diff --git a/examples/completed-retry-guard.ts b/examples/completed-retry-guard.ts
new file mode 100644
index 00000000..2f74a3ee
--- /dev/null
+++ b/examples/completed-retry-guard.ts
@@ -0,0 +1,54 @@
+import { File, UploadxResponse } from '@uploadx/core';
+import { RequestHandler } from 'express';
+/* eslint-disable @typescript-eslint/no-namespace */
+declare global {
+  namespace Express {
+    interface Response {
+      finishUpload: (uploadxResponse: UploadxResponse) => this;
+    }
+  }
+}
+/**
+ *
+ * @param busyResponse
+ * @param timeout seconds
+ */
+export const completedRetryGuard: (
+  busyResponse: UploadxResponse,
+  timeout?: number
+) => RequestHandler = (busyResponse, timeout = 100) => {
+  const lock: Record<string, UploadxResponse> = {};
+
+  return async (req, res, next) => {
+    const { name: filename } = req.body as File;
+    function send(response: UploadxResponse) {
+      const { statusCode = 200, ...body } = response;
+      res.status(statusCode).json(body);
+    }
+    const done = () =>
+      new Promise<UploadxResponse>(resolve => {
+        let i = 0;
+        (function scan() {
+          if (lock[filename].statusCode !== busyResponse.statusCode || i++ > timeout) {
+            return resolve(lock[filename]);
+          }
+          setTimeout(scan, 1000);
+        })();
+      });
+
+    res.finishUpload = (uploadxResponse: UploadxResponse) => {
+      lock[filename] = uploadxResponse;
+      return res;
+    };
+
+    if (lock[filename]) {
+      send(await done());
+      return;
+    }
+
+    lock[filename] = busyResponse;
+    // prevent resend last chunk
+    send(busyResponse);
+    next();
+  };
+};
diff --git a/examples/express.ts b/examples/custom-validators.ts
similarity index 86%
rename from examples/express.ts
rename to examples/custom-validators.ts
index 41417df8..f09b1067 100644
--- a/examples/express.ts
+++ b/examples/custom-validators.ts
@@ -22,8 +22,7 @@ const onComplete: OnComplete<DiskFile, UploadxResponse<OnCompleteBody>> = file =
   return {
     statusCode: 200,
     message,
-    id: file.id,
-    headers: { ETag: file.id }
+    id: file.id
   };
 };
 
@@ -34,11 +33,15 @@ const storage = new DiskStorage({
   validation: {
     mime: { value: ['video/*'], response: [415, { message: 'video only' }] },
     size: {
-      value: 500_000,
+      value: 500_000_000,
       isValid(file) {
         this.response = [
           412,
-          { message: `The file size(${file.size}) is larger than ${this.value as number} bytes` }
+          {
+            message: `File size(${file.size}) exceeds maximum permitted size of ${
+              this.value as number
+            } bytes`
+          }
         ];
         return file.size <= this.value;
       }
diff --git a/examples/package.json b/examples/package.json
index 522d2791..462a3579 100644
--- a/examples/package.json
+++ b/examples/package.json
@@ -4,13 +4,13 @@
   "private": true,
   "scripts": {
     "basic": "tsnd -r tsconfig-paths/register -r dotenv/config express-basic",
-    "express": "tsnd -r tsconfig-paths/register -r dotenv/config express",
+    "custom-validators": "tsnd -r tsconfig-paths/register -r dotenv/config custom-validators",
     "gcs": "tsnd -r tsconfig-paths/register -r dotenv/config express-gcs",
     "gcs:direct": "tsnd -r tsconfig-paths/register -r dotenv/config gcs-direct",
     "node": "tsnd -r tsconfig-paths/register -r dotenv/config node-http-server",
     "s3": "tsnd -r tsconfig-paths/register -r dotenv/config express-s3",
     "tus": "tsnd -r tsconfig-paths/register -r dotenv/config express-tus",
-    "fastify": "tsnd -r tsconfig-paths/register -r dotenv/config fastify",
+    "processing": "tsnd -r tsconfig-paths/register -r dotenv/config processing",
     "express-polling": "tsnd -r tsconfig-paths/register -r dotenv/config express-polling"
   },
   "dependencies": {
diff --git a/examples/processing.ts b/examples/processing.ts
new file mode 100644
index 00000000..41bccff3
--- /dev/null
+++ b/examples/processing.ts
@@ -0,0 +1,36 @@
+import { DiskFile, DiskStorage, Uploadx } from '@uploadx/core';
+import { createHash } from 'crypto';
+import * as express from 'express';
+import { createReadStream } from 'fs';
+import { join } from 'path';
+import { completedRetryGuard } from './completed-retry-guard';
+
+const app = express();
+
+const uploadDirectory = 'upload';
+
+const fileHash: (filePath: string) => Promise<string> = filePath =>
+  new Promise(resolve => {
+    const hash = createHash('sha256');
+    createReadStream(filePath)
+      .on('data', data => hash.update(data))
+      .on('end', () => resolve(hash.digest('hex')));
+  });
+
+const storage = new DiskStorage({ directory: uploadDirectory });
+
+const onComplete: express.RequestHandler = async (req, res, next) => {
+  const file = req.body as DiskFile;
+  try {
+    const sha256 = await fileHash(join(uploadDirectory, file.name));
+    res.finishUpload({ statusCode: 200, body: { id: file.id, sha256 } });
+  } catch (error) {
+    res.finishUpload({ statusCode: 422, body: { error: 'File hash calculation error' } });
+  }
+};
+
+const uploadx = new Uploadx({ storage });
+
+app.all('/files', uploadx.upload, completedRetryGuard({ statusCode: 202 }, 60), onComplete);
+
+app.listen(3002, () => console.log('listening on port:', 3002));