Download file in C# .Net Core

Question

Hi All,

I am developing an application in angular and .NET Core. I need to implement download file functionality where user will be able to download file from URL in downloads folder. I came to know that WebClient is obsolete and can not be used in .NET Core for downloading a file.

Please advise how can I achieve the same ASAP.

Thanks and Regards,
Pratham

Answer 1

Hi @Pratham Jain ,

I need to implement download file functionality where user will be able to download file from URL in downloads folder.

To download file from the file folder (in the wwwroot folder, if the file folder doesn't in the wwwroot folder, refer to this link), you can get the file path via the IWebHostEnvironment, then read the file content and return a File object to the client.

[Route("api/[controller]")]  
[ApiController]  
public class ToDoController : ControllerBase  
{  
    private readonly IWebHostEnvironment environment;  
    public ToDoController(IWebHostEnvironment hostEnvironment)  
    {   
        environment = hostEnvironment;  
    }  
    [HttpGet("download")]  
    public IActionResult Download()  
    {  
        var filepath = Path.Combine(environment.WebRootPath, "images", "Image1.png");  
        return File(System.IO.File.ReadAllBytes(filepath), "image/png", System.IO.Path.GetFileName(filepath));  
    }  

Then, in the Index view page, we can add a hyperlink to call this API method and download file:

<a href='~/api/Todo/download' download>Download File From Folder</a>  

To download file from URL, you can use HttpClient or IHttpClientFactory, refer to the following code:

Create a DownloadExtention.cs :

public static class DownloadExtention  
{   
    public static async Task<byte[]?> GetUrlContent(string url)  
    {  
        using (var client = new HttpClient())  
        using (var result = await client.GetAsync(url))  
            return result.IsSuccessStatusCode ? await result.Content.ReadAsByteArrayAsync() : null;  
    }  
}  

Then in the API method, create a method as below:

    [HttpGet("downloadfromurl")]  
    public IActionResult DownloadFromUrl(string url)  
    {  
        var result = DownloadExtention.GetUrlContent(url);  
        if (result != null)  
        {   
            return File(result.Result, "image/png", "test.jpg");  
        }  
        return Ok("file is not exist");  
    }  

Then, add the download hyperlink:

<a href='~/api/Todo/downloadfromurl?url=https://www.learningcontainer.com/wp-content/uploads/2020/07/Large-Sample-Image-download-for-Testing.jpg' download>Download File</a>  

The output as below:

---

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Best regards,
Dillion

Answer 2

Hi ZhiLv-MSFT,

Many thanks for your response to my question. I have followed the same approach advised by you but receiving the below error in browser:

error: SyntaxError: Unexpected token '%', "%PDF-1.4 %"... is not valid JSON at JSON.parse(

Http failure during parsing for http://localhost:5157/api/downloadFile?filePath=2022\Aug\completed\27eagfh-cf32-5c3f-8d48-1231d2312dsdaCompleted.pdf"

I am using the below code-

 public override async Task<ActionResult<string>> HandleAsync([FromQuery]string filePath, CancellationToken cancellationToken = default)  
            {  
                try  
                {  
                    var filePathWithName = "https://test-file-directory.mywebsite.com/" + filePath.Replace("\\", "/");  
                    var result = await _downloadService.GetUrlContent(filePathWithName);  
                    if (result != null)  
                    {  
                        return File(result, "APPLICATION/octet-stream", Path.GetFileName(filePath));  
                    }  
                    return Ok("file is not exist");  
                }  
                catch (Exception ex)  
                {  
                    _logger.LogError(ex, $"Error while downloading the file");  
                    return StatusCode(StatusCodes.Status500InternalServerError);  
                    throw;  
                }  
            }  
      
            public async Task<byte[]?> GetUrlContent(string url)  
            {  
                using (var client = new HttpClient())  
                using (var result = await client.GetAsync(url))  
                    return result.IsSuccessStatusCode ? await result.Content.ReadAsByteArrayAsync() : null;  
            }  
  

Please advise if I am missing anything in above code.

Thanks and Regards,
Pratham Jain

Answer 3

Hi @Zhi Lv - MSFT ,

Many thanks for your response to my question. I have followed the same approach advised by you but receiving the below error in browser:

error: SyntaxError: Unexpected token '%', "%PDF-1.4 %"... is not valid JSON at JSON.parse(

Http failure during parsing for http://localhost:5157/api/downloadFile?filePath=2022\Aug\completed\27eagfh-cf32-5c3f-8d48-1231d2312dsdaCompleted.pdf"

I am using the below code-

 public override async Task<ActionResult<string>> HandleAsync([FromQuery]string filePath, CancellationToken cancellationToken = default)  
            {  
                try  
                {  
                    var filePathWithName = "https://test-file-directory.mywebsite.com/" + filePath.Replace("\\", "/");  
                    var result = await _downloadService.GetUrlContent(filePathWithName);  
                    if (result != null)  
                    {  
                        return File(result, "APPLICATION/octet-stream", Path.GetFileName(filePath));  
                    }  
                    return Ok("file is not exist");  
                }  
                catch (Exception ex)  
                {  
                    _logger.LogError(ex, $"Error while downloading the file");  
                    return StatusCode(StatusCodes.Status500InternalServerError);  
                    throw;  
                }  
            }  
      
            public async Task<byte[]?> GetUrlContent(string url)  
            {  
                using (var client = new HttpClient())  
                using (var result = await client.GetAsync(url))  
                    return result.IsSuccessStatusCode ? await result.Content.ReadAsByteArrayAsync() : null;  
            }  

Please advise if I am missing anything in above code.

Thanks and Regards,
Pratham Jain

Answer 4

That looks like a client error. it appears the client is expecting a json response, not a binary stream.

type the url in browser address bar. it should save the file. this will verify the server is correct.

on the client side, you are probably using ajax and specific json response. not sure what you are typing to do client side, but you will need to use the blob datatype, and maybe fileapi

Answer 5

I need the requirement to download a file using a web URL. I received a pdf file and a working file through the below code but some time pdf file is half blank and some of the content is blank.

It's perfectly working in WebAPI code which is in .Net core but the same code and method is used in a console application. that is causing the issue.

string PageURL="https://test.com/my-services/v1/maintenancereceipts/statement/pdf?AN=123";
string fileName ="C:\\test\\API\\Upload\\123.pdf";

if (!System.IO.File.Exists(fileName))
{
    WebClient client = new WebClient();
    Thread.Sleep(1000);
    client.DownloadFile(url, fileName);
}