diff --git a/routes/api/file/[id].ts b/routes/api/file/[id].ts
index 3963120..1520766 100644
--- a/routes/api/file/[id].ts
+++ b/routes/api/file/[id].ts
@@ -17,8 +17,9 @@ export const handler: Handlers = {
             return new Response("File not found.", { status: 404 });
         }
         const opts: GetFileResponseOptions = {};
-        const range = req.headers.get("range");
-        if (range) opts.range = range;
+        opts.range = req.headers.get("range");
+        opts.if_modified_since = req.headers.get("If-Modified-Since");
+        opts.if_unmodified_since = req.headers.get("If-Unmodified-Since");
         return await get_file_response(f.path, opts);
     },
 };
diff --git a/server/get_file_response.ts b/server/get_file_response.ts
index 6eaf599..7414e13 100644
--- a/server/get_file_response.ts
+++ b/server/get_file_response.ts
@@ -8,6 +8,8 @@ export type GetFileResponseOptions = {
     chunk?: number;
     /**@default {false} */
     combineRange?: boolean;
+    if_modified_since?: string;
+    if_unmodified_since?: string;
     mimetype?: string;
     range?: string;
 };
@@ -21,6 +23,12 @@ export async function get_file_response(
     }
     const i = await Deno.stat(path);
     const mimetype = opts && opts.mimetype ? opts.mimetype : mime.getType(path);
+    if (opts?.if_modified_since && i.mtime) {
+        const s = i.mtime.toUTCString();
+        if (opts.if_modified_since === s) {
+            return new Response(null, { status: 304 });
+        }
+    }
     const f = await Deno.open(path);
     const close_f = () => {
         try {
@@ -32,6 +40,12 @@ export async function get_file_response(
     const chunk = opts && opts.chunk && opts.chunk > 0 ? opts.chunk : 4096;
     try {
         if (opts && opts.range) {
+            if (opts.if_unmodified_since && i.mtime) {
+                const s = i.mtime.toUTCString();
+                if (opts.if_unmodified_since !== s) {
+                    return new Response("", { status: 412 });
+                }
+            }
             const combine = opts.combineRange || false;
             const ranges = parse_range(i.size, opts.range, combine);
             if (ranges === -1) {
@@ -107,6 +121,7 @@ export async function get_file_response(
                     "Content-Range": `bytes ${start}-${end - 1}/${i.size}`,
                 };
                 if (mimetype) headers["Content-Type"] = mimetype;
+                if (i.mtime) headers["Last-Modified"] = i.mtime.toUTCString();
                 return new Response(readable, { status: 206, headers });
             } else {
                 let ri = 0;
@@ -225,6 +240,7 @@ export async function get_file_response(
                     "Content-Type":
                         `multipart/byteranges; boundary=${boundary}`,
                 };
+                if (i.mtime) headers["Last-Modified"] = i.mtime.toUTCString();
                 return new Response(readable, { status: 206, headers });
             }
         } else {
@@ -232,6 +248,7 @@ export async function get_file_response(
                 "Content-Length": i.size.toString(),
             };
             if (mimetype) headers["Content-Type"] = mimetype;
+            if (i.mtime) headers["Last-Modified"] = i.mtime.toUTCString();
             return new Response(f.readable, { headers });
         }
     } catch (e) {
diff --git a/static/sw.ts b/static/sw.ts
index da2f303..7b1afb9 100644
--- a/static/sw.ts
+++ b/static/sw.ts
@@ -42,6 +42,10 @@ function match_url(u: URL) {
 
 /**@ts-ignore */
 self.addEventListener("fetch", async (e: FetchEvent) => {
+    const u = new URL(e.request.url);
+    if (u.origin === self.location.origin && u.pathname.startsWith("/api/")) {
+        return;
+    }
     if (!inited) await deleteOldCaches();
     const r = e.request;
     const responseFromCache = await caches.match(r);