1 files changed, 44 insertions, 0 deletions
diff --git a/workhorse/internal/imageresizer/image_resizer_caching.go b/workhorse/internal/imageresizer/image_resizer_caching.go
new file mode 100644
index 00000000000..bbe0e3260d7
--- /dev/null
+++ b/workhorse/internal/imageresizer/image_resizer_caching.go
@@ -0,0 +1,44 @@
+// This file contains code derived from https://github.com/golang/go/blob/master/src/net/http/fs.go
+//
+// Copyright 2020 GitLab Inc. All rights reserved.
+// Copyright 2009 The Go Authors. All rights reserved.
+
+package imageresizer
+
+import (
+	"net/http"
+	"time"
+)
+
+func checkNotModified(r *http.Request, modtime time.Time) bool {
+	ims := r.Header.Get("If-Modified-Since")
+	if ims == "" || isZeroTime(modtime) {
+		// Treat bogus times as if there was no such header at all
+		return false
+	}
+	t, err := http.ParseTime(ims)
+	if err != nil {
+		return false
+	}
+	// The Last-Modified header truncates sub-second precision so
+	// the modtime needs to be truncated too.
+	return !modtime.Truncate(time.Second).After(t)
+}
+
+// isZeroTime reports whether t is obviously unspecified (either zero or Unix epoch time).
+func isZeroTime(t time.Time) bool {
+	return t.IsZero() || t.Equal(time.Unix(0, 0))
+}
+
+func setLastModified(w http.ResponseWriter, modtime time.Time) {
+	if !isZeroTime(modtime) {
+		w.Header().Set("Last-Modified", modtime.UTC().Format(http.TimeFormat))
+	}
+}
+
+func writeNotModified(w http.ResponseWriter) {
+	h := w.Header()
+	h.Del("Content-Type")
+	h.Del("Content-Length")
+	w.WriteHeader(http.StatusNotModified)
+}