I'm trying to create an API that downloads a specific file from the server in ASP.Net Core.
I'm Using the ASP.NET Boilerplate.
I've tried every solution i found, and non of them helped me.
most of the solutions I've tried, implements something like this:
public async Task<IActionResult> Download(string filename)
{
if (filename == null)
return Content("filename not present");
var path = Path.Combine(
Directory.GetCurrentDirectory(),
"wwwroot", filename);
var memory = new MemoryStream();
using (var stream = new FileStream(path, FileMode.Open))
{
await stream.CopyToAsync(memory);
}
memory.Position = 0;
return File(memory, GetContentType(path), Path.GetFileName(path));
}
And when using it, I always get an error on the last line Non-invocable member 'File' cannot be used like a method.
If you're seeing this error during compilation, it's probably because the compiler thinks you're trying to invoke the constructor on the System.IO.File class instead of invoking the File() method on the System.Web.Mvc.Controller class.
Try to call the method by explicitly scoping it to the instance with this.File(...).
Related
I'm trying to return a file from an action in ASP.NET Core:
public IActionResult GetFile(string filePath) {
return File("/home/me/file.png", "application/octet-stream");
}
However, I get a
System.IO.FileNotFoundException
in my browser window:
An unhandled exception occurred while processing the request.
FileNotFoundException: Could not find file: /home/me/file.png
Microsoft.AspNetCore.Mvc.Infrastructure.VirtualFileResultExecutor.ExecuteAsync(ActionContext context, VirtualFileResult result)
I've tried checking if the file exists using System.IO.File.Exists and looking for it in Directory.GetFiles, which both say the file does exist. I've also tried changing the media type to image/png, but that doesn't help anything.
Why am I getting this error, and how can I fix it?
This is what I use in an application, and it works perfectly:
[HttpGet]
[Route("download")]
public async Task<iactionresult> Download([FromQuery] string file) {
var uploads = Path.Combine(_hostingEnvironment.WebRootPath, "uploads");
var filePath = Path.Combine(uploads, file);
if (!System.IO.File.Exists(filePath))
return NotFound();
var memory = new MemoryStream();
using (var stream = new FileStream(filePath, FileMode.Open))
{
await stream.CopyToAsync(memory);
}
memory.Position = 0;
return File(memory, GetContentType(filePath), file);
}
This snippet is from here: my code is slightly different.
I'm trying out a few things with Blazor and I'm still new to it. I'm trying to get a file stream to download to the browser. What's the best way to download a file from Blazor to browser?
I've tried using a method in my razor view that returns a stream but that didn't work.
//In my Blazor view
#code{
private FileStream Download()
{
//get path + file name
var file = #"c:\path\to\my\file\test.txt";
var stream = new FileStream(test, FileMode.OpenOrCreate);
return stream;
}
}
The code above doesn't give me anything, not even an error
Another solution is to add a simple api controller endpoint using endpoints.MapControllerRoute. This will work only with server side blazor though.
Ex:
endpoints.MapBlazorHub();
endpoints.MapControllerRoute("mvc", "{controller}/{action}");
endpoints.MapFallbackToPage("/_Host");
Then add a controller. For example:
public class InvoiceController : Controller
{
[HttpGet("~/invoice/{sessionId}")]
public async Task<IActionResult> Invoice(string sessionId, CancellationToken cancel)
{
return File(...);
}
}
Usage in a .razor file:
async Task GetInvoice()
{
...
Navigation.NavigateTo($"/invoice/{orderSessionId}", true);
}
Although the above answer is technically correct, if you need to pass in a model -POST-, then NavigationManager won't work. In which case you, must likely end up using HttpClient component. If so wrap the response.Content -your stream- in a DotNetStreamReference instance - new DotNetStreamReference(response.Content). This will create a ReadableStream. Then create the blob with the content. Keep in mind DotNetStreamReference was recently introduced with .NET 6 RC1. As of now the most efficient way. Otherwise, you can use fetch API and create a blob from the response.
I wound up doing it a different way, not needing NavigationManager. It was partially taken from the Microsoft Docs here. In my case I needed to render an Excel file (using EPPlus) but that is irrelevant. I just needed to return a Stream to get my result.
On my Blazor page or component when a button is clicked:
public async Task GenerateFile()
{
var fileStream = ExcelExportService.GetExcelStream(exportModel);
using var streamRef = new DotNetStreamReference(stream: fileStream);
await jsRuntime.InvokeVoidAsync("downloadFileFromStream", "Actual File Name.xlsx", streamRef);
}
The GetExcelStream is the following:
public static Stream GetExcelStream(ExportModel exportModel)
{
var result = new MemoryStream();
ExcelPackage.LicenseContext = LicenseContext.Commercial;
var fileName = #$"Gets Overwritten";
using (var package = new ExcelPackage(fileName))
{
var sheet = package.Workbook.Worksheets.Add(exportModel.SomeUsefulName);
var rowIndex = 1;
foreach (var dataRow in exportModel.Rows)
{
...
// Add rows and cells to the worksheet
...
}
sheet.Cells.AutoFitColumns();
package.SaveAs(result);
}
result.Position = 0; // This is required or no data is in result
return result;
}
This JavaScript is in the link above, but adding it here as the only other thing I needed.
window.downloadFileFromStream = async (fileName, contentStreamReference) => {
const arrayBuffer = await contentStreamReference.arrayBuffer();
const blob = new Blob([arrayBuffer]);
const url = URL.createObjectURL(blob);
const anchorElement = document.createElement("a");
anchorElement.href = url;
anchorElement.download = fileName ?? "";
anchorElement.click();
anchorElement.remove();
URL.revokeObjectURL(url);
}
I would like to delete a temporary file after returning it form action. How can i achieve that with ASP.NET Core:
public IActionResult Download(long id)
{
var file = "C:/temp/tempfile.zip";
var fileName = "file.zip;
return this.PhysicalFile(file, "application/zip", fileName);
// I Would like to have File.Delete(file) here !!
}
The file is too big for returning using memory stream.
File() or PhysicalFile() return a FileResult-derived class that just delegates processing to an executor service. PhysicalFileResult's ExecuteResultAsync method calls :
var executor = context.HttpContext.RequestServices
.GetRequiredService<IActionResultExecutor<PhysicalFileResult>>();
return executor.ExecuteAsync(context, this);
All other FileResult-based classes work in a similar way.
The PhysicalFileResultExecutor class essentially writes the file's contents to the Response stream.
A quick and dirty solution would be to create your own PhysicalFileResult-based class that delegates to PhysicalFileResultExecutor but deletes the file once the executor finishes :
public class TempPhysicalFileResult : PhysicalFileResult
{
public TempPhysicalFileResult(string fileName, string contentType)
: base(fileName, contentType) { }
public TempPhysicalFileResult(string fileName, MediaTypeHeaderValue contentType)
: base(fileName, contentType) { }
public override async Task ExecuteResultAsync(ActionContext context)
{
try {
await base.ExecuteResultAsync(context);
}
finally {
File.Delete(FileName);
}
}
}
Instead of calling PhysicalFile() to create the PhysicalFileResult you can create and return a TempPhysicalFileResult, eg :
return new TempPhysicalFileResult(file, "application/zip"){FileDownloadName=fileName};
That's the same thing PhysicalFile() does :
[NonAction]
public virtual PhysicalFileResult PhysicalFile(
string physicalPath,
string contentType,
string fileDownloadName)
=> new PhysicalFileResult(physicalPath, contentType) { FileDownloadName = fileDownloadName };
A more sophisticated solution would be to create a custom executor that took care eg of compression as well as cleaning up files, leaving the action code clean of result formatting code
You can create a FileStream that deletes the underlying file as soon as the stream is closed. With the option DeleteOnClose.
As the stream is closed automatically after download, the file is deleted.
var fileStream = new FileStream(
Path.GetTempFileName(),
FileMode.Create,
FileAccess.ReadWrite,
FileShare.Read,
4096,
FileOptions.DeleteOnClose);
// add something to the file
fileStream.Position = 0;
return File(fileStream, MediaTypeNames.Application.Octet);
It would be hard to do this within the same request as the requests ends directly after the streaming is complete. A better option might be to run a timed background task via a hosted service which periodically removes all files (e.g. with a last write time of >5 minutes ago) from the temp directory.
Since the file is big one solution is to send a token (like a guid) along side the request. Only once the download has been completed you want to delete the file (otherwise you risk losing it). So using that token the client will make a new request using the aforementioned token. So you will know that the download was successful and that you can proceed to delete the file.
I suggest using a Dictionary to map a token to a file.
Deleting on one request seems like a bad practice due to the fact that you can easily lose the file.
Also you can use Henk Mollema answer to be certain that all files are cleared periodically if that is what you are trying to achieve.
You can load content of file. delete file and send content in response. in MVC you can return a file in response. check the snippet below
public FileResult Download()
{
var fileName = $"client-file-name.ext";
var filepath = $"filepath";
byte[] fileBytes = System.IO.File.ReadAllBytes(filepath);
//delete file here
return File(fileBytes, "application/x-msdownload", fileName);
}
I'm encountering a problem sending files stored in a database back to the user in ASP.NET MVC. What I want is a view listing two links, one to view the file and let the mimetype sent to the browser determine how it should be handled, and the other to force a download.
If I choose to view a file called SomeRandomFile.bak and the browser doesn't have an associated program to open files of this type, then I have no problem with it defaulting to the download behavior. However, if I choose to view a file called SomeRandomFile.pdf or SomeRandomFile.jpg I want the file to simply open. But I also want to keep a download link off to the side so that I can force a download prompt regardless of the file type. Does this make sense?
I have tried FileStreamResult and it works for most files, its constructor doesn't accept a filename by default, so unknown files are assigned a file name based on the URL (which does not know the extension to give based on content type). If I force the file name by specifying it, I lose the ability for the browser to open the file directly and I get a download prompt. Has anyone else encountered this?
These are the examples of what I've tried so far.
//Gives me a download prompt.
return File(document.Data, document.ContentType, document.Name);
//Opens if it is a known extension type, downloads otherwise (download has bogus name and missing extension)
return new FileStreamResult(new MemoryStream(document.Data), document.ContentType);
//Gives me a download prompt (lose the ability to open by default if known type)
return new FileStreamResult(new MemoryStream(document.Data), document.ContentType) {FileDownloadName = document.Name};
Any suggestions?
UPDATE:
This questions seems to strike a chord with a lot of people, so I thought I'd post an update. The warning on the accepted answer below that was added by Oskar regarding international characters is completely valid, and I've hit it a few times due to using the ContentDisposition class. I've since updated my implementation to fix this. While the code below is from my most recent incarnation of this problem in an ASP.NET Core (Full Framework) app, it should work with minimal changes in an older MVC application as well since I'm using the System.Net.Http.Headers.ContentDispositionHeaderValue class.
using System.Net.Http.Headers;
public IActionResult Download()
{
Document document = ... //Obtain document from database context
//"attachment" means always prompt the user to download
//"inline" means let the browser try and handle it
var cd = new ContentDispositionHeaderValue("attachment")
{
FileNameStar = document.FileName
};
Response.Headers.Add(HeaderNames.ContentDisposition, cd.ToString());
return File(document.Data, document.ContentType);
}
// an entity class for the document in my database
public class Document
{
public string FileName { get; set; }
public string ContentType { get; set; }
public byte[] Data { get; set; }
//Other properties left out for brevity
}
public ActionResult Download()
{
var document = ...
var cd = new System.Net.Mime.ContentDisposition
{
// for example foo.bak
FileName = document.FileName,
// always prompt the user for downloading, set to true if you want
// the browser to try to show the file inline
Inline = false,
};
Response.AppendHeader("Content-Disposition", cd.ToString());
return File(document.Data, document.ContentType);
}
NOTE: This example code above fails to properly account for international characters in the filename. See RFC6266 for the relevant standardization. I believe recent versions of ASP.Net MVC's File() method and the ContentDispositionHeaderValue class properly accounts for this. - Oskar 2016-02-25
I had trouble with the accepted answer due to no type hinting on the "document" variable: var document = ... So I'm posting what worked for me as an alternative in case anybody else is having trouble.
public ActionResult DownloadFile()
{
string filename = "File.pdf";
string filepath = AppDomain.CurrentDomain.BaseDirectory + "/Path/To/File/" + filename;
byte[] filedata = System.IO.File.ReadAllBytes(filepath);
string contentType = MimeMapping.GetMimeMapping(filepath);
var cd = new System.Net.Mime.ContentDisposition
{
FileName = filename,
Inline = true,
};
Response.AppendHeader("Content-Disposition", cd.ToString());
return File(filedata, contentType);
}
To view file (txt for example):
return File("~/TextFileInRootDir.txt", MediaTypeNames.Text.Plain);
To download file (txt for example):
return File("~/TextFileInRootDir.txt", MediaTypeNames.Text.Plain, "TextFile.txt");
note: to download file we should pass fileDownloadName argument
Darin Dimitrov's answer is correct. Just an addition:
Response.AppendHeader("Content-Disposition", cd.ToString()); may cause the browser to fail rendering the file if your response already contains a "Content-Disposition" header. In that case, you may want to use:
Response.Headers.Add("Content-Disposition", cd.ToString());
I believe this answer is cleaner, (based on
https://stackoverflow.com/a/3007668/550975)
public ActionResult GetAttachment(long id)
{
FileAttachment attachment;
using (var db = new TheContext())
{
attachment = db.FileAttachments.FirstOrDefault(x => x.Id == id);
}
return File(attachment.FileData, "application/force-download", Path.GetFileName(attachment.FileName));
}
Below code worked for me for getting a pdf file from an API service and response it out to the browser - hope it helps;
public async Task<FileResult> PrintPdfStatements(string fileName)
{
var fileContent = await GetFileStreamAsync(fileName);
var fileContentBytes = ((MemoryStream)fileContent).ToArray();
return File(fileContentBytes, System.Net.Mime.MediaTypeNames.Application.Pdf);
}
FileVirtualPath --> Research\Global Office Review.pdf
public virtual ActionResult GetFile()
{
return File(FileVirtualPath, "application/force-download", Path.GetFileName(FileVirtualPath));
}
Action method needs to return FileResult with either a stream, byte[], or virtual path of the file. You will also need to know the content-type of the file being downloaded. Here is a sample (quick/dirty) utility method. Sample video link
How to download files using asp.net core
[Route("api/[controller]")]
public class DownloadController : Controller
{
[HttpGet]
public async Task<IActionResult> Download()
{
var path = #"C:\Vetrivel\winforms.png";
var memory = new MemoryStream();
using (var stream = new FileStream(path, FileMode.Open))
{
await stream.CopyToAsync(memory);
}
memory.Position = 0;
var ext = Path.GetExtension(path).ToLowerInvariant();
return File(memory, GetMimeTypes()[ext], Path.GetFileName(path));
}
private Dictionary<string, string> GetMimeTypes()
{
return new Dictionary<string, string>
{
{".txt", "text/plain"},
{".pdf", "application/pdf"},
{".doc", "application/vnd.ms-word"},
{".docx", "application/vnd.ms-word"},
{".png", "image/png"},
{".jpg", "image/jpeg"},
...
};
}
}
If, like me, you've come to this topic via Razor components as you're learning Blazor, then you'll find you need to think a little more outside of the box to solve this problem. It's a bit of a minefield if (also like me) Blazor is your first forray into the MVC-type world, as the documentation isn't as helpful for such 'menial' tasks.
So, at the time of writing, you cannot achieve this using vanilla Blazor/Razor without embedding an MVC controller to handle the file download part an example of which is as below:
using Microsoft.AspNetCore.Mvc;
using Microsoft.Net.Http.Headers;
[Route("api/[controller]")]
[ApiController]
public class FileHandlingController : ControllerBase
{
[HttpGet]
public FileContentResult Download(int attachmentId)
{
TaskAttachment taskFile = null;
if (attachmentId > 0)
{
// taskFile = <your code to get the file>
// which assumes it's an object with relevant properties as required below
if (taskFile != null)
{
var cd = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment")
{
FileNameStar = taskFile.Filename
};
Response.Headers.Add(HeaderNames.ContentDisposition, cd.ToString());
}
}
return new FileContentResult(taskFile?.FileData, taskFile?.FileContentType);
}
}
Next, make sure your application startup (Startup.cs) is configured to correctly use MVC and has the following line present (add it if not):
services.AddMvc();
.. and then finally modify your component to link to the controller, for example (iterative based example using a custom class):
<tbody>
#foreach (var attachment in yourAttachments)
{
<tr>
<td>#attachment.Filename </td>
<td>#attachment.CreatedUser</td>
<td>#attachment.Created?.ToString("dd MMM yyyy")</td>
<td><ul><li class="oi oi-circle-x delete-attachment"></li></ul></td>
</tr>
}
</tbody>
Hopefully this helps anyone who struggled (like me!) to get an appropriate answer to this seemingly simple question in the realms of Blazor…!
All the documentation / tutorials / questions about processing a file uploaded using FormData to a ASP.NET WebAPI handler use MultipartFormDataStreamProvider to process the multipart stream to split it into the relevant form fields and files.
var root = HttpContext.Current.Server.MapPath("~/App_Data");
var provider = new MultipartFormDataStreamProvider(root);
await Request.Content.ReadAsMultipartAsync(provider);
foreach (MultipartFileData file in provider.FileData)
{
// File
}
However, the files are automatically written to a directory during processsing.
It seems a lot of hassle when I could just use HttpContext.Current.Request.Files[0].InputStream to access a given file stream directly in memory.
How can WebAPI just access the file stream directly without the IO overhead of using MultipartFormDataStreamProvider?
Official tutorial: http://www.asp.net/web-api/overview/advanced/sending-html-form-data,-part-2
Solved:
Use the existing simple MultipartMemoryStreamProvider. No custom classes or providers required. This differers from the duplicate question which solved the solution by writing a custom provider.
Then use it in a WebAPI handler as so:
public async Task<IHttpActionResult> UploadFile()
{
if (!Request.Content.IsMimeMultipartContent())
{
return StatusCode(HttpStatusCode.UnsupportedMediaType);
}
var filesReadToProvider = await Request.Content.ReadAsMultipartAsync();
foreach (var stream in filesReadToProvider.Contents)
{
var fileBytes = await stream.ReadAsByteArrayAsync();
}
return StatusCode(HttpStatusCode.OK);
}