I have an API endpoint that returns file as attachment. for example if I access www.myfileservice.com/api/files/download/123 I could download the file directly. My requirement is to use this endpoint in another ASP.Net MVC project. So if the user hits www.mymvcapplication.com/File/DownloadDocument/123 it should also download the same file. Internally the action method should call the file service API and return the result as it is. This is the code I am using:
FileController.cs:
public HttpResponseMessage DownloadDocument(int Id)
{
return new DocumentClient().DownloadDocument(Id);
}
DocumentClient.cs:
public class DocumentClient
{
private string documentServiceURL = string.Empty;
private static string downloadDocumentUri = "api/files/download/";
protected HttpClient documentClient = null;
public DocumentClient()
{
documentServiceURL = "www.myfileservice.com";
documentClient = new HttpClient();
documentClient.BaseAddress = new Uri(documentServiceURL);
}
public HttpResponseMessage DownloadDocument(int Id)
{
return documentClient.GetAsync(String.Format("{0}/{1}", downloadDocumentUri, Id)).Result;
}
}
The code above is not giving any error but only printing the response in browser window(Content-Length, Content-Disposition etc). I need to download the file instead.
I think the best is to return a FileResult from your controller:
public FileResult DownloadDocument(int Id)
{
var document = new DocumentClient().DownloadDocument(Id);
//do the transformation here
//...
//I don't know what is your file's extension, please replace "application/zip" if
//needed
return File(finalResult, "application/zip", fileName);
}
I have a full engine that relies on abstractions based on user interactions. This works great with WPF/Xamarin app, cause I can implements this abstractions with window/form.
I have a little problem for porting this engine into ASP MVC.
A simple example can be show as this.
Abstraction interface (simplified)
public interface IQuestionBox
{
Task<bool> ShowYesNoQuestionBox(string message);
}
For WPF, it's really simple, I implement this interface as return the result of a window by calling ShowDialog().
In a simple business class, I can have this kind of calls (simplified) :
public async Task<string> GetValue(IQuestionBox qbox)
{
if(await qbox.ShowYesNoQuestionBox("Question ?"))
{
return "Ok";
}
return "NOk";
}
I really don't see how can I implement this kind of behavior in ASP, due to stateless of HTTP, knowing that this kind of call can be as various as domain/business need. The way I think it should be done is by returning a PartialView to inject into popup, but I don't see how to do this without breaking all the process ...
Anyone has ever done this ?
as I've said, I strongly doesn't recommend this pratice, but its possible, bellow the code that allows to do it, let's go:
To become it's possible I abused the use from TaskCompletionSource, this class allow us to set manually result in a task.
First we need to create a structure to encapsulate the process:
public class Process
{
// this dictionary store the current process running status, you will use it to define the future answer from the user interaction
private static Dictionary<string, Answare> StatusReport = new Dictionary<string, Answare>();
// this property is the secret to allow us wait for the ShowYesNoQuestion call, because til this happen the server doesn't send a response for the client.
TaskCompletionSource<bool> AwaitableResult { get; } = new TaskCompletionSource<bool>(true);
// here we have the question to interact with the user
IQuestionBox QuestionBox { get; set; }
// this method, receive your bussiness logical the receive your question as a parameter
public IQuestionBox Run(Action<IQuestionBox> action)
{
QuestionBox = new QuestionBox(this);
// here we create a task to execute your bussiness logical processment
Task.Factory.StartNew(() =>
{
action(QuestionBox);
});
// and as I said we wait the result from the processment
Task.WaitAll(AwaitableResult.Task);
// and return the question box to show the messages for the users
return QuestionBox;
}
// this method is responsable to register a question to receive future answers, as you can see, we are using our static dictionary to register them
public void RegisterForAnsware(string id)
{
if (StatusReport.ContainsKey(id))
return;
StatusReport.Add(id, new Answare()
{
});
}
// this method will deliver an answer for this correct context based on the id
public Answare GetAnsware(string id)
{
if (!StatusReport.ContainsKey(id))
return Answare.Empty;
return StatusReport[id];
}
// this method Releases the processment
public void Release()
{
AwaitableResult.SetResult(true);
}
// this method end the process delivering the response for the user
public void End(object userResponse)
{
if (!StatusReport.ContainsKey(QuestionBox.Id))
return;
StatusReport[QuestionBox.Id].UserResponse(userResponse);
}
// this method define the answer based on the user interaction, that allows the process continuing from where it left off
public static Task<object> DefineAnsware(string id, bool result)
{
if (!StatusReport.ContainsKey(id))
return Task.FromResult((object)"Success on the operation");
// here I create a taskcompletaionsource to allow get the result of the process, and send for the user, without it would be impossible to do it
TaskCompletionSource<object> completedTask = new TaskCompletionSource<object>();
StatusReport[id] = new Answare(completedTask)
{
HasAnswared = true,
Value = result
};
return completedTask.Task;
}
}
After that the question implementation
public interface IQuestionBox
{
string Id { get; }
Task<bool> ShowYesNoQuestionBox(string question);
HtmlString ShowMessage();
}
class QuestionBox : IQuestionBox
{
Process CurrentProcess { get; set; }
public string Id { get; } = Guid.NewGuid().ToString();
private string Question { get; set; }
public QuestionBox(Process currentProcess)
{
CurrentProcess = currentProcess;
CurrentProcess.RegisterForAnswer(this.Id);
}
public Task<bool> ShowYesNoQuestionBox(string question)
{
Question = question;
CurrentProcess.Release();
return AwaitForAnswer();
}
public HtmlString ShowMessage()
{
HtmlString htm = new HtmlString(
$"<script>showMessage('{Question}', '{Id}');</script>"
);
return htm;
}
private Task<bool> AwaitForAnswer()
{
TaskCompletionSource<bool> awaitableResult = new TaskCompletionSource<bool>(true);
Task.Factory.StartNew(() =>
{
while (true)
{
Thread.Sleep(2000);
var answare = CurrentProcess.GetAnswer(this.Id);
if (!answare.HasAnswered)
continue;
awaitableResult.SetResult(answare.Value);
break;
}
});
return awaitableResult.Task;
}
}
The differences for yours implementaion are:
1 - I create an Identifier to know for who I have to send the aswer, or just to stop the process.
2 - I receive a Process as parameter, because this allows us to call the method
CurrentProcess.Release(); in ShowYesNoQuestion, here in specific, releases the process to send the response responsable to interact with the user.
3 - I create the method AwaitForAnswer, here one more time we use from the TaskCompletionSource class. As you can see in this method we have a loop, this loop is responsable to wait for the user interaction, and til receive a response it doesn't release the process.
4 - I create the method ShowMessage that create a simple html script alert to simulate the user interaction.
Then a simple process class as you should be in your bussiness logical:
public class SaleService
{
public async Task<string> GetValue(IQuestionBox qbox)
{
if (await qbox.ShowYesNoQuestionBox("Do you think Edney is the big guy ?"))
{
return "I knew, Edney is the big guy";
}
return "No I disagree";
}
}
And then the class to represent the user answer
public class Answer
{
// just a sugar to represent empty responses
public static Answer Empty { get; } = new Answer { Value = true, HasAnswered = true };
public Answer()
{
}
// one more time abusing from TaskCompletionSource<object>, because with this guy we are abble to send the result from the process to the user
public Answer(TaskCompletionSource<object> completedTask)
{
CompletedTask = completedTask;
}
private TaskCompletionSource<object> CompletedTask { get; set; }
public bool Value { get; set; }
public bool HasAnswered { get; set; }
// this method as you can see, will set the result and release the task for the user
public void UserResponse(object response)
{
CompletedTask.SetResult(response);
}
}
Now we use all the entire structure create for this:
[HttpPost]
public IActionResult Index(string parametro)
{
// create your process an run it, passing what you want to do
Process process = new Process();
var question = process.Run(async (questionBox) =>
{
// we start the service
SaleService service = new SaleService();
// wait for the result
var result = await service.GetValue(questionBox);
// and close the process with the result from the process
process.End(result);
});
return View(question);
}
// here we have the method that deliver us the user response interaction
[HttpPost]
public async Task<JsonResult> Answer(bool result, string id)
{
// we define the result for an Id on the process
var response = await Process.DefineAnswer(id, result);
// get the response from process.End used bellow
// and return to the user
return Json(response);
}
and in your view
<!-- Use the question as the model page -->
#model InjetandoInteracaoComUsuario.Controllers.IQuestionBox
<form asp-controller="Home" asp-action="Index">
<!-- create a simple form with a simple button to submit the home -->
<input type="submit" name="btnDoSomething" value="All about Edney" />
</form>
<!-- in the scripts section we create the function that we call on the method ShowMessage, remember?-->
<!-- this method request the action answer passing the questionbox id, and the result from a simple confirm -->
<!-- And to finalize, it just show an alert with the process result -->
#section scripts{
<script>
function showMessage(message, id) {
var confirm = window.confirm(message);
$.post("/Home/Answer", { result: confirm, id: id }, function (e) {
alert(e);
})
}
</script>
#Model?.ShowMessage()
}
As I've said, I realy disagree with this pratices, the correct should to write a new dll, to support the web enviroment, but I hope it help you.
I put the project on github to you can download an understand all the solution
I realy hope it can help you
You can create a web socket connection from client side to server side. And work with front-end content with web socket request. It could be implemented as following:
Client side:
$app = {
uiEventsSocket : null,
initUIEventsConnection : function(url) {
//create a web socket connection
if (typeof (WebSocket) !== 'undefined') {
this.uiEventsSocket = new WebSocket(url);
} else if (typeof (MozWebSocket) !== 'undefined') {
this.uiEventsSocket = new MozWebSocket(url);
} else {
console.error('WebSockets unavailable.');
}
//notify if there is an web socket error
this.uiEventsSocket.onerror = function () {
console.error('WebSocket raised error.');
}
this.uiEventsSocket.onopen = function () {
console.log("Connection to " + url + " established");
}
//handling message from server side
this.uiEventsSocket.onmessage = function (msg) {
this._handleMessage(msg.data);
};
},
_handleMessage : function(data){
//the message should be in json format
//the next line fails if it is not
var command = JSON.parse(data);
//here is handling the request to show prompt
if (command.CommandType == 'yesNo') {
var message = command.Message;
var result = confirm(message);
//not sure that bool value will be successfully converted
this.uiEventsSocket.send(result ? "true" : "false");
}
}
}
And init it from ready or load event:
window.onload = function() { $app.initUIEventsConnection(yourUrl); }
Note that you url should begin with ws:// instead of http:// and wss:// instead of https:// (Web Sockets and Web Sockets Secure).
Server side.
Here is a good article for how to setup web sockets at asp.net core application or you could find another one. Note that you should group web socket connections from single user and if you want to send a message to the concrete user, you should send message for every connection from this user.
Every web socket you should accept with AcceptWebSocketAsync() method call and then add instance of this web socket to singleton, which contains a set of web sockets connection groupped by user.
The following class will be used to operate commands:
public class UICommand
{
public string CommandType { get; set; }
public string Message { get; set; }
public Type ReturnType { get; set; }
}
And a full code of singleton for handling sockets
public class WebSocketsSingleton
{
private static WebSocketsSingleton _instance = null;
//here stored web sockets groupped by user
//you could use user Id or another marker to exactly determine the user
private Dictionary<string, List<WebSocket>> _connectedSockets;
//for a thread-safety usage
private static readonly ReaderWriterLockSlim Locker = new ReaderWriterLockSlim();
public static WebSocketsSingleton Instance {
get {
if (this._instance == null)
{
this._instance = new WebSocketsSingleton();
}
return this._instance;
}
}
private WebSocketsSingleton()
{
this._connectedSockets = new Dictionary<string, List<WebSocket>>();
}
/// <summary>
/// Adds a socket into the required collection
/// </summary>
public void AddSocket(string userName, WebSocket ws)
{
if (!this._connectedSockets.ContainsKey(userName))
{
Locker.EnterWriteLock();
try
{
this._connectedSockets.Add(userName, new List<WebSocket>());
}
finally
{
Locker.ExitWriteLock();
}
}
Locker.EnterWriteLock();
try
{
this._connectedSockets[userName].Add(ws);
}
finally
{
Locker.ExitWriteLock();
}
}
/// <summary>
/// Sends a UI command to required user
/// </summary>
public async Task<string> SendAsync(string userName, UICommand command)
{
if (this._connectedSockets.ContainsKey(userName))
{
var sendData = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(command));
foreach(var item in this._connectedSockets[userName])
{
try
{
await item.SendAsync(new ArraySegment<byte>(sendData), WebSocketMessageType.Text, true, CancellationToken.None);
}
catch (ObjectDisposedException)
{
//socket removed from front end side
}
}
var buffer = new ArraySegment<byte>(new byte[1024]);
var token = CancellationToken.None;
foreach(var item in this._connectedSockets[userName])
{
await Task.Run(async () => {
var tempResult = await item.ReceiveAsync(buffer, token);
//result received
token = new CancellationToken(true);
});
}
var resultStr = Encoding.Utf8.GetString(buffer.Array);
if (command.ReturnType == typeof(bool))
{
return resultStr.ToLower() == "true";
}
//other methods to convert result into required type
return resultStr;
}
return null;
}
}
Explanation:
on establishing connection from web socket it will be added with
AddSocket method
on sending request to show a message, the required command will be passed into SendAsync method
the command will be serialized to JSON (using Json.Net, however you could serialize in your way) and send to all sockets, related to the required user
after the command sent, application will wait for respond from front end side
the result will be converted to required type and sent back to your IQuestionBox
In the web socket handling your should add some kind of the following code:
app.Use(async (http, next) =>
{
if (http.WebSockets.IsWebSocketRequest)
{
var webSocket = await http.WebSockets.AcceptWebSocketAsync();
var userName = HttpContext.Current.User.Identity.Name;
WebSocketsSingleton.Instance.AddSocket(userName, webSocket);
while(webSocket.State == WebSocketState.Open)
{
//waiting till it is not closed
}
//removing this web socket from the collection
}
});
And your method implementation of ShowYesNoQuestionBox should be kind of following:
public async Task<bool> ShowYesNoQuestionBox(string userName, string text)
{
var command = new UICommand
{
CommandType = "yesNo",
Message = text,
ReturnType = typeof(bool)
};
return await WebSocketsSingleton.Instance.SendAsync(string userName, command);
}
Note that there should be added userName to prevent sending the same message to all of the connected users.
WebSocket should create the persistent connection between server and client sides, so you could simply send commands in two ways.
I am kindly new to Asp.Net Core, so the final implementation could be a bit different from this.
It's actually much the same, except your UI is sort of disconnected and proxied with the HTTP protocol for the most part.
you essentially need to build the same code as your WPF code but then in the browser construct ajax calls in to the controller actions to apply your logic.
To clarify ...
so lets say you are building up a process over a series of questions that based on the users answer you put different steps in to the process.
You can either ...
build the process in the database
build it in session on the server
build it on the client as a js object
then do a post for execution ofthe constructed process.
think of the "statelessness" as a series of short interactions, but the state you keep between them can be done either on the client, in a db or in the users logged in session on the web server.
In your controller you can add an ActionResult that will give you the html response to your jquery modal popup request. Here is an example
public class MController : Controller {
public ActionResult doWork(requirement IQuestionBox)
{
// model is already modelBound/IOC resolved
return PartialView("_doWork", requirement );
}
}
//scripts
$(function(){
$.ajax({
url:"/m/doWork",
type:"get",
success:function(data){
$modal.html(data); // bind to modal
}
});
});
Apologies for not fully understanding the question.
hope this helps!
I have the following Web Api
public class ApiTestController : ApiController
{
// GET api/<controller>
[HttpGet]
public string UploadImage(int id)
{
return "You entered = " + id;
}
}
which when run and I enter /api/ApiTest/3 it hits it and returns You entered 3
Now in my seperate MVC application I'm trying to reference the same api method by doing the following
private const string WebUrl = "http://localhost:1769/api/ApiTest/";
//
// GET: /Home/
public ActionResult Index()
{
try
{
var test = GetInvoiveNo(3);
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
return View();
}
public string GetInvoiveNo(int id)
{
var uri = WebUrl + id;
using (var httpClient = new HttpClient())
{
Task response = httpClient.GetStringAsync(uri);
return JsonConvert.DeserializeObjectAsync<string>(response.ToString()).Result;
}
}
But I get the error:
one or more errors occurred
so I take a look into the inner exception and this is what it says:
Unexpected character encountered while parsing value: S. Path '', line 0, position 0."}
Now I'm not sure what I've done wrong here so if someone can kindly tell me or give me a simple example I'd appreciate it.
Your problem is that your response is not in proper format.
In below code you try to user response.ToString() which is wrong and you have to user result of response.
public string GetInvoiveNo(int id)
{
var uri = WebUrl + id;
using (var httpClient = new HttpClient())
{
var response = httpClient.GetStringAsync(uri);
return JsonConvert.DeserializeObjectAsync<string>(response.Result).Result;
}
}
I used to use ASMX web services, however have since read (and been told) that a better way to request data from a client etc is to use web API's with MVC.
I have created an MVC 4 web api application and getting to grips with how it works.
Currently I have a single public string in my valuesControllers -
public class ValuesController : ApiController
{
// GET api/values/5
public string Get(int id)
{
return "value";
}
}
And I am currently trying to call this in my client like this -
class Product
{
public string value { get; set; }
}
protected void Button2_Click(object sender, EventArgs e)
{
RunAsync().Wait();
}
static async Task RunAsync()
{
using (var client = new HttpClient())
{
try
{
client.BaseAddress = new Uri("http://localhost:12345/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
// HTTP GET
HttpResponseMessage response = await client.GetAsync("api/values/5");
if (response.IsSuccessStatusCode)
{
Product product = await response.Content.ReadAsAsync<Product>();
Console.WriteLine("{0}", product.value);
}
}
catch(Exception ex)
{
Console.WriteLine(ex.Message.ToString());
}
}
}
On debugging I can step through the request and enter the web API code successfully however on the line -
Product product = await response.Content.ReadAsAsync<Product>();
This fails and enters my catch with the exception -
Error converting value "value" to type 'myDemo.Home+Product'. Path '', line 1, position 7.
Why is this?
Why is this?
Because from your controller action you are returning a string, not a Product which are 2 quite different types:
public string Get(int id)
{
return "value";
}
so make sure that you are consistently reading the value on the client:
if (response.IsSuccessStatusCode)
{
string result = await response.Content.ReadAsAsync<string>();
Console.WriteLine("{0}", result);
}
Of course if you modified your API controller action to return a Product:
public Product Get(int id)
{
Product product = ... go fetch the product from the identifier
return product;
}
your client code would work as expected.
I have a controller action that downloads a file from an azure blob based on the container reference name (i.e. full path name of the file in the blob). The code looks something like this:
public FileContentResult GetDocument(String pathName)
{
try
{
Byte[] buffer = BlobStorage.DownloadFile(pathName);
FileContentResult result = new FileContentResult(buffer, "PDF");
String[] folders = pathName.Split(new char[] { '\\' }, StringSplitOptions.RemoveEmptyEntries);
// get the last one as actual "file name" based on some convention
result.FileDownloadName = folders[folders.Length - 1];
return result;
}
catch (Exception ex)
{
// log error
}
// how to handle if file is not found?
return new FileContentResult(new byte[] { }, "PDF");
}
The BlobStorage class there is my helper class to download the stream from the blob.
My question is stated in the code comment: How should I handle the scenario when the file/stream is not found? Currently, I am passing an empty PDF file, which I feel is not the best way to do it.
The correct way to handle a not found in a web application is by returning a 404 HTTP status code to the client which in ASP.NET MVC terms translates into returning a HttpNotFoundResult from your controller action:
return new HttpNotFoundResult();
Ahh, oops, didn't notice you were still on ASP.NET MVC 2. You could implement it yourself because HttpNotFoundResult was introduced only in ASP.NET MVC 3:
public class HttpNotFoundResult : ActionResult
{
public override void ExecuteResult(ControllerContext context)
{
if (context == null)
{
throw new ArgumentNullException("context");
}
context.HttpContext.Response.StatusCode = 404;
}
}
In ASP.NET Core, use NotFound()
Your controller must inherit of Controller and the method must return ActionResult
Example:
public ActionResult GetFile(string path)
{
if (!File.Exists(path))
{
return NotFound();
}
try
{
return new FileContentResult(File.ReadAllBytes(path), "application/octet-stream");
}
catch (FileNotFoundException)
{
return NotFound();
}
}
Note: the above code doesn't handle all cases of file operations errors as invalid chars in path or file unavailability (because it is beyond the scope of the current answer) and proper responses (like restricted file access due to permissions or else)