How to Upload Large Files in KMM using Ktor: A Step-by-Step Guide

Are you tired of struggling with large file uploads in your KMM (Kotlin Multiplatform Mobile) project using Ktor? Look no further! In this comprehensive guide, we’ll take you through the process of uploading large files seamlessly and efficiently. Buckle up, and let’s dive in!

What’s the Problem with Large File Uploads?

Uploading large files can be a daunting task, especially when working with mobile devices. The main challenge lies in handling the file size, memory constraints, and network limitations. With KMM, you can share code between Android and iOS, but that doesn’t mean you’re exempt from the constraints of mobile devices.

Large file uploads can lead to:

• Memory issues: Large files can consume a significant amount of memory, causing app crashes and instability.
• Network congestion: Uploading large files can clog the network, leading to slow uploads and frustrated users.
• Inconsistent behavior: Different devices and platforms may handle large file uploads differently, making it difficult to maintain consistency.

Why Choose Ktor for File Uploads?

Ktor is a modern, lightweight, and versatile web framework for Kotlin. It provides a robust and efficient way to handle file uploads, making it an excellent choice for your KMM project. With Ktor, you can:

• Handle large files with ease: Ktor allows you to upload files of any size, without worrying about memory constraints.
• Stream files: Ktor enables you to stream files, reducing the memory footprint and improving performance.
• Customize file handling: Ktor provides extensive customization options, allowing you to tailor file uploads to your specific needs.

Setting Up Ktor for File Uploads

Before we dive into the meat of the article, let’s set up a basic Ktor project for file uploads. Follow these steps:

1. Create a new KMM project in Android Studio or IntelliJ IDEA.
2. Add the Ktor dependencies to your build.gradle file:

   dependencies {
     implementation "io.ktor:ktor-server-core:$ktor_version"
     implementation "io.ktor:ktor-server-netty:$ktor_version"
     implementation "io.ktor:ktor-client-okhttp:$ktor_version"
   }

3. Create a new Ktor application instance and configure it for file uploads:

   fun main() {
     embeddedServer(Netty, port = 8080) {
       routing {
         post("/upload") {
           // File upload logic will go here
         }
       }
     }.start(wait = true)
   }

Uploading Large Files with Ktor

Now that we have our Ktor setup ready, let’s focus on uploading large files. We’ll use a combination of Ktor’s built-in features and some clever tricks to ensure efficient and reliable file uploads.

Step 1: Create a File Upload Endpoint

Create a new endpoint to handle file uploads:

routing {
  post("/upload") {
    val call = call
    val request = call.receive()
    val file = request.get("file")

    // File upload logic will go here
  }
}

In this example, we’re using Ktor’s built-in MultiPartFormData feature to receive the uploaded file.

Step 2: Stream the File

To avoid memory issues, we’ll stream the file directly to the server:

file?.let { file ->
  val outputStream = File("uploads/${file.originalFileName}").outputStream()
  call.response.header("Content-Disposition", "attachment; filename=${file.originalFileName}")
  call.response.pipeline.intercept(SendPipeline) { message ->
    when (message) {
      is OutgoingContent.ReadChannelContent -> {
        message.readChannel.copyTo(outputStream)
      }
    }
  }
}

By streaming the file, we’re reducing the memory footprint and improving performance.

Step 3: Handle File Upload Progress

To provide a better user experience, let’s track the file upload progress:

call.response.header("X-Upload-Progress", "true")
val uploadProgress = AtomicInteger(0)

call.response.pipeline.intercept(SendPipeline) { message ->
  when (message) {
    is OutgoingContent.ReadChannelContent -> {
      message.readChannel.copyTo(outputStream) { bytesRead ->
        uploadProgress.addAndGet(bytesRead.toInt())
        call.response.header("X-Upload-Progress", "${uploadProgress.get()}")
      }
    }
  }
}

Now, you can track the file upload progress and display it to the user.

Step 4: Handle File Upload Completion

Finally, let’s handle the file upload completion:

call.response.pipeline.intercept(SendPipeline) { message ->
  when (message) {
    is OutgoingContent.ReadChannelContent -> {
      message.readChannel.copyTo(outputStream) { bytesRead ->
        // Upload complete, handle accordingly
        call.response.header("X-Upload-Complete", "true")
      }
    }
  }
}

Now, you can take further actions, such as saving the file to a database or performing additional processing.

Conclusion

Uploading large files in KMM using Ktor is a breeze! With these steps, you can ensure efficient, reliable, and scalable file uploads that won’t bog down your mobile app. Remember to:

• Stream files to reduce memory constraints.
• Track file upload progress for a better user experience.
• Handle file upload completion for further processing.

By following this guide, you’ll be well on your way to creating a robust and performant file upload system for your KMM project. Happy coding!

KMM Version	Ktor Version	Minimum Android SDK
1.5.10	1.6.0	21

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