Add basic ETag support to cinodefs web interface

pkg/cinodefs/httphandler/http.go

@@ -17,6 +17,7 @@ limitations under the License.
 package httphandler
 
 import (
+	"crypto/sha256"
 	"errors"
 	"fmt"
 	"io"
@@ -80,6 +81,11 @@ func (h *Handler) serveGet(w http.ResponseWriter, r *http.Request, log *slog.Log
 		return
 	}
 
+	if h.handleEtag(w, r, fileEP, log) {
+		// Client ETag matches, can optimize out the data
+		return
+	}
+
 	rc, err := h.FS.OpenEntrypointData(r.Context(), fileEP)
 	if h.handleHttpError(err, w, log, "Error opening file") {
 		return
@@ -102,3 +108,16 @@ func (h *Handler) handleHttpError(err error, w http.ResponseWriter, log *slog.Lo
 	}
 	return false
 }
+
+func (h *Handler) handleEtag(w http.ResponseWriter, r *http.Request, ep *cinodefs.Entrypoint, log *slog.Logger) bool {
+	currentEtag := fmt.Sprintf("\"%X\"", sha256.Sum256(ep.Bytes()))
+
+	if strings.Contains(r.Header.Get("If-None-Match"), currentEtag) {
+		log.Debug("Valid ETag found, sending 304 Not Modified")
+		w.WriteHeader(http.StatusNotModified)
+		return true
+	}
+
+	w.Header().Set("ETag", currentEtag)
+	return false
+}

pkg/cinodefs/httphandler/http_test.go

@@ -96,15 +96,27 @@ func (s *HandlerTestSuite) setEntry(t *testing.T, data string, path ...string) {
 	require.NoError(t, err)
 }
 
-func (s *HandlerTestSuite) getEntry(t *testing.T, path string) (string, string, int) {
-	resp, err := http.Get(s.server.URL + path)
+func (s *HandlerTestSuite) getEntryETag(t *testing.T, path, etag string) (string, string, string, int) {
+	req, err := http.NewRequest(http.MethodGet, s.server.URL+path, nil)
+	require.NoError(t, err)
+
+	if etag != "" {
+		req.Header.Set("If-None-Match", etag)
+	}
+
+	resp, err := http.DefaultClient.Do(req)
 	require.NoError(t, err)
 	defer resp.Body.Close()
 
 	data, err := io.ReadAll(resp.Body)
 	require.NoError(t, err)
 
-	return string(data), resp.Header.Get("content-type"), resp.StatusCode
+	return string(data), resp.Header.Get("content-type"), resp.Header.Get("ETag"), resp.StatusCode
+}
+
+func (s *HandlerTestSuite) getEntry(t *testing.T, path string) (string, string, int) {
+	data, contentType, _, code := s.getEntryETag(t, path, "")
+	return data, contentType, code
 }
 
 func (s *HandlerTestSuite) getData(t *testing.T, path string) string {
@@ -119,6 +131,28 @@ func (s *HandlerTestSuite) TestSuccessfulFileDownload() {
 	require.Equal(s.T(), "hello", readBack)
 }
 
+func (s *HandlerTestSuite) TestEtag() {
+	s.setEntry(s.T(), "hello", "file.txt")
+
+	readBack, _, etag, code := s.getEntryETag(s.T(), "/file.txt", "")
+	require.NotEmpty(s.T(), etag)
+	require.Greater(s.T(), len(etag), 10)
+	require.Equal(s.T(), http.StatusOK, code)
+	require.Equal(s.T(), "hello", readBack)
+
+	readBack, _, _, code = s.getEntryETag(s.T(), "/file.txt", etag)
+	require.Equal(s.T(), http.StatusNotModified, code)
+	require.Empty(s.T(), readBack)
+
+	s.setEntry(s.T(), "updated", "file.txt")
+
+	readBack, _, etag2, code := s.getEntryETag(s.T(), "/file.txt", etag)
+	require.Equal(s.T(), http.StatusOK, code)
+	require.Greater(s.T(), len(etag2), 10)
+	require.NotEqual(s.T(), etag, etag2)
+	require.Equal(s.T(), "updated", readBack)
+}
+
 func (s *HandlerTestSuite) TestNonGetRequest() {
 	t := s.T()
 	resp, err := http.Post(s.server.URL, "text/plain", strings.NewReader("Hello world!"))