c# - How to download a large file (via HTTP) in .NET?

C# - How to download a large file (via HTTP) in .NET?

Downloading large files over HTTP in C#/.NET involves using HttpClient to handle the download process efficiently. Here's a step-by-step guide on how to achieve this:

Using HttpClient to Download a Large File

  1. Initialize HttpClient and HttpClientHandler:

    • HttpClient provides methods to send HTTP requests and receive HTTP responses from a specified URI.
    • HttpClientHandler allows configuration of the HTTP request (like timeout, credentials, etc.).

  2. Send GET Request and Download the File:

    • Use HttpClient.GetAsync to send a GET request asynchronously and receive an HttpResponseMessage.
    • Use HttpResponseMessage.Content.ReadAsStreamAsync to read the content of the response as a stream and download the file.

  3. Write Stream to File:

    • Use a FileStream to write the downloaded content to a file on disk. This allows handling large files without consuming too much memory.

Here's a sample code snippet demonstrating how to download a large file using HttpClient in C#:

using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public class FileDownloader { private const string downloadUrl = "https://example.com/largefile.zip"; private const string saveFilePath = "C:\\Downloads\\largefile.zip"; // Replace with your desired save path public async Task DownloadFileAsync() { using (HttpClient httpClient = new HttpClient()) { using (HttpResponseMessage response = await httpClient.GetAsync(downloadUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); // Ensure the server returns a success status code using (Stream contentStream = await response.Content.ReadAsStreamAsync()) { using (FileStream fileStream = new FileStream(saveFilePath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true)) { await contentStream.CopyToAsync(fileStream); } } } } Console.WriteLine("Download completed!"); } }

Explanation:

  • HttpClient.GetAsync: Initiates a GET request to the specified URI asynchronously.
  • HttpResponseMessage.Content.ReadAsStreamAsync: Reads the content of the HTTP response as a stream asynchronously.
  • FileStream: Writes the downloaded content to a file (saveFilePath) on disk.
  • CopyToAsync: Asynchronously reads the content from one stream (contentStream) and writes it to another (fileStream).

Usage:

Call DownloadFileAsync method to initiate the download asynchronously:

class Program { static async Task Main(string[] args) { FileDownloader downloader = new FileDownloader(); await downloader.DownloadFileAsync(); } }

Notes:

  • Error Handling: Ensure to handle exceptions appropriately, especially when dealing with network operations (HttpClient and file operations).
  • Performance: Adjust buffer sizes (8192 in the FileStream constructor) based on your specific needs and file size.
  • Cancellation and Progress: For more advanced scenarios, consider adding cancellation and progress reporting mechanisms.

This approach efficiently downloads large files over HTTP using C#/.NET's HttpClient with asynchronous operations, ensuring both performance and reliability.

Examples

  1. How to download a large file in C# using HttpClient

    Description: This query focuses on using the HttpClient class to download a large file in C#.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task DownloadFileAsync(string fileUrl, string destinationPath) { using (HttpClient client = new HttpClient()) using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true)) { await contentStream.CopyToAsync(fileStream); } } }

  2. How to show download progress for a large file in C#

    Description: This query involves showing the download progress of a large file using HttpClient.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task DownloadFileWithProgressAsync(string fileUrl, string destinationPath) { using (HttpClient client = new HttpClient()) using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); var totalBytes = response.Content.Headers.ContentLength.GetValueOrDefault(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true)) { byte[] buffer = new byte[8192]; int bytesRead; long totalBytesRead = 0; while ((bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length)) > 0) { await fileStream.WriteAsync(buffer, 0, bytesRead); totalBytesRead += bytesRead; Console.WriteLine($"Downloaded {totalBytesRead} of {totalBytes} bytes ({(double)totalBytesRead / totalBytes:P2})"); } } } }

  3. How to handle timeouts when downloading a large file in C#

    Description: This query addresses handling timeouts when downloading a large file using HttpClient.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task DownloadFileWithTimeoutAsync(string fileUrl, string destinationPath, TimeSpan timeout) { using (HttpClient client = new HttpClient { Timeout = timeout }) using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true)) { await contentStream.CopyToAsync(fileStream); } } }

  4. How to resume a paused download in C#

    Description: This query involves resuming a paused download using the Range header with HttpClient.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task ResumeDownloadAsync(string fileUrl, string destinationPath) { long existingLength = 0; if (File.Exists(destinationPath)) { existingLength = new FileInfo(destinationPath).Length; } using (HttpClient client = new HttpClient()) { client.DefaultRequestHeaders.Range = new System.Net.Http.Headers.RangeHeaderValue(existingLength, null); using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Append, FileAccess.Write, FileShare.None, 8192, true)) { await contentStream.CopyToAsync(fileStream); } } } }

  5. How to download a large file in chunks in C#

    Description: This query focuses on downloading a large file in chunks to avoid memory issues.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task DownloadFileInChunksAsync(string fileUrl, string destinationPath, int chunkSize = 8192) { using (HttpClient client = new HttpClient()) using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write, FileShare.None, chunkSize, true)) { byte[] buffer = new byte[chunkSize]; int bytesRead; while ((bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length)) > 0) { await fileStream.WriteAsync(buffer, 0, bytesRead); } } } }

  6. How to use WebClient to download a large file in C#

    Description: This query involves using the WebClient class to download a large file.

    Code:

    using System; using System.Net; public void DownloadFileUsingWebClient(string fileUrl, string destinationPath) { using (WebClient client = new WebClient()) { client.DownloadFile(fileUrl, destinationPath); } }

  7. How to use HttpWebRequest to download a large file in C#

    Description: This query focuses on using HttpWebRequest to download a large file.

    Code:

    using System; using System.IO; using System.Net; public void DownloadFileUsingHttpWebRequest(string fileUrl, string destinationPath) { HttpWebRequest request = (HttpWebRequest)WebRequest.Create(fileUrl); using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) using (Stream responseStream = response.GetResponseStream()) using (FileStream fileStream = new FileStream(destinationPath, FileMode.Create)) { responseStream.CopyTo(fileStream); } }

  8. How to handle authentication when downloading a large file in C#

    Description: This query addresses handling authentication when downloading a large file using HttpClient.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task DownloadFileWithAuthenticationAsync(string fileUrl, string destinationPath, string username, string password) { using (HttpClientHandler handler = new HttpClientHandler { Credentials = new NetworkCredential(username, password) }) using (HttpClient client = new HttpClient(handler)) using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true)) { await contentStream.CopyToAsync(fileStream); } } }

  9. How to download a large file asynchronously in C#

    Description: This query focuses on downloading a large file asynchronously using HttpClient.

    Code:

    using System; using System.IO; using System.Net.Http; using System.Threading.Tasks; public async Task DownloadFileAsync(string fileUrl, string destinationPath) { using (HttpClient client = new HttpClient()) using (HttpResponseMessage response = await client.GetAsync(fileUrl, HttpCompletionOption.ResponseHeadersRead)) { response.EnsureSuccessStatusCode(); using (Stream contentStream = await response.Content.ReadAsStreamAsync(), fileStream = new FileStream(destinationPath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true)) { await contentStream.CopyToAsync(fileStream); } } }

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