Asp Core serve file via Web Api - asp.net

I am trying to figure out how i can transfer a file from my web api to my angular 5 front end and download it.
My Angular 5 front end is simple (i am using FileSaver package to help):
filedownload.component.html
<button (click)="downloadFile(document)">Download</button>
filedownload.component.ts
downloadFile(document) {
this.http.get("http://localhost:8080/"+document.id+).subscribe(
data => {
const dataFile = data;
saveAs(dataFile, document.filename);
},
err => { console.info(err); }
);
}
On my web api i have no idea how to construct the response.
So far i only have:
[HttpGet("{id}"]
public async Task<IActionResult> GetFile(Guid id) {
var testFileInfo = _dbcontext.UploadedFile.GetById(id);
var filePath = Path.Combine("C:\FileRepo", testFileInfo.Filename);
// what do i do here? i got no clue
throw new NotImplementedException();
}
I have tried experimenting with various examples online but nothing seems to work.
The idea is that web api would serve any range of files back to the front end, depending on whats on server.
File sizes range from 100kb to 50mb at this stage, file can be bigger once i implement archiving and zipping of multiple files.

If you want your API to return a file you can use this simple code:
[HttpGet("{id}")]
public IActionResult Get(Guid id)
{
var bytes = System.IO.File.ReadAllBytes(#"YourFilePAth");
return File(bytes, "application/octet-stream", "YourFileName.extension");
}

It is wiser to use a stream:
[HttpGet("{id}")]
public IActionResult Get(Guid id)
{
var stream = System.IO.File.OpenRead(#"YourFilePAth");
return File(stream, "application/octet-stream", "YourFileName.extension");
}

Related

.Net Core - Send image through api = Resource interpreted as Document but transferred with MIME type image/jpeg

In the wwwroot folder of my .Net Core MVC application, I have some images. I need to serve these pictures to TopDesk, where I can put in a url which gets embedded. I have no influence on Topdesk. I can only change the way the image is served.
When I use a direct link to the image, it works. The image gets embedded
Example of direct url:
https://my.web.site/images/image001.jpeg
But there is a limited embedded size (600px) so i need to resize the images. For that purpose I wrote a very simple api controller:
[HttpGet]
[Route("api/Images/GetImage/{id}")]
public IActionResult GetImage(string id)
{
try
{
var pad = $"c:\\Images\\{id}";
if(System.IO.File.Exists(path))
{
var fileBytes = System.IO.File.ReadAllBytes(path);
var smallImage = ..... doing resizing;
new FileExtensionContentTypeProvider().TryGetContentType(Path.GetFileName(path), out var contentType);
return File(smallImage , contentType ?? "application/octet-stream", $"{id}");
}
return NotFound();
}
catch(Exception ex)
{
return BadRequest(ex.Message);
}
}
but the url
https://my.web.site/api/images/GetImage/image001.jpeg
results in
Resource interpreted as Document but transferred with MIME type
image/jpeg
The image doesn't show.
When i test the url in Postman, it returns the image without warning.
What am i missing here?
Instead of returning a File, try using FileContentResult instead:
[HttpGet]
[Route("api/Images/GetImage/{id}")]
public IActionResult GetImage(string id)
{
try
{
var path = $"c:\\Images\\{id}";
if(System.IO.File.Exists(path))
{
var fileBytes = System.IO.File.ReadAllBytes(path);
var smallImage = ..... doing resizing;
new FileExtensionContentTypeProvider().TryGetContentType(Path.GetFileName(path), out var contentType);
return new FileContentResult(fileBytes, contentType ?? "application/octet-stream");
}
return NotFound();
}
catch(Exception ex)
{
return BadRequest(ex.Message);
}
}
When navigating to /GetImage/{id} with a browser, you will see that with File the browser tends to download the file, but with FileContentResult it displays the image in the browser tab directly, which is the same behavior as using static files. This is probably happening because of the Response Headers being added when using File/FileContentResult (probably a Content-Disposition header). Not sure how TopDesk is using these images though.
Off-topic: It's also a good practice to not instantiate a FileExtensionContentTypeProvider with every request. Instead, you can register it as a singleton in your Startup.cs like:
services.AddSingleton(new FileExtensionContentTypeProvider());
and inject it in your controller's constructor.

Unable to upload file as FormData to ASP.net from Angular

I am trying to upload a file from my angular code to an ASP.net backend.
My Angular code sends the object using FormData:
public uploadFiles(files) {
console.log(files);
if(files.length < 1) return;
const formData = new FormData();
files.forEach(file => {
console.log(file);
formData.append(file.name, file);
})
this._http.postFile('/order-processing/import-orders','application/x-www-form-urlencoded' ,formData).pipe(finalize(() => {
console.log("Finalized");
})).subscribe((val: any) => {
console.log('ORDER SUBMITTED', val);
}, error => {
console.log(error);
});
}
With the post file method looking like:
public postFile(path: string, contentType:string, body: FormData) : Observable<any> {
let headers = {
'Content-Type': contentType,
'Authorization': this.authToken
}
return this._http.post(environment.API_URL + path, body, {
headers
});
}
My ASP.net endpoint looks like:
[HttpPost, Route("hospitality/order-processing/import-orders")]
[RequestSizeLimit(2147483648)]
[DisableRequestSizeLimit]
public IActionResult UploadFile()
{
try
{
//var req = Request.Form.Files;
var file = Request.Form.Files;
string folderName = "Uploads";
string webRootPath = _hostingEnvironment.WebRootPath;
string newPath = Path.Combine(webRootPath, folderName);
if (!Directory.Exists(newPath))
{
Directory.CreateDirectory(newPath);
}
return Json("Upload Successful.");
}
catch (Exception e)
{
return Json("Failed:" + e);
}
}
If I check the network tab on my browser when I send the file, it says that my object is in the call, great, but for some reason it doesn't get picked up on the backend and when I step through the code it is not there.
I get different errors when I modify this code slightly. The error for the code in the state it is in now is "Form key or value length limit 2048 exceeded", however sometimes I get array out of bounds errors, or content boundary limit exceeded errors, it's enough to make you want to slam you face into your keyboard continually.
The whole point of this is to be able to upload an excel file to ASP.net code running in an AWS lambda, which then inserts rows in a RDS database. Am I going about this the right way? Is there a better way to achieve what I am trying to do? If not then what is wrong with my code that doesn't allow me to upload a file to a Web API?!
Thanks
It seems that you're trying to set the limit of the request but the message states that the problem is with form key or value length.
Try setting the RequestFormLimits and check if that helps.
[HttpPost, Route("hospitality/order-processing/import-orders")]
[RequestFormLimits(KeyLengthLimit = 8192, ValueLengthLimit = 8192)]
public IActionResult UploadFile()

Assembly.UnsafeLoadFrom causes web app crash

I am trying to load a DLL from internet, more specifically it is Azure storage (Blob), so I used "Assembly.UnsafeLoadFrom" like this:
Assembly.UnsafeLoadFrom(#"https://accountname.blob.core.windows.net/test/calculator.dll");
But becuaset this specific call, my web app (published) returns:
"The specified CGI application encountered an error and the server
terminated the process."
The weird part is if I am using my local build, it is fine. there is no crash and the return result is correct.
I am using Visual Studio 2015 and .net 5.
Please let me know how to resolve this issue or how to debug it.
Thanks
For a simple way, you could achieve your purpose by the following code:
calculator.dll
public class Calculator
{
public string HelloWorld(string userName)
{
return string.Format("Hello world, {0}!", userName);
}
}
HomeController.cs
public async Task<ActionResult> Index()
{
string url = "https://brucechen.blob.core.windows.net/dll/calculator.dll";
HttpClient client = new HttpClient();
var bytes = await client.GetByteArrayAsync(url);
//load assembly from bytes
Assembly assembly = Assembly.Load(bytes);
var calc = assembly.CreateInstance("calculator.Calculator");
//invoke the method and get result
var result = calc.GetType().InvokeMember("HelloWorld", BindingFlags.InvokeMethod, null, calc, new[] { "Bruce" });
ViewData["result"] = result;
return View();
}
Result

Web API Async Upload with XmlHttpRequest to get progress

I'm trying to drag and drop file upload with a progress bar.
I have a div which is listening to files being dropped on which is working perfectly.
I'm then..
//Setting up a XmlHttpRequest
xhr = new XMLHttpRequest();
//Open connection
xhr.open("post", "api/ImageUpload", true);
// Set appropriate headers
xhr.setRequestHeader("Content-Type", "multipart/form-data");
xhr.setRequestHeader("X-File-Type", uf.type);
xhr.setRequestHeader("X-File-Name", uf.name);
xhr.setRequestHeader("X-File-Size", uf.size);
This sends fine, with the stream as the body of the request to the Web API (not async).
[System.Web.Mvc.HttpPost]
public string Post()
{
Stream stream = HttpContext.Current.Request.InputStream;
String filename = HttpContext.Current.Request.Headers["X-File-Name"];
FileModel file = uploadService.UploadFile(stream, filename);
return file.Id.ToString();
}
I'm trying to chance the request to "public async Task< string> Post(){ }
If the method was using a multipart form on the page instead of XmlHttpRequest I would have used "await Request.Content.ReadAsMultipartAsync(provider)" but this doesn't seem to be populated at the time I need it.
So what is the correct was to handle and an Async call from XmlHttpRequest on a Web API in order to record progress during the request with XHR's progress event?
I have looked at a great deal of pages so far to find a solution but this is the page I have used primarily.
http://robertnyman.com/html5/fileapi-upload/fileapi-upload.html
Thanks for any help
Oliver
It looks like someone else had the same question with you and got an answer yet. please have a look at ASP.NET MVC 4 Web Api ajax file upload.
And here is an example from microsoft http://www.asp.net/web-api/overview/working-with-http/sending-html-form-data,-part-2.
I combined the two above solution together and worked for me (just adjust a little bit)
one line change in Javascritp
xhr.open("post", "api/upload", true);
Save the file using stream
public class UploadController : ApiController
{
public async Task<HttpResponseMessage> PostFormData()
{
string root = HttpContext.Current.Server.MapPath("~/App_Data");
var fileName = Path.Combine(root, Request.Headers.GetValues("X-File-Name").First());
try
{
var writer = new StreamWriter(fileName);
await Request.Content.CopyToAsync(writer.BaseStream);
writer.Close();
return Request.CreateResponse(HttpStatusCode.OK);
}
catch (System.Exception e)
{
return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, e);
}
}
}

how to read multi part form data in .net web api controller

public class Sampleontroller:apicontroller
{
public void PostBodyMethod() {
HttpRequestMessage request=this.request;
//How to read the multi part data in the method
}
}
I am sending a multi part data to webapi controller.
How to read the contents in the method?
An 'async' example:
public async Task<HttpResponseMessage> PostSurveys()
{
// Verify that this is an HTML Form file upload request
if (!Request.Content.IsMimeMultipartContent("form-data"))
{
return Request.CreateResponse(HttpStatusCode.BadRequest);
}
//Destination folder
string uploadFolder = "mydestinationfolder";
// Create a stream provider for setting up output streams that saves the output under -uploadFolder-
// If you want full control over how the stream is saved then derive from MultipartFormDataStreamProvider and override what you need.
MultipartFormDataStreamProvider streamProvider = new MultipartFormDataStreamProvider(uploadFolder );
MultipartFileStreamProvider multipartFileStreamProvider = await Request.Content.ReadAsMultipartAsync(streamProvider);
// Get the file names.
foreach (MultipartFileData file in streamProvider.FileData)
{
//Do something awesome with the files..
}
}
Have a look at the article by Mike Wasson:
http://www.asp.net/web-api/overview/working-with-http/sending-html-form-data,-part-2
Or if you are doing file uploads, here: www.strathweb.com/2012/08/a-guide-to-asynchronous-file-uploads-in-asp-net-web-api-rtm/

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