.Fatalf(`Unexpected header value, got %q instead of %q`, actual, expected)
+		}
+	}
+}