Build an HTTP server on Android to upload large files using NanoHTTPD and Jetpack Compose UI, Kotlin SDL

Android HTTP & File Server using NanoHTTPD + Jetpack Compose

In this post, we’ll walk through how to build an HTTP server inside an Android app using NanoHTTPD and a modern Jetpack Compose UI, Kotlin DSL, capable of uploading large files over 10GB directly to the device's internal storage.

---

🧩 Tech Stack

• 🧠 NanoHTTPD: Lightweight Java HTTP server
• 🖼 Jetpack Compose: Declarative Kotlin UI framework
• 🗂 ViewModel & Kotlin DSL: For clean state and UI control
• 📁 Custom File Upload Logic: Efficient streaming to disk

🐙 Source Code on GitHub https://github.com/WPSeven/Android-Http-File-Server

---

🚀 Why This?

Mobile apps typically don't expose HTTP endpoints, but with custom tooling, you can:

• Turn your phone into a local file server
• Receive large files over Wi-Fi
• Avoid needing ADB or USB transfers for big files (like 10GB+ videos)

---

📦 Core Server Logic (NanoHTTPD)

We extend NanoHTTPD and override serve() to handle multipart/form-data uploads.

HttpServer.java

public class HttpServer extends NanoHTTPD {
    public HttpServer(int port, Context context, UploadCallback callback) {
        super(port);
        // Store context, callback
    }

    @Override
    public Response serve(IHTTPSession session) {
        // Handle file uploads using NanoFileUpload
    }
}   

This is backed by a NanoFileUpload helper that uses streaming APIs to save files directly to disk without memory overflows.

---

💾 Streaming File Uploads

To handle large files, we stream the file upload chunk by chunk.

NanoFileUpload.java

public void handleUpload(IHTTPSession session) {
    // Parse multipart content using NanoHTTPD's TempFileManager
    // Write input stream directly to a FileOutputStream
}

🧠 Jetpack Compose UI

Your app includes a clean Kotlin DSL-based UI using Jetpack Compose to control the server.

MainScreen.kt

@Composable
fun MainScreen(viewModel: MainViewModel) {
    Column {
        Text("Android File Server")
        Button(onClick = { viewModel.toggleServer() }) {
            Text(if (viewModel.isRunning) "Stop Server" else "Start Server")
        }
        Text("Status: ${viewModel.statusText}")
    }
}

🧠 ViewModel Orchestration

MainViewModel.kt

class MainViewModel : ViewModel() {
    private var server: HttpServer? = null

    fun toggleServer() {
        if (server == null) {
            startServer()
        } else {
            stopServer()
        }
    }

    private fun startServer() {
        server = HttpServer(8080, context, uploadCallback)
        server?.start()
    }
}

The server is toggled via ViewModel, ensuring lifecycle-aware control.

---

⚙️ Handling Large File Uploads (Up to 10GB+)

The core feature is robust large file upload support. Here's what powers it under the hood:

✅ Multipart Upload Handling

We configure DiskFileItemFactory and NanoFileUpload to support very large uploads (10GB):

DiskFileItemFactory factory = new DiskFileItemFactory();
factory.setSizeThreshold(1024 * 1024); // 1MB memory buffer
factory.setRepository(mContext.getCacheDir()); // Temp storage
mFileUpload = new NanoFileUpload(factory);
mFileUpload.setFileSizeMax(10L * 1024 * 1024 * 1024); // 10GB

We also attach a ProgressListener to emit real-time upload progress back to the UI:

mFileUpload.setProgressListener((bytesRead, contentLength, items) -> {
    int progress = (int) (bytesRead * 100 / contentLength);
    mStatusUpdateListener.onUploadingProgressUpdate(progress);
});

🧠 HTML + JS File Upload UI (Web Browser)

When you visit / in a browser, the server responds with an HTML page that includes an upload form and a progress bar, using pure JS:

<form onsubmit='return uploadFile();'>
  <input type='file' id='fileInput' name='file'><br>
  <input type='submit' value='Upload File'>
</form>
<div class='progress'>
  <div id='progressBar' class='progress-bar'></div>
</div>

JavaScript handles the progress updates:

xhr.upload.onprogress = function(e) {
  var percentComplete = (e.loaded / e.total) * 100;
  document.getElementById('progressBar').style.width = percentComplete + '%';
};

📊 Upload Streaming & Disk Write

To save the uploaded file in chunks:

    private static final int BUFFER_SIZE = 1024 * 1024;
    private static final int CHUNK_SIZE = 10 * 1024 * 1024;

    private void copyInputStreamToFile(InputStream input, File file, long contentLength) throws IOException {
        try (FileOutputStream output = new FileOutputStream(file)) {
            byte[] buffer = new byte[BUFFER_SIZE];
            long count = 0;
            long lastProgressUpdate = 0;
            int n;

            while (-1 != (n = input.read(buffer))) {
                output.write(buffer, 0, n);
                count += n;

                // Update progress less frequently to reduce UI updates
                long currentTime = System.currentTimeMillis();
                if (currentTime - lastProgressUpdate > 500) { // Update every 500ms
                    int progress = (int)((count * 100) / contentLength);
                    if (mStatusUpdateListener != null) {
                        mStatusUpdateListener.onUploadingProgressUpdate(progress);
                    }
                    lastProgressUpdate = currentTime;
                }

                // Add small delay between large chunks to prevent buffer overflow
                if (count % CHUNK_SIZE == 0) {
                    Thread.sleep(50);
                }
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }

📡 Uploading Files to Android from PC using browser or command-line Once running:

1. Find your Android device’s IP on Wi-Fi.
2. Use browser or curl:

Browser 'http://192.168.1.175:8080/'

📸 Screenshot:

Command-line

curl -F "file=@bigfile.iso" http://192.168.1.x:8080

This is critical for handling large files without crashing.

With just a few files, you can turn your Android device into a full-fledged local http file server.

---

🧱 Source Code on GitHub https://github.com/WPSeven/Android-Http-File-Server

---

💡 #Kotlin #Compose #Android #HttpServer #FileServer #DevTips