File Downloader Library

A lightweight Android file downloader library built with Kotlin, Coroutines, and HttpURLConnection.

Supports pause, resume, progress tracking, and multiple downloads with a clean API.

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✨ Features

• Download files using HttpURLConnection
• Pause / Resume downloads
• Progress callbacks
• Cancel downloads
• Error handling
• Resume support using HTTP Range headers
• Lightweight – no heavy dependencies
• Works with Kotlin and Java
• Works with Kotlin projects only ✅

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📁 Project Structure

file_downloader_library
│
├── manifests
│
└── kotlin+java
    │
    └── com.suman.network_library
        │
        ├── internal
        │   ├── DownloadDispatchers
        │   ├── DownloaderConfig
        │   ├── DownloadRequest
        │   ├── DownloadRequestQueue
        │   ├── DownloadTask
        │   └── NetworkMonitor
        │
        ├── local_storage
        │   ├── DatabaseHelper
        │   ├── DownloadDbHelper
        │   ├── DownloadEntity
        │   ├── DownloadStates
        │   └── Mapper.kt
        │
        ├── network
        │
        ├── utils
        │   ├── Constants
        │   ├── FileNameUtils
        │   └── Utils.kt
        │
        ├── Downloader
        └── DownloaderConfig

⚙️ System Flow / Architecture

The downloader is designed as a queue-based, coroutine-driven system to efficiently manage multiple downloads with support for pause, resume, and progress tracking.

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🔁 How it Works

• Download requests are created using the Downloader API
• Each request is added to a DownloadRequestQueue
• A dispatcher manages execution and controls parallel downloads
• Each request is processed as a separate DownloadTask
• Downloads run using Kotlin Coroutines for non-blocking execution
• Progress and state are stored in a local database
• On resume, downloads continue from the last saved byte using HTTP Range headers

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🔄 Flow Summary

Request → Queue → Dispatcher → Task → Network → File System ↓ Database (Progress / State)

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⚡ Key Highlights

• Queue-based system → Efficient request management
• Coroutine-powered → Lightweight and asynchronous
• Parallel downloads → Multiple files can download simultaneously
• Persistent state → Supports resume even after interruption
• Clean separation → API, queue, worker, and storage layers

🎥 Demo

📦 Installation

Step 1: Add JitPack repository

Add JitPack to your root build.gradle.

allprojects {
    repositories {
        google()
        mavenCentral()
        maven { url 'https://jitpack.io' }
    }
}

---

Step 2: Add dependency

implementation 'com.github.Suman942:file-downloader:1.0.2'

---

🚀 Initialize Downloader

val downloader = Downloader.create(context)

Recommended:

• Initialize in Application class
• Or provide using Dagger / Hilt

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📥 Create Download Request

val request = Downloader.download(
    url = "...",
    destination = "...",
    fileName = "..."
)

Example

val request = downloader.newReqBuilder(
    "https://example.com/file.mp4",
    Environment.getExternalStoragePublicDirectory(
        Environment.DIRECTORY_DOWNLOADS
    ).absolutePath,
    "video.mp4"
).build()

---

⬇️ Start Download

val id = downloader.enqueue(
    request,
    onStart = { id ->
        println("Download started: $id")
    },
    onProgress = { id, progress ->
        println("Progress: $progress%")
    },
    onPause = { id ->
        println("Download paused")
    },
    onResume = { id, bytes ->
        println("Resumed from $bytes bytes")
    },
    onCancel = { id ->
        println("Download cancelled")
    },
    onComplete = { id ->
        println("Download completed")
    },
    onError = { id, error ->
        println("Error: $error")
    }
)

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⏸ Pause Download

downloader.pause(id)

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▶ Resume Download

downloader.resume(id)

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❌ Cancel Download

downloader.cancel(id)

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Why this library?

Android's default DownloadManager has limitations:

• Limited customization
• No fine-grained progress control
• Hard to integrate with modern architecture

This library solves these using coroutines and a custom queue system.

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👨‍💻 Author

Suman Shil

GitHub:
https://github.com/Suman942

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Medium

https://medium.com/@suman.shil.942/building-a-lightweight-android-file-downloader-library-using-kotlin-coroutines-and-b51396cb0af3

LinkedIn

https://www.linkedin.com/in/suman-shil-204177191/

📄 License

MIT License