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…!
Related
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 = $"filepath";
byte[] fileBytes = System.IO.File.ReadAllBytes(filepath);
//delete file here
return File(fileBytes, "application/x-msdownload", fileName);
}
I'm trying to pass a CSV file to my backend to utilize a library for parsing CSV data.
I've got an Angular7 front end with a C# .Net Core MVC backend utilizing the HttpClient in typescript in order to pass data and objects to and from the backend.
I've tried a number of solutions but with minimal success (the closest being that I can reach the controller in my code, but the file never gets passed in).
I'm trying to avoid doing any kind of serialization or conversion of the CSV until it hits the controller so I'd like to find a solution where I can send the whole of the CSV to the backend.
Any help would be appreciated.
service.ts
// Parse CSV
// The CSV always reaches this part of the code and I can inspect it.
parseCsv$(file: File): Observable<Dto> {
const request$ = this.http.post<Dto>(
location.origin + '/api/csvimport',
file,
{ headers: new HttpHeaders({ 'Content-Type': 'multipart/form-data' }) }
).pipe(
map((response: <Dto>) => response)
);
request$.subscribe();
return request$;
}
CsvImportController.cs
[HttpPost]
[ProducesResponseType(typeof(Dto), 200)]
// The 'file' variable below is always null
public async Task<IActionResult> ParseCsv([FromBody]IFormFile file)
{
// do work here
You should not use FromBody parameter in File Upload.
You should either use, request.Form.Files collection to get the uploaded file,
OR
you can use IList in the controller action as shown below.
Below API gets list of files which are then saved in the temp folder on server.
[HttpPost("UploadFiles")]
public async Task<IActionResult> Post(List<IFormFile> files)
{
long size = files.Sum(f => f.Length);
// full path to file in temp location
var filePath = Path.GetTempFileName();
foreach (var formFile in files)
{
if (formFile.Length > 0)
{
using (var stream = new FileStream(filePath, FileMode.Create))
{
await formFile.CopyToAsync(stream);
}
}
}
// process uploaded files
// Don't rely on or trust the FileName property without validation.
return Ok(new { count = files.Count, size, filePath});
}
Hope this helps.
So I was able to figure this out,
I needed to change File to a FileList and then use FormData to append the file. I also needed to drop my content header as letting the backend handle typing the content itself stopped errors from being thrown. In my controller I had to use an IEnumerable<IFormFile> for this to fully work.
I don't fully understand why I had to use a FileList when only
uploading one file, but this was required in order to send along the
file. If I find out more, I will update my answer.
EDIT: Addressing the above, in the MDN documentation, it states that "All <input> element nodes have a files attribute of type FileList on them which allows access to the items in this list" (https://developer.mozilla.org/en-US/docs/Web/API/FileList) So in order to access one file, you actually need to access the first index (FileList[0]) of the FileList array. I may be misunderstanding this, so feel free to comment.
service.ts
parseCsv$(files: FileList): Observable<Dto> {
const formData = new FormData();
Array.from(files).forEach(
(file: File) => formData.append(file.name, file)
);
return this.http.post<Dto>(
location.origin + '/api/csvimport',
formData)
.pipe(
map((response: <Dto>) => response)
);
}
CsvImportController.cs
[HttpPost]
[ProducesResponseType(typeof(Dto), 200)]
public async Task<IActionResult> ParseCsv(IEnumerable<IFormFile> files)
{
// Work here...
I am using ServiceStack for a simple web application. The main purpose is to let a user download a file. I am using an HttpResult as follows:
public class FileDownloadService : Service
{
public object Any()
{
string fileFullPath = "...";
string mimeType = "application/pdf";
FileInfo fi = new FileInfo(fileFullPath);
byte[] reportBytes = File.ReadAllBytes(fi.FullName);
result = new HttpResult(reportBytes, mimeType);
return result;
}
}
This opens a dialog in the user's browser and the user can specify where to save the file. A default name is specified, which is the name of the restPath of ServiceStack.
My question is: is it possible to specify a custom file name for when the user chooses to save (changing the default one)? I tried to work with HttpResult properties, but no luck.
Thanks in advance!
You should set the 'Content-Disposition' header on the HTTP result. That allows to set the filename:
public object Any()
{
string fileFullPath = "...";
string mimeType = "application/pdf";
FileInfo fi = new FileInfo(fileFullPath);
byte[] reportBytes = File.ReadAllBytes(fi.FullName);
result = new HttpResult(reportBytes, mimeType);
result.Headers.Add("Content-Disposition", "attachment;filename=YOUR_NAME_HERE.pdf;");
return result;
}
I have found the solution. I was deceived by the readonly properties of the HttpResult.
In order to change the default file name, I discovered that I have to add the following line, that treats the content-disposition:
result.Headers[HttpHeaders.ContentDisposition] = "attachment; filename=\"UserSurname_UserName.pdf\"";
Thank you all for your time!
If I understood your question correctly, what you want is the user wants to rename the file. This is nothing to do with the server. The user has to do some changes in the brwoser he is uses.
e.g Firefox - Tools > Options > General
Then check the "Always ask me where to save files"
Chrome - Settings > Downloads
Then check the "Ask where to save each file before "
Then it will open file browser where to save, you may change your file name what ever your wanted
currently I am trying to create two controller methods reading from file and writing to same file:
public ActionResult UploadText(string name)
{
var path = Path.Combine(Server.MapPath("~/text/"), name);
var fileContents = System.IO.File.ReadAllText(path);
ViewData["text"] = fileContents;
ViewData["textName"] = name;
return View();
}
[HttpPost]
public ActionResult TextPost(string textName)
{
string text = Request["text-content"];
var path = Path.Combine(Server.MapPath("~/text/"), textName);
System.IO.File.WriteAllText(path, text);
return RedirectToAction("Index");
}
Reading file content and writing to it works, but it cannot be read second time, File can't be accessed because it is being used by another process error appears.
What am I doing wrong?
System.IO.File.ReadAllText and System.IO.File.WriteAllText both close the file after they and finished with the file per the documentation. The issue stems from the async nature of the web and well if you have more than one request while the file is open you will get the error you are seeing. Here are some MSDN examples to get you started.
Here are a couple more links for your pleasure
simultaneous read-write a file in C#
How to both read and write a file in C#