I have some PDFs stored in my dropbox location and want users to be able to retrieve them via a call to an API.
[HttpGet("{key}")]
public async Task<ActionResult> GetPDF(string key) {
string? path = GetPath(key);
if (path == null) {
return NotFound();
}
using(System.Net.Http.HttpClient wc = new System.Net.Http.HttpClient()) {
try {
using(System.IO.Stream stream = await wc.GetStreamAsync(path)) {
// using(System.IO.Stream stream = wc.GetStreamAsync(path).GetAwaiter().GetResult()) {
return new FileStreamResult(stream, "application/pdf");
}
} catch(System.Exception ex) {
return NotFound();
}
}
}
It runs right through, without hitting the exception, and returns, then gives the error
The ReadAsync method cannot be called when another read operation is pending.
Waiting for the async method didn't help.
Your primary issue appears to be that the stream has been disposed before the function returns. FileStreamResult will dispose the stream, you don't need to do that.
Also, HttpClient should be a global field, otherwise you could get socket exhaustion issues.
HttpClient wc = new HttpClient();
[HttpGet("{key}")]
public async Task<ActionResult> GetPDF(string key)
{
string? path = GetPath(key);
if (path == null)
{
return NotFound();
}
try
{
var stream = await wc.GetStreamAsync(path);
return new FileStreamResult(stream, "application/pdf");
}
catch(System.Exception ex)
{
return NotFound();
}
}
Related
Problem
I want to return a file in my ASP.Net Web API Controller, but all my approaches return the HttpResponseMessage as JSON.
Code so far
public async Task<HttpResponseMessage> DownloadAsync(string id)
{
var response = new HttpResponseMessage(HttpStatusCode.OK);
response.Content = new StreamContent({{__insert_stream_here__}});
response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
return response;
}
When I call this endpoint in my browser, the Web API returns the HttpResponseMessage as JSON with the HTTP Content Header set to application/json.
If this is ASP.net-Core then you are mixing web API versions. Have the action return a derived IActionResult because in your current code the framework is treating HttpResponseMessage as a model.
[Route("api/[controller]")]
public class DownloadController : Controller {
//GET api/download/12345abc
[HttpGet("{id}")]
public async Task<IActionResult> Download(string id) {
Stream stream = await {{__get_stream_based_on_id_here__}}
if(stream == null)
return NotFound(); // returns a NotFoundResult with Status404NotFound response.
return File(stream, "application/octet-stream", "{{filename.ext}}"); // returns a FileStreamResult
}
}
Note:
The framework will dispose of the stream used in this case when the response is completed. If a using statement is used, the stream will be disposed before the response has been sent and result in an exception or corrupt response.
You can return FileResult with this methods:
1: Return FileStreamResult
[HttpGet("get-file-stream/{id}"]
public async Task<FileStreamResult> DownloadAsync(string id)
{
var fileName="myfileName.txt";
var mimeType="application/....";
Stream stream = await GetFileStreamById(id);
return new FileStreamResult(stream, mimeType)
{
FileDownloadName = fileName
};
}
2: Return FileContentResult
[HttpGet("get-file-content/{id}"]
public async Task<FileContentResult> DownloadAsync(string id)
{
var fileName="myfileName.txt";
var mimeType="application/....";
byte[] fileBytes = await GetFileBytesById(id);
return new FileContentResult(fileBytes, mimeType)
{
FileDownloadName = fileName
};
}
Here is a simplistic example of streaming a file:
using System.IO;
using Microsoft.AspNetCore.Mvc;
[HttpGet("{id}")]
public async Task<FileStreamResult> Download(int id)
{
var path = "<Get the file path using the ID>";
var stream = File.OpenRead(path);
return new FileStreamResult(stream, "application/octet-stream");
}
Note:
Be sure to use FileStreamResult from Microsoft.AspNetCore.Mvc and not from System.Web.Mvc.
ASP.NET 5 WEB API & Angular 12
You can return a FileContentResult object (Blob) from the server. It'll not get automatically downloaded. You may create an anchor tag in your front-end app programmatically and set the href property to an object URL created from the Blob by the method below. Now clicking on the anchor will download the file. You can set a file name by setting the 'download' attribute to the anchor as well.
downloadFile(path: string): Observable<any> {
return this._httpClient.post(`${environment.ApiRoot}/accountVerification/downloadFile`, { path: path }, {
observe: 'response',
responseType: 'blob'
});
}
saveFile(path: string, fileName: string): void {
this._accountApprovalsService.downloadFile(path).pipe(
take(1)
).subscribe((resp) => {
let downloadLink = document.createElement('a');
downloadLink.href = window.URL.createObjectURL(resp.body);
downloadLink.setAttribute('download', fileName);
document.body.appendChild(downloadLink);
downloadLink.click();
downloadLink.remove();
});
}
Backend
[HttpPost]
[Authorize(Roles = "SystemAdmin, SystemUser")]
public async Task<IActionResult> DownloadFile(FilePath model)
{
if (ModelState.IsValid)
{
try
{
var fileName = System.IO.Path.GetFileName(model.Path);
var content = await System.IO.File.ReadAllBytesAsync(model.Path);
new FileExtensionContentTypeProvider()
.TryGetContentType(fileName, out string contentType);
return File(content, contentType, fileName);
}
catch
{
return BadRequest();
}
}
return BadRequest();
}
Following is the basic example of returning file (e.g Image file) in .NET Core Web API:
<img src="#Url.Action("RenderImage", new { id = id})" alt="No Image found" />
Below is the code for returning File from controller to view. Following is Action method which will return file:
[Route("api/[controller]")]
public class DownloadController : Controller
{
//GET api/download/123
[HttpGet]
public async Task<IActionResult> RenderImage(string userId)
{
//get Image file using _fileservice from db
var result = await _fileService.getFile(userId);
if (result.byteStream == null)
return NotFound();
return File(result.byteStream, result.ContentType, result.FileName);
}
}
Note:
Our file should be first converted into byte[] and then saved in database as varbinary(max) in order to retrieve.
FileStreamResult works for me. and File is not an IActionResult. I don't know how it can work.
add
builder.Services.AddSingleton();
in
Program.cs
[HttpGet("{fileId}")]
public ActionResult GetFile(string fileId)
{
string pathToFile = "test.rar";
if (!System.IO.File.Exists(pathToFile))
{
return NotFound();
}
if(!_fileExtensionContentTypeProvider.TryGetContentType(pathToFile,
out var ContentType))
{
ContentType = "application/octet-stream";
}
var byets=System.IO.File.ReadAllBytes(pathToFile);
return File(byets, ContentType, Path.GetFileName(pathToFile));
}
}
Somehow I end up with the rare situation that an id is returned, but the blob hasn't been saved. Is there anything I'm missing in below code regarding C# 6 async in catch-statements or maybe an odd bug in the Azure libraries?
private async Task<string> Save(Stream stream)
{
var id = Guid.NewGuid();
var blob = ...;
try
{
await blob.UploadFromStreamAsync(stream);
}
catch
{
if (await blob.ExistsAsync())
{
await blob.DeleteAsync();
}
throw;
}
return id;
}
Problem
I want to return a file in my ASP.Net Web API Controller, but all my approaches return the HttpResponseMessage as JSON.
Code so far
public async Task<HttpResponseMessage> DownloadAsync(string id)
{
var response = new HttpResponseMessage(HttpStatusCode.OK);
response.Content = new StreamContent({{__insert_stream_here__}});
response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
return response;
}
When I call this endpoint in my browser, the Web API returns the HttpResponseMessage as JSON with the HTTP Content Header set to application/json.
If this is ASP.net-Core then you are mixing web API versions. Have the action return a derived IActionResult because in your current code the framework is treating HttpResponseMessage as a model.
[Route("api/[controller]")]
public class DownloadController : Controller {
//GET api/download/12345abc
[HttpGet("{id}")]
public async Task<IActionResult> Download(string id) {
Stream stream = await {{__get_stream_based_on_id_here__}}
if(stream == null)
return NotFound(); // returns a NotFoundResult with Status404NotFound response.
return File(stream, "application/octet-stream", "{{filename.ext}}"); // returns a FileStreamResult
}
}
Note:
The framework will dispose of the stream used in this case when the response is completed. If a using statement is used, the stream will be disposed before the response has been sent and result in an exception or corrupt response.
You can return FileResult with this methods:
1: Return FileStreamResult
[HttpGet("get-file-stream/{id}"]
public async Task<FileStreamResult> DownloadAsync(string id)
{
var fileName="myfileName.txt";
var mimeType="application/....";
Stream stream = await GetFileStreamById(id);
return new FileStreamResult(stream, mimeType)
{
FileDownloadName = fileName
};
}
2: Return FileContentResult
[HttpGet("get-file-content/{id}"]
public async Task<FileContentResult> DownloadAsync(string id)
{
var fileName="myfileName.txt";
var mimeType="application/....";
byte[] fileBytes = await GetFileBytesById(id);
return new FileContentResult(fileBytes, mimeType)
{
FileDownloadName = fileName
};
}
Here is a simplistic example of streaming a file:
using System.IO;
using Microsoft.AspNetCore.Mvc;
[HttpGet("{id}")]
public async Task<FileStreamResult> Download(int id)
{
var path = "<Get the file path using the ID>";
var stream = File.OpenRead(path);
return new FileStreamResult(stream, "application/octet-stream");
}
Note:
Be sure to use FileStreamResult from Microsoft.AspNetCore.Mvc and not from System.Web.Mvc.
ASP.NET 5 WEB API & Angular 12
You can return a FileContentResult object (Blob) from the server. It'll not get automatically downloaded. You may create an anchor tag in your front-end app programmatically and set the href property to an object URL created from the Blob by the method below. Now clicking on the anchor will download the file. You can set a file name by setting the 'download' attribute to the anchor as well.
downloadFile(path: string): Observable<any> {
return this._httpClient.post(`${environment.ApiRoot}/accountVerification/downloadFile`, { path: path }, {
observe: 'response',
responseType: 'blob'
});
}
saveFile(path: string, fileName: string): void {
this._accountApprovalsService.downloadFile(path).pipe(
take(1)
).subscribe((resp) => {
let downloadLink = document.createElement('a');
downloadLink.href = window.URL.createObjectURL(resp.body);
downloadLink.setAttribute('download', fileName);
document.body.appendChild(downloadLink);
downloadLink.click();
downloadLink.remove();
});
}
Backend
[HttpPost]
[Authorize(Roles = "SystemAdmin, SystemUser")]
public async Task<IActionResult> DownloadFile(FilePath model)
{
if (ModelState.IsValid)
{
try
{
var fileName = System.IO.Path.GetFileName(model.Path);
var content = await System.IO.File.ReadAllBytesAsync(model.Path);
new FileExtensionContentTypeProvider()
.TryGetContentType(fileName, out string contentType);
return File(content, contentType, fileName);
}
catch
{
return BadRequest();
}
}
return BadRequest();
}
Following is the basic example of returning file (e.g Image file) in .NET Core Web API:
<img src="#Url.Action("RenderImage", new { id = id})" alt="No Image found" />
Below is the code for returning File from controller to view. Following is Action method which will return file:
[Route("api/[controller]")]
public class DownloadController : Controller
{
//GET api/download/123
[HttpGet]
public async Task<IActionResult> RenderImage(string userId)
{
//get Image file using _fileservice from db
var result = await _fileService.getFile(userId);
if (result.byteStream == null)
return NotFound();
return File(result.byteStream, result.ContentType, result.FileName);
}
}
Note:
Our file should be first converted into byte[] and then saved in database as varbinary(max) in order to retrieve.
FileStreamResult works for me. and File is not an IActionResult. I don't know how it can work.
add
builder.Services.AddSingleton();
in
Program.cs
[HttpGet("{fileId}")]
public ActionResult GetFile(string fileId)
{
string pathToFile = "test.rar";
if (!System.IO.File.Exists(pathToFile))
{
return NotFound();
}
if(!_fileExtensionContentTypeProvider.TryGetContentType(pathToFile,
out var ContentType))
{
ContentType = "application/octet-stream";
}
var byets=System.IO.File.ReadAllBytes(pathToFile);
return File(byets, ContentType, Path.GetFileName(pathToFile));
}
}
I'm currently developing an Android app using the Xamarin framework, so I'm writing it in c#. In this app I'm fetching data from a REST-api, like this:
//Method implemented from interface IOnScrollListener
public async void OnScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
{
//lots of other stuff that's not important for this example
List<Message> messageList = await PopulateMessagebox(arg1, arg2));
}
The method is being called when you reach the bottom of a list (hence the IOnScrollListener implementation). However; the screen freezes when I reach the bottom, and the method is being invoked. And I'm curious as to how this can be, considering I'm using an ansync method call? Shouldn't it run on another thread, allowing the main thread to be uninterrupted/not having to wait?
How would I go about fixing this, so that the app would be responsive while it, in the background, fetches additional info from the API?
Edit: Here's the populateMessageBox-method
public async Task<List<Message>> PopulateMessagebox(Constants.MMBType type, int skipSize)
{
string messagesJson = await _dal.GetMessageBox(type, skipSize, url);
var mess = new List<Message>();
try
{
if (!string.IsNullOrEmpty(messagesJson))
{
mess = Serializer.DeserializeMessagebox(messagesJson);
}
}
catch (Exception e)
{
Logger.Logg("Failed to de-serialize the messagebox:" + e);
throw new AppException(ErrorMessages.SerializationError);
}
return mess;
}
public async Task<string> GetMessageBox(Constants.MMBType type, int skipSize, string url)
{
return await GetMessageBoxJSON(type, skipSize, url);
}
--
private async Task<string> GetMessageBoxJSON(Constants.MMBType type, int skipSize, string url)
{
string res = null;
if (type == Constants.MMBType.Messagebox)
{
string param = string.Format("?$filter=Status ne '{0}' and Status ne '{1}'&$skip={2}",
Constants.NO.Nob.Status.Sent, Constants.NO.Nob.Status.SentCorres, skipSize);
string request = url + param;
res = await DownloadAndHandle(request);
}
And a couple more calls like this, ends us up here:
protected virtual async Task<string> SetupAndDownloadString(string uri)
{
string responseText;
if (Session.CookieJar.Size() > 0)
{
var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Get, uri);
request.Headers.Add("ApiKey", AppContext.ApiKey);
request.Headers.Add("Accept", Constants.ApiFormat);
request.Headers.Add("Cookie", Session.CookieJar.ToString());
HttpResponseMessage response = await client.SendAsync(request);
responseText = response.Content.ReadAsStringAsync().Result;
}
else
{
throw new AppException(ErrorMessages.InsufficientAuthorization);
}
return responseText;
}
I'm having a problem with an async method that I implemented. The method basically makes a HttpRequest to a resource and deserializes the string if the request is successful. I wrote a test for the method, and it works. But the method does never return when I call it from a controller?
public async Task<IEnumerable<T>> Get()
{
try
{
var resourceSegmentUri = new Uri(_uri, UriKind.Relative);
var response = await _client.GetAsync(resourceSegmentUri);
if (response.IsSuccessStatusCode)
{
var submission = await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<IEnumerable<T>>(submission);
}
if (response.Content != null)
{
var message = response.Content.ReadAsStringAsync();
throw new WebException(message.Result, (WebExceptionStatus)response.StatusCode);
}
}
catch (WebException e)
{
Logger.Error("GET Request failed with status: {0}", e.Status);
throw;
}
throw new Exception();
}
Code that never returns:
public ActionResult Index()
{
var api = new Api();
var test = api.Get().Result; //Never returns
return View();
}
Test that works:
[Test]
public void GetShouldReturnIfSuccessfulRequest()
{
var api = new Api();
var submission = api.Get();
Console.WriteLine(JsonConvert.SerializeObject(submission));
Assert.NotNull(submission);
}
Does anyone know the problem?
You've got a deadlock because you're calling .Result in your controller action.
If you use async/await then you have to use asynchronous actions too.
So something like this should fix it:
public async Task<ActionResult> Index()
{
var api = new Api();
var test = await api.Get(); // Should return
}
There's a comprehensive article about this here: Using Asynchronous Methods in ASP.NET MVC 4