How can I get the file size from a URL in SwiftUI?

To retrieve the file size from a URL in SwiftUI, you’ll typically make a network request to fetch the file's metadata, specifically the content length. You can achieve this by using URLSession to perform an HTTP HEAD request, which retrieves header information without downloading the entire file. Here’s how to do it:

1. Create a Function to Get the File Size:

- This function will take a URL string as input and return the file size (in bytes) as an optional integer. It uses URLSession to fetch only the headers, which will include the Content-Length field.

2. Example Code:

import Foundation

func getFileSize(from urlString: String) async -> Int? {
   guard let url = URL(string: urlString) else {
     return nil
   }

   var request = URLRequest(url: url)
   request.httpMethod = "HEAD"

   do {
     let (_, response) = try await URLSession.shared.data(for: request)

     if let httpResponse = response as? HTTPURLResponse,
       let contentLength = httpResponse.allHeaderFields["Content-Length"] as? String,
       let fileSize = Int(contentLength) {
        return fileSize
     }
   } catch {
     print("Error fetching file size: \(error)")
   }
   return nil
}

3. Using the Function in SwiftUI View:

- Call the getFileSize function in your SwiftUI view, preferably inside a task modifier when you want to fetch file sizes asynchronously.

import SwiftUI

struct ContentView: View {
  @State private var fileSize: Int? = nil
  let fileUrl = "https://example.com/yourfile.pdf" // Replace with your actual URL

  var body: some View {
    VStack {
      if let size = fileSize {
        Text("File size: \(size) bytes")
      } else {
        Text("Fetching file size...")
      }
    }
    .task {
      fileSize = await getFileSize(from: fileUrl)
    }
  }
}

4. Important Considerations:

- Error Handling: The example includes basic error handling, but you may need to expand it to handle various network issues or server errors gracefully. Also, make sure the server provides the Content-Length header in its response. Some servers might not provide this header, and in such cases, this method won’t work.

- Asynchronous Operation: Always use async/await when making network calls to keep your UI responsive. The task modifier ensures this.

- Security: Be aware of potential security risks when working with external URLs. Validate all inputs and avoid executing code based on unverified data.

- Performance: Using an HTTP HEAD request is better than fetching the entire file for just the file size since it reduces network load and processing time.

- URL Validity: Before making a request, ensure the URL is valid.

This approach lets you efficiently retrieve the file size from a URL in your SwiftUI applications. It uses modern Swift concurrency features to ensure a smooth and responsive user experience.

Learn more about this