Downloading Files in Zip Format in .NET Core Web API

Introduction

In many web applications, there arises a need to download multiple files as a single zip archive. This scenario is common when dealing with document management systems, exporting data, or providing bulk downloads. In this article, we will explore how to enable users to download files in a zip format from a .NET Core Web API.

Prerequisites

To follow along with this tutorial, it's assumed that you have a basic understanding of .NET Core Web API and Visual Studio or any other preferred integrated development environment (IDE).

Step 1. Setting up the .NET Core Web API project

Open Visual Studio and create a new .NET Core Web API project.

Configure the project as per your requirements, including selecting a target framework and naming the project.

Step 2. Adding Required NuGet Packages

Right-click on the project in the Solution Explorer and select "Manage NuGet Packages."

Search for and install the "System.IO.Compression" and "System.IO.Compression.FileSystem" packages. These packages provide the necessary classes to work with ZIP files.

Step 3. Creating the File Download Endpoint

Create a new controller (or you can use an existing one also) that will handle the file download in zip format. In this example, we'll create a simple controller named FileController.

Add a new action method with an appropriate route to handle the file download.

Code Example

#nullable disable

using Microsoft.AspNetCore.Mvc;
using System.IO.Compression;

namespace ZipDownload.Controllers {
  [ApiController]
  [Route("api/files")]
  public class FilesController: ControllerBase {
    private readonly IWebHostEnvironment _hostEnvironment;

    public FilesController(IWebHostEnvironment hostEnvironment) {
      _hostEnvironment = hostEnvironment;
    }

    [HttpGet]
    [Route("download-zip")]
    public IActionResult DownloadFiles() {
      try {
        var folderPath = Path.Combine(_hostEnvironment.ContentRootPath, "FilesToDownload");

        // Ensure the folder exists
        if (!Directory.Exists(folderPath))
          return NotFound("Folder not found.");

        // Get a list of files in the folder
        var files = Directory.GetFiles(folderPath);

        if (files.Length == 0)
          return NotFound("No files found to download.");

        // Create a temporary memory stream to hold the zip archive
        using(var memoryStream = new MemoryStream()) {
          // Create a new zip archive
          using(var zipArchive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true)) {
            foreach(var file in files) {
              var fileInfo = new FileInfo(file);

              // Create a new entry in the zip archive for each file
              var entry = zipArchive.CreateEntry(fileInfo.Name);

              // Write the file contents into the entry
              using(var entryStream = entry.Open())
              using(var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read)) {
                fileStream.CopyTo(entryStream);
              }
            }
          }

          memoryStream.Seek(0, SeekOrigin.Begin);

          // Return the zip file as a byte array
          return File(memoryStream.ToArray(), "application/zip", "files.zip");
        }
      } catch (Exception ex) {
        return StatusCode(500, $ "An error occurred: {ex.Message}");
      }
    }
  }
}